Thyristor-assisted on-load tap-changer and associated method

Abstract

A thyristor-supported on-load tap-changer, characterized in that it is constructed from a tap selector and a switch; wherein the tap selector is connected to the switch, and after the tap selector has selected the current collector of a regulating transformer, a load switching of the current collector is realized by the switch; wherein the switch comprises a first main switch (K21-1), a second main switch (K22-1), a first thyristor auxiliary circuit (I) and a second thyristor auxiliary circuit (II), a piezoresistor (R) and a first terminal (J1) as well as a second terminal (J2) and a third terminal (J3); wherein one end of the first main switch (K21-1) is connected to the first terminal (J1) and the other end of the first main switch (K21-1) is connected to the third terminal (J3); wherein the first thyristor auxiliary circuit (I) is connected in parallel with the first main switch (K21-1); wherein one end of the second main switch (K22-1) is connected to the second terminal (J2) and the other end of the second main switch (K22-1) is connected to the third terminal (J3); wherein the second thyristor auxiliary circuit (II) is connected in parallel with the second main switch (K22-1); wherein the end of the first main switch (K21-1) connected to the first terminal (J1) and the end of the second main switch (K21-2) connected to the second terminal (J2) are further connected to the piezoresistor (R); wherein a pair of switches is arranged respectively in the first thyristor auxiliary circuit (I) and in the second thyristor auxiliary circuit (II) to control state switching of the corresponding thyristor auxiliary circuit, wherein the first thyristor auxiliary circuit (I) comprises a first switch (K23-1) of the first thyristor auxiliary circuit (I) and a second switch (K25-1) of the first thyristor auxiliary circuit (I), and wherein the second thyristor auxiliary circuit (II) comprises a first switch (K24-1) of the second thyristor auxiliary circuit (II) and a second switch (K26-1) of the second thyristor auxiliary circuit (II).

Description

Field of the invention

[0001] The present invention relates to the technical field of energy transmission and transformation in energy systems and in particular to a thyristor-supported on-load tap changer and an associated method. State of the art

[0002] The operating mode of a power system is constantly changing, and this change in operating mode causes fluctuations in the bus line voltage. The power system has strict requirements regarding the fluctuation range of the bus line voltage. Therefore, a technology for regulating the bus line voltage is required. The most direct way to regulate the voltage is to change the transformer tap changer. However, in the power system's load transfer process, a very high-tech on-load tap changer is required to change the transformer tap without causing a power outage.

[0003] Currently, reactive on-load tap-changers and resistive on-load tap-changers are the most widely used types worldwide. The inventions in patents US3176089, US5128605, and US7880341 disclose reactive on-load tap-changers, while the inventions in patents US4081741 and US4520246 disclose resistive on-load tap-changers. The reactors of reactive on-load tap-changers are powered for a long time, have a relatively large capacity, and are used only in the United States worldwide; in other countries, resistive on-load tap-changers are mostly used. Resistive on-load tap-changers suffer from the problem of heat generation, and a significant temperature rise occurs when the on-load tap-changer's current collector is switched multiple times within a short period of time. Therefore, the switching time of the on-load tap-changer is strictly limited within a certain time.

[0004] The performance of the on-load tap-changer is improved by a thyristor circuit in the invention of US Patent No. 4,622,513. One of the features of the invention is that when the switch is turned off from a switched power path, an overvoltage-triggering thyristor circuit of a switching path is automatically turned on to quickly connect and switch the load current. The disadvantage of the overvoltage-triggering thyristor circuit is that it generates a very large pulse noise every 10 milliseconds. Therefore, appropriate anti-interference and safety measures are required to ensure reliable operation of the on-load tap-changer.Another aspect of the invention is that a bidirectional parallel thyristor is triggered by a current transformer to assist a mechanical switch to disconnect the switched current path. The bidirectional parallel thyristor is connected in parallel with the mechanical switch, and the bidirectional parallel thyristor may be accidentally turned on by pulse noise, causing a short circuit. Therefore, the overvoltage triggering thyristor circuit in the invention is connected in series with a turn-on resistor to limit the potential short circuit and improve the operational reliability of the thyristor. In this way, although US 4 622 513 A reduces the heating of the junction resistance, the heating problem of the junction resistance is not completely solved. Patent specification US 7 595 614 B2 is an improvement of US 4 622 513.In patent US7595614, the contact resistance is removed with its serial connection to the overvoltage triggering thyristor circuit, which solves the heating problem of the contact resistance. Since the contact resistance is removed to limit the short-circuit circuit, in the event of a short-circuit circuit, the short-circuit circuit is very large. In US7595614, protection is only achieved by a fuse, and the reaction speed of the fuse is slow, so the safety is low. In patent US7595614, the bidirectional parallel thyristor is still triggered by the current transformer to disconnect the switched current path, and no new anti-interference measure is added, so the reliability is poor.

[0005] In the inventions of patents US4622513 and US7595614, a bidirectional parallel thyristor circuit is triggered by the secondary current of the current transformer to turn on and turn off a bidirectional parallel thyristor. The reliability of the trigger circuit is poor. The inventions of patents US4622513 and US7595614 employ a traditional complicated mechanical cam-sliding mechanism and an energy storage mechanism, which generate significant vibration and noise during operation. Therefore, failure is prone to occur and more frequent operations cannot be performed.

[0006] CN 1 02 779 667 A relates to the technical field of energy transmission and conversion of electrical energy systems, in particular to a tap changer.

[0007] US 2009 / 0 146 637 A1 relates to the field of voltage regulation or control systems, in particular to an improved tap change method and system for power supply. Brief description of the invention

[0008] The object of the present invention is to (1) solve the above problems and overcome the disadvantages by providing an overvoltage tripping thyristor circuit-based on-load tap changer which has no contact resistance, a very short short-circuit extent, and high safety and reliability; further (2) bring advantages by providing an on-load tap changer in which the on-load tap selector does not require a mechanical connection to a changeover switch, in which the logical relationships are clear, which has a simple structure and is convenient to coordinate; and (3) provide an on-load tap changer which is even simpler in construction and even more economical.

[0009] A type of thyristor-assisted on-load tap-changer that includes: A thyristor-based on-load tap changer comprising a main circuit and a transition circuit, the main circuit being constructed of a switch K1, the transition circuit being composed of a linear reactor L1, a saturable reactor L2, and an overvoltage tripping thyristor circuit connected in series; one end of the switch K1 is switched between a tap selector terminal I and a tap selector terminal II via a changeover switch K5, and one end of the linear reactor L1 is switched between the tap selector terminal I and the tap selector terminal II by a changeover switch K6; and the switch K1 and the other end of the overvoltage tripping thyristor circuit are connected to a common terminal.

[0010] A thyristor-based on-load tap changer comprising a main circuit and a transition circuit; wherein the main circuit is composed of a saturable reactor L4 and a control switch K10 that controls a thyristor switch, which are connected in series; wherein the transition circuit is composed of a linear reactor L1, a saturable reactor L2, and an overvoltage release thyristor circuit, which are connected in series; one end of the saturable reactor L4 is switched between a tap selector terminal I and a tap selector terminal II via a changeover switch K5, one end of the linear reactor L1 is switched between the tap selector terminal I and the tap selector terminal II by a changeover switch K6; and wherein the thyristor switch and the other end of the overvoltage release thyristor circuit are connected to a common terminal.

[0011] A thyristor-based on-load tap changer comprising a main circuit and a transfer circuit; wherein the main circuit is composed of a saturable reactor L4 and a thyristor switch controlled by a control switch K10, which are connected in series; the transfer circuit is composed of a linear reactor L1, a saturable reactor L2, and an overvoltage tripping thyristor circuit, which are connected in series; one end of the saturable reactor L4 is commonly connected to one end of the transfer switches K15, K14, and the other ends of the transfer switches K15, K14 are respectively connected to tap selector terminals I, II; one end of the linear reactor L1 is commonly connected to one end of the transfer switches K17, K16, and the other ends of the transfer switches K17, K16 are respectively connected to tap selector terminals I, II;the thyristor switch and the other end of the voltage-triggering thyristor circuit are connected to a common terminal; a main contact of an odd-numbered side K11 is further connected between the tap selector terminal I and the common terminal, and a main contact of an even-numbered side K12 is further connected between the tap selector terminal II and the common terminal.

[0012] The reactance of the linear reactor L1 is greater than zero and less than Z 1 ; Z 1 is equal to a quotient obtained by dividing a rated voltage between the tap selector terminals I, II by rated load current.

[0013] The linear reactor L1 and the saturable reactor L2 are combined into a reactor L3; the reactor L3 comprises a closed-circuit magnetic flux iron core and a coil L3, wherein a part of the closed-circuit section of the magnetic flux iron core has a larger cross-sectional area and the cross-sectional areas of the remaining sections of the iron core are smaller; the coil L3 is wound on the iron core around the section with the larger cross-sectional area; when the electric current is relatively small, the closed-circuit iron core is unsaturated; the coil L3 is equivalent to the saturable reactor L12; when the current is relatively large, the iron core is saturated at the section with the smaller cross-sectional area of ​​the closed-circuit iron core and the iron core is unsaturated at the section with the larger cross-sectional area;the reactance of the coil L3 is rapidly reduced to a smaller value, and the coil L3 is equivalent to the linear reactor L1 at this time;

[0014] The overvoltage release thyristor circuit includes: a fuse FU1 connected in series with a pair of thyristors D1, D2 connected in reverse parallel to form a main circuit of the overvoltage release thyristor circuit; a resistor R1 and a capacitor C1 connected in reverse parallel to both ends of the thyristors D1, D2 after being connected in series; gate electrodes and cathodes of the two thyristors D1, D2 are respectively connected to capacitors C2, C3, resistors R2, R3 and diodes D3, D4; the gate electrodes of the two thyristors D1, D2 are further respectively connected to the input terminal of a full-bridge rectifier composed of diodes D5, D6, D7, D8;the output end of the full-bridge rectifier is connected to a voltage regulator tube D9, the cathode of the voltage regulator tube D9 being connected to the output end anode of the full-bridge rectifier, and the anode of the voltage regulator tube D9 being connected to the output end cathode of the full-bridge rectifier, the stabilized voltage of the above-mentioned voltage regulator tube D9 being equal to U; 1 =k 1 U 2 where k 1 where is a reliability coefficient and has a value between 1.2 and 2; and U 2 the peak value of the operating frequency rated voltage for the connection between the tap selector terminals I,II of the on-load tap changer.

[0015] The thyristor switch includes the following: a fuse FU1 connected in series with a pair of thyristors D1, D2 connected in reverse parallel to form a main circuit; a resistor R1 and a capacitor C1 connected in reverse parallel to the two ends of the thyristors D1, D2; the gate electrodes and cathodes of the two thyristors D1, D2 are respectively connected to capacitors C2, C3, resistors R2, R3 and diodes D3, D4; the gate electrodes of the two thyristors D1, D2 are further respectively connected to the input terminal of a full-bridge rectifier composed of diodes D5, D6, D7, D8;a voltage regulator tube D11 and a voltage regulator tube D9 are connected in series in a rectified manner, whereupon the serial anodes of the voltage regulator tube D11, D9 are connected to the cathodes of the full-bridge rectifier, the serial cathodes of the voltage regulator tube D11, D9 being connected to the anodes of the full-bridge rectifier; the anode of a diode D10 being connected to the anode of the full-bridge rectifier, the cathode of the diode D10 being connected to one end of the switch K10, and the other end of the switch K10 being connected to the cathode of the full-bridge rectifier; the stabilized voltage value U3 of the series-connected voltage regulator tube D11 and voltage regulator tube D9 is equal to U; 3 = k 2 (U 1 +U 2 ); where k 2 a reliability coefficient and a value of 1.1 to 1.5, U 1 =k 1 U 2 is; k 1is a reliability coefficient and has a value of 1.2 to 2; U 2 denotes the peak value of the operating frequency rated operating voltage for the connection between the tap selector terminals 1, 2 of the on-load tap changer; the sum of the positive tube voltage drops of all semiconductors of a gate electrode trigger loop of the thyristor D1 or D2 is approximately 1.5; U 4 denotes the maximum current and includes the transient peak value of the short-circuit current that may flow through it, as well as the positive tube voltage drop across the main circuit of the thyristor D1 or D2.

[0016] The terminal of a non-common terminal of the main circuit and the terminal of a non-common terminal of the transfer circuit are further connected to a bidirectional voltage stabilizing circuit; the voltage stabilizing value of the bidirectional voltage stabilizing circuit is greater than the peak value of the operating frequency rated voltage for the connection between the tap selector terminals I, II of the on-load tap-changer and less than the stabilized voltage U 1 of the voltage regulator tube D9.

[0017] The switches (contacts) are interlocking contactors and are composed of closing coils, tripping coils, main contacts, and auxiliary contacts; or they are non-interlocking contactors, which are composed of closing coils, main contacts, and auxiliary contacts; the coils are energized or their current is interrupted to turn the switches (contacts) on and off.

[0018] To achieve the above-mentioned object, the present invention uses the following technical solutions: A thyristor-assisted on-load tap changer is constructed according to claim 1 of the present invention. A thyristor-assisted on-load tap changer is constructed according to claim 1 of the present invention.

[0019] According to claim 3 of the present invention, the thyristor auxiliary circuit I and the thyristor auxiliary circuit II have the same structure and comprise: a pair of thyristors D1, D2 constructed in reverse and in parallel to form a main circuit of the thyristor auxiliary circuit; a resistor R1 and a capacitor C1 connected in reverse parallel to the two ends of the thyristors D1, D2; wherein the gate electrodes and cathodes of the two thyristors D1, D2 are each connected to capacitors C2, C3, resistors R2, R3 and diodes D3, D4; the anodes of the diodes D3, D4 are each connected to the gate electrodes of the thyristors D1, D2 and the cathodes of the diodes D3, D4 are each connected to the cathodes of the thyristors D1, D2; wherein the input terminal of the full-bridge rectifier constructed from the diodes D5, D6, D7, D8 is connected, after the serial connection, to a normally open switch KB between the gate electrodes of the two thyristors D1, D2; the output end of the full-bridge rectifier is connected to the voltage regulator tube D9, the cathode of the voltage regulator tube D9 being connected to the output end of the cathode of the full-bridge rectifier; the diodes D13, D14, D15 are connected in series in the same direction, and also the diodes D16, D17, D18 are connected in series in the same direction, the two diode strings being connected in series with the normally open switch KA after being reversely connected in parallel and then connected between the gate electrodes of the two thyristors D1, D2.

[0020] According to claim 4 of the present invention, in the current collector terminal of the regulating transformer, the terminal located entirely in the center is defined as the zero line, wherein the zero line and an adjacent current collector terminal of the regulating transformer are each connected to two terminals of the primary coil of the transformer T2, and the terminal of a secondary coil of the transformer provides AC control voltage; one terminal of the AC control voltage is defined as the zero line, wherein the zero line of the primary coil of the transformer T2 is connected to the zero line of the secondary coil of the transformer T2; the AC control voltage terminal is also used as an input for a DC voltage stabilization power supply module, wherein the DC voltage stabilization power supply module provides DC control voltage for the switch, wherein the low-potential DC control voltage terminal is defined as the zero line of the DC control voltage, and wherein the zero line of the DC control voltage is connected to the zero line of the AC control voltage.

[0021] The operating method of the thyristor-supported on-load tap changer is carried out according to claim 5 of the present invention.

[0022] According to claim 6 of the present invention, when switching from conducting terminal J1 of the switch of the on-load tap-changer with the common terminal J3 to conducting terminal J2 with the common terminal J3, the time interval between turning off switch K23-1 and turning on switch K24-1 is greater than 20 milliseconds; When switching from conducting terminal J2 of the on-load tap-changer switch to common terminal J3 to conducting terminal J1 to common terminal J3, the time interval between switching off switch K24-1 and switching on switch K23-1 is greater than 20 milliseconds.

[0023] The advantageous effects of the present invention are: removing the contact resistance, solving the resistance heating problem; in situations with high safety requirements, measures can be taken to limit the short-circuit circuit, thus ensuring the safety of the overvoltage release thyristor circuit and the transistor switching circuit. The overvoltage release thyristor circuit and the transistor switching circuit are provided with stronger anti-noise measures to ensure the reliable operation of the thyristor-based on-load tap-changer even under strong pulse noise conditions. No electric current is generated during the process of breaking and conducting the mechanical switch, thereby realizing arc-free switching; and the switch contact is not damaged by frequent activation.The energy storage mechanism of the traditional on-load tap-changer can be eliminated, thereby shortening the overall operating time of the thyristor-based on-load tap-changer. The complex mechanical linkage mechanism, especially the energy storage mechanism, is eliminated to reduce the volume and weight of the on-load tap-changer, thereby reducing the failure rate. A control circuit in the form of an intermediate relay (contactor) ensures that the transition to the operating program of the next switch only occurs after the operation of one switch is completed, thus increasing reliability.The realization of the operation of the tap selector does not require any intervention by the tap selector, the switch is started to operate as soon as the operation of the tap selector is completed; there is no intervention of the tap selector in the switching process; no restriction of a mechanical connection is necessary between the tap selector and the switch, the logical relationships are clear and the interaction is practical.

[0024] For the thyristor-assisted on-load tap-changer, the electrical switches can be manually operated to achieve load switching of the switch in sequential operation; the electrical switch can be driven by a mechanical linkage mechanism to achieve load switching of the switch in sequential manner; the electrical switch can be controlled by the contacts of a contactor (relay) to achieve load switching of the switch in sequential manner; a variety of methods can be employed, making the application flexible.The operating state of the main contact is reflected by the auxiliary contact of the relay (contactor), ensuring that the transition to the operating program of the next switch only occurs once the operating state of a specific switch is confirmed, and that the transition to the operating program of the next switch occurs immediately once the operating state of the specific switch is determined; thus achieving a perfect combination of speed and reliability. Apart from the main switch, a thyristor-based on-load tap-changer does not require any other large-capacity relay (contactor); only the contact of a small-capacity relay is needed to control the switching on and off of a thyristor trigger circuit, to switch a high-current thyristor on and off, and in turn toggle the on-load tap-changer.The on-load tap-changer is structurally simple, convenient to control, and cost-effective. The main switch and the contact of the small-capacity relay (contactor) are implemented in an arc-free manner. During the inactive period of the on-load tap-changer, there is no electrical voltage in the thyristor auxiliary circuit, so the safety of the thyristor auxiliary circuit is relatively high. The voltage difference between the control power supply potential and the switch contact of the switch of the thyristor-based on-load tap-changer is small, and the dielectric strength requirements of the insulating material between them are low. Especially for the diverter switch of a 10 kV system, the on-load tap-changer of the present invention can be implemented using a conventional AC contactor to reduce manufacturing costs. Brief description of the drawings Fig. 1 shows the structure and connection type of an existing on-load tap-changer. Fig. Figure 2 shows the structure and connection type of a thyristor-based on-load tap-changer. Fig. 3 shows an overvoltage release thyristor circuit. Fig. Figure 4 shows the serial connection of an overvoltage release thyristor circuit. Fig. 5 shows a reactor setup. Fig. Figure 6 shows the structure and connection method of a second type of thyristor-assisted on-load tap-changer. Fig. 7 shows an n thyristor circuit. Fig. 8 shows the structure and connection method of a third embodiment of a thyristor-based on-load tap changer. Fig. 9 shows the control circuit of the switch of the third embodiment of the thyristor-supported on-load tap changer. Fig. 10 shows a control circuit of a switch of a thyristor-supported on-load tap changer. Fig. 11 shows the control circuit of a switch of a second embodiment of a thyristor-supported on-load tap changer. Fig. 12 shows the structure of a switch of a fourth embodiment of a thyristor-based on-load tap changer. Fig. 13 shows a thyristor auxiliary circuit. Fig. 14 shows the structure of a switch of a fifth embodiment of a thyristor-based on-load tap changer. Fig. 15a shows a control circuit of a switching state of the third embodiment. Fig. 15b shows a control circuit of a switching state of the fourth embodiment. Fig. Figure 16 shows the power supply structure of a thyristor-based on-load tap changer. Description of the preferred embodimentsEmbodiment 1:

[0025] The present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0026] Fig. Figure 1 shows the operating principle structure and connection type of an existing on-load tap-changer. The on-load tap-changer consists of a tap selector and a switch. The tap selector is connected to the switch, and after the tap selector selects a current collector of a regulating transformer, the switch performs load switching of the current collector. The operating principle of the on-load tap-changer's tap selector is well known; the special feature of the on-load tap-changer is the switch, where the so-called on-load tap-changer generally refers to the switch (selector switch) on the on-load tap-changer.

[0027] The basic structure and connection type of a thyristor-supported on-load tap-changer are described in Fig. 2. It includes two tap selector terminals I1, II2, a common terminal 3, two changeover switches K5, K6, a main vacuum switch K1, an overvoltage release thyristor circuit 4, a linear reactor L1, a saturable reactor L2, and a bidirectional voltage stabilizing circuit 7; one current collector terminal of the changeover switch K5 and one current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal I1, the other current collector terminal of the changeover switch K5 and the other current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal II2; the common terminal of the changeover switch K5 is connected to the common terminal 3 of the on-load tap changer via the main vacuum switch K1 to form a main circuit;The common terminal of the switch K6 is connected in series with the common terminal 3 of the on-load tap-changer through the linear reactor L1, the saturable reactor L2, and the overvoltage trigger thyristor circuit 4 to form a transition circuit; and the bidirectional voltage stabilizing circuit 7 is connected between the common terminal of the switch K5 and the common terminal of the switch K6.

[0028] The overvoltage release thyristor circuit 4 is as in Fig. 3. A fuse FU1 is connected in series with a pair of thyristors D1, D2 connected in reverse parallel to form a main circuit. A resistor R1 and a capacitor C1 are connected in reverse parallel to both ends of the thyristors D1, D2 after being connected in series to achieve oscillation damping in processes that turn the thyristors D1, D2 on and off, so as to prevent false activation due to excessively rapid voltage rise at the both ends of the thyristors D1, D2.The gate electrodes and cathodes of the two thyristors D1, D2 are respectively connected to capacitors C2, C3 and resistors R2, R3 to resist noise; the anodes of the diodes D3, D4 are respectively connected to the cathodes of the thyristors, and the cathodes of the diodes are respectively connected to the gate electrodes of the thyristors to protect the gate electrodes and cathodes from being disrupted by a reverse voltage and to provide a reverse current path.The gate electrodes of the two thyristors D1, D2 are further connected to the input terminal of a full-bridge rectifier composed of diodes D5, D6, D7, D8; the output end of the full-bridge rectifier is connected to a voltage regulator tube D9, the cathode of the voltage regulator tube D9 being connected to the output end anode of the full-bridge rectifier, and the anode of the voltage regulator tube D9 being connected to the output end cathode of the full-bridge rectifier, D9 utilizing multiple low-voltage level voltage regulator tubes D9 connected in series to obtain a high-voltage level voltage regulator tube.

[0029] The stabilized voltage of the voltage regulator tube D9 should be greater than the peak value of the maximum normal voltage between the tap selector terminals I1 and II2 to ensure that the voltage regulator tube D9 does not conduct when performing on-load voltage regulation within the maximum normal fluctuation range. If the stabilized voltage of the voltage regulator tube D9 is too large, the withstand voltage of the main vacuum breaker K1 must be increased, and the withstand voltages of the thyristors D1 and D2 must be increased, increasing the volume and investment of the on-load tap-changer. If the stabilized voltage of the voltage regulator tube D9 is too large, the interference influence of the overvoltage tripping thyristor circuit 4 with respect to other devices increases, and the reliability of the thyristor-based on-load tap-changer is relatively poor.In particular, if the stabilized voltage of the voltage regulator tube D9 is too high, the interference from the overvoltage tripping thyristor circuit 4 will generate a transient DC voltage component, causing the regulating transformer to generate a magnetizing current surge, which triggers a protective trip. The stabilized voltage of the voltage regulator tube D9 cannot be too high to ensure the reliable operation of the thyristor-based on-load tap-changer. Therefore, the stabilized voltage of the voltage regulator tube D9 is equal to U. 1 =k 1 U 2 ; k 1 is a reliability coefficient and has a value of 1.2 to 2; U 2 denotes the peak value of the operating frequency rated voltage for the connection between the tap selector terminals 1, 2 of the on-load tap-changer. It is preferred that k 1 is 1.5.

[0030] The conduction of the tap selector terminal I1 of the thyristor-assisted on-load tap-changer with the common terminal 3 can be switched to conduct the tap selector terminal II2 with the common terminal 3; the conduction of the tap selector terminal II2 with the common terminal 3 can be switched to conduct the tap selector terminal I1 with the common terminal 3.

[0031] The operating principle of switching the conduction of the tap selector terminal I1 of the on-load tap-changer with the common terminal 3 to the conduction of the tap selector terminal II2 with the common terminal 3 is as follows: (1) The changeover switch K6 is switched; the overvoltage release thyristor circuit 4 is turned on, and the stabilized voltage of the voltage regulator tube D9 is greater than the peak value of the maximum normal AC voltage between the tap selector terminals I1, II2, whereby the voltage regulator tube D9 is not conductive, and the thyristors D1, D2, which are connected in reverse and in parallel, are not triggered; the overvoltage release thyristor circuit 4 is not conductive at this time; (2) The main vacuum switch K1 is turned off; the main circuit is turned off, and the potential of terminal 3 connected to a load drops rapidly; the voltages at the two ends of the overvoltage triggering thyristor circuit 4 rise rapidly when the instantaneous voltage value is greater than the stabilized voltage of the voltage regulator tube D9, at which time the voltage regulator tube D9 conducts to trigger the conduction of the thyristor D1 or D2, and the transition circuit is automatically turned on; load current flows in from the tap selector terminal II2 and out through the transition circuit from the common terminal 3; since the electric current is alternating current, the overvoltage triggering thyristor circuit 4 automatically breaks the current loop once when the current crosses zero;After that, the voltages at both ends of the overvoltage trigger thyristor circuit 4 rise again, and the overvoltage trigger thyristor circuit 4 conducts again. The voltages at the two ends of the overvoltage trigger thyristor circuit 4 are pulse voltages that undergo positive and negative transformations every 10 milliseconds; the pulse peak value is equal to the stabilized voltage of the voltage regulator tube D9. The pulse voltage that alternates positive and negative has little influence on the load current and also does not affect the load voltage waveform; the load current is transferred through the main circuit to the transition circuit. (3) the switch K5 is switched; (4) the main vacuum switch K1 is turned on; the load current flows through the main vacuum switch K1, and the overvoltage release thyristor circuit 4 is reduced to zero.

[0032] If the main vacuum switch K1 is not turned off, the overvoltage tripping thyristor circuit 4 will be subject to interference and form a short circuit due to improper conduction. For a large-capacity power system, if the reactance of the linear reactor L1 is zero, a very large short circuit will be formed. At this time, as long as the reactance of the linear reactor L1 is slightly greater than zero, the effect of limiting the short circuit is very obvious. Therefore, for the safety of the thyristor-assisted on-load tap-changer, the reactance of the linear reactor L1 must be strictly above zero. When the reactance of the reactor L1 is large, the advantages are that the formed short circuit is small and there is good safety.The disadvantage is that reactor L1 may potentially generate significant interference. In particular, the DC component causes an iron-core transformer to generate a magnetizing current surge, which can cause significant damage. For reactor L1, a balance must be struck between limiting the short-circuit duration and reducing interference. Considering that the overvoltage release thyristor circuit can limit the short-circuit duration to half a circuit, as long as the short-circuit duration is no greater than ten times the rated operating current of the thyristor, which ensures the safety of the thyristor, the reactance of reactor L1 should be greater than zero and less than Z. 1 be; Z 1is equal to a quotient obtained by subtracting a rated load current from the rated voltage between the tap selector terminals 1, 2. The reactance of the linear reactor L1 should be greater than zero and less than about 0.1Z 1 To reduce the volume, reactor L1 is preferably an air-gapped iron core reactor.

[0033] The fuse FU1 can interrupt the short circuit to serve as backup protection of the thyristor D1 (D2).

[0034] One function of the saturable reactor L2 is to reduce the rate of current flow increase during the conduction of the thyristor D1 (D2). The other function of the saturable reactor L2 is to cooperate with the resistor R1 and the capacitor C1 to increase the noise protection capabilities of the overvoltage triggering thyristor circuit 4. The noise immunity for narrow voltage pulses is greater than that of a linear reactor.

[0035] The function of the bidirectional voltage stabilization circuit 7 is to ensure that the voltages at the two ends of the bidirectional voltage stabilization circuit 7 do not exceed a voltage stabilization value, wherein the voltage stabilization value of the bidirectional voltage stabilization circuit 7 is greater than U 2 and smaller than the stabilized voltage U 1of the voltage regulator tube D9. When the voltage between the tap selector terminals I1, II2 is a normal rated voltage, the bidirectional voltage stabilizing circuit 7 is rendered non-conductive; in the case of a higher noise voltage between the tap selector terminals I1, II2, the noise is reduced to ensure that the noise voltage is not greater than the stabilized voltage U1 of the voltage regulator tube D9 in the overvoltage triggering thyristor circuit 4, so as to prevent the noise between the tap selector terminals I1, II2 from triggering the overvoltage triggering thyristor circuit 4 and generating the short-circuit. If other circuits can already eliminate the noise between the tap selector terminals I1, II2, the bidirectional voltage stabilizing circuit 7 can be omitted.The bidirectional voltage stabilization circuit 7 can be achieved by a piezoresistor or by a pair of high-power voltage regulator tubes connected in reverse series.

[0036] When the thyristor-assisted on-load tap-changer is applied with an extra-high voltage level, the withstand voltages of the existing thyristors D1 and D2 are insufficient. Multiple overvoltage tripping thyristor circuits 4 can be connected in series to improve the operating voltage. Fig. Figure 4 shows a series connection of three stages of the overvoltage release thyristor circuits. R4 denotes a dividing resistor; when multiple overvoltage release thyristor circuits are connected in series, R4 equalizes the voltages of the overvoltage release thyristor circuits.

[0037] The thyristor-supported on-load tap-changer from Fig. 2 is equipped with a linear reactor L1 and a saturable reactor L2. As in Fig. As shown in Figure 5, to further simplify the design, the linear reactor L1 and the saturable reactor L2 can be combined into a single reactor L3. The reactor L3 is equipped with a closed-circuit magnetic flux iron core 5 and a coil L3, wherein a part of the closed-circuit portion of the magnetic flux iron core 5 has a larger cross-sectional area, while the cross-sectional area of ​​the remaining portion of the iron core is smaller; the coil L3 is wound on the iron core at the portion with the larger cross-sectional area. When the electric current is relatively small, the closed-circuit iron core is unsaturated; the coil L3 is equivalent to the saturable reactor L2.When the current is relatively large, the iron core at the portion with the smaller cross-sectional area of ​​the closed-circuit iron core is saturated, and the iron core at the portion with the larger cross-sectional area is unsaturated; the reactance of the coil L3 is rapidly reduced to a smaller value, and at this time, the coil L3 is equivalent to the linear reactor L1.

[0038] As in Fig. As shown in Figure 5, a reactor L3 can be used instead of the linear choke coil L1 and the saturable choke L2 to reduce the reactor volume. Example 2:

[0039] A second embodiment of the thyristor-supported on-load tap-changer is as in Fig. 6. It includes two tap selector terminals I1, II2, a common terminal 3, two changeover switches K5, K6, a control switch K10 controlled by a thyristor switch 6, an overvoltage release thyristor circuit 4, a linear reactor L1, two saturable reactors L2, L4, and a bidirectional voltage stabilizing circuit 7. One current collector terminal of the changeover switch K5 and one current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal I1, and the other current collector terminal of the changeover switch K5 and the other current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal II2. the common terminal of the changeover switch K5 is connected in series with the common terminal 3 of the on-load tap-changer via the saturable reactor L4 and the thyristor switch 6, which is controlled by a control switch K10, to form a main circuit;The common terminal of the changeover switch K6 is connected in series with the common terminal 3 of the on-load tap-changer through the linear reactor L1, the saturable reactor L2, and the overvoltage tripping thyristor circuit 4 to form a transient circuit; the bidirectional voltage stabilizing circuit 7 is connected between the common terminal of the changeover switch K5 and the common terminal of the changeover switch K6.

[0040] The circuit of a thyristor switch 6 is controlled by a control switch K10, as shown in Fig. 7, where Fig. 7 a variation of Fig. 3. What are the identical areas of Fig. 7 and Fig. 3, the features and parameters are also the same and should not be repeated here unnecessarily.

[0041] The difference between Fig. 7 and Fig. 3 is as follows: A diode D10 and the control switch K10 were added. The anode of the diode D10 is connected to the anode of a full-bridge rectifier composed of the diodes D5, D6, D7, and D8, and the cathode of the diode D10 is connected to one end of the switch K10, and the other end of the switch K10 is connected to the cathode of a full-bridge rectifier composed of the diodes D5, D6, D7, and D8. As can be seen from Fig. As can be seen in Figure 7, thyristor switch 6 conducts when switch K10 conducts, and when switch K10 stops conducting, thyristor switch 5 also stops conducting. After control switch K10 is turned on, the electric current flowing through control switch K10 is the thyristor trigger current, and the electric current is very small. The conduction or de-conduction of the high-current path of thyristor switch 6 can be controlled by control switch K10 with a small capacitance to reduce the electric arc generated by turning off the load current and to increase the control speed and sensitivity of the switch.

[0042] The difference between Fig. 7 and Fig. 3 also lies in the following: A voltage regulator tube D11 has been added. The voltage regulator tube D11 and the voltage regulator tube D9 are connected in series in the same direction to take the place of the original voltage regulator tube D9. The voltage regulator tube D11 and the voltage regulator tube D9 are connected in series to achieve the following two functions: (1) Overvoltage protection of the thyristor switch 6. (2) When the thyristor switch 6 is applied to a high-voltage level on-load tap changer, the withstand voltages of the existing thyristors D1, D2 may not be sufficient, and a plurality of thyristor switches 6 must be connected in series to increase the operating voltage, as shown in Fig. 4. Since each stage of the thyristor switch 6 has a control switch K10, the operation of the respective control switches K10 may be asynchronous, and in view of the fact that the operation of the respective control switches K10 may be asynchronous, the voltage regulator tube D11 and the voltage regulator tube D9 can ensure that the thyristor switch 6 operates correctly.

[0043] If the stabilized voltage of the series-connected voltage regulator tube D11 and the voltage regulator tube D9 is too low, the pulse generated by the overvoltage triggering thyristor circuit 4 will cause the thyristor switch 6 to conduct improperly. If the stabilized voltage of the series-connected voltage regulator tube D11 and the voltage regulator tube D9 is too high, the withstand voltages of the thyristors D1 and D2 must be increased, which will result in an increased volume and investment in the on-load tap changer. If the stabilized voltage of the voltage regulator tube D9 is too high, a plurality of series-connected thyristor switches 6 cannot achieve the function according to point (2). After the series connection of the voltage regulator tube D11 and the voltage regulator tube D9, the stabilized voltage U 3 = k 2 (U 1 +U 2 ); k 2denotes a reliability coefficient and has a value of 1.1 to 1.5.

[0044] When the thyristor D1 (D2) is conducting, the thyristor D1 (D2) has a forward voltage drop, and the forward voltage drop of the thyristor D1 (D2) increases with the electric current flowing through it. The following is assumed: The forward voltage drop of the maximum current (including the instantaneous peak value of the short-circuit current that may flow through it) flowing through the thyristor D1 (D2) is U 4When switch K10 is turned on, the electric current first flows through diode D10 and switch K10 to trigger the gate electrode of thyristor D1 (D2), causing thyristor D1 (D2) to conduct. The voltages at both ends of thyristor D1 (D2) rapidly drop to the forward voltage drop, and when the sum of the tube forward voltage drops of all semiconductors connected in series in the trigger circuit to the gate electrode of thyristor D1 (D2) is greater than U 4 is, the electric current of the gate electrode circuit automatically disappears; if the sum of the tube forward voltage drops of all semiconductors connected in series in the trigger circuit of the gate electrode of the thyristor D1 (D2) is less than U 4is, high current flows through the gate electrode circuit of the thyristor D1 (D2) and damages the thyristor D1 (D2). If the sum of the tube forward voltage drops of all semiconductors of the trigger circuit of the gate electrode of the thyristor D1 (D2) is less than 1.2U 4 If the voltage drop is too high, a plurality of diodes can be connected in series to form D10 to increase the forward voltage drop of diode D10. If too many diodes D10 are connected in series, heating will be increased and the zero-current waveform will become deficient. The sum of the tube forward voltage drops of all semiconductors of the trigger circuit of the gate electrode of thyristor D1 (D2) is reasonably close to 1.5U. 4 . The sum of the forward voltage drops of the diodes D4, D7, D10, D6 and the gate electrode of the thyristor D1 is approximately 1.5U 4where the sum of the forward voltage drop of the diodes D3, D8, D10, D5 plus the gate electrode of the thyristor D2 is about 1.5U 4 lies.

[0045] In this embodiment, a combination of saturable reactor L4 and thyristor switch 6 is used to replace the main vacuum switch K1 of the main circuit in Embodiment 1. The main vacuum switch K1 itself has very strong anti-interference capability, but its operation requires greater mechanical force, resulting in sluggish operation. Electric arcing occurs during contact release, generating interference with other semiconductor devices. The control switch K10 of the thyristor switch 6 can be a miniature single-contact relay or a non-contact solid-state switch. The control voltage of the non-contact solid-state switch is small, the operation is faster, and the sensitivity is even higher. The interference with other semiconductor devices is small.The operating principle of the contactless solid-state switch and its control circuit is well known and will not be repeated here. The weak point of the thyristor switch 6 is that it can be subject to faulty operation due to interference pulses. To increase the interference immunity of the thyristor switch 6, saturable reactors L4 are connected in series. One function of the saturable reactor L4 is to reduce the rate of increase of the electric current at the conducting moment of the thyristor D1 (D2) in the thyristor switch 6. The other function of the saturable reactor L4 is that the saturable reactor L4 interacts with the resistor R1 and the capacitor C1 in the thyristor switch 6 to increase the interference immunity of the thyristor switch 6.

[0046] The working process of switching the conduction of the tap selector terminal I1 of the on-load tap-changer with the common terminal 3 to the conduction of the tap selector terminal II2 with the common terminal 3 is as follows: (1) switching of the changeover switch K6; (2) turning off the control switch K10; turning off the main circuit and automatically turning on the transfer circuit; (3) switching of the changeover switch K5; (4) turning on the control switch K10. Example 3:

[0047] A third embodiment of the thyristor-supported on-load tap-changer is as shown in Fig. 8. It includes: two tap selector terminals I1, II2, a common terminal 3, a main contact of an odd side K11, a main contact of an even side K12, four transfer switches K14, K15, K16, K17, an overvoltage release thyristor circuit 4, a thyristor switch 6 controlled by a control switch K10, a linear reactor L1, two saturable reactors L2, L4, and a bidirectional voltage stabilizing circuit 7; a tap selector terminal I1 is connected to the transfer switches K15, K17, respectively, and the tap selector terminal II2 is connected to the transfer switches K14, K16, respectively. the other terminals of the transfer switches K14, K15 are connected in common and are also connected in series with the common terminal 3 of the on-load tap-changer through the saturable reactor L4 and the thyristor switch 6 controlled by the control switch K10 to form a main circuit;the other terminals of the transfer switches K16, K17 are connected in common and are also connected in series with the common terminal 3 of the on-load tap-changer through the linear reactor L1, the saturable reactor L2, and the overvoltage tripping thyristor circuit 4 to form a transfer circuit; the two ends of the odd-numbered side main contact K11 are respectively connected to the tap selector terminal I1 and the common terminal 3 of the on-load tap-changer, and the two ends of the even-numbered side main contact K12 are respectively connected to the tap selector terminal II2 and the common terminal 3 of the on-load tap-changer; the bidirectional voltage stabilizing circuit 7 is connected between the connection terminal of the transfer switches K14, K15 and the connection terminal of the transfer switches K16, K17.

[0048] The thyristor switch 6 is controlled by the switch K10; if K10 is turned on, the thyristor switch 6 conducts, and if K10 is turned off, the thyristor switch 6 does not conduct.

[0049] In Fig. 8, the main contact 11 on the odd-numbered side and the main contact K12 on the even-numbered side are contactors with locks, consisting of closing coils, trip coils (blocking release), main contacts, and auxiliary contacts. The four transfer switches K14, K15, K16, and K17 are contactors without locks, consisting of closing coils, main contacts, and auxiliary contacts.

[0050] The odd-side main contact K11 and the even-side main contact K12 are used for long-term power supply. The thyristor switch 6 and the overvoltage release thyristor circuit 4 can operate in short-term mode, and the thyristor D1 (D2) does not require a complex heat dissipation device.

[0051] The control circuit of the switch for switching the conduction of the tap selector terminal I1 of the on-load tap changer with the common terminal 3 to the conduction of the tap selector terminal II2 with the common terminal 3 is as in Fig. 9 shown.

[0052] M+ denotes a positive bus line for controlling the power supply, whereas M- denotes a negative bus line for controlling the power supply; K11-T denotes the trip coil (blocking release) of the contactor K11, where K11-1, K11-2 are the auxiliary contacts of the contactor K11; K12-H is the closing coil of the contactor K12, where K12-1 is the auxiliary contact of the contactor K12.K14-1, K14-2, K15-1, K15-2, K16-1 and K16-2 respectively denote auxiliary contacts of the transfer switches K14, K15, K16, where K10-1, K10-2, K10-3 denote the auxiliary contacts of the control switch K10 and KC1, KC2, KC3 and KC4 denote intermediate relays; BH denotes an output protection contact for when the operation of the on-load tap-changer is protected and prohibited, wherein contact BH is opened to interrupt the power supply to the control circuit M1; X1-2 denotes a command contact of a tap selector of the on-load tap-changer, wherein when the tap selector of the on-load tap-changer selects the current collector, contact X1-2 is turned on to notify the control circuit of the on-load tap-changer that it can start operation.

[0053] After being connected in series with the BH contact, the positive bus line M+ for power supply control is connected to one end of the KC1-2 contact, and the other end of the KC1-2 contact is connected to an M1 bus line; a node between the BH contact and the KC1-2 contact connects the auxiliary contact K12-1, the X1-2 contact and the KC1 coil in series with the M- bus line; the KC1-1 contact is also connected in parallel with the two ends of the X1-2 contact; M1 connects the KC3-1 contact and the K15 coil in series with the M- bus line; M1 connects the KC15-1 contact, the KC2-2 contact and the K10 coil in series with the M- bus line; M1 connects the KC2-3 contact and the K14-1 contact with a node between the KC2-2 contact and the K10 coil in series. a node between contact K15-1 and coil KC2-2 connects contact K10-1 and coil K11-T to bus line M- in series;M1 serially connects contact K16-1, contact K11-1, and coil K16 to bus line M-; a node between contact K16-1 and contact K11-1 is connected to the cathode of a diode D12, and a node between contact K10-1 and coil K11-T is connected to an anode of a diode D12; M1 serially connects contact K16-2 and coil KC2 to bus line M-; contact KC2-1 is connected in parallel to contact K16-2; M1 connects contact K11-2, contact KC2-4, contact K10-2, and coil KC3 to bus line M-; M1 serially connects contact KC3-2 to a node between contact K10-2 and coil KC3; a node between contact KC2-4 and contact K10-2 connects contact K15-2 and coil K14 in series with bus line M-; the node between contact KC2-4 and contact K10-2 connects contact K14-2, contact K10-3, and coil KC4 in series with bus line M-;a node between contact K14-2 and contact K10-3 connects contact KC4 and coil K12-H in series with bus line M-.;

[0054] The working process of switching from conducting the tap selector terminal I1 with the common terminal 3 to conducting the tap selector terminal II2 with the common terminal 3 is explained below: When contact X1-2 is turned on, contact K12 and contact X1-2 are turned on, coil KC1 is energized, contacts KC1-1, KC1-2 are turned on, and control circuit M1 transmits power and is self-maintained.

[0055] The normally open contact KC3-1 is switched on, the coil K15 is energized, the transfer switch K15 is switched off Fig. 8 is turned on, the thyristor switch 6 controlled by a control switch K10 is connected in parallel with the main contact K12 of the odd-numbered side; the contact K15-1 is turned on and the normally closed contact KC2-2 is turned on to connect to the coil K10, and the thyristor switch 6 controlled by the control switch K10 of the odd-numbered side Fig. 8 is switched on; contact K15-1 is switched on, contact K10-1 is switched on to establish a line to coil K11-T, the main contact K11 of the odd-numbered side of the Fig. 8 is turned off, the load current is transferred to the path of the thyristor switch 6; the contact K15-1 is turned on, the contact K10-1 is turned on, the contact K11-1 is turned on to establish a conduction to the K16 coil; the contact K16-1 is turned on to achieve self-maintenance of the conduction of the K16 coil, the transfer switch K16 off Fig. 8 is switched on, and the overvoltage release thyristor circuit 4 is switched on; the contact K16-2 is switched on to achieve conduction of the coil KC2, and KC2-1 is switched on to achieve self-maintenance for the conduction of the coil KC2; the contact KC2-2 is switched off, the coil K10 is no longer supplied with current, the thyristor switch 6 is switched off Fig. 8, which is controlled by a control switch K10, is turned off, and the load current is transferred to the path of the overvoltage release thyristor circuit 4; the contact K10-1 is turned off, the diode D12 prevents K16-1 from sending current to the coil K11-T; the contact K11-2 is turned on, the contact KC2-4 is turned on, the contact K10-2 is turned on to achieve conduction of the coil KC3; the contact KC3-2 is turned on to achieve self-maintenance for the conduction of the coil KC3; the contact KC3-1 is turned off, the coil K15 is no longer supplied with current; the transfer switch K15 of the Fig. 8 is switched off, the contact K15-2 is switched on to achieve a line of the coil K14, the transfer switch K14 from Fig. 8 is switched on to establish a parallel connection of the thyristor switch 6 controlled by a control switch K10 with the overvoltage release thyristor circuit 4; the contact K14-1 is switched on to ensure conduction of the coil K10 again, the thyristor switch 6 from Fig. 8, which is controlled by the control switch K10, is switched on again, and the load current is again transferred to the path of the thyristor switch 6, which is controlled by a control switch K10; the contact K10-3 is switched on to achieve conduction of the coil KC4; the contact KC4 is switched on to achieve conduction of the coil K12-H, the main contact K12 off Fig. 8 is turned on, the load current is transferred to the path of the main contact K12 to establish the conduction of the tap selector terminal II2 with the common terminal 3; at the same time, the normally closed contact K12 is turned off, the coil KC1 is no longer supplied with current, and the contact KC1-1 and contact KC1-2 are turned off to turn off the power supply of the control circuit, and the entire group of the control circuit is reset.

[0056] In the switch control circuit, the transition switch K15 is turned on first, followed by the control switch K10; the program is therefore straightforward. It is also possible to turn on the transition switch K15 and the control switch K10 simultaneously to reduce the total program time. In the switch control circuit, the odd-side main contact K11 is turned off first, and only after the load current has been transferred to the path of the thyristor switch 6 is the transition switch K16 turned on to allow access to the overvoltage trigger thyristor circuit 4; the program is therefore straightforward. It is also possible to turn off the odd-side main contact K12 and turn on the transition switch K16 at the same time to reduce the total program time.

[0057] For the control circuit of the switch for switching the conduction of the tap selector terminal II2 of the on-load tap-changer with the common terminal 3 to the conduction of the tap selector terminal I1 with the common terminal 3, see the interpretation of the above procedures, which will not be repeated again unnecessarily.

[0058] Traditional on-load tap-changers use a motor rotation drive mode, with a total operating time of 4.4 seconds, and the selector switch activity time of only 40 milliseconds. Most of this time is spent on energy accumulation and the preparation time of the mechanical mechanism. Regarding the thyristor-based on-load tap-changer, which uses an overvoltage tripping thyristor circuit 4 instead of a contact resistance R, the selector switch operating time is extended without generating heat and damaging the device. This eliminates the energy-accumulating mechanical mechanism and reduces the total operating time of the thyristor-based on-load tap-changer.The complicated mechanical connection mechanism and energy-accumulating mechanical mechanism are eliminated to reduce the volume and weight of the on-load tap-changer, thus reducing the failure rate. In particular, a control circuit such as an intermediate relay (contactor) can be used to realize sequential operation of the switch. The control method using an intermediate relay (contactor) can ensure that a particular switch only transitions to the next switch operation program after its operation is completed, thus increasing reliability.The operation of the tap selector does not require any intervention from the switch, and only after the tap selector completes its operation does the switch start operating, and no intervention from the tap selector is required for the switching process; and no bracket for the mechanical connection device is required between the tap selector and the switch, the logical relationship is clear, the structure is simple, and the coordination is convenient.

[0059] With regard to the Fig. In the thyristor-based on-load tap-changer shown in Figure 8, no electric current is generated during the switching-on or switching-off process of conducting the odd-side main contact K11, the even-side main contact K12, and the four transfer switches K14, K15, K16, and K17; electric arc-free switching is achieved, and frequent operation does not cause damage to the switch contact.

[0060] Modifications can be made to the thyristor-based on-load tap-changer based on the present embodiment as desired. For example: (1) A set of overvoltage release thyristor circuit 4, transistor switch 6, linear reactor L1, and a saturable reactor L2 can be added; thus, two of the four transition switches K14, K15, K16, and K17 can be omitted. This achieves the goal of reducing the number of mechanical switches. (2) The overvoltage release thyristor circuit 4 and the transistor switch 6 have a large number of identical elements and circuits; Fig. 3 and Fig. 7 can be combined to form a set of a new combined circuit, wherein the combined circuit can be switched between the two functions of the main circuit and the transfer switch by means of switching miniature switches, whereby one set of circuits has two functions. After being connected in series with the set of such a combined circuit, a transfer switch is connected in parallel to the tap selector terminal I1 and the common terminal 3; after being connected in series with another such set of a combined circuit, it is connected in parallel to the tap selector terminal II2 and the common terminal 3, so as to reduce the number of high-voltage mechanical switches, reduce the semiconductor elements, decrease the number of operating steps, and shorten the switching time.

[0061] If desired, the control circuit of the switch, which is located in Fig. 9 can be modified based on the present embodiment. A control circuit with an equivalent program and timing sequence can be implemented by various methods. The control circuit can be realized not only by the logical coordination of miniature intermediate relays, but also by using semiconductor devices. This is well known and will not be unnecessarily repeated here. Example 4:

[0062] The basic structure and connection type of a thyristor-supported on-load tap-changer is as in Fig. 2. It includes: two tap selector terminals I1, II2, a common terminal 3, two changeover switches K5, K6, a main vacuum switch K1, an overvoltage release thyristor circuit 4, a linear reactor L1, a saturable reactor L2, and a bidirectional voltage stabilizing circuit 7; a current collector terminal of a changeover switch K5 and a current collector terminal of a changeover switch K6 are commonly connected to the tap selector terminal I1, the other current collector terminal of the changeover switch K5 and the other current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal II2; the common terminal of the changeover switch K5 is connected through the main vacuum switch K1 to the common terminal 3 of the on-load tap changer to form a main circuit;The common terminal of the changeover switch K6 is connected in series with the common terminal 3 of the on-load tap-changer via the linear reactor L1, the saturable reactor L2, and the overvoltage tripping thyristor circuit 4 to form a transition circuit; a bidirectional voltage stabilizing circuit 7 is connected between the common terminal of the changeover switch K5 and the common terminal of the changeover switch K6.

[0063] The main vacuum switch K1 and the changeover switches K5, K6 are constructed from contactors with locks, closing coils, trip coils, main contacts and auxiliary contacts.

[0064] The sequential operation of the switches is realized by a control circuit of a switch of the on-load tap-changer, as shown in Fig. 10. M+ denotes a positive bus line for controlling the power supply, whereas M- denotes a negative bus line for controlling the power supply; K1-T is the trip coil of the K1 switch, and K1-H, K5-H, and K6-H are the closing coils of the switches K1, K5, and K6, respectively. Wherein K1-1, K1-2, K5-1, K5-2, K6-1, K6-2, and K6-3 are the auxiliary contacts of the switches K1, K5, and K6, and KC1 and KC2 are intermediate relays; BH denotes an output protection contact for when the operation of the on-load tap-changer is protected and inhibited, and when the BH contact is turned off, the power supply to the control circuit M1 is interrupted; X1-2 denotes a command contact of the tap selector of the on-load tap-changer, and after the tap selector of the on-load tap-changer selects the current collector, the contact X1-2 is turned on to notify the control circuit on the on-load tap-changer to start operation.

[0065] The switch control circuit controls the power supply contact sequence of the switch coil according to the contact operation sequence, achieving sequential operation of a series of electrical switches and the load circuit of the on-load tap-changer. For the working procedures of the switch control circuit, see Example 3; this will not be redundantly repeated here. Example 5:

[0066] The basic structure and connection type of a thyristor-supported on-load tap-changer are described in Fig. 6. It includes two tap selector terminals I1, II2, a common terminal 3, two changeover switches K5, K6, a thyristor switch 6 controlled by a control switch 10, an overvoltage release thyristor circuit 4, a linear reactor L1, two saturable reactors L2, L4, and a bidirectional voltage stabilizing circuit 7; one current collector terminal of the changeover switch K5 and one current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal I1, the other current collector terminal of the changeover switch K5 and the other current collector terminal of the changeover switch K6 are commonly connected to the tap selector terminal II2; the common terminal of the changeover switch K5 is connected to the common terminal 3 of the on-load tap changer by means of the saturable reactor L4 and the thyristor switch 6 controlled by the control switch K10 to form a main circuit;The common terminal of the switch K6 is connected in series with the common terminal 3 of the on-load tap-changer through the linear reactor L1, the saturable reactor L2, and the overvoltage trigger thyristor circuit 4 to form a transition circuit; the bidirectional voltage stabilizing circuit 7 is connected between the common terminal of the switch K5 and the common terminal of the switch K6.

[0067] The control switch K10 and the changeover switches K5, K6 are contactors with locks and are composed of closing coils, tripping coils, main contacts and auxiliary contacts.

[0068] The sequential operation of the switches is achieved by a control circuit of the switch of the on-load tap-changer, as in Fig. 11. M+ denotes a positive bus line for controlling the power supply, M- denotes a negative bus line for controlling the power supply; K10-T denotes a trip coil of the switch K10, and K10-H, K5-H, K6-H denote the closing coils of the switches K10, K5, and K6, respectively. K10-1, K10-2, K5-1, K5-2, K6-1, K6-2, and K6-3 are auxiliary contacts of the switches K10, K5, and K6, respectively; KC1 and KC2 denote intermediate relays; BH denotes an output protection contact; when the operation of the on-load tap-changer is protected and inhibited, the BH contact is turned off to cut off the power source of the control circuit M1. X1-2 denotes a command contact of a tap selector on an on-load tap-changer, and after the tap selector on the on-load tap-changer selects a current collector, the X1-2 contact is turned on to inform the control circuit of the on-load tap-changer that operation can begin.

[0069] The switch control circuit controls the contact operation sequence and the power supply connection sequence of the control circuit coil to implement the sequential operation of a series of electrical switches, thus completing the on-load tap-changer's load switching. For information on the switch control circuit's working procedures, see Example 3. It will not be redundantly repeated here. Example 6:

[0070] In embodiments 1, 2, 3, 4, and 5, the switch of the on-load tap-changer is commonly referred to as an on-load tap-changer. In the following embodiments 6, 7, 8, and 9, for the sake of clarity, the tap selectors of the thyristor-based on-load tap-changer and the switch are specifically referred to as tap selector 10 and switch 11, respectively. Tap selector 10 is connected to the current collectors of the regulating transformer, switch 11 is connected to tap selector 10, and after tap selector 10 selects the current collector of the regulating transformer, switch 11 implements load switching of two current collectors of the regulating transformer. A tap selector terminal I1 and terminal J1 of switch 11 are connected at one point.Therefore, the tap selector terminal I1 and the terminal J1 of the switch 11 can be considered as the same terminal; the tap selector terminal II2 and the terminal J2 of the switch 11 are connected at one point, which makes it possible to assume that the tap selector terminal II2 and the terminal J2 of the switch 11 are the same terminal; a common terminal 3 on the on-load tap changer is actually a switch terminal J3.

[0071] In some application situations, L1 in the switch (as in Fig. 8) of the third embodiment of the thyristor-based on-load tap-changer can be eliminated, while the rest can still function. This further improves efficiency with a small loss of safety.

[0072] In some application situations, L1, L2, L4 in the switch (as in Fig. 8) of the third embodiment of the thyristor-based on-load tap-changer can be eliminated, while the rest can still function. This further improves efficiency with a small loss of safety.

[0073] If L1, L2 and L4 in the switch (as in Fig. 8) of the third embodiment of the thyristor-based on-load tap-changer have been eliminated, the thyristor switch 6 in the main circuit and the overvoltage release thyristor circuit 4 in the transition circuit can be replaced by the Fig. 13 shown thyristor auxiliary circuit; KA in the thyristor auxiliary circuit as shown in Fig. 13, represents K10, KB is turned off, and the thyristor auxiliary circuit is equivalent to the thyristor switch 6; KA in the Fig. The auxiliary thyristor circuit shown in Figure 13 is turned off and KB is turned on, and the auxiliary thyristor circuit is equivalent to the overvoltage release thyristor circuit 4. In this way, two auxiliary thyristor circuits (first auxiliary thyristor circuit I and second auxiliary thyristor circuit II) each form two loops, where both loops can each have a main circuit and a transition circuit. By controlling the four small capacitance switches KA (K23-1) and KB (K25-1) in the first auxiliary thyristor circuit I, KA (K24-1) and KB (K26-1) in the second auxiliary thyristor circuit II, the same function as K14, K15, K16, and K17 in Fig. 8. When the first auxiliary thyristor circuit I is used as the main circuit, the second auxiliary thyristor circuit II is used as the transition circuit; when the second auxiliary thyristor circuit II is used as the main circuit, the first auxiliary thyristor circuit I is used as the transition circuit.

[0074] The structure and connection method of the switch 11 of the fourth embodiment of the thyristor-based on-load tap-changer is as shown in Fig. 12: It comprises a main switch K21-1 and a main switch K22-1, a first thyristor auxiliary circuit I and a second thyristor auxiliary circuit II and a piezoresistor R, three terminals J1, J2, J3; terminal J1 is connected to the odd-numbered terminal of the tap selector, terminal J2 is connected to the even-numbered terminal of the tap selector and terminal J3 is a common terminal.One end of the main switch K21-1 is connected to terminal J1, the other end of the main switch K21-1 is connected to terminal J3; the auxiliary thyristor circuit I is connected in parallel with the main switch K21-1; one end of the main switch K22-1 is connected to terminal J2, the other end of the main switch K22-1 is connected to terminal J3; the auxiliary thyristor circuit II is connected in parallel with the main switch K22-1; the end of the auxiliary thyristor circuit I close to J1 and the end of the auxiliary thyristor circuit II close to J2 are further connected to the piezoresistor R. The functions and requirements of the piezoresistor R are the same as those in 7 in the . Fig. 8. Therefore, this will not be repeated again unnecessarily.

[0075] The thyristor auxiliary circuit I and the thyristor auxiliary circuit II have the same structure and parameters, so only a single schematic diagram is provided, as in Fig. 13. They include: a pair of thyristors D1, D2 connected in reverse parallel to form a main circuit of the thyristor auxiliary circuit; a resistor R1 and a capacitor C1 are connected in series and also connected to the two ends of the thyristors D1, D2, which are connected in reverse parallel; the gate electrodes and the cathodes of the two thyristors D1, D2 are respectively connected to the capacitors C2, C3, the resistors R2, R3 and the diodes D3, D4; the anodes of the diodes D3, D4 are respectively connected to the gate electrodes of the thyristors D1, D2; and the cathodes of the diodes D3, D4 are respectively connected to the cathodes of the thyristors D1, D2; the gate electrodes of the thyristors D1, D2 and the cathodes of the diodes D3, D4 are respectively connected to the cathodes of the thyristors D1, D2;The input terminal of a full-bridge rectifier composed of diodes D5, D6, D7, and D8 is connected between the gate electrodes of two thyristors D1, D2 after being connected in series with a switch KB. The output end of the full-bridge rectifier is connected to a voltage regulator tube D9, and the cathode of the voltage regulator tube D9 is connected to another output end of the full-bridge rectifier. Diodes D13, D14, and D15 are connected in series in the same direction, and diodes D16, D17, and D18 are connected in series in the same direction. The two diode strings are connected in series with a switch KA after being reversed and connected in parallel. They are also connected between the gate electrodes of the two thyristors D1, D2.

[0076] KA of the thyristor auxiliary circuit I in Fig. 12 is indicated by K23-1, KB in the Fig. 12 is indicated by K25-1; KA of the thyristor auxiliary circuit II in the Fig. 12 is indicated by K24-1, KB in the Fig. 12 is indicated by K26-1.

[0077] Under the condition that KB is turned off, the thyristor auxiliary circuits I and II are equivalent to a control switch controlled by KA. Fig. 13 shows that when switch KA is turned on, the auxiliary thyristor circuit conducts, and when the conduction of switch KA is turned off, the conduction of the auxiliary thyristor circuit is also interrupted. After switch KA is turned on, the current flowing through switch KA is very small. The conduction or interruption of the high-voltage path of thyristors D1, D2 can be controlled by a small-capacitance switch KA to reduce the electric arc generated by the interruption of the load current and to increase the control speed and sensitivity of the switch. When switch KA is turned on, current flows through switch KA and opens the gate electrode of thyristor D1 (D2), causing thyristor D1 (D2) to conduct.The voltage at both ends of thyristor D1 (D2) drops rapidly toward the forward voltage drop of thyristor D1 (D2), and when the sum of the tube forward voltage drops of all semiconductors connected in series in the trigger circuit of the gate electrode of thyristor D1 (D2) is greater than the forward voltage drop of thyristor D1 (D2), the electric current of the trigger circuit of the gate electrode of thyristor D1 (D2) automatically disappears; and when the sum of the tube forward voltage drops of all semiconductors connected in series in the trigger circuit of the gate electrode of thyristor D1 (D2) is smaller than the forward voltage drop of thyristor D1 (D2), a large current flows through the trigger circuit of the gate electrode of thyristor D1 (D2), resulting in damage to thyristor D1 (D2). Fig. 13, diodes D13, D14, and D15 are connected in the same direction to form a diode string, and diodes D16, D17, and D18 are connected in the same direction to form another diode string. The two diode strings are connected between the gate electrodes of the two thyristors D1 and D2, after being connected in reverse parallel and in series with the normally open switch KB to improve the sum of the forward voltage drops of the trigger circuit of the thyristor D1 (D2). The more diodes connected in series, the better it can ensure that the current flowing through the switch KA is zero when the thyristor D1 and D2 is conducting; however, if too many diodes are connected in series, heating will increase and the zero-sequence current waveform will be deficient. It is appropriate to connect three diodes in series, positive and negative.

[0078] Under the condition that KA is turned off and KB is turned on, the auxiliary thyristor circuit I and the auxiliary thyristor circuit II are equivalent to the overvoltage release thyristor circuit. The stabilized voltage of a voltage regulator tube D9 is U 1 =k 1 U 2 ; k 1 is a reliability coefficient and has a value between 1.2 and 2; U 2 denotes the peak value of the operating frequency rated voltage for the connection between the connection terminals J1, J2 of the transfer switch and the tap selector of the thyristor-assisted on-load tap-changer. Preferably, k 1 a value of 1.5, which is relatively good. The operating characteristics of the overvoltage release thyristor circuit are the same as those in Example 1 and will therefore not be repeated unnecessarily. The auxiliary thyristor circuits I and II are structurally simple and highly reliable.

[0079] The conduction of terminal J1 of the on-load tap-changer switch with the common terminal J3 can be switched to the conduction of terminal J2 with the common terminal J3; the conduction of terminal J2 of the on-load tap-changer switch with the common terminal J3 can be switched to the conduction of terminal J1 with the common terminal J3. The operating procedure for switching the conduction of terminal J1 of the on-load tap-changer switch with the common terminal J3 to the conduction of terminal J2 with the common terminal J3 is as follows: Before switching, the main switch K21-1 is turned on, the main switch K22-1 is turned off, and the switches K23-1, K24-1, K25-1, and K26-1 are turned off. A power system is formed by the common terminal J3, the main switch K21-1, switch 11, terminal J1, and tap selector 10 with an odd-numbered current collector of the regulating transformer. The on-load tap changer receives a control command and first instructs tap selector 10 to select an even-numbered corresponding current collector switch, thus completing the selection of tap selector 10. The operating sequence of switch 11 is as follows: (1) Switch K23-1 is turned on; switch K26-1 is turned off. When switch K23-1 is turned on, auxiliary thyristor circuit I acts as the access circuit of the line switch. Switch K26-1 is turned on, and auxiliary thyristor circuit II acts as the access circuit of the overvoltage trigger thyristor circuit. Since the peak value of the maximum normal AC voltage is lower than the stabilized voltage of voltage regulator tube D9, voltage regulator tube D9 does not conduct, and the overvoltage trigger thyristor circuit does not conduct. (2) The main switch K21-1 is turned off. The load current is transferred to the thyristor auxiliary circuit I. (3) Switch K23-1 is turned off. The current of the n-type auxiliary thyristor circuit I is interrupted at a current zero crossing. At the moment of interruption of the current of the n-type auxiliary thyristor circuit I, the potential of terminal J3 drops (or rises) rapidly; the voltages at the two ends of the n-type auxiliary thyristor circuit II (overvoltage trigger thyristor circuit) generate instantaneous overvoltages. When the instantaneous overvoltage value reaches the stabilized voltage of the voltage regulator tube D9, the conduction of thyristor D1 or thyristor D2 is triggered, and the load current then flows in from terminal J2 and out from the common terminal J3 via the auxiliary thyristor circuit II. The load current is transferred from the auxiliary thyristor circuit I to the n-type auxiliary thyristor circuit II. (4) Switch K24-1 is turned on. Thyristor auxiliary circuit II is used as a line for the switch's access circuit. (5) The main switch K22-1 is turned on. The load current is transferred from the thyristor auxiliary circuit II to the main switch K22-1. (6) The entire group is reset.

[0080] From the above, it can be seen that switch K24-1 must be turned on only after switch K23-1 has been turned off, and the current of the thyristor auxiliary circuit I must be interrupted at the current zero crossing. Otherwise, if the current of the thyristor auxiliary circuit I is interrupted before the current zero crossing and switch K24-1 is turned on too early, the thyristor auxiliary circuit I and the thyristor auxiliary circuit II will create a short-circuit. However, the time between the turning off of switch K23-1 and the interruption of the current of the thyristor auxiliary circuit I at the current zero crossing is not clear. To ensure that switch 24-1 is not turned on until the current of the thyristor auxiliary circuit I has been interrupted at the current zero crossing, the time between the turning off of switch 23-1 and the turning on of switch 24-1 should be greater than 20 milliseconds.

[0081] Similarly, the operation of switching the conduction of terminal J2 of the on-load tap-changer switch with the common terminal J3 to conducting terminal J1 with the common terminal J3 is as follows: Before switching, the main switch K22-1 is turned on, the main switch K21-1 is turned off, and the switches K23-1, K24-1, K25-1, K26-1 are turned off; after the tap selector 10 has performed the selection of a current collector of a transformer; (1) the switch K24-1 is turned on; the switch K25-1 is turned on; (2) the main switch K22-1 is turned off; (3) the switch K24-1 is turned off; (4) the switch K23-1 is turned on; (5) the main switch K21-1 is turned on; (6) the entire group is reset.

[0082] The time between turning off switch K24-1 and turning on switch K23-1 should be greater than 20 milliseconds.

[0083] The switches K21-1, K22-1, K23-1, K24-1, K25-1, K26-1 can be operated manually, and the electrical switches are operated manually to become active sequentially to achieve the load switching of the switch.

[0084] Thyristor auxiliary circuit I and thyristor auxiliary circuit II are connected in series with a saturable reactor L2 to increase the safety of switch 11 of the fourth embodiment of a thyristor-based on-load tap-changer, while slightly reducing efficiency. In practical applications, the balance between safety and efficiency can be considered.

[0085] In comparison of Fig. 12 and Fig. 8 the following is shown: L1, L2, L4 from Fig. 8 are in Fig. 12 has been eliminated, and the four large-capacity switches K14, K15, K16, K17 have also been eliminated. K21-1 in Fig. 12 is equivalent to K11 in Fig. 8, K22-1 in Fig. 12 is equivalent to K12 in Fig. 8, and a nonlinear resistor R in Fig. 12 is equivalent to a bidirectional voltage stabilizing circuit 7 in Fig. 8. In Fig. 12, four small capacity switches K23-1, K24-1, K25-1, K26-1 are used to replace the functions of the large capacity switches K14, K15, K16, K17 and switch K10 in Fig. 8. The switches that are in Fig. 12 are economically more efficient than those in Fig. 8 and are also more convenient to control. Example 7:

[0086] In Embodiment 6, the switches K21-1, K22-1, K23-1, K24-1, K25-1, and K26-1 can be manually operated, and the electrical switches are manually operated to sequentially achieve load switching of the switch 11. In fact, with regard to the switches K21-1, K22-1, K23-1, K24-1, K25-1, and K26-1, the electrical switches can be driven by a mechanical link mechanism to sequentially achieve load switching of the switch 11; however, the electrical switches can also be controlled by the contacts of a contactor (relay) to sequentially achieve load switching of the switch 11; a variety of methods can be employed, thereby providing flexibility in application.

[0087] In a variety of applications, the switches K21-1, K22-1, K23-1, K24-1, K25-1 and K26-1 are controlled by a contactor (relay) in order to realize the sequential load switching of the switch 11 even more simply and economically.The main switch K21-1 and the main switch K22-1 are contactors with locking devices and are composed of closing coils, trip coils (blocking solution), main contacts (main switches) and auxiliary contacts, while the switches K23-1, K24-1, K25-1 and K26-1 are contactors (or relays) without locking devices and are composed of closing coils, main contacts (switches) and auxiliary contacts. The operating state of the main contact is reflected by the auxiliary contact of the relay (contactor), ensuring that the transition to the operating program of the next switch occurs only after the operating state of a specific switch is confirmed, and that the transition to the operating program of the next switch occurs immediately after the operating state of the specific switch is determined; thus achieving a perfect combination of speed and reliability.

[0088] In the Fig. With the structure of switch 11 of the fourth embodiment of an on-load tap-changer with a thyristor as shown in FIG. 12, no large-capacity contactor (relay) is required other than the main switch. Switches K23-1, K24-1, K25-1, and K26-1 are each small-capacity switches, and the thyristor trigger circuit can be realized by turning on and off a small-capacity contactor (relay) to turn on and off a high-current thyristor, thereby switching the on-load tap-changer. The switch 11 of the on-load tap-changer, implemented by a contactor (relay), ensures that the switch of the on-load tap-changer is structurally simple, convenient in control, and inexpensive.

[0089] The main switch is switched on and off under the condition that the voltages at both ends of the switch are zero, and the main switch is also operated in an arc-free manner. The contactors (relays) K23-1, K24-1, K25-1, and K26-1 can also be operated in an arc-free manner.

[0090] The control circuit of the switch 11 for switching the conduction of the terminal J1 with the common terminal J3 of the fourth embodiment of thyristor-supported on-load tap-changer is switched by a contactor (relay) to a conduction of the terminal J2 with the common terminal J3, as shown in Fig. 15 (a).

[0091] M+ denotes a positive bus line for controlling the power supply, whereas M- denotes a negative bus line for controlling the power supply; K21T denotes a trip coil (blocking release) of a K21 contactor, where K21-1 denotes the main contact of the K21 contactor, and K21-2 denotes the auxiliary contact of the K21 contactor; K22H denotes a closing coil of the K22 contactor, K22-1 denotes the main contact of the K22 contactor, and K22-2 denotes the auxiliary contact of the K22 contactor. K23-1, K23-2, K23-3 denote the contacts of a relay K23, K24-1, K24-2 denote the contacts of a relay K24, K26-1, K26-2 denote the contacts of a relay K26, K1C-1, K1C-2 denote the contacts of a relay K1C, KC2-1, KC2-2 denote the contacts of a relay KC2, KC3-1 denotes the contact of a relay KC3 and KC4-1, KC4-2, KC4-3 denote the contacts of a relay KC4.

[0092] A normally open contact K21-2 and a relay coil K1C are connected in series between the bus lines M+ and M-; the normally open contact K21-2 is also connected at both ends in parallel with the normally open contact K1C-1. A normally open contact K1C-2 is connected between a bus line A and the bus M+. A normally closed contact KC2-1 and a relay coil K23 are connected in series between the bus line A and the bus line M-. A relay coil K26 is connected in series between the bus line A and the bus line M-. A normally open contact K26-2, a normally open contact K23-2 and the contactor trip coil K21T are connected in series between the bus line A and the bus M-. A normally closed contact K21-4 and a relay coil KC2 are connected in series with the bus line A and the bus M-.A normally open contact KC2-2, a normally closed contact K23-3, and a relay coil KC3 are connected in series between the bus line A and the bus line M-. A normally open contact KC3-1 and a relay coil KC4 are connected in series between the bus line A and the bus line M+. A normally open contact KC4-1 and a relay coil K24 are connected between a bus line A and a bus line M-. A normally open contact KC4-2, a normally open contact K24-2, and a contactor closing coil K22H are connected between the bus line A and the bus M-.

[0093] Its operating sequence is as follows: The bus lines M+, M- are connected to the power source. Contact K21-2 is switched on, relay K1C is activated, contact K1C-1 is switched on, relay K1C maintains itself. Contact K1C-2 is switched on. Contact KC2-1 is switched on, relay K23 is activated, contact K23-1 is switched off. Fig. 12 is switched on, the thyristor auxiliary circuit I is connected and acts as a switch. Relay K26 is activated, contact 26-1 is Fig. 12 is turned on, the auxiliary thyristor circuit II is turned on to serve as the overvoltage release thyristor circuit, and the overvoltage release thyristor circuit is not conducting. Contact K26-2 is turned on, contact K23-2 is turned on, the contactor trip coil K21T is energized, and the main contact K21-1 of the contactor is off. Fig. 12 is switched off. Contact K21-4 is switched on, relay KC2 is activated. Contact KC2-1 is switched off, relay K23 returns, contact K23-1 is switched off. Fig. 12 is turned off, and the current path of the thyristor auxiliary circuit I is interrupted at the current zero crossing. At the moment when the thyristor auxiliary circuit I interrupts the current flow at the current zero crossing, the thyristor auxiliary circuit II is connected to serve as an overvoltage release thyristor circuit. Contact KC2-2 is turned on, contact K23-3 is turned on, and relay KC3 is activated. Contact KC3-1 is turned on, and relay KC4 is activated. Contact KC4-1 is turned on, relay K24 is activated, and contact K24-1 of the thyristor auxiliary circuit II is off. Fig. 12 is turned on, and the auxiliary thyristor circuit II acts as a switch to conduct the circuit. Since the operating time of the relays KC3, KC4, and K24 is approximately 15 milliseconds, it can be ensured that contact KC4-1 is turned on more than 20 milliseconds after contact K23-1 is turned off, so that no short-circuit is created. Contact KC4-2 is turned on, contact K24-2 is turned on, and the contactor closing coil K22H is energized; the main contact K22-1 is off. Fig. 12 is switched on and the load current is transferred to circuits J3 and J2.

[0094] Similarly, the following design can be carried out: The control circuit of the switch for switching the conduction of the terminal J2 of the fourth embodiment of the thyristor-assisted on-load tap-changer with the common terminal J3 to the conduction of the terminal J1 with the common terminal J3, as shown in Fig. 15 (b). The operation Fig. 15 (b) is Fig. 15 (a) is very similar and will not be explained again unnecessarily. Example 8:

[0095] The operating power source of switch 11 of an on-load tap-changer is usually a local 220V low-voltage power supply. When a regulating transformer is connected in a Y-shape, a transformer current collector is close to a ground wire, and the electrical voltage of the transformer current collector is relatively low; the voltage between the contacts of switches K21-1, K22-1, K23-1, K24-1, K25-1, K26-1 and the operating power source is relatively low. If the coils of a regulating transformer are connected in a delta shape, the voltages of the contacts of the switches K21-1, K22-1, K23-1, K24-1, K25-1, K26-1 are high, and the voltage between the contacts of the switches K21-1, K22-1, K23-1, K24-1, K25-1, K26-1 and the operating power source is relatively high. The contacts of the switches K21-1, K22-1, K23-1, K24-1, K25-1, K26-1 and the operating power source must be well insulated, and the high-voltage insulating material is expensive.

[0096] This embodiment provides a power supply structure of a thyristor-assisted on-load tap-changer with lower insulation requirements between the contacts of switches K21-1, K22-1, K23-1, K24-1, K25-1, K26-1 and the operating power source. For ease of illustration, the structure and connection type of a thyristor-assisted on-load tap-changer of the current collector terminal are shown as in Fig. 16. It is assumed that the regulating transformer T1 has five current collector terminals, each connected to the input terminals B1, B2, B3, B4, and B5 of a tap selector 10 of the thyristor-based on-load tap-changer; the output terminal of the tap selector 10 is connected to the input terminals J1, J2 of a switch; a common terminal J3 of the switch 11 is connected to the power system.

[0097] For the current collector terminals B1, B2, B3, B4, and B5 of the regulating transformer, the centermost terminal (B3) is defined as the zero line; furthermore, it is connected to one terminal of the primary coil of a transformer T2; the current collector terminal B2 (or B4) of the regulating transformer close to the zero line is connected to another terminal of the primary coil of the transformer T2. The terminals B6 and B7 of a secondary coil of the transformer T2 supply an AC control voltage (e.g., AC 220V) for switch 11 of the thyristor-assisted on-load tap-changer; one terminal of the AC control voltage is defined as a zero line, and the zero line of the primary coil of the transformer T2 is connected to the zero line of the secondary coil of the transformer T2.

[0098] An AC control voltage terminal is used for input to a DC voltage stabilization power supply module 12; the DC voltage stabilization power supply module 12 outputs a DC voltage (such as B8, B9, 24 DC) or a plurality of DC voltages. The output of the DC voltage stabilization power supply module 12 supplies a DC control voltage to the switch 11 of the thyristor-based on-load tap-changer; the low-potential terminal is defined as the zero line, and the zero line of the DC control voltage is connected to the zero line of the AC control voltage.

[0099] The power supply of switch 11 of the original on-load tap-changer is a local low-voltage power supply, and the zero potential of the local low-voltage power supply is the same as the ground potential. When switch 11 of the on-load tap-changer is controlled by a contactor, the ground voltage of switch 11 is equal to the ground voltage of a specific terminal at terminals B1, B2, B3, B4, and B5, where terminals B1, B2, B3, B4, and B5 are all high voltages. The coil of the contactor is connected to the control power supply, and the potential difference between the contact and the coil is very high, so an expensive high-voltage contactor is required.

[0100] In this embodiment, the power supply to switch 11 of the thyristor-based on-load tap-changer is provided via a transformer T2, and the transformer T2 provides power only to the thyristor-based on-load tap-changer, with a small capacitance because the transformer is a small-capacity transformer. The neutral line of the power supply has the same potential as B3, and the maximum potential difference between the contact and the coil is equal to the potential difference between B1 and B3. The insulating withstand voltage requirements between the contactor coil and the switch are reduced, resulting in reduced manufacturing costs. In particular, with respect to on-load tap-changers of a 10 kV system, the potential difference between B1 and B3 is 5%, namely 500 VAC.The switch 11 of the thyristor-assisted on-load tap-changer can be made from a conventional AC contactor to reduce manufacturing costs.

[0101] The potential of the neutral line is equal to the potential of the central terminal among B1, B2, B3, B4 and B5, and the potential is very high; therefore, the withstand voltage between the neutral line and the ground is the maximum normal voltage between the B1 and B0 terminals of the regulating transformer to avoid insulation breakdown between the neutral line and the ground.

[0102] If the tap selector 10 of the thyristor-based on-load tap-changer also uses a contactor (relay) for implementation, the structure of the operating current source of the tap selector 10 of the on-load tap-changer is as shown in Fig. 16. The analysis procedure is the same as above and is therefore not repeated unnecessarily. Example 9:

[0103] The operating time of an on-load tap-changer in a power system is very short, and an on-load tap-changer is mostly in an inactive state. During the inactive period of the on-load tap-changer, when both ends of a thyristor auxiliary circuit are energized, the safety is relatively poor; when both ends of the thyristor auxiliary circuit are de-energized, the safety is relatively high. Fig. As for the structure of the changeover switch of the fourth embodiment of the thyristor-assisted on-load tap-changer shown in FIG. 12, it is relatively well-suited to allow only one current collector of the switch terminal J1 and the switch terminal J2 to be connected to the transformer during normal operation. For example, conducting the on-load tap-changer switch terminal J1 with a common terminal J3 is switched to conducting the switch terminal J2 with the common terminal J3. After the changeover of the changeover switch is completed, the tap selector disconnects the connection of J1 to the transformer. At this time, the voltages at both ends of the thyristor auxiliary circuit I and the thyristor auxiliary circuit II are zero, which ensures good safety.

[0104] During normal operation, when terminal J1 and terminal J2 of the transfer switch are still connected to the transformer and not disconnected, the structure of the switch of the fifth embodiment of the thyristor-assisted load tap-changer can be selected, wherein the switch includes a main switch K21-1, a main switch K22-1, a switch K27-1, a switch K28-1, a thyristor auxiliary circuit I, a thyristor auxiliary circuit II, a piezoresistor R, and three terminals J1, J2, and J3; one end of the main switch K21-1 is connected to terminal J1, and the other end of the main switch K21-1 is connected to terminal J3; one end of the thyristor auxiliary circuit I is connected to terminal J3, and the other side of the thyristor auxiliary circuit I is connected to terminal J1 through the switch K27-1. one end of the main switch K22-1 is connected to terminal J2 and the other end to terminal J3;One end of the thyristor auxiliary circuit II is connected to terminal J3, and the other end of the thyristor auxiliary circuit II is connected to terminal J2 through the switch K28-1; the end of the thyristor auxiliary circuit I connected to the switch K27-1 and the end of the thyristor auxiliary circuit II connected to the switch K28-1 are further connected to the piezoresistor R. This is as shown in ; Fig. 14 shown.

[0105] During the inactive time of the on-load tap-changer, K27-1 and K28-1 are turned off, and the electrical voltages at the two ends of the auxiliary thyristor circuit I and the auxiliary thyristor circuit II are each zero. Before the on-load tap-changer switch operates, K27-1 and K28-1 are turned on. After the on-load tap-changer switch operates, K27-1 and K28-1 are immediately turned off. The operating actions of the switch contacts K27-1 and K28-1 can be realized by an AC contactor. When the coil of an AC contactor K27 is energized, contact 27-1 of the contactor performs an operating action, and when the coil of the AC contactor 28 is energized, contact 28-1 of the AC contactor performs an operating action.Before the switch and the thyristor-based on-load tap-changer start operating, the coils of contactors K27 and K28 are first energized, and then the switch enters the operating program. After the thyristor-based on-load tap-changer has completed its operation, the power supply to the coils of the AC contactors K27 and K28 is cut off.

[0106] The remaining structure and the program of the fifth embodiment of the thyristor-supported on-load tap-changer are the same as in embodiment 6 and will not be explained again here unnecessarily.

[0107] The thyristor-based on-load tap changer and the associated method of the present invention can be completely designed and manufactured by existing technology, thus offering a wide application prospect. List of reference symbols 1 tap selector connection I 2 Step selector connection II 3 common connection 4 Overvoltage release thyristor circuit 5 reactor iron core 6 thyristor switches 7 bidirectional voltage stabilization circuit I first thyristor auxiliary circuit II second thyristor auxiliary circuit 10 step selectors 11 switches 12 DC voltage stabilization power supply module

Claims

[1] Thyristor-assisted on-load tap changer, characterized by that it is constructed from a tap selector and a switch; the tap selector is connected to the switch, and after the tap selector has selected the current collector of a regulating transformer, the switch implements a load switching of the current collector; wherein the switch comprises a first main switch (K21-1), a second main switch (K22-1), a first thyristor auxiliary circuit (I) and a second thyristor auxiliary circuit (II), a piezoresistor (R) and a first terminal (J1) as well as a second terminal (J2) and a third terminal (J3); wherein one end of the first main switch (K21-1) is connected to the first terminal (J1) and the other end of the first main switch (K21-1) is connected to the third terminal (J3); wherein the first thyristor auxiliary circuit (I) is connected in parallel with the first main switch (K21-1); wherein one end of the second main switch (K22-1) is connected to the second terminal (J2) and the other end of the second main switch (K22-1) is connected to the third terminal (J3); wherein the second thyristor auxiliary circuit (II) is connected in parallel with the second main switch (K22-1); wherein the end of the first main switch (K21-1) connected to the first terminal (J1) and the end of the second main switch (K21-2) connected to the second terminal (J2) are further connected to the piezoresistor (R); wherein a pair of switches is arranged respectively in the first thyristor auxiliary circuit (I) and in the second thyristor auxiliary circuit (II) to control state switching of the corresponding thyristor auxiliary circuit, wherein the first thyristor auxiliary circuit (I) comprises a first switch (K23-1) of the first thyristor auxiliary circuit (I) and a second switch (K25-1) of the first thyristor auxiliary circuit (I), and wherein the second thyristor auxiliary circuit (II) comprises a first switch (K24-1) of the second thyristor auxiliary circuit (II) and a second switch (K26-1) of the second thyristor auxiliary circuit (II). [2] Thyristor-assisted on-load tap-changer, characterized by the following: a tap selector and a switch; wherein the tap selector is connected to the switch, and after the tap selector has selected the current collector of a regulating transformer, a load switching of the current collector is realized by the switch; wherein the switch comprises a first main switch (K21-1), a second main switch (K22-1), a first switch (K27-1), a second switch (K28-1), a first thyristor auxiliary circuit (I) and a second thyristor auxiliary circuit (II), a piezoresistor R and a first terminal (J1) and a second terminal (J2) and a third terminal (J3); wherein one end of the second main switch (K22-1) is connected to the first terminal (J1) and the other end of the second main switch (K22-1) is connected to the third terminal (J3); wherein one end of the thyristor auxiliary circuit (I) is connected to the third terminal (J3) and the other end of the thyristor auxiliary circuit is connected to the first terminal (J1) through the first switch (K27-1); wherein one end of the second main switch (K22-1) is connected to the second terminal (J2) and the other end of the main switch is connected to the third terminal (J3); one end of the thyristor auxiliary circuit (II) is connected to the third terminal (J3) and the other end of the thyristor auxiliary circuit (II) is connected to the second terminal (J2) through the second switch (K28-1); wherein the other end of the thyristor auxiliary circuit (I) is connected to the first switch (K27-1) and the other end of the thyristor auxiliary circuit (II) is connected to the second switch (K28-1), these being further connected to the piezoresistor (R); wherein a pair of switches is provided in each of the thyristor auxiliary circuit (I) and the thyristor auxiliary circuit (II) to control a state switch of the thyristor auxiliary circuit, wherein the first thyristor auxiliary circuit (I) comprises a first switch (K23-1) of the first thyristor auxiliary circuit (I) and a second switch (K25-1) of the first thyristor auxiliary circuit (I), and wherein the second thyristor auxiliary circuit (II) comprises a first switch (K24-1) of the second thyristor auxiliary circuit (II) and a second switch (K26-1) of the second thyristor auxiliary circuit (II). [3] Thyristor-assisted on-load tap-changer according to claim 1 or 2, characterized by , that: the thyristor auxiliary circuit (I) and the thyristor auxiliary circuit (II) have the same structure: a pair of thyristors (D1, D2) are constructed in reverse and in parallel to form a main circuit of the thyristor auxiliary circuit; a resistor (R1) and a capacitor (C1) are connected in reverse parallel to the two ends of the thyristors (D1, D2); Gate electrodes and cathodes of the two thyristors (D1, D2) are each connected to capacitors (C2, C3), resistors (R2, R3) and diodes (D3, D4); wherein the anodes of the diodes (D3, D4) are each connected to the gate electrodes of the thyristors (D1, D2) and the cathodes of the diodes (D3, D4) are each connected to the cathodes of the thyristors (D1, D2); wherein the input terminal of the full-bridge rectifier constructed from the diodes (D5, D6, D7, D8) is connected, after the series connection, to a normally open switch (KB) between the gate electrodes of the two thyristors (D1, D2); wherein the output end of the full-bridge rectifier is connected to the voltage regulator diode (D9), the cathode of the voltage regulator diode (D9) being connected to the output end of the anode of the full-bridge rectifier, wherein the anode of the voltage regulator diode (D9) is connected to the output end of the cathode of the full-bridge rectifier; wherein the diodes (D13, D14, D15) are connected in series in the same direction and the diodes (D16, D17, D18) are also connected in series in the same direction, wherein the two diode strings are connected in series with the normally open switch (KA), after being reversely connected in parallel, and then connected between the gate electrodes of the two thyristors (D1, D2). [4] Thyristor-assisted on-load tap-changer according to claim 1 or 2, characterized bythat: in the current collector terminals of the regulating transformer, the terminal located right in the middle is defined as the zero line, wherein the zero line and an adjacent current collector terminal of the regulating transformer are each connected to two terminals of the primary coil of the transformer (T2) and the terminal of a secondary coil of the transformer (T2) provides AC control voltage; wherein one terminal of the AC control voltage is defined as the zero line, wherein the zero line of the primary coil of the transformer (T2) is connected to the zero line of the secondary coil of the transformer (T2);the AC control voltage terminal is also used as an input for a DC voltage stabilization power supply module, wherein the DC voltage stabilization power supply module provides DC control voltage for the switch, wherein the low potential terminal of the DC control voltage is defined as the zero line of the DC control voltage, and wherein the zero line of the DC control voltage is connected to the zero line of the AC control voltage; [5] Operating method for thyristor-supported on-load tap-changer according to claim 1 or 2, characterized by : a. Operating method of switching the conduction of the first terminal (J1) of the switch of the on-load tap-changer with the common third terminal (J3) to the conduction of the second terminal (J2) with the common third terminal (J3) as follows: (1) Turning on the first switch (K23-1) of the first thyristor auxiliary circuit (I) and turning on the second switch (K26-1) of the second thyristor auxiliary circuit (II); (2) Turning off the first main switch (K21-1); (3) Turning off the first switch (K23-1) of the first thyristor auxiliary circuit (I); (4) Turning on the first switch (K24-1) of the second thyristor auxiliary circuit (II); (5) Turning on the second main switch (K22-1); (6) Resetting the entire group; b. Operating method of switching the conduction of the second terminal (J2) of the switch of the on-load tap-changer with the common third terminal (J3) to conducting the first terminal (J1) with the common third terminal (J3) as follows: (1) Turning on the first switch (K24-1) of the second auxiliary thyristor circuit (II) and turning on the second switch (K25-1) of the first auxiliary thyristor circuit (I); (2) Turning off the second main switch (K22-1); (3) Turning off the first switch (K24-1) of the second auxiliary thyristor circuit (II); (4) Turning on the first switch (K23-1) of the first auxiliary thyristor circuit (I); (5) Turning on the first main switch (K21-1); (6) Resetting the entire group. [6] Operating method according to claim 5, characterized bythat when switching the conduction from the first terminal (J1) of the switch of the on-load tap-changer with the common third terminal (J3) to the conduction of the second terminal (J2) with the common third terminal (J3), the time interval between the switching off of the first switch (K23-1) of the first thyristor auxiliary circuit (I) and the switching on of the first switch (K24-1) of the second thyristor auxiliary circuit (II) is greater than 20 milliseconds; wherein when switching the conduction from the second terminal (J2) of the switch of the on-load tap-changer with the common third terminal (J3) to the conduction of the first terminal (J1) with the common third terminal (J3), the time interval between the switching off of the first switch (K24-1) of the second thyristor auxiliary circuit (II) and the switching on of the first switch (K23-1) of the first thyristor auxiliary circuit (I) is greater than 20 milliseconds.

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