A load regulating switch, a voltage regulating transformer and a dynamic load regulating method

Abstract

This invention provides an on-load tap changer, a tap-changing transformer, and a dynamic on-load tap-changing method. The tap-changing transformer has multiple sub-windings connected in series. Each sub-winding includes a forward winding and a reverse winding. One end of the forward winding and the reverse winding are fixedly connected, and the other end is connected through the on-load tap changer. During the entire closing and opening process of the on-load tap changer, the power electronic switch can protect the contacts of the main relay and the auxiliary relay. The two relays also protect each other, achieving arc-free closing and opening, which greatly extends the life of the relays. Furthermore, the on-load tap changer, composed of relays and power electronic switches, has a simple structure, small size, low power consumption, light weight, low cost, and high reliability. When the on-load tap changer is applied to an on-load tap-changing transformer, by dynamically adjusting the closing and opening of the on-load tap changer, the forward winding and the reverse winding are connected in parallel or disconnected, achieving dynamic, arc-free, fast, stable, safe, and reliable voltage regulation.

Description

Technical Field

[0001] This invention relates to the field of power distribution transformer technology, and in particular to an on-load tap changer, a tap-changing transformer, and a dynamic on-load tap-changing method. Background Technology

[0002] Voltage quality is a crucial indicator for assessing the service level of a power grid. In particular, the magnitude of voltage deviation directly impacts the quality and output of industrial products, people's normal work and lives, and the safe and economical operation of the power grid. The most common method for voltage control in distribution networks is voltage regulation through distribution transformers. Currently, distribution transformers are divided into two types: off-load tap-changing transformers and on-load tap-changing transformers. While off-load tap-changing transformers offer advantages such as reliable operation and low cost, they also have disadvantages such as requiring power outages and having a limited voltage regulation range. On-load tap-changing transformers are increasingly widely used in power systems, playing a vital role in improving system voltage quality and power supply reliability.

[0003] However, most traditional on-load tap changers in on-load tap changers that drive load voltage regulation use current-limiting resistor transitions and oil arc extinguishing, immersing the tap changer contacts in transformer oil. Generally, the tap changer is very large, and the large arc generated when switching loads can easily burn the contacts, causing the transformer oil to deteriorate, affecting the transformer's insulation characteristics and service life. Therefore, the transformer oil needs to be changed regularly, resulting in high operating costs. Moreover, the tap changer has a slow voltage regulation response speed, cannot be operated frequently, has low efficiency, a complex mechanical transmission structure, a high failure rate, and a large maintenance workload. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide an on-load tap changer, a tap-changing transformer, and a dynamic on-load tap-changing method to improve the safety and reliability of the on-load tap-changing transformer.

[0005] This invention provides an on-load tap changer, comprising a main relay, an auxiliary relay, a power electronic switch, and a relay control module; the stationary contact of the main relay is connected to the stationary contact of the auxiliary relay, and the moving contact of the main relay is connected to a first terminal of the power electronic switch; the moving contact of the auxiliary relay is connected to a second terminal of the power electronic switch; the relay control module is used to control the closing of the main relay and the auxiliary relay when the input voltage crosses zero, and to control the opening of the main relay and the auxiliary relay when the output current crosses zero.

[0006] According to an on-load tap changer provided by the present invention, the power electronic switch is a diode, the cathode of the diode serves as the first terminal of the power electronic switch, and the anode of the diode serves as the second terminal of the power electronic switch.

[0007] According to the present invention, an on-load tap changer is provided, wherein the power electronic switch is a thyristor, an IGBT, or a MOSFET.

[0008] According to an on-load tap changer provided by the present invention, the relay control module includes: a measurement and control unit for detecting the input voltage and the output current, and sending control commands to a triggering unit; the triggering unit is used to provide trigger signals to the main relay and the auxiliary relay according to the control commands.

[0009] According to an on-load tap changer provided by the present invention, the relay control module further includes a control power supply unit, which is used to supply power to the control coils of the main relay and the auxiliary relay according to the trigger signal.

[0010] According to an on-load tap changer provided by the present invention, the closing and opening time of the main relay is within 10ms, and the closing and opening time of the auxiliary relay is within 10ms.

[0011] According to the present invention, the main relay of an on-load tap changer is a magnetic latching relay.

[0012] According to the present invention, the number of on-load tap changers is determined by using a 1248 encoding method based on the number of voltage regulation stages of the transformer.

[0013] The present invention also provides an on-load tap-changing transformer, comprising: a low-voltage side and a high-voltage side, wherein the low-voltage side includes a low-voltage winding, and the high-voltage side includes the aforementioned on-load tap-changing switch, and further includes a high-voltage side winding; the high-voltage side winding includes a fixed winding and a tap-changing winding connected in series; the tap-changing winding is a series connection of multiple sets of sub-windings, each set of sub-windings including a forward winding and a reverse winding, wherein one end of the forward winding and the reverse winding are fixedly connected, and the other end is connected through the on-load tap-changing switch.

[0014] The present invention also provides a dynamic on-load tap-changing method for the above-mentioned on-load tap-changing transformer, comprising: generating a tap-changing command based on the output voltage of the on-load tap-changing transformer on the low-voltage side; controlling the closing of the main relay and the auxiliary relay at the zero-crossing moment of the input voltage according to the tap-changing command, and controlling the opening of the main relay and the auxiliary relay at the zero-crossing moment of the output current.

[0015] This invention provides an on-load tap changer, a tap-regulating transformer, and a dynamic on-load tap-regulating method. The tap-regulating transformer has multiple sets of sub-windings connected in series. Each set of sub-windings includes a forward winding and a reverse winding. One end of the forward winding and the reverse winding are fixedly connected, and the other end is connected through the on-load tap changer. During the entire closing and opening process of the on-load tap changer, the power electronic switch can protect the contacts of the main relay and the auxiliary relay. The two relays also protect each other, achieving arc-free closing and opening, which greatly extends the life of the relays. Furthermore, the on-load tap changer, composed of relays and power electronic switches, has a simple structure, small size, low power consumption, light weight, low cost, and high reliability. When the on-load tap changer is applied to an on-load tap-regulating transformer, by dynamically adjusting the closing and opening of the on-load tap changer, the forward winding and the reverse winding are connected in parallel or disconnected, achieving dynamic, arc-free, fast, stable, safe, and reliable voltage regulation. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of an on-load tap changer provided by the present invention;

[0018] Figure 2 This is a simplified mathematical model diagram of a 400V distribution network containing distributed photovoltaic power, provided by the present invention.

[0019] Figure 3 This is a schematic diagram of the on-load voltage regulating circuit structure provided by the present invention;

[0020] Figure 4 This is a schematic diagram of voltage analysis of two coupled coils provided by the present invention;

[0021] Figure 5 This is a schematic diagram of another on-load tap changer provided by the present invention;

[0022] Figure 6 This is a schematic diagram of the 9-level on-load tap changer structure of a 10kV distribution transformer provided by the present invention;

[0023] Figure 7 This is a connection structure diagram of a coil and an on-load tap changer using the 1248 encoding method provided by the present invention;

[0024] Figure 8 This is a schematic diagram of a 9-level voltage regulation circuit using the 1248 encoding method provided by the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] The following is combined with Figures 1-8 This invention describes an on-load tap changer, a tap-changing transformer, and a dynamic on-load tap-changing method.

[0027] Please refer to Figure 1 , Figure 1 This is a schematic diagram of an on-load tap changer provided by the present invention.

[0028] This invention provides an on-load tap changer, comprising a main relay 1, an auxiliary relay 2, a power electronic switch 3, and a relay control module 4; the stationary contact of the main relay 1 is connected to the stationary contact of the auxiliary relay 2, and the moving contact of the main relay 1 is connected to the first terminal of the power electronic switch 3; the moving contact of the auxiliary relay 2 is connected to the second terminal of the power electronic switch 3; the relay control module 4 is used to control the closing of the main relay 1 and the auxiliary relay 2 when the input voltage crosses zero, and to control the opening of the main relay 1 and the auxiliary relay 2 when the output current crosses zero.

[0029] In recent years, with the development of distributed photovoltaic (PV) construction, for example, a village in northern China has 137 distributed PV power stations with a total capacity of 1128kW, involving 7 transformer substations. Faced with a large influx of PV power, the substation grid connection rate is as high as 64%, exceeding the grid's capacity. The weak absorption capacity of the regional power grid results in low power generation efficiency for some users, impacting residents' economic benefits.

[0030] With the large-scale integration of distributed photovoltaic (PV) systems, problems such as power backfeeding from the grid and overvoltage at users have gradually emerged. For example, in one power grid, there are currently 143,000 PV-connected distribution transformers, accounting for 33% of public distribution transformers, of which 117,000 transformers are experiencing power backfeeding. Taking a certain region as an example, 89% of PV users have experienced overvoltage problems, with 36% of users experiencing overvoltages exceeding 1.14 times their rated voltage, posing a significant challenge to the safe use of electrical equipment by users.

[0031] Please refer to Figure 2 , Figure 2 A simplified mathematical model diagram of a 400V distribution network containing distributed photovoltaic power, provided by this invention.

[0032] The power factor of 400V distribution networks is generally very high, close to 1.0. To simplify the derivation and calculation, we assume that all impedances are resistive. Based on a simple mathematical model of a 400V distribution network containing distributed photovoltaic power, we can derive:

[0033] U L =(I s +I p )*Z

[0034] Among them, U L U is the load voltage. S For the power supply voltage, I s For the power supply current, I p Z is the photovoltaic current source current. L For load, z p Z represents the internal impedance of the photovoltaic current source. s Z is the internal impedance of the power supply, Z0 is the line impedance, and Z is the Z0 internal impedance. L and z p The equivalent impedance after parallel connection is Z = Z L *z p / (Z L +z p )

[0035] It can be seen that when I p When increasing, maintain U L Stability only requires reducing I s And / or Z, where decreasing Z increases the load, which is more costly to achieve.

[0036] Because of I s =(U S -U L ) / (z s +Z0), for an established distribution network, (z s +Z0) remains basically unchanged, so it mainly affects I. s What changes is U S This refers to the output voltage of the distribution transformer. Therefore, on-load tap changing is one of the main measures to dynamically change the output voltage of the distribution transformer.

[0037] To address the technical problems of existing mechanical on-load tap changers, such as large electric arcs during load switching, easy contact erosion leading to transformer oil deterioration and high operating costs, slow voltage regulation response, infrequent operation, low efficiency, complex mechanical transmission structure, high failure rate, and heavy maintenance workload, this invention proposes an on-load tap changer, a voltage regulating transformer, and a dynamic on-load voltage regulation method using coupled inductance theory and AC soft-switching technology. When applied to low-voltage distribution transformers, this invention can increase the distributed photovoltaic absorption capacity of the distribution area to over 90%, while maintaining controllable costs.

[0038] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the on-load voltage regulating circuit provided by the present invention.

[0039] This invention proposes an on-load tap-changing circuit, which consists of multiple sub-windings connected in series. Each sub-winding includes a forward winding and a reverse winding. One end of the forward and reverse windings is fixedly connected, and the other end is connected via an on-load tap changer. The addition of the reverse winding partially cancels out the magnetic flux of the forward winding, thus effectively changing the voltage ratio between the primary and secondary sides of the transformer. The number of turns, material, and cross-sectional area of ​​the forward and reverse windings can be the same. Assuming the fixed winding is wound in the forward direction, the forward winding in the tap-changing winding is connected in series with the fixed winding. In each sub-tapping winding, under voltage action, if the on-load tap changer is closed, the forward and reverse windings with the same number of turns are connected in parallel. When currents of the same direction and magnitude flow through both windings, their magnetic fluxes cancel each other out, effectively acting as two parallel wires, becoming a non-inductive resistor with a very small resistance. If the on-load tap changer is open, since there is no current in the reverse winding, it does not affect the magnetic flux generated by the current in the forward winding.

[0040] To simplify the explanation, we will use a reverse winding as an example, and to highlight the key points, Figure 3 The transformer core is not shown. Assume the number of turns in the forward fixed windings at both ends is m, totaling 2m, and the number of turns in the middle forward winding is n. The forward winding and the fixed winding are connected in series. The number of turns in the reverse winding is n. One end of the middle forward winding is fixedly connected to one end of the reverse winding, and the other end of the reverse winding is connected to the other end of the middle forward winding via an on-load tap changer K. When the on-load tap changer K is open, the reverse winding has no effect; when the on-load tap changer K is closed, it is equivalent to the reverse winding and the forward winding being connected in parallel. Since their helical directions are opposite and their number of turns is the same, the magnetic flux cancels out under the action of current in the same direction, and the overall effect is resistance. Therefore, when the on-load tap changer K is open, the equivalent number of turns in the on-load tap changer circuit is 2m+n; when the on-load tap changer K is closed, the equivalent number of turns in the on-load tap changer circuit is 2m. Thus, the opening and closing of the on-load tap changer K regulates the equivalent number of turns in the on-load tap changer circuit.

[0041] Please refer to Figure 4 , Figure 4 This is a schematic diagram of voltage analysis for two coupled coils provided by the present invention.

[0042] Decompose the coils of the forward winding and the reverse winding. Assume that the two ends of the intermediate coil of the forward winding are A and B, and the two ends of the coil of the reverse winding are C and D, and the applied voltage is U. 施 If current i flows from A to B, then the magnetic flux... direction such as Figure 4 As shown. Based on the definition of the same-name terminals of a transformer, A and D can be identified as the same-name terminals. Therefore, the induced electromotive force U of the reverse winding... 感 C is positive and D is negative. Since both coils have the same number of turns, U... 施 =U 感 If A and C are connected together, due to U 施 =U 感 Therefore, B and D have the same potential, meaning there is no potential difference between them. If a switch is connected between B and D, then there are almost no requirements on the withstand voltage of the switch contacts.

[0043] Furthermore, based on the single-end opposite-side connection method of two coupled inductors, it can be deduced that the potentials of terminals B and D are the same after terminals A and C are connected together.

[0044] The on-load tap changer of the present invention includes a main relay 1, an auxiliary relay 2, a power electronic switch 3, and a relay control module 4.

[0045] The relay control module 4 controls the closing of the main relay 1 and the auxiliary relay 2 based on the zero-crossing moment of the input voltage. Specifically, before the on-load tap changer closes, both the main relay 1 and the auxiliary relay 2 are in the open state. When the input voltage crosses from positive to negative, the relay control module 4 controls the auxiliary relay 2 to close. During the closing process of the auxiliary relay 2, due to the blocking effect of the power electronic switch 3, there is no current in the circuit, so the contacts of the auxiliary relay 2 will not arc. After the auxiliary relay 2 closes, when the input voltage crosses from negative to positive, current flows in the circuit due to the closing effect of the power electronic switch 3. At this time, the relay control module 4 controls the main relay 1 to close. Since the voltage across the contacts of the main relay 1 is close to zero, arcing also does not occur. Afterwards, to extend the life of the auxiliary relay 2, the auxiliary relay 2 is then opened, thus completing the closing process of the on-load tap changer.

[0046] The relay control module 4 controls the opening of the main relay 1 and the auxiliary relay 2 based on the zero-crossing moment of the output current. Specifically, before the on-load tap changer opens, the main relay 1 is closed and the auxiliary relay 2 is open. The relay control module 4 then controls the auxiliary relay 2 to close. During the closing of the auxiliary relay 2, since the main relay 1 is closed, the contacts of the auxiliary relay 2 do not arc. After the auxiliary relay 2 closes, the relay control module 4 controls the main relay 1 to open when the output current crosses from negative to positive. Due to the bypass closing effect of the series circuit of the power electronic switch 3 and the auxiliary relay 2 in the positive current direction, the voltage across the contacts of the main relay 1 is close to zero, and no arcing occurs. The auxiliary relay 2 is opened after the output current crosses from positive to zero, thus completing the opening process of the on-load tap changer.

[0047] During the entire closing and opening process of the on-load tap changer, the power electronic switch 3 plays a dual role in protecting the contacts of the main relay 1 and the auxiliary relay 2. The two relays also protect each other, achieving arc-free closing and opening, thus achieving the effect of "AC soft switching" and greatly extending the life of the relays.

[0048] The relay control module 4 may include, but is not limited to, a microcontroller. The main relay 1, auxiliary relay 2, and power electronic switch 3 operate in a certain time sequence to realize the automated action of closing and opening the relays, and complete the switching of the transformer windings. The entire voltage regulation process does not require human intervention.

[0049] By coordinating the switching of the main relay 1, auxiliary relay 2, and power electronic switch 3 in the on-load tap changer, the reverse winding can be connected to the forward winding in parallel, thereby reducing or maintaining the original equivalent winding turns. Furthermore, the operation of the on-load tap changer can eliminate the generation of electric arcs during voltage regulation. Through the combined use of multiple tap-changing sub-windings and the on-load tap changer, the number of regulation levels can be increased several times over, increasing the voltage regulation range and accuracy of the distribution transformer. This keeps the voltage fluctuations at the load end within a reasonable range, greatly improving the safety and reliability of the transformer.

[0050] Please refer to Figure 5 , Figure 5 This is a schematic diagram of another on-load tap changer provided by the present invention.

[0051] In a preferred embodiment, the power electronic switch 3 is a diode, with the cathode of the diode serving as the first terminal of the power electronic switch 3 and the anode of the diode serving as the second terminal of the power electronic switch 3.

[0052] In this embodiment, the on-load tap changer includes a main relay 1, an auxiliary relay 2, a diode D, and a relay control module 4. Specifically, the stationary contact of the main relay 1 and the stationary contact of the auxiliary relay 2 are connected together to form a power input terminal in, which is connected to a tap of the high-voltage winding. The moving contact of the main relay 1 is connected in parallel with the cathode of the diode D to form a power output terminal out, which is connected to a tap of the voltage regulating winding. Then, the moving contact of the auxiliary relay 2 is connected to the anode of the diode D.

[0053] The relay control module 4 controls the closing of the main relay 1 and the auxiliary relay 2 at the zero-crossing point of the input voltage. Specifically, before the on-load tap changer closes, both the main relay 1 and the auxiliary relay 2 are in the open state. When the input voltage crosses from positive to negative, the relay control module 4 controls the auxiliary relay 2 to close. During the closing process of the auxiliary relay 2, due to the reverse blocking of diode D, there is no current in the circuit, so the contacts of the auxiliary relay 2 will not arc. After the auxiliary relay 2 closes, when the input voltage crosses from negative to positive, due to the forward conduction of diode D, current flows in the circuit. At this time, the relay control module 4 controls the main relay 1 to close. Since the voltage across the contacts of the main relay 1 is close to zero, arcing also does not occur. Afterwards, to extend the life of the auxiliary relay 2, the auxiliary relay 2 is then opened, thus completing the closing process of the on-load tap changer.

[0054] The relay control module 4 controls the disconnection of the main relay 1 and the auxiliary relay 2 at the moment the output current crosses zero. Specifically, before the on-load tap changer disconnects, the main relay 1 is in the closed state and the auxiliary relay 2 is in the open state. The relay control module 4 controls the auxiliary relay 2 to close. During the closing process of the auxiliary relay 2, since the main relay 1 is in the closed state, the contacts of the auxiliary relay 2 do not arc. After the auxiliary relay 2 closes, the relay control module 4 controls the main relay 1 to disconnect when the output current crosses from negative to positive. Due to the bypass closing effect of the series circuit of diode D and auxiliary relay 2 in the forward current, the voltage across the contacts of the main relay 1 is close to zero and no arc is generated. The auxiliary relay 2 disconnects after the series circuit of diode D and auxiliary relay 2 crosses from positive to zero, thus completing the disconnection process of the on-load tap changer.

[0055] Diodes have unidirectional conduction capabilities. Under forward bias, a diode has very low resistance and is in a closed state, acting like a closed switch. Under reverse bias, its resistance is very high and it is in a closed state, acting like an open switch. These switching characteristics of diodes can be used to construct various logic circuits.

[0056] Of course, the anode of the diode also serves as the first terminal of the power electronic switch, and the cathode of the diode serves as the second terminal of the power electronic switch. The principle is the same, only the zero-crossing time of the voltage (current) controlling the closing or opening of the relay is selected differently, which will not be elaborated here.

[0057] Therefore, this invention does not generate transformer losses, and since the on-load tap changer does not spark or arc when it operates, this will greatly extend the service life of the on-load tap changer. At the same time, it also enables frequent and dynamic adjustments to the on-load tap changer of the transformer, which is very beneficial to improving the power supply quality of the power grid.

[0058] In a preferred embodiment, the power electronic switch 3 is a thyristor, an IGBT (Insulated Gate Bipolar Transistor), or a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor).

[0059] Because of the use of electronic switches such as IGBTs and thyristors, especially IGBTs which have advantages such as fast switching speed, good thermal stability, low drive power, and simple drive circuit, IGBTs not only have good switching characteristics, but also eliminate the generation of conventional switching arcs during the transition process.

[0060] MOSFETs offer high control accuracy and a very short closing time, typically not exceeding a quarter of an AC cycle, thus allowing full utilization of their overcurrent characteristics.

[0061] In a preferred embodiment, the relay control module 4 includes: a measurement and control unit for detecting input voltage and output current and sending control commands to the triggering unit; the triggering unit is used to provide trigger signals to the main relay 1 and the auxiliary relay 2 according to the control commands.

[0062] In this embodiment, the relay control module 4 includes a measurement and control unit and a triggering unit. The measurement and control unit first measures the input voltage at the power input terminal in and the output current at the power output terminal out, providing a reference for the operation of the voltage regulating switch. The triggering unit generates a trigger signal according to the control command, closing or opening the main relay 1 or the auxiliary relay 2, so that the reverse winding is connected to the forward winding in parallel, thereby achieving the purpose of dynamic on-load voltage regulation.

[0063] In a preferred embodiment, the relay control module 4 further includes a control power supply unit, which supplies power to the control coils of the main relay 1 and the auxiliary relay 2 according to the trigger signal.

[0064] In this embodiment, the relay control module 4 further includes a control power supply unit. The control coil of the auxiliary relay 2... Apply a "+" power supply. Applying a negative power supply closes the contacts, and disconnecting the DC power supply opens the contacts. Main relay 1 has two control coils. and Applying a DC pulse will close the contacts of main relay 1. and Applying a DC pulse will open the contacts of main relay 1, and both coils are prohibited from having DC pulses applied simultaneously.

[0065] In order to achieve rapid voltage regulation of the transformer, as a preferred embodiment, the closing and opening time of the main relay 1 is within 10ms, and the closing and opening time of the auxiliary relay 2 is within 10ms, so that the transformer can quickly regulate voltage when using this on-load tap changer.

[0066] In a preferred embodiment, the main relay 1 is a magnetic latching relay, and the auxiliary relay 2 is a magnetic latching relay or a conventional relay.

[0067] In order to reduce the power consumption of the on-load tap changer, in this embodiment, the main relay 1 is a magnetic latching relay, and the auxiliary relay 2 is a magnetic latching relay or a conventional relay. These relays have advantages such as safety and reliability, long life, only pulse excitation required, low power consumption, strong load capacity, and small size. This can reduce the size of the transformer on-load tap changer and reduce the overall cost of the on-load tap changer.

[0068] Of course, when selecting diode D and auxiliary relay 2, attention should be paid to their half-wave peak withstand current.

[0069] As a preferred embodiment, the number of on-load tap changers is determined based on the number of voltage regulation stages of the transformer using the 1248 coding method.

[0070] Specifically, considering the 10kV / 400V on-load tap-changing distribution transformer used in mixed distributed photovoltaic and load applications, the output of photovoltaic power may vary greatly and frequently, requiring multiple adjustments.

[0071] Please refer to Figure 6 , Figure 6 A schematic diagram of the 9-level on-load tap changer structure of a 10kV distribution transformer provided by the present invention.

[0072] The 10kV high-voltage side winding has a structure with 9 taps and 8 on-load tap changers. The high-voltage winding is wound in the forward direction, and the tap-changing winding is wound in the reverse direction, with opposite ends (non-identical terminals) connected. ① in the diagram represents the number of coil turns corresponding to a basic tap-changing level difference. This structure can achieve 9 levels of linear tap regulation. Assuming the turns ratio is k (high voltage: low voltage) when all switches are open, the turns ratios corresponding to sequentially closing K1, K2...K8 are 0.975k, 0.95k...0.8k.

[0073] Clearly, this structure requires eight on-load tap changers, which is a relatively large number.

[0074] Please refer to Figure 7 , Figure 7 The diagram shows the connection structure of the coil and on-load tap changer using the 1248 encoding method provided by the present invention.

[0075] Using the 1248 encoding method reduces the number of taps and on-load tap changers, enabling an 8-level voltage regulation structure. In the diagram, ①, ②, and ④ represent the number of coil turns corresponding to one, two, and four basic voltage regulation levels, respectively. Using this encoding method, only three on-load tap changers are needed to achieve 8 levels of voltage regulation, which is significantly faster than... Figure 7 The structure is superior and the voltage regulation accuracy is higher.

[0076] Assuming the turns ratio is k (high voltage: low voltage) when all switches are open, and a basic voltage regulation step difference is 2.5%, the turns ratios corresponding to the opening and closing combinations of K1, K2, and K3 are shown in Table 1 below.

[0077] Table 1. Voltage Regulation Levels

[0078]

[0079]

[0080] Note: ○ indicates open, ┃ indicates closed.

[0081] Please refer to Figure 8 , Figure 8 A schematic diagram of a 9-stage voltage regulation circuit using the 1248 encoding method provided by the present invention.

[0082] To achieve 9-level voltage regulation, an on-load tap changer and a coil corresponding to the basic voltage regulation level are required. When K1, K2, K3 and K4 are all closed, the turns ratio is 0.8k.

[0083] The circuit is arranged using a 1248 encoding method, and the number of coils in the on-load tap changer and the regulating winding is the same. Assuming the number of coils in the on-load tap changer and the regulating winding is n, and the number of regulating stages is N, then n and N are constrained by the following relationship.

[0084] 2 (n-1) <N≤2 n

[0085] Where n = 1, 2, ... For example, when n = 3, the value range of N is 5 to 8; when n = 4, the value range of N is 9 to 16.

[0086] Similarly, the above examples can also be applied to on-load tap-changing transformers with higher voltage levels (33kV, 110kV, etc.), adjustable reactors in other high-voltage applications, and adjustable inductors, which will not be elaborated further in this invention.

[0087] Furthermore, even if individual on-load tap changers fail, the overall operation of the transformer will not be affected; of course, there is no need to set current-limiting resistors; and the connection at the tap does not require high-voltage switches, which greatly reduces the manufacturing and maintenance costs of the transformer.

[0088] The present invention also provides an on-load tap-changing transformer, comprising: a low-voltage side and a high-voltage side, the low-voltage side including a low-voltage winding, the high-voltage side including the aforementioned on-load tap-changing switch, and further including a high-voltage side winding; the high-voltage side winding including a fixed winding and a tap-changing winding connected in series; the tap-changing winding is a series connection of multiple sub-windings, each sub-winding including a forward winding and a reverse winding, one end of the forward winding and the reverse winding being fixedly connected, and the other end being connected through the on-load tap-changing switch.

[0089] For an introduction to the on-load tap-changing transformer provided by this invention, please refer to the above-described on-load tap-changing switch embodiment; the invention will not be described again here.

[0090] The present invention also provides a dynamic on-load tap-changing method for the above-mentioned on-load tap-changing transformer, comprising: generating a tap-changing command based on the output voltage of the on-load tap-changing transformer on the low-voltage side; and controlling the closing of the main relay and the auxiliary relay at the zero-crossing moment of the input voltage and controlling the opening of the main relay and the auxiliary relay at the zero-crossing moment of the output current, based on the tap-changing command.

[0091] The on-load tap-changing method of this invention controls the number of reverse-wound coils connected in parallel to the forward-wound coils in the multi-segment sub-winding of the high-voltage side tap-changing winding based on the voltage change on the low-voltage side of the tap-changing transformer. Specifically, the low-voltage side monitoring system detects the output voltage of the on-load tap-changing transformer, processes the data, generates a tap-changing command, and sends the command to the high-voltage side monitoring system. The command transmission can be wireless or fiber optic communication. Finally, the high-voltage side monitoring system, based on the tap-changing command, controls the closing of the main relay and auxiliary relay at the zero-crossing moment of the input voltage, achieving parallel connection of the reverse winding to the forward winding; and controls the opening of the main relay and auxiliary relay at the zero-crossing moment of the output current, disconnecting the reverse winding from the forward winding, thereby changing the equivalent turns ratio and thus altering the low-voltage side voltage.

[0092] For example, when the input voltage crosses zero from positive to negative, the control coil of auxiliary relay 2 is powered to control the closing of auxiliary relay 2; when the input voltage crosses zero from negative to positive, a DC pulse is supplied to the first control coil of main relay 1 to control the closing of main relay 1; when the output current crosses zero from negative to positive, a DC pulse is supplied to the second control coil of main relay 1 to control the opening of main relay 1; when the output current crosses zero from positive to negative, the power supply to the control coil of auxiliary relay 2 is disconnected to control the opening of auxiliary relay 2.

[0093] It should be noted that the operating coil of the main relay 1 only requires pulse excitation.

[0094] For an introduction to the on-load tap changing method of the dynamic on-load tap changing transformer provided by the present invention, please refer to the above-described on-load tap changing switch embodiment. The present invention will not be repeated here.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An on-load tap changer, characterized in that, Includes main relays, auxiliary relays, power electronic switches, and relay control modules; The stationary contact of the main relay is connected to the stationary contact of the auxiliary relay, and the moving contact of the main relay is connected to the first terminal of the power electronic switch. The moving contact of the auxiliary relay is connected to the second terminal of the power electronic switch; The relay control module is used to control the closing of the main relay and the auxiliary relay when the input voltage crosses zero, and to control the opening of the main relay and the auxiliary relay when the output current crosses zero.

2. The on-load tap changer according to claim 1, characterized in that, The power electronic switch is a diode, with the cathode of the diode serving as the first terminal and the anode of the diode serving as the second terminal.

3. The on-load tap changer according to claim 1, characterized in that, The power electronic switch is a thyristor, IGBT, or MOSFET.

4. The on-load tap changer according to claim 1, characterized in that, The relay control module includes: The measurement and control unit is used to detect the input voltage and the output current, and send control commands to the triggering unit; The triggering unit is used to provide trigger signals to the main relay and the auxiliary relay according to the control command.

5. The on-load tap changer according to claim 4, characterized in that, The relay control module further includes a control power supply unit, which is used to supply power to the control coils of the main relay and the auxiliary relay according to the trigger signal.

6. The on-load tap changer according to claim 1, characterized in that, The closing and opening times of the main relay are both within 10ms, and the closing and opening times of the auxiliary relay are both within 10ms.

7. The on-load tap changer according to claim 1, characterized in that, The main relay is a magnetic latching relay.

8. The on-load tap changer according to any one of claims 1 to 7, characterized in that, The number of on-load tap changers is determined based on the number of voltage regulation stages of the transformer using the 1248 coding method.

9. An on-load tap-changing transformer, characterized in that, It includes a low-voltage side and a high-voltage side. The low-voltage side includes a low-voltage winding, and the high-voltage side includes an on-load tap changer as described in any one of claims 1 to 8, and also includes a high-voltage side winding. The high-voltage side winding includes a fixed winding and a tap-regulating winding connected in series. The tap-regulating winding consists of multiple sets of sub-windings connected in series. Each set of sub-windings includes a forward winding and a reverse winding. One end of the forward winding and the reverse winding are fixedly connected, and the other end is connected through the on-load tap changer.

10. A dynamic on-load tap-changing method applied to the on-load tap-changing transformer of claim 9, characterized in that, include: A voltage regulation command is generated based on the output voltage of the on-load tap-changing transformer on the low-voltage side. According to the voltage regulation command, the main relay and the auxiliary relay are controlled to close when the input voltage crosses zero, and the main relay and the auxiliary relay are controlled to open when the output current crosses zero.

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