JP2016173971A - Dc shut-off device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC shut-off device capable of shutting off a fault point at a low cost.SOLUTION: The DC shut-off device is a device for shutting off a fault point in DC current power transmission systems D1 and D2 which are connected to each other by two power transmission lines W1 and W2. The DC shut-off device includes: an electric reactor L1 which is serially connected to the power transmission line W1; a mechanical shut-off device M1 which has a mechanical contact; a semiconductor shut-off device S1 which is connected in parallel to the electric reactor L1 and the mechanical shut-off device M1; and a semiconductor shut-off device S2 which is connected to a node between the electric reactor L1 and a mechanical shut-off device M1 and the power transmission line W2.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a DC interrupting device that isolates an accident point in a DC power transmission system.

  From the viewpoint of reducing environmental impact and diversifying power sources, power generation using renewable energy such as wind power generation and solar power generation has been spreading. These wind power and solar power generation have been increasing in scale, and are beginning to be put into practical use in offshore wind power generation, solar light in desert areas, solar thermal power generation, and the like. Since offshore and desert are geographically distant from demand areas such as urban areas, large power is transmitted over long distances. For such long-distance high-power transmission, high-voltage direct current (HVDC), which has a lower transmission cost than an AC transmission system, is applied.

  When HVDC is applied to long-distance high-current power transmission, it is possible to construct a high-efficiency system with low cost and low power transmission loss compared to an AC power transmission system. However, when a system accident caused by lightning strikes occurs, it is difficult to isolate the accident location. For example, when a mechanical contact is used, in an AC power transmission system, current can be interrupted at a current zero point that occurs every half cycle at a frequency of 50 Hz or 60 Hz. However, since a zero current point does not occur with a direct current, the current cannot be interrupted with a mechanical contact.

  Therefore, in the conventional HVDC, a DC circuit breaker having a configuration in which an LC circuit is connected in parallel to a mechanical circuit breaker has been proposed. In this circuit breaker, when the circuit breaker is closed, the circuit breaker is closed to cause a resonance current to flow from the LC circuit to the mechanical circuit breaker, thereby generating a current zero point for the mechanical circuit breaker to realize the circuit breaker. However, when the amplitude of the resonance current is not greater than a certain value, a zero current point cannot be created, so that it takes time until the amplitude is obtained, and it may take time to cut off. From such a background, a method of performing high-speed cutoff using a semiconductor element has been proposed.

International Publication No. 2012/045360 Specification European Patent Application No. 0867998

  However, in the interruption method using semiconductor elements, all of the transmitted power always passes through a plurality of semiconductor elements. Therefore, a large conduction loss occurs due to the resistance of the semiconductor element. Due to the increase in loss due to the semiconductor element, power transmission efficiency is reduced during normal operation. Therefore, in order to cover the decrease in power transmission efficiency, the apparatus has been increased in size and cost.

  The embodiment of the present invention has been proposed in order to solve the above-described problems of the prior art. The purpose is to provide a DC circuit breaker that can cut off the accident point and reduce the cost.

  A DC interrupting device according to an embodiment for achieving the above object is a DC interrupting device for disconnecting an accident point in a DC transmission system connected by two transmission lines, and is connected in series to the first transmission line. A first semiconductor breaker connected in parallel to the first reactor, the first mechanical disconnector having a mechanical contact, the first reactor, and the first mechanical disconnector; And a connection point between the first reactor and the first mechanical disconnector, and a second semiconductor circuit breaker connected to a second power transmission line.

It is a circuit diagram showing an example of composition of a direct-current circuit breaker of a 1st embodiment. In the DC circuit breaker according to the first embodiment, it is a path diagram showing a current path during steady operation. In the DC circuit breaker according to the first embodiment, it is a path diagram showing a current path when a ground fault occurs. In the DC circuit breaker according to the first embodiment, it is a path diagram showing a current path when the semiconductor circuit breaker is closed after an accident occurs. In the direct-current circuit breaker of 1st Embodiment, it is a path | route diagram which shows the electric current path | route at the time of opening a 1st semiconductor circuit breaker and a mechanical circuit breaker after accident occurrence. In the direct-current circuit breaker of 1st Embodiment, it is a route diagram which shows the electric current path | route at the time of opening a 2nd semiconductor circuit breaker after accident occurrence. It is a graph which shows the result of having measured the current of each composition part in the direct-current circuit breaker of a 1st embodiment. It is a circuit diagram which shows an example of a structure of the DC circuit breaker of 2nd Embodiment. It is a circuit diagram which shows the other structure of the direct-current circuit breaker of 2nd Embodiment. It is a circuit diagram which shows an example of a structure of the direct current | flow interruption | blocking apparatus of 3rd Embodiment. It is a circuit diagram which shows the other structure of the DC circuit breaker of 3rd Embodiment. It is a circuit diagram which shows the other structure of the DC circuit breaker of 4th Embodiment. It is a circuit diagram which shows the other structural example of a semiconductor cutoff device.

[First Embodiment]
[1. Constitution]
A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an example of the configuration of the DC interrupter of this embodiment. The direct current interrupt device interrupts direct current flowing through the direct current power transmission system. In the present embodiment, the DC power transmission systems D1 and D2 are connected by two power transmission lines W1 and W2. In the DC power transmission system D1, the side to which the transmission line W1 is connected is the positive side, and the side to which the transmission line W2 is connected is the negative side. During steady operation, current flows from the DC power transmission system D1 to the DC power transmission system D2 via the power transmission line W1. The DC interrupter is connected to two power transmission lines W1 and W2. The system impedance in the figure indicates the resistance of cables and overhead wires.

  The DC power transmission device includes reactors L1 and L2, a mechanical contact type current disconnector M1 (hereinafter referred to as a mechanical disconnector M1), and semiconductor breakers S1 and S2. A circuit in which reactors L1 and L2 and a mechanical disconnector M1 are connected in series is connected to the power transmission line W1. Specifically, from the DC power transmission system D1 side, the reactor L1, the mechanical disconnector M1, and the reactor L1 are arranged in this order. A semiconductor circuit breaker S1 is connected in parallel to the reactor L1 and the mechanical circuit breaker M1. The semiconductor circuit breaker S2 is connected between the connection point of the reactor L1 and the mechanical disconnector M1 and the power transmission line W2.

  The mechanical disconnector M1 has a mechanical contact. The mechanical disconnector M1 is configured to have a withstand voltage that can withstand a DC voltage necessary for disconnecting the accident point in a state where the mechanical contact is disconnected. The semiconductor circuit breakers S1 and S2 can use self-extinguishing switching elements such as IGBTs. Each of the semiconductor circuit breakers S1 and S2 is connected in parallel with non-linear element arresters A1 and A2 that conduct when a predetermined voltage or more is applied. The nonlinear element arresters A1 and A2 protect the semiconductor from overvoltage.

  The contacts of the semiconductor circuit breakers S1 and S2 and the mechanical disconnector M1 are opened and closed by a control device (not shown) configured by a computer including a CPU and a memory and operating with a predetermined program and a dedicated electronic circuit. The control device detects the state of the DC power transmission systems D1 and D2 and automatically opens and closes the contacts, but can be manually operated by an operator via the control device.

[2. Operation]
The operation of the DC interrupter of this embodiment will be described with reference to FIGS. In addition, the current state in each component will be described with reference to the graph shown in FIG. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the current value. In the following description, a state where the contact is closed is expressed as an on state, and a state where the contact is opened is expressed as an off state.

(1) During steady operation First, during steady operation, as shown in FIG. 2, the mechanical disconnector M1 is turned on and the semiconductor breakers S1 and S2 are turned off. Therefore, when power is exchanged from the DC power transmission system D1 to the DC power transmission system D2, power flows through the reactor L1, the mechanical disconnector M1, and the reactor L2, as indicated by thick arrows in the figure. That is, power can be interchanged without passing through a semiconductor with a large power loss. In FIG. 7, the values up to point A indicate the current value of each component during steady operation.

(2) When Accident Occurs Next, as shown in FIG. 3, an operation when a transmission line ground fault occurs on the DC power transmission system D2 side will be described. When a system fault such as a power transmission line ground fault occurs, the system voltage is applied to the system impedance and reactors L1 and L2. In FIG. 7, the accident occurrence time is shown as point A. In this case, the system impedance and the% impedance of the reactors L1 and L2 are small and the resistance is small with respect to the characteristic impedance of the transmission power. The system current of M1 and reactors L1 and L2 rises instantaneously.

  When such an accident occurs, as shown in FIG. 4, the semiconductor circuit breakers S1 and S2 are turned on (point B in FIG. 7). Then, as indicated by the hatched arrows in FIG. 4, from the positive side of the DC power transmission system D1, via the system impedance, the semiconductor circuit breaker S1, the mechanical disconnector M1, the semiconductor circuit breaker S2, and the DC power transmission system D1. A current path P1 leading to the negative side is formed.

  When the current path P1 is formed, the reactor L1 is short-circuited at both ends by the semiconductor breaker S1 and the mechanical disconnector M1. Therefore, the voltage applied to both ends of the reactor L1 is reduced, and the current flowing through the reactor L1 hardly changes and becomes a constant value as shown between the points B and C in FIG. In addition, the ground fault point and the negative side of the DC power transmission system D1 are connected through the mechanical disconnector M1 and the semiconductor circuit breaker S2 to have the same potential. Therefore, the voltage applied to both ends of reactor L2 decreases, and the amount of change in the current flowing through reactor L2 decreases as shown between points B and C in FIG.

  As described above, the reactors L1 and L2 are short-circuited by turning on the semiconductor circuit breakers S1 and S2, so that the voltage applied to the reactors L1 and L2 is applied to the system impedance. Therefore, the current flowing through the system impedance further increases as shown between points B and C in FIG. As described above, since the semiconductor circuit breakers S1 and S2 are turned on, the current flowing through the reactor L1 has a constant value. Therefore, the increase in the current flowing through the system impedance flows to the negative side of the DC power transmission system D1 via the semiconductor circuit breaker S1, the mechanical disconnector M1, and the semiconductor circuit breaker S2.

  As is clear from a comparison of FIGS. 3 and 4, the current flowing through the mechanical disconnector M1 when an accident occurs is in a direction opposite to the current flowing through the mechanical disconnector M1 before the accident occurs. Therefore, if the current flowing through the system impedance increases when an accident occurs, the current in the reverse direction flowing through the mechanical disconnector M1 gradually increases, and the current flowing through the mechanical disconnector M1 before that will be canceled out. . As shown between point B and point C in FIG. 7, the current flowing through the mechanical disconnector M1 gradually decreases. As a result, a current zero point is formed in the mechanical disconnector M1 (point Z in FIG. 7), and as shown in FIG. 5, the mechanical disconnector M1 is shifted to the OFF state at the current zero point.

  After the mechanical disconnector M1 is shifted to the off state, the semiconductor circuit breaker S1 is shifted to the off state (point C in FIG. 7), and the current flowing through the reactor L2 is interrupted as shown in FIG. Since the inductive energy accumulated in the reactor L2 is attenuated by the semiconductor circuit breaker S1 and the arrester A1, an excessive voltage is not applied to the semiconductor circuit breaker S1.

  Finally, as shown in FIG. 6, the semiconductor circuit breaker S2 is turned off (point D in FIG. 7), and the current flowing through the semiconductor circuit breaker S2 is interrupted. By this operation, the system impedance and the current flowing through the reactor L1 are cut off. With the above operation, the ground fault point and the healthy DC power transmission system D1 are disconnected, and the fault point can be removed.

[3. Effect]
The operational effects of the present embodiment as described above are as follows.
(1) The DC interrupting device of the present embodiment is a DC interrupting device that disconnects an accident point in the DC power transmission systems D1, D2 connected by two power transmission lines W1, W2, and is connected in series to the power transmission line W1. A reactor L1, a mechanical disconnector M1 having a mechanical contact, a semiconductor circuit breaker S1 connected in parallel to the reactor L1 and the mechanical disconnector M1, a connection point between the reactor L1 and the mechanical disconnector M1, and a transmission line And a semiconductor circuit breaker S2 connected to W2.

  Therefore, in the steady operation, no current passes through the semiconductor element, so that no conduction loss occurs due to the resistance of the semiconductor element. Therefore, it is possible to provide a DC circuit breaker that suppresses an increase in size of the device and is reduced in cost. In addition, when an accident occurs, a current zero point can be formed, so that the current can be interrupted using the mechanical disconnector M1 having a mechanical contact.

(2) During the steady operation of the DC power transmission systems D1 and D2, the mechanical disconnector M1 is turned on and the semiconductor breakers S1 and S2 are turned off. Therefore, in the steady operation, no current passes through the semiconductor element, so that no conduction loss occurs due to the resistance of the semiconductor element. Therefore, it is possible to provide a DC circuit breaker that suppresses an increase in size of the device and is reduced in cost.

(3) When an accident occurs in the DC power transmission systems D1 and D2, the semiconductor breakers S1 and S2 are turned on, the mechanical disconnector M1 is turned off at the current zero point, and then the semiconductor breakers S1 and S2 In order to isolate the accident point. Accordingly, when an accident occurs, it is possible to form a zero current point, so that the current can be interrupted using the mechanical disconnector M1 having a mechanical contact. In addition, since the contact of the mechanical circuit breaker M1 can be shifted to the OFF state at the current zero point, a phenomenon in which an electric current continues to flow by drawing an arc as in the case of direct current conduction does not occur. Therefore, even when a disconnector that does not have the ability to interrupt the arc current is used, the opening can be performed. Therefore, it is possible to provide a DC cut-off device with a lower cost.

[Second Embodiment]
The configuration of the DC interrupter of the second embodiment is basically the same as that of the first embodiment. However, in the DC interrupter of this embodiment, as shown in FIG. 8, a mechanical contact type current disconnector M1 (hereinafter referred to as a mechanical disconnector M2) is connected in series to the reactor L2. The structure of the mechanical disconnector M2 is the same as that of the mechanical disconnector M1.

  In the DC interrupter as described above, the following operational effects can be obtained in addition to the above embodiment. As described above, the semiconductor circuit breaker S1 interrupts the current flowing through the reactor L2. The withstand voltage required at the time of this interruption is about the voltage generated at both ends of the reactor L1, and is a voltage lower than the DC transmission system voltage. However, immediately after the semiconductor circuit breaker S2 is turned off, a voltage between the DC power transmission system D1 and the ground fault point is applied to the semiconductor circuit breaker S1. Therefore, even if the withstand voltage required at the time of interruption is low, the withstand voltage about the DC transmission system voltage is finally required. Therefore, conventionally, in order to obtain a withstand voltage about the DC transmission system voltage, for example, a plurality of semiconductor elements are connected in series to configure the semiconductor circuit breaker S2.

  However, in this embodiment in which the mechanical disconnector M2 is connected, the mechanical disconnector M2 is opened after the semiconductor circuit breaker S1 is turned off when an accident occurs. Therefore, the voltage after the semiconductor circuit breaker S2 is turned off is applied to the mechanical disconnector M2. From the above, the withstand voltage of the semiconductor circuit breaker S1 is only the withstand voltage necessary for interrupting the current flowing through the reactor L2.

  In addition, as shown in FIG. 9, the mechanical disconnector M2 can obtain the same operation effect even if it is configured in series with the semiconductor circuit breaker S1. That is, as shown by the oblique lines in FIG. 9, the same effect can be obtained by connecting the mechanical disconnector M2 to a circuit to which a voltage is applied after the semiconductor circuit breaker S2 is turned off.

  As described above, the present embodiment includes the mechanical disconnector M2 (FIG. 8) connected in series to the reactor L2 or the mechanical disconnector M2 (FIG. 9) connected in series to the semiconductor circuit breaker S1. Therefore, the voltage after the semiconductor circuit breaker S2 is turned off can be applied to the mechanical disconnector M2 having a high breakdown voltage. For this reason, the semiconductor circuit breaker S1 only needs to have a withstand voltage component necessary for interrupting the current flowing through the reactor L2. Since the breakdown voltage of the semiconductor circuit breaker S1 is reduced, for example, the number of necessary semiconductor elements can be reduced. Since the mechanical disconnector M2 is less expensive than the semiconductor element, the cost of the semiconductor breaker S1 can be reduced by using the mechanical disconnector M2 to provide a low-cost DC interrupter.

[Third Embodiment]
The configuration of the DC circuit breaker of the third embodiment is basically the same as that of the second embodiment. However, as shown in FIGS. 10 and 11, a vacuum circuit breaker V is connected in parallel to the reactor L1 and the mechanical circuit breaker M1 instead of the semiconductor circuit breaker S1. That is, in the said embodiment, it is set as the structure which interrupts | blocks with the vacuum circuit breaker V the electric current of the reactor L2 which the semiconductor circuit breaker S1 interrupted | blocked.

  Similar to the second embodiment, in this embodiment, the mechanical disconnector M2 (FIG. 10) connected in series to the reactor L2 or the mechanical disconnector M2 (FIG. 11) connected in series to the vacuum circuit breaker V is used. Have. Therefore, the voltage after the semiconductor circuit breaker S2 is turned off can be applied to the mechanical disconnector M2 having a high breakdown voltage. Therefore, the vacuum circuit breaker V should just have a pressure | voltage resistant component required when interrupting | blocking the electric current which flows through the reactor L2. Therefore, a vacuum circuit breaker V having a low breakdown voltage of several kV can be used instead of the semiconductor circuit breaker S1. Since the vacuum circuit breaker V is less expensive than the semiconductor circuit breaker S1, it is possible to provide a DC circuit breaker with a lower cost.

[Fourth Embodiment]
The configuration of the DC circuit breaker of the fourth embodiment is basically the same as that of the first embodiment. However, as shown in FIG. 12, the semiconductor circuit breakers S1 and S2 are configured to connect a switching element and a voltage dividing resistor in parallel to obtain a gate drive power supply for the switching element. That is, the voltage dividing resistors R1 and R2 are connected in parallel to the semiconductor switching element. A gate drive circuit C is connected to the voltage dividing resistors R1 and R2. The gate drive circuit C is a circuit that drives the gate G of the switching element.

  The semiconductor circuit breakers S1 and S2 are turned off during steady operation. In this case, a voltage is applied between the collector and the emitter of the switching element by the system voltage. This voltage is divided and taken in by the voltage dividing resistors R1 and R2, and is stepped down to a voltage suitable for gate driving. Therefore, in the event of an accident, the gate circuit C drives the gate G with the reduced voltage, so that the semiconductor circuit breakers S1 and S2 are turned on.

  For example, when a plurality of switching elements are connected in series, each switching element requires a power source. Therefore, a power supply of several hundred kV may be required. When a voltage of several hundred kV is sent from the ground, it is necessary to arrange a transformer having a withstand voltage corresponding to the voltage, and the cost of the DC interrupter increases. However, in this embodiment, the switching element and the voltage dividing resistors R1 and R2 are connected in parallel. Therefore, since the switching element can cover each power source, it is possible to provide a low-cost DC interrupter.

[Other Embodiments]
(1) In the above embodiment, one self-extinguishing element is used as the semiconductor breakers S1 and S2, and the nonlinear element arresters A1 and A2 are connected in parallel. However, various configurations can be adopted as the semiconductor circuit breakers S1 and S2. For example, as shown in FIG. 13A, only a self-extinguishing element may be used. As shown in FIG. 13B, a self-extinguishing switching element and a diode may be connected in parallel. As shown in FIG. 13 (c), a self-extinguishing type switching element may be connected in anti-series to cut off bidirectional current. As shown in FIG. 13 (d), self-extinguishing switching elements may be connected in series to improve the breakdown voltage of the semiconductor circuit breakers S1 and S2. If comprised in this way, it will become possible to apply the DC interrupting device of the said embodiment to the DC transmission system of a higher voltage.

(2) Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

D1, D2 ... DC power transmission system W1, W2 ... Transmission lines L1, L2 ... Reactors S1, S2 ... Semiconductor breakers A1, A2 ... Arrester M1, M2 ... Mechanical disconnector V ... Vacuum breaker G ... Gate C ... Gate drive circuit R1, R2 ... Voltage divider resistors

Claims (8)

A DC interrupting device for disconnecting an accident point in a DC transmission system connected by two transmission lines,
A first reactor connected in series to the first power transmission line; a first mechanical disconnector having a mechanical contact;
A first semiconductor circuit breaker connected in parallel to the first reactor and the first mechanical disconnector;
A DC circuit breaker comprising: a connection point between the first reactor and the first mechanical disconnector; and a second semiconductor circuit breaker connected to a second power transmission line.   The first mechanical circuit breaker is turned on and the first semiconductor breaker and the second semiconductor circuit breaker are turned off during steady operation of the DC power transmission system. The DC interrupter according to 1. If an accident occurs in the DC transmission system,
Turning on the first semiconductor circuit breaker and the second semiconductor circuit breaker;
At the current zero point, turn off the first mechanical disconnector;
3. The DC circuit breaker according to claim 1, wherein the fault point is separated by sequentially turning off the first semiconductor circuit breaker and the second semiconductor circuit breaker. 4. The second reactor connected in series to the first mechanical disconnector and the second mechanical disconnector connected in series to the second reactor, further comprising: The DC interrupter according to one item.   The DC breaker according to any one of claims 1 to 3, further comprising a second mechanical disconnector connected in series to the first semiconductor breaker.   6. The direct current according to claim 4, wherein instead of the first semiconductor circuit breaker, a vacuum circuit breaker is connected in parallel to the first reactor and the first mechanical disconnector. Shut-off device.   6. The first semiconductor circuit breaker or the second semiconductor circuit breaker includes a plurality of self-extinguishing switching elements connected in series. The direct current circuit breaker described. The first semiconductor circuit breaker or the second semiconductor circuit breaker is configured such that a switching element and a voltage dividing resistor are connected in parallel, and the gate driving power source of the switching element is obtained by the voltage dividing resistor. The direct-current circuit breaker according to any one of claims 1 to 5 and 7.