On-load tap changer

Abstract

To provide an on-load tap changer with a relatively simple configuration of a circuit related to a gate terminal of a thyristor.SOLUTION: In a voltage adjuster, an on-load tap changer including a plurality of changeover switches and a driving part 32 that drives the plurality of changeover switches to turn the switches on and conduct electricity includes a first thyristor Th11 and a second thyristor Th12 in which the plurality of changeover switches are each inversely connected in parallel, an inter-gate switch S1 is arranged between the first thyristor and a gate of the second thyristor, a first resistor R1 is arranged in parallel between a gate and cathode of the first thyristor for a PN joining part J3 formed by the cathode and gate of the first thyristor, and a second resistor R2 is arranged between the gate and a cathode of the second thyristor for a PN joining part formed by the cathode and gate of the second thyristor, and the driving part performs open-closing control of the inter-gate switch to thereby control the conduction at the changeover switches.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a load tap changer.

Background Art

[0002] A so-called indirect switching type voltage regulator includes a series transformer in which a secondary winding is connected in series to a distribution line, a regulating transformer in which a primary winding is connected in parallel to the distribution line and a plurality of taps are provided on the secondary winding, and a tap changer that switches the plurality of taps and connects them to the primary winding of the series transformer (for example, Patent Document 1). Patent Document 1 describes a tap switching device using a solid-state contactor including three pairs of thyristors connected in inverse parallel, one control power supply unit, and a control unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the tap switching device of Patent Document 1, the circuit related to the gate terminals of the thyristors connected in inverse parallel is not considered in terms of having a relatively simple configuration.

[0005] The present invention has been made in view of such circumstances, and provides a tap switching device capable of having a relatively simple configuration for a circuit related to the gate terminals of thyristors connected in inverse parallel.

Means for Solving the Problems

[0006] A load tap changer according to one aspect of the present disclosure is a load tap changer including a plurality of switching switches for switching a plurality of taps of a winding of a tapped transformer, and a driving unit that drives the plurality of switching switches to be turned on and conduct. Each of the plurality of switching switches includes a first thyristor and a second thyristor connected in inverse parallel. A gate-to-gate switch is disposed between the gate of the first thyristor and the gate of the second thyristor. A first resistor is disposed in parallel with respect to a PN junction formed by the cathode and the gate of the first thyristor between the gate and the cathode of the first thyristor. A second resistor is disposed in parallel with respect to a PN junction formed by the cathode and the gate of the second thyristor between the gate and the cathode of the second thyristor. The driving unit controls conduction in the switching switch by performing opening and closing control of the gate-to-gate switch.

[0007] In this aspect, the on-load tap changer includes a switching switch for switching and selecting the taps of the regulating transformer, and a driving unit that drives the switching switch to be on or off when performing control to switch the taps. The on-load tap changer configured in this way is included in a voltage regulating device configured by, for example, an LVR (Low Voltage Regulator) or a TVR (Thyristor type Step Voltage Regulator). That is, the voltage regulating device includes a series transformer, a regulating transformer, and an on-load tap changer. The on-load tap changer includes a switching switch for switching and selecting the taps of the regulating transformer, and a control unit and a driving unit that perform control to switch the taps by turning the switching switch on or off. The on-load tap changer constitutes a part of the voltage regulating device. The on-load tap changer has a plurality of taps, and a plurality of switching switches are provided in parallel according to the number of the taps. Each of the plurality of switching switches includes two thyristors composed of a first thyristor and a second thyristor connected in inverse parallel, and a gate-to-gate switch that connects the gates (control terminals) of the first thyristor and the second thyristor. When driving each switching switch to be on based on a driving signal from a control unit that controls the switching of the switching switch, the driving unit can turn on (conductive state) the thyristor (the thyristor on the forward bias side) connected in the forward direction with respect to the polarity of the applied voltage by turning on (closing) the gate-to-gate switch. That is, by closing (turning on) the gate-to-gate switch provided between the gate of the first thyristor and the gate of the second thyristor, the first thyristor and the second thyristor can be turned on (conductive state) using the power supply of the circuit to which the gates of these first thyristor and the second thyristor are connected (the circuit connected to the anodes and cathodes of these thyristors). In a state where the gate-to-gate switch is open (off) (when open), since no current flows through the gate of the thyristor (the thyristor on the forward bias side) connected in the forward direction with respect to the polarity of the applied voltage via the gate-to-gate switch, the thyristor on the forward bias side can be turned off (open state).In each of these two thyristors (the first thyristor and the second thyristor), resistors (the first resistor and the second resistor) are arranged in parallel with respect to the PN junction formed by the cathode and the gate. In this way, the resistor (parallel resistor) additionally arranged for the thyristor forms part of a path for flowing a current (gate current) from the cathode of the thyristor on the reverse bias side to the gate of the thyristor on the forward bias side with respect to the polarity of the applied voltage. The resistor (parallel resistor) may have a sufficiently small resistance value (for example, 50 Ω) as compared with the impedance at the time of reverse bias in the PN junction at the anode and the PN junction between the anode and the gate. By providing a gate-to-gate switch between the gate of the first thyristor and the gate of the second thyristor in this way, it is possible to perform opening and closing control of the switching switch using the power supply of the circuit to which the thyristor is connected, and it is possible to eliminate the need to provide the gate power supply separately from the power supply of the circuit to which the thyristor is connected. Further, in the first thyristor and the second thyristor, by adding a resistor (parallel resistor) arranged in parallel with respect to the PN junction (junction) formed by the cathode and the gate, even if the voltage is relatively low (for example, less than 1 V) with respect to the forward PN junction, if a voltage division occurs even slightly when showing the forward characteristic, it is possible to suppress the occurrence of malfunction such as the gate current flowing and the thyristor arcing. Therefore, by using these gate-to-gate switch and resistor (parallel resistor), it is possible to configure a load tap changer in which the circuit related to the gate terminals of the thyristors connected in inverse parallel is relatively simple and inexpensive.

[0008] In a load tap changer according to an aspect of the present disclosure, a first capacitor is arranged in parallel with the first resistor between the gate and the cathode of the first thyristor, and a second capacitor is arranged in parallel with the second resistor between the gate and the cathode of the second thyristor.

[0009] In this aspect, for each of the thyristors (the first thyristor and the second thyristor), for each of the additionally arranged resistors (the first resistor and the second resistor), capacitors (the first capacitor and the second capacitor) are arranged in parallel. Accordingly, a first parallel circuit is constituted by the first resistor and the first capacitor, and a second parallel circuit is constituted by the second resistor and the second capacitor. By arranging (connecting) the capacitors in parallel with the resistors in this way, when the gate-to-gate switch is opened and closed (turned on / turned off), a relatively large change (temporal change) occurs in the voltage or current of the gate terminal included in the parallel circuit formed by these capacitors and resistors. Even when noise or the like occurs, it is possible to suppress or prevent the occurrence of malfunction by removing the noise. That is, the capacitor connected in parallel with the resistor can function as a noise removal capacitor for preventing malfunction.

[0010] In the load tap changer according to one aspect of the present disclosure, the gate-to-gate switch is constituted by an insulated bidirectional semiconductor element.

[0011] In this aspect, across both ends of the inter-gate switch, substantially all circuit voltages in the circuit to which the thyristor is connected appear (all voltages are applied). On the other hand, the inter-gate switch is configured as an insulated bidirectional semiconductor element such as a phototriac, for example, to insulate the control circuit for controlling the opening and closing of the inter-gate switch from the circuit to which the thyristor is connected (the circuit to which the voltage for performing voltage transformation is applied), and the influence from a relatively high voltage to be transformed can be mitigated for the control circuit. In the inter-gate switch configured with a phototriac or the like, the element connecting between the gates of the first thyristor and the second thyristor (the triac section in the phototriac) can ensure reliability by using an element capable of bearing the circuit voltage. The voltage resistance of the inter-gate switch may be equal to or higher than the voltage resistance of each of the thyristors (the first thyristor, the second thyristor). Thereby, while suppressing the component cost due to the thyristor, the reliability in the load tap changer can be effectively ensured. Note that in this aspect, the inter-gate switch is an insulated bidirectional semiconductor element such as a phototriac, but is not limited thereto. The inter-gate switch may be configured by, for example, a mechanical relay, a circuit using a photovoltaic coupler and a MOS relay, or a photo MOS relay.

[0012] In the load tap changer according to one aspect of the present disclosure, a snubber circuit is arranged in parallel with the first thyristor or the second thyristor.

[0013] In this aspect, the on-load tap changer includes a snubber circuit, and the snubber circuit is arranged (connected) in parallel with the first thyristor, the second thyristor, or both (the first thyristor and the second thyristor). That is, the first thyristor and the second thyristor are connected in parallel (antiparallel) with the directions of their anodes and cathodes reversed, and a parallel circuit including the snubber circuit is formed. By connecting the snubber circuit in parallel to the first thyristor and the second thyristor connected in this antiparallel manner, the snubber circuit can be shared for both the first thyristor and the second thyristor. By using the snubber circuit connected in parallel in this way, a sharp change in the voltage applied to or the current flowing through the gate terminal can be mitigated, and the burden on the gate terminal can be dispersed to the snubber circuit, thereby ensuring reliability.

[0014] In the on-load tap changer according to one aspect of the present disclosure, the drive unit starts conduction of the current in the changeover switch by closing the inter-gate switch. From the time when the drive unit closes the inter-gate switch until one of the first thyristor or the second thyristor arcs, current flows through either the first resistor or the second resistor connected in parallel to the other thyristor, thereby causing conduction of the current in the changeover switch.

[0015] In this aspect, the drive unit drives the gate switch connected to the gate terminals of the two thyristors (the first thyristor and the second thyristor) constituting the changeover switch to turn on (transition to a closed state) based on a drive signal from a control unit that controls the switching of the changeover switch. At this time, from the moment the gate switch is turned on until the forward thyristor arcs with respect to the polarity of the applied voltage, a current flows through the gate of the forward thyristor via the resistor and the gate switch connected to the reverse thyristor, and this current flows from the gate to the cathode of the forward thyristor and passes through the forward thyristor. After the forward thyristor is closed (conducting state) by the current flowing through the gate, a current flows from the anode to the cathode in the forward thyristor, and this current passes through the forward thyristor. Therefore, the time lag from the moment the gate switch is turned on until the forward thyristor arcs can be mitigated. By providing a resistor (parallel resistor) connected in parallel to the PN junction (junction: J3) formed by the cathode and the gate in this way, the voltage division ratio by the gate voltage is made very small, and for example, even when the gate switch is closed (turned on) at the moment when the phase of the circuit voltage is 90 degrees or 270 degrees, reliability can be ensured. That is, the moment when the phase of the circuit voltage becomes 90 degrees or 270 degrees is a case where the magnitude of the gate voltage and the time change (dv / dt) of the gate voltage are in the most severe state, but even in such a case, the opening and closing control of the changeover switch can be surely performed.

Advantages of the Invention

[0016] It is possible to provide a load tap changer that simplifies the circuit regarding the gate terminals of thyristors connected in inverse parallel.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0018] (Embodiment 1) Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a voltage regulating device including a switching switch Th1 according to Embodiment 1. The voltage regulating device 100 is configured by, for example, an LVR (Low Voltage Regulator) or a TVR (Thyristor type Step Voltage Regulator). In the forward power transmission state, it adjusts a single-phase AC voltage supplied from the power supply side on the left side of the paper surface and distributes single-phase AC to the load side on the right side of the paper surface via the distribution lines 1u, 1v. The voltage regulating device 100 adjusts a single-phase AC voltage supplied from the load side on the right side of the paper surface in the reverse power transmission state and distributes single-phase AC to the power supply side on the left side of the paper surface via the distribution lines 1u, 1v. Alternatively, the voltage regulating device 100 may be one that adjusts and distributes a three-phase AC voltage.

[0019] The voltage adjustment device 100 includes series transformers 11 and 12 in which secondary windings 112 and 122 are connected in series to distribution lines 1u and 1v respectively, and an adjustment transformer 2 (a tapped transformer) in which a winding 20 is connected in parallel to the distribution lines 1u and 1v. The secondary winding 112 of the series transformer 11 is provided on the distribution line 1u, and the secondary winding 122 of the series transformer 12 is provided on the distribution line 1v. That is, the voltage adjustment device 100 includes two series transformers 11 and 12. The voltage adjustment device 100 further includes a load tap changer 3 provided between the winding 20 of the adjustment transformer 2 and the primary windings 111 and 121 of the series transformers 11 and 12 respectively. The load tap changer 3 and the adjustment transformer 2 constitute a load tap changing transformer 200.

[0020] In the series transformers 11 and 12, primary windings 111 and 121 correspond to the secondary windings 112 and 122 respectively. The primary windings 111 and 121 are connected in parallel such that voltages with opposite phases are induced in the secondary windings 112 and 122 respectively. Let the terminals of the primary windings 111 and 121 corresponding to the load-side terminals of the secondary windings 112 and 122 be u1 and v1 respectively. Also, let the terminals of the primary windings 111 and 121 corresponding to the power supply-side terminals of the secondary windings 112 and 122 be u2 and v2 respectively.

[0021] The adjustment transformer 2 is a single-winding transformer that shares a part of the primary winding and the secondary winding. The winding 20 of the adjustment transformer 2 is connected between the distribution lines 1u and 1v. The winding 20 of the adjustment transformer 2, which is a single-winding transformer, includes a series winding 20a (Nt1) and a shunt winding 20b (Nt2), and the series winding 20a (Nt1) and the shunt winding 20b (Nt2) are divided by an intermediate tap t2. In terms of the number of turns of these shunt winding 20b (Nt2) and series winding 20a (Nt1), the number of turns of the shunt winding 20b (Nt2) may be larger than the number of turns of the series winding 20a (Nt1) (Nt2 > Nt1). In this case, the number of turns of the primary winding is the total value (Nt1 + Nt2) of the series winding 20a (Nt1) and the shunt winding 20b (Nt2). The number of turns of the secondary winding varies depending on the tap position.

[0022] The winding 20 has taps t1 and t3 drawn from one end and the other end, and an intermediate tap t2 located between the one end and the other end, which divides the winding 20 into a series winding 20a (Nt1) and a shunt winding 20b (Nt2). For the winding 20, any one of the taps t1 to t3 is connected to the primary-side terminals u2 and v1 of the series transformer 1a via the on-load tap changer 3, and the same or another one of them is connected to the primary-side terminals u1 and v2 of the series transformer 1a via the on-load tap changer 3. The case where the same tap is connected to each of the primary-side terminals of the series transformer 1a is the case of a through tap.

[0023] In this embodiment, the regulating transformer 2 is assumed to be a single-winding transformer, but it is not limited thereto, and the regulating transformer 2 may be a multi-winding transformer. When the regulating transformer 2 is a multi-winding transformer, the primary winding 21 is connected between the distribution lines 1u and 1v. The secondary winding 22 corresponding to the primary winding 21 has taps t1 and t3 drawn from one end and the other end, and an intermediate tap t2 drawn from between the one end and the other end, and tap control is performed in the same manner as in the case where the regulating transformer 2 is a single-winding transformer.

[0024] In order to measure the voltage applied to the winding 20 of the regulating transformer 2, the primary winding of the measuring transformer PT2 may be connected between the distribution lines 1u and 1v. The measuring transformer PT2 can measure the secondary-side voltage value (V2m) indicating the voltage on the load side. Further, the primary winding of the measuring transformer PT1 may be connected between the distribution lines 1u and 1v on the power supply side of the series transformer. The measuring transformer PT1 can measure the primary-side voltage value (V1m) indicating the voltage on the power supply side. Instead of the measuring transformer PT1 and the measuring transformer PT2, for example, means such as resistor voltage division may be used to detect the voltage between the distribution lines 1u and 1v.

[0025] The on-load tap changer 3 has six switching switches ThA, ThB, ThC, Th1, Th2, and Th3 for switching the taps t1 to t3 of the winding 20 of the regulating transformer 2. The configuration of the tap changer is not limited to that shown in FIG. 1. For example, it may be a configuration including a tap selection switch for polarity switching that switches the polarity of the voltage applied to the series transformer 1a.

[0026] The on-load tap changer 3 further includes a control unit 31 for controlling the switching of each of the above switching switches, and a driving unit 32 for driving each switching switch to be on based on a driving signal from the control unit 31. The secondary windings of the measuring transformer PT1, the measuring transformer PT2, and the current transformer CT1 (corresponding to the current detection unit) described later are connected to the control unit 31. The connection between the control unit 31 and the measuring transformer PT1, the measuring transformer PT2, and the current transformer CT1, and the connection between the driving unit 32 and each switching switch are not shown in the figure.

[0027] The control unit 31 is constituted by, for example, a microcomputer or the like, and has a CPU (Central Processing Unit) not shown in the figure and a storage unit 311 such as a ROM or a RAM. Voltage adjustment is controlled according to a control program stored in advance in the storage unit 311 such as a ROM. Information generated temporarily may be stored in the RAM. The storage unit 311 stores a tap position table and reference voltage values (V2ref: secondary-side reference voltage value, V1ref: primary-side reference voltage value) described later. The control unit 31 has a timer counter for measuring the elapsed time.

[0028] The tap t1 of the winding 20 is connected to one end of the changeover switches ThA and Th1 via a protective fuse (not shown; the same applies hereinafter), the tap t2 is connected to one end of the changeover switches ThB and Th2 via a fuse, and the tap t3 is connected to one end of the changeover switches ThC and Th3 via a fuse. The other ends of the changeover switches ThA, ThB, and ThC are connected to the terminals u1 and v2 on the primary side of the series transformer 1a via the connection line 3u. The other ends of the changeover switches Th1, Th2, and Th3 are connected to the terminals u2 and v1 on the primary side of the series transformer 1a via the connection line 3v.

[0029] Between the connection lines 3u and 3v, a series circuit of a current-limiting resistor RS and a short-circuiting switch ThS and both ends of a triac Tr1 (semiconductor switch) are connected. A triggering circuit Tg1 is connected to both ends of the triac Tr1, and the voltage across both ends of the triac Tr1 is supplied to the triggering circuit Tg1. The output of the triggering circuit Tg1 is connected to the gate of the triac Tr1.

[0030] On the output side of the connection point between the triac Tr1 and the above series circuit in the connection line 3u, the primary winding of a current transformer CT1 may be coupled in order to measure the line current of the single-phase alternating current output by the on-load tap changer 3. The primary winding of the CT1 may be coupled to the connection line 3v to measure the line current of the single-phase alternating current.

[0031] The short-circuiting switch ThS is for connecting and disconnecting the current-limiting resistor RS between the taps in order to short-circuit between the taps via the current-limiting resistor RS during the process of switching the taps t1 to t3. The triac Tr1 is triggered when an overcurrent is detected and each changeover switch is protected, or when the operation of the on-load tap changer 3 is stopped. In this case, since the terminals u1 and u2 and the terminals v1 and v2 on the primary side of the series transformer 1a are short-circuited, it is possible to prevent the primary side of the series transformer 1a from being in an open state.

[0032] By providing the current transformer CT1 at the above-described position, the currents flowing through the changeover switch and the short-circuiting switch ThS can be measured. When the triac Tr1 arcs, the current transformer CT1 can measure the current flowing from the primary windings 111 and 121 of the series transformer 1a to the triac Tr1. Therefore, for example, when a short-circuit accident occurs in the distribution lines 1u and 1v, the maximum current flowing through the distribution lines 1u and 1v can be calculated. When it is not necessary to detect the current flowing through the triac Tr1, the position where the current transformer CT1 is provided is not limited to the above-described position, and may be a position closer to the winding 20 than the connection point with the triac Tr1 on the connection line 3u. In the present embodiment, the triac Tr1 has been described, but the present invention is not limited thereto, and a circuit in which two thyristors are connected in antiparallel may be used instead of the triac Tr1.

[0033] FIG. 2 is a circuit diagram showing a configuration example of the changeover switch Th1. The configuration of each switch will be described using the changeover switch Th1 as an example. The same applies to the other changeover switches Th2, Th3, ThA, ThB, ThC and the short-circuiting switch ThS. The changeover switch Th1 includes a first thyristor Th11 and a second thyristor Th12 connected in antiparallel, and a gate switch S1 that openably and closably connects between the gate terminals of the first thyristor Th11 and the second thyristor Th12. That is, in the changeover switch Th1, the first thyristor Th11 and the second thyristor Th12 that conduct in one direction from the anode to the cathode are connected in parallel (antiparallel) so that the anodes and cathodes are opposite to each other. The anode of the first thyristor Th11 and the cathode of the second thyristor Th12 are connected to the connection line 3v. The cathode of the first thyristor Th11 and the anode of the second thyristor Th12 are connected to the tap t1 of the winding 20 of the regulating transformer 2.

[0034] The first thyristor Th11 and the second thyristor Th12 are arranged in the order of p-type semiconductor, n-type semiconductor, p-type semiconductor, and n-type semiconductor in the forward direction from the anode (A) to the cathode (K). A depletion layer is formed between the n-type semiconductor on the anode side and the p-type semiconductor of the gate (G). A PN junction is formed between these adjacent p-type semiconductor and n-type semiconductor. Therefore, in the first thyristor Th11 and the second thyristor Th12, a PN junction (junction: J1) between the p-type semiconductor and the n-type semiconductor on the anode side, a PN junction (junction: J2, depletion layer) between the n-type semiconductor on the anode side and the p-type semiconductor of the gate, and a PN junction (junction: J3) between the p-type semiconductor of the gate and the n-type semiconductor on the cathode side are formed.

[0035] The gate (G) of the second thyristor Th12 and the gate (G) of the first thyristor Th11 are connected to be openable and closable by a gate-to-gate switch S1 composed of an insulated bidirectional semiconductor element such as a phototriac. In this embodiment, the triac part in the phototriac is arranged between the gate terminals, and the photodiode part is arranged in a control circuit connected to the drive part. The drive part turns on the phototriac (on: when the switch is closed) by passing a current through the photodiode of the phototriac based on a drive signal from a control part that controls the switching of the switching switch Th1. In this embodiment, the gate-to-gate switch S1 is a phototriac, but is not limited thereto, and may be composed of, for example, a mechanical relay, a photovoltaic coupler and a circuit using a MOS relay, or a photo MOS relay.

[0036] For the PN junction (junction: J3) between the p-type semiconductor of the gate and the n-type semiconductor on the cathode side in the first thyristor Th11, the first resistor R1 and the first capacitor C1 are arranged in parallel. Therefore, a first parallel circuit composed of the PN junction (junction: J3), the first resistor R1, and the first capacitor C1 is formed between the cathode in the first thyristor Th11 and the phototriac (triac part).

[0037] For the PN junction (junction: J3) between the p-type semiconductor of the gate and the n-type semiconductor on the cathode side in the second thyristor Th12, the second resistor R2 and the second capacitor C2 are arranged in parallel. Therefore, a second parallel circuit composed of the PN junction (junction: J3), the second resistor R2, and the second capacitor C2 is formed between the cathode in the second thyristor Th12 and the phototriac (triac part).

[0038] In the illustration of this embodiment, when a positive voltage is applied to the upper side, that is, the anode side of the first thyristor Th11 (the cathode side of the second thyristor Th12), the gate voltage (the voltage between the gate and the cathode: the voltage between G and K) in the state where the gate-to-gate switch S1 is open (off) (when the switch is open) will be described.

[0039] The first thyristor Th11 is configured such that a positive voltage is applied to the anode side and a negative voltage is applied to the cathode side from an external (power supply). In this case, the PN junction (junction: J1) between the p-type semiconductor and the n-type semiconductor on the anode side of the first thyristor Th11 and the PN junction (junction: J3) between the p-type semiconductor of the gate and the n-type semiconductor on the cathode side are forward-biased. Only the PN junction (junction: J2) between the n-type semiconductor on the anode side and the p-type semiconductor of the gate in the first thyristor Th11 is reverse-biased. Therefore, most of the impedance between the anode and the cathode (between A-K) is due to the PN junction (junction: J2), and between the gate and the cathode (between G-K), it becomes the parallel combined impedance of the first resistor R1 (e.g., 50 Ω) and the forward bias (low impedance) of the PN junction (junction: J3). Thus, the value of the parallel combined impedance is less than 50 Ω. At this time, the voltage burden ratio between the gate and the cathode (between G-K) with respect to the anode and the cathode (between A-K) is, for example, less than 0.0001% (1 ppm = 50 / 50 M) when the impedance at the reverse bias of the PN junction (junction: J2) is 50 MΩ.

[0040] The second thyristor Th12 is such that a negative voltage is applied to the anode side and a positive voltage is applied to the cathode side from the outside (power supply). In this case, the PN junction (junction: J1) between the p-type semiconductor and the n-type semiconductor on the anode side of the second thyristor Th12, and the PN junction (junction: J3) between the p-type semiconductor of the gate and the n-type semiconductor on the cathode side are reverse-biased. Only the PN junction (junction: J2) between the n-type semiconductor on the anode side and the p-type semiconductor of the gate in the second thyristor Th12 is forward-biased. Therefore, most of the impedance between the anode and the cathode (between A and K) is due to the PN junction (junction: J1), and between the gate and the cathode (between G and K), it becomes the parallel combined impedance of the second resistor R2 (for example, 50 Ω) and the reverse bias (high impedance) of the PN junction (junction: J3). Thus, the value of the parallel combined impedance is approximately 50 Ω. At this time, the burden voltage ratio between the gate and the cathode (between G and K) with respect to between the anode and the cathode (between A and K) is less than 0.0001% (1 ppm = 50 / 50M) when the impedance at the reverse bias of the PN junction (junction: J1) is 50 MΩ, for example.

[0041] Due to the operation described above, when the gate-to-gate switch S1 is open (when the switch is released), almost all of the circuit voltage (+V: a relatively high voltage to be transformed) appears (is applied) across both ends of the gate-to-gate switch S1. In contrast, the gate-to-gate switch S1 can ensure reliability by using an element or mechanism (mechanical contact) that can bear the circuit voltage (+V).

[0042] The constants (rated voltage, current, power, capacitance, resistance value, etc.) of the first resistor R1, the second resistor R2, the second capacitor C2, and the first capacitor C1 connected in parallel in this way may be determined based on the nature of the power supply of the circuit to which the thyristors (the first thyristor Th11 and the second thyristor Th12) are connected, and the type or specifications of the thyristors. For example, when controlling at any phase with a commercial frequency AC power supply, in the worst case where the magnitude of the gate current and the time change of the gate current (di / dt) are the most severe, it is the case where the switching switch Th1 is closed (the gate-to-gate switch S1 is closed: on) when the phase of the circuit current is 90 degrees or 270 degrees. Also, in the worst case where the magnitude of the gate voltage and the time change of the gate voltage (dv / dt) are the most severe, it is the case where the switching switch Th1 is closed (the gate-to-gate switch S1 is closed: on) when the phase of the circuit voltage is 90 degrees or 270 degrees. At this time, regarding the gate voltage, since the voltage division ratio is extremely small, it does not pose a problem.

[0043] When the magnitude of the gate current and the time change of the gate current (di / dt) or the time change of the gate voltage (dv / dt) pose a problem, the constants of the resistors (the first resistor R1, the second resistor R2) and the capacitors (the first capacitor C1, the second capacitor C2) connected in parallel may be set, or a snubber circuit described later may be arranged in parallel. Thereby, while alleviating a steep change in voltage or current, the burden on the gate terminal can be dispersed to these snubber circuits, etc., to ensure reliability.

[0044] FIG. 3 is an explanatory diagram showing the current flow in the switching switch Th1 until the first thyristor Th11 arcs when the current flows from top to bottom. FIG. 4 is an explanatory diagram showing the current flow in the switching switch Th1 from the completion of the arcing of the first thyristor Th11 to the current zero crossing when the current flows from top to bottom. FIG. 5 is an explanatory diagram showing the current flow in the switching switch Th1 until the second thyristor Th12 arcs when the current flows from bottom to top. FIG. 6 is an explanatory diagram showing the current flow in the switching switch Th1 from the completion of the arcing of the second thyristor Th12 to the current zero crossing when the current flows from bottom to top. When an AC voltage of commercial frequency is applied to the switching switch Th1, the polarity of the applied voltage is reversed based on the frequency. In the illustration in this embodiment, the explanation will be divided into the case where the current flows from top to bottom and the case where the current flows from bottom to top due to the reversal of the voltage polarity.

[0045] When the current flows from top to bottom, the first thyristor Th11 is in the forward direction and the second thyristor Th12 is in the reverse direction with respect to the current (the applied positive voltage). At this time, the current flow until the first thyristor Th11 arcs from the point when the gate-to-gate switch S1 is closed (on: when the switch is closed) will be explained.

[0046] From the upper branch point that branches into the path to the cathode of the second thyristor Th12 and the path to the anode of the first thyristor Th11, the current flowing toward the second thyristor Th12 passes through the second resistor R2 and the gate-to-gate switch S1 and flows into the gate of the first thyristor Th11. The current flowing into the gate of the first thyristor Th11 flows through the cathode of the first thyristor Th11 (or the path to which the cathode terminal is connected) to the lower branch point that branches into the path to the anode of the second thyristor Th12 and the path to the cathode of the first thyristor Th11, thereby passing through the switching switch Th1.

[0047] When current flows into the gate of the first thyristor Th11 through the second resistor R2 and the inter-gate switch S1, thereafter, the first thyristor Th11 completes arcing and enters the conduction state (on: closed circuit state). From the time of completion of arcing until the current zero-crossing due to the AC voltage, the current from the upper branch point passes through the anode to the cathode of the first thyristor Th11 and flows to the lower branch point, thereby passing through the switching thyristor Th1. At this time, even if the inter-gate switch S1 is turned off (opened), the current continues to flow until the current zero-crossing due to the latch of the first thyristor Th11. Even when the inter-gate switch S1 is maintained in the on state, the internal resistance of the first thyristor Th11 in the conduction state (when closed) is extremely small compared to the resistance value of the second resistor R2 (for example, 50 Ω). Therefore, almost all of the current flows through the first thyristor Th11 with substantially little shunting through the path of the second resistor R2.

[0048] When the current flows from bottom to top, for the current (the applied positive voltage), the first thyristor Th11 is in the reverse direction and the second thyristor Th12 is in the forward direction. At this time, the current flow from the time when the inter-gate switch S1 is closed (on: when the switch is closed) until the second thyristor Th12 arcs is explained.

[0049] From the lower branch point that branches into the path to the cathode of the first thyristor Th11 and the path to the anode of the second thyristor Th12, the current flowing toward the first thyristor Th11 passes through the first resistor R1 and the inter-gate switch S1 and flows into the gate of the second thyristor Th12. The current flowing into the gate of the second thyristor Th12 flows to the upper branch point that branches into the path to the cathode of the second thyristor Th12 and the path to the anode of the first thyristor Th11 through the cathode of the second thyristor Th12 (or the path to which the cathode terminal is connected), thereby passing through the switching thyristor Th1.

[0050] When current flows into the gate of the second thyristor Th12 through the first resistor R1 and the inter-gate switch S1, thereafter, the second thyristor Th12 completes ignition and enters the conduction state (on: closed state). From the time of ignition completion until the current zero-crossing by the AC voltage, the current from the lower branch point passes through the anode to the cathode of the second thyristor Th12 and flows to the upper branch point, thereby passing through the switching thyristor Th1. At this time, even if the inter-gate switch S1 is turned off (opened), the current continues to flow until the current zero-crossing due to the latch of the second thyristor Th12. Even when the inter-gate switch S1 maintains the on state, the internal resistance of the second thyristor Th12 in the conduction state (when closed) is extremely small compared to the resistance value of the first resistor R1 (for example, 50 Ω). Therefore, almost all the current flows through the second thyristor Th12 with almost no shunt through the path of the first resistor R1.

[0051] (Embodiment 2) FIG. 7 is a circuit diagram showing a configuration example of the switching thyristor Th1 according to Embodiment 2 (snubber circuit). In the present embodiment, a snubber circuit is arranged (connected) in parallel to the first thyristor Th11, the second thyristor Th12, or both (the first thyristor Th11 and the second thyristor Th12). The snubber circuit may be configured, for example, as an RC snubber circuit in which a resistor and a capacitor are connected in series. Alternatively, the snubber circuit may be composed of only a capacitor.

[0052] The snubber circuit is provided between an upper branch point that branches into a path to the cathode of the second thyristor Th12 and a path to the anode of the first thyristor Th11, and a lower branch point that branches into a path to the anode of the second thyristor Th12 and a path to the cathode of the first thyristor Th11, thereby constituting a parallel circuit with the first thyristor Th11 and the second thyristor Th12 connected in anti-parallel.

[0053] Therefore, it is not necessary to connect a snubber circuit to each of the first thyristor Th11 and the second thyristor Th12. Since the two thyristors connected in antiparallel are connected in pairs at the same location on the circuit, a single snubber circuit can be shared by the first thyristor Th11 and the second thyristor Th12 and integrated into one. By using the snubber circuits connected in parallel in this way, for example, when the gate-to-gate switch S1 is turned on or off, a sharp change in the voltage applied to or the current flowing through the gate terminal of the first thyristor Th11 or the second thyristor Th12 can be mitigated, and the burden on the gate terminal can be dispersed to the snubber circuit, thereby ensuring reliability.

[0054] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is indicated not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

[0055] Regarding the plurality of claims described in the claims, they can be combined with each other regardless of the citation format. In the claims, multiple dependent claims dependent on a plurality of claims are described. In the claims, multiple dependent claims dependent on multiple dependent claims are not described, but multiple dependent claims dependent on multiple dependent claims may be described.

Description of Reference Numerals

[0056] 1u, 1v distribution lines, 100 voltage regulator, 11, 12 series transformers, 111, 121 primary windings, 112, 122 secondary windings, u1, u2, v1, v2 terminals, 200 on-load tap-changing transformer, 2 regulating transformer, 20 winding, 20a series winding, 20b shunt winding, 21 primary winding, 22 secondary winding, t1, t2, t3 taps, 3 on-load tap-changer, 31 control unit (microcomputer), 311 memory unit, 32 drive unit, Th1, Th2, Th3, ThA, ThB, ThC switching switches, Th11 first thyristor, R1 first resistor, C1 first capacitor, Th12 second thyristor, R2 second resistor, C2 second capacitor, S1 gate-to-gate switch, 3u, 3v connection lines, ThS cross-linking switch, RS current-limiting resistor, PT1, PT2 measuring transformers, CT1 current transformer, Tr1 triac, Tg1 ignition circuit

Claims

1. A load tap changer comprising a plurality of switching switches for switching a plurality of taps of a winding of a tapped transformer, and a driving unit for driving and conducting the plurality of switching switches, Each of the plurality of switching switches includes a first thyristor and a second thyristor connected in inverse parallel, A gate switch is disposed between the gate of the first thyristor and the gate of the second thyristor, A first resistor is disposed in parallel with respect to the PN junction formed by the cathode and the gate of the first thyristor between the gate and the cathode of the first thyristor, A second resistor is disposed in parallel with respect to the PN junction formed by the cathode and the gate of the second thyristor between the gate and the cathode of the second thyristor, The driving unit controls conduction in the switching switch by performing opening and closing control of the gate switch, Load tap changer.

2. A first capacitor is disposed in parallel with respect to the first resistor between the gate and the cathode of the first thyristor, A second capacitor is disposed in parallel with respect to the second resistor between the gate and the cathode of the second thyristor, The load tap changer according to claim 1.

3. The gate switch is composed of an insulated bidirectional semiconductor element, The load tap changer according to claim 2.

4. A snubber circuit is disposed in parallel with respect to the first thyristor or the second thyristor, The load tap changer according to claim 2.

5. The driving unit starts conduction of current in the switching switch by closing the gate switch, From the time when the drive unit closes the gate-to-gate switch until one of the first thyristor or the second thyristor arcs over, current flows through either the first resistor or the second resistor connected in parallel to the other thyristor, thereby enabling current conduction in the switching switch. The on-load tap changer according to any one of claims 1 to 4.

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