Patent Application
20170352508
The present invention relates to a high voltage DC circuit breaker and, more particularly, to a high voltage DC circuit breaker that interrupts a fault current flowing through a high voltage DC transmission line with a configuration in which a vacuum circuit breaker and a gas circuit breaker are connected in series with each other.
Generally, a high voltage DC circuit breaker refers to a switching device that can interrupt an electric current flowing through a high voltage (i.e. 15 kV or higher) transmission line, such as a high voltage direct current (HVDC) transmission system. The high voltage DC circuit breaker functions to interrupt a fault current when a certain fault occurs in a DC transmission line. This also can be applied to a medium voltage DC distribution system that distributes electric power of medium-level voltages ranging from 1 to 50 kV.
As to a high voltage DC circuit breaker, when a fault current occurs in a system, a main switch is opened to disconnect a faulty circuit, thereby interrupting the flow of a fault current from the faulty circuit. However, since there is no zero current point on a DC transmission line, when a main switch is opened, an arc generated between terminals of the main switch is not extinguished. Therefore, a fault current flows through the arc. That is, the fault current fails to be interrupted.
In order to solve these problems, a vacuum interrupter (VI) has been developed to prevent an arc from being generated when a main switch CB is switched off. However, it is difficult to apply an existing vacuum interrupter to a high voltage DC circuit breaker due to a low rated voltage thereof.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a high voltage DC circuit breaker having a configuration in which a gas circuit breaker and a vacuum circuit breaker are connected in series such that, when a fault occurs in a DC transmission line, the vacuum circuit breaker having a low rated voltage and a high current interruption performance primarily interrupts a fault current and the gas circuit breaker subsequently operates to provide a dielectric strength.
Another object of the present invention is to provide a high voltage DC circuit breaker in which a gas circuit breaker operates a predetermined time after the gas circuit breaker operates, in which the gas circuit breaker starts operating before the operation period of the vacuum circuit breaker 110 terminates such that operation times of the vacuum circuit breaker and the gas circuit breaker partially overlap.
In order to accomplish the above object, according to one aspect, there is provided a high voltage DC circuit breaker ac including:
a vacuum circuit breaker installed on a direct current (DC) transmission line to interrupt a current in the DC transmission line by operating when a fault occurs on one side or a remaining side on the DC transmission line; an LC circuit connected in parallel with the vacuum circuit breaker 110 and including a capacitor and a reactor connected in series with each other to induce LC resonance; a first bidirectional switching device connected in series with the LC circuit and switching currents flowing in both forward and backward directions; and a second bidirectional switching device connected in parallel with the LC circuit and switching currents to induce LC resonance in both forward and backward directions.
In the present invention, the high voltage DC circuit breaker further includes a charging resistor to charge the capacitor 131 to a voltage Vc, and the charging resistor 160 is provided between a ground and a contact point between the LC circuit and the first bidirectional switching device.
In the present invention, the first and second bidirectional switching devices respectively include a pair of switches G1 and G2 connected in parallel and arranged to be counter to each other and a pair of switches G3 and G3 connected in parallel and arranged to be counter to each other, in which the switches G1 to G4 are turn-on controllable switches or turn-on/turn-off controllable switches.
In the present invention, when a fault occurs at the one side on the DC transmission line, a current in the DC transmission line is interrupted in the following manner: while two contacts of the vacuum circuit breaker are separated from each other, in a state in which the switches G1 and G2 of the first bidirectional switching device are in an OFF state, one switch G4 of the second bidirectional switching device is turned on such that the capacitor is charged to a voltage −Vc through the LC resonance between the reactor and the capacitor of the LC circuit; and subsequently the switch G4 is turned off and the switch G2 of the first bidirectional switching device is turned on such that the vacuum circuit breaker is supplied with a current due to the voltage −Vc charged in the capacitor; and the current supplied from the capacitor makes a zero current between the two contact points of the vacuum circuit breaker.
In the present invention, when a fault occurs at the remaining side of the DC transmission line, a current in the DC transmission line is interrupted in the following manner: while two contacts of the vacuum circuit breaker are separated from each other, in a state in which the switches G3 and G4 of the second bidirectional switching device are in an OFF state, the switch G1 of the first bidirectional switching device is turned such that the vacuum circuit breaker is supplied with a current due to the voltage +Vc that is preliminarily charged in the capacitor of the LC circuit; and the supplied current makes a zero current between the two contacts of the vacuum circuit breaker.
In the present invention, when a predetermined time elapses from operation of the vacuum circuit breaker in which the contacts of the vacuum circuit breaker are separated from each other, the gas circuit breaker operates. That is, the gas circuit breaker starts operating before the vacuum circuit breaker stops operating, such that there is an operation overlap period during which both of the vacuum circuit breaker and the gas circuit breaker operate.
As described above, according to the present invention, since the vacuum circuit breaker and the gas circuit breaker in the high voltage DC circuit breaker are connected in series with each other, it is possible to exploit both a good arc extinguishing performance of a vacuum medium and a high voltage withstanding performance of a gas.
In addition, in the high voltage DC circuit breaker according to the present invention, when a fault occurs on a DC transmission line, the vacuum circuit breaker primarily interrupts a fault current, and the gas circuit breaker connected in series with the vacuum circuit breaker subsequently operates only to recover dielectric strength. Therefore, some parts such as an arc contact used for arc extinguishment and a gas blower nozzle, which were necessarily provided in conventional circuit breakers, are not required. In addition, since the non-linear resistor is provided only in the vacuum circuit breaker and it is not necessary for the gas circuit breaker to be provided with the non-linear resistor, the number of the non-linear resistors can be reduced. Therefore, it is possible to reduce the size and cost of the DC circuit breaker.
In addition, according to the present invention, a vacuum circuit breaker for a high voltage of 145 kV or higher, which is currently difficult to implement due to technical constraints, is not required, it is possible to increase feasibility of a high voltage DC circuit breaker for 320 kV or higher.
Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In addition, descriptions of known functions or constructions which have been deemed to unnecessarily obscure the gist of the present invention will be below.
With reference to
The vacuum circuit breaker 110 is connected in series with a gas circuit breaker 120. The gas circuit breaker 120 includes a gas circuit breaker (GCB) using gas such as SF6, thereby having a high insulation performance and a high arc extinguishment performance.
In the high voltage DC circuit breaker 110 according to the present invention, the vacuum circuit breaker 110 and the gas circuit breaker 120 are provided on a DC transmission line and connected in series with each other. When a fault occurs at one side or the remaining side on the DC transmission line, in order to interrupt a fault current flowing through the DC transmission line, the vacuum circuit breaker 110 primarily operates, and the gas circuit breaker 120 subsequently operates after a predetermined time elapses from the beginning of the operation of the vacuum circuit breaker 110. Specifically, the vacuum circuit breaker 110 operates such that two contacts therein separate from each other to interrupt a fault current in the DC transmission line. When a predetermined time elapses after the vacuum circuit breaker 110 operates such that the two contacts thereof separate from each other, the gas circuit breaker 120 starts operating. In this case, the gas circuit breaker 120 starts operating before a preset operation period of the vacuum circuit breaker 110 terminates. Thus, there is an operation overlap period during which both of the two circuit breakers 110 and 120 operate together. This operation time setting is designed for the reason described below. Namely, when a high voltage is applied to the high voltage DC transmission line, while the vacuum circuit breaker 110 interrupts a fault current, the gas circuit breaker 120 is supposed to provide a dielectric strength to withstand the high voltage. That is, the interruption of a fault current is performed by the vacuum circuit breaker 110 having a relatively low rated voltage and a high current interruption performance, and the recovery of a dielectric strength after application of the high voltage is performed by the gas circuit breaker 120. As described above, the gas circuit breaker 120 does not perform a current interruption function. Therefore, it is not necessary for the gas circuit breaker 120 to include parts for arc extinguishment, such as an arc contact, a nozzle, or the like, which were necessarily provided in conventional gas circuit breakers.
According to the embodiment of the present invention, when a high voltage is applied to the DC transmission line 10, a large amount of current flows through the vacuum circuit breaker 110. For this reason, when a fault occurs, the vacuum circuit breaker 110 operates such that its two contacts separate from each other. Due to the separated contacts, a fault current is interrupted. In this case, since a high voltage is applied between the two contacts, an additional device is required to rapidly interrupt a large amount of fault current.
Specifically, in the high voltage DC circuit breaker 100 according to the embodiment of the present invention, a series-connected circuit of an LC circuit 130 and a first bidirectional switching device 140 is connected in parallel with the vacuum circuit breaker 110. In addition, a second bidirectional switching device 150 is connected in parallel with the LC circuit 130. The LC circuit 130 includes a capacitor 131 and a reactor 132 connected in series. The bidirectional switching devices 140 and 150 respectively include a pair of switches G1 and G2 connected in parallel and arranged to be counter to each other and a pair of switches G3 and G4 connected in parallel and arranged to be counter to each other. Due to this structure, the bidirectional switching devices 140 and 150 can pass currents in both forward and backward directions. Although not illustrated in the drawings, the switching operations of the switches G1 to G4 are controlled by a controller (not shown). The switches G1 to G4 are turn-on controllable power semiconductor devices. For example, the turn-on controllable power semiconductor device may be a thyristor. Examples of the turn-on/turn-off controllable power semiconductor device include a gate turn-off thyristor (GTO), an insulated gate commutated thyristor (IGCT), and an insulated gate bipolar transistors (IGBT).
In addition, in the high voltage DC circuit breaker 100 according to the embodiment of the present invention, preferably a charging resistor 160 for charging the capacitor 131 is connected between a ground GND and a contact point between the LC circuit 130 and the first bidirectional switching device. Through the charging resistor 160, the capacitor 131 of the LC circuit 130 is initially charged to a DC voltage Vc.
In addition, according to the embodiment, a non-linear resistor 170 is connected in parallel with the vacuum circuit breaker 110. The non-linear resistor 170 is to prevent an overvoltage that is higher than a rated voltage from being applied between terminals of the high voltage DC circuit breaker 100 when the vacuum circuit breaker 110 interrupts a fault current. When a voltage higher than a predetermined reference voltage is applied between the terminals of the high voltage DC circuit breaker 100 due to a certain fault, the non-linear resistor is automatically turned on to consume the high voltage. The non-linear resistor 170 can be implemented as a varistor.
An operation in the case in which a current flows from the A side to the B side will be first described below. When the high voltage DC circuit breaker 100 according to the present invention is in normal condition, the two contacts of the vacuum circuit breaker 110 are in contact with each other such that a normal current flows from the A side to the B side. In this case, both of the first bidirectional switching device 140 and the second bidirectional switching device 150 are in an OFF state, thereby blocking the flow of a current. For this reason, when a high voltage is applied to the high voltage DC transmission line 10, a normal current flows through the DC transmission line 10 via the two contacts of the vacuum circuit breaker 110 and is also supplied to the capacitor 131 and the reactor 132 of the LC circuit 130 and the charging resistor 160, thereby charging the capacitor 131 to a DC voltage +Vc.
When a fault occurs at the B side, as illustrated in
Subsequently, as illustrated in
In this case, the current supplied to the vacuum circuit breaker 110 functions to interrupt a fault current within the vacuum circuit breaker 110. Preferably, this current is counter to the fault current in the direction and larger than the fault current in the amount. In this way, the amount of the reverse current supplied to the vacuum circuit breaker to interrupt the fault current is determined depending on the capacity of the capacitor 131. Accordingly, it is preferable that the capacity of the capacitor 131 is determined depending on design conditions of a high voltage DC transmission line to which the high voltage DC circuit breaker 100 according to the embodiment of the present invention is applied.
When the fault current is interrupted in the vacuum circuit breaker 110 as described above, the voltage at the A side rapidly rises to be higher than that at the B side. For this reason, when a predetermined time elapses from the beginning of the operation of the vacuum circuit breaker 110, the gas circuit breaker 120 starts operating, thereby providing a dielectric strength to withstand the increased voltage of the A side. Specifically, since the vacuum circuit breaker 110 and the gas circuit breaker 120 are connected in series, when a fault current occurs in the DC transmission line, the vacuum circuit breaker 110 starts operating at an early stage such that the two contacts are separated from each other, thereby primarily interrupting the fault current. After that, when a predetermined time elapses, the gas circuit breaker 120 operates to block the DC transmission line. In this way, the gas circuit breaker 120 operates to insulate the A side from the high voltage. As described above, according to the present invention, the vacuum circuit breaker 110 functions to interrupt a fault current and the gas circuit breaker 120 functions to recover a dielectric strength. To this end, according to the present invention, while the vacuum circuit breaker 110 operates such that the two contacts thereof are separated from each other, when a predetermined time elapses, the gas circuit breaker 120 starts operating. In this case, the gas circuit breaker 120 starts operating before the operation period of the vacuum circuit breaker 110 terminates. That is, it is important to provide an operation overlap period during which both of the two circuit breakers 110 and 120 operate together. The reason of this operation time overlap will be described below. The vacuum circuit breaker 110 has a high current interruption performance but has a low rated voltage. Therefore, its dielectric strength for a high voltage is low, and thus a load applied to internal parts or devices is increased by the high voltage applied when the vacuum circuit breaker 110 early operates to interrupt a current. In order to reduce this load, the gas circuit breaker 120 having a high dielectric strength is configured to operate before the circuit is completely blocked by the vacuum circuit breaker 110. That is, since the vacuum circuit breaker 110 primarily interrupts a fault current, the gas circuit breaker 120 needs not include various parts for arc extinguishment, for example, an arc contact, nozzle, etc. which were necessarily provided in conventional arts, thereby simplifying the structure of the circuit breaker and rescuing the manufacturing cost thereof.
Meanwhile, when a current flows from the B side to the A side, an operation described below is performed. When the high voltage DC circuit breaker 100 according to the present invention is in normal condition, the two contacts of the vacuum circuit breaker 110 are in contact with each other such that a normal current can flow from the B side to the A side. In this case, both of the first bidirectional switching device 140 and the second bidirectional switching device 150 are in an OFF state, whereby the flow of a current is blocked. Therefore, when a high voltage is applied to the high voltage DC transmission line 10, a normal current flows through the DC transmission line 10 via the two contacts of the vacuum circuit breaker 110, and at this time the normal current that has passed the vacuum circuit breaker 110 is supplied to the capacitor 131 and the reactor 132 of the LC circuit 130 and the charging resistor 160, whereby the capacitor 131 is charged to the DC voltage +Vc.
In the case in which a fault occurs at the A side, as illustrated in
The current supplied to the vacuum circuit breaker 110 functions to interrupt the fault within the vacuum circuit breaker 110, and is preferably counter to the fault current in the direction and larger than the fault current in the amount. The amount of the reverse current used to interrupt the fault current is determined depending on the capacity of the capacitor. Accordingly, the capacity of the capacitor 131 is determined depending on design conditions of a high voltage DC transmission line to which the high voltage DC circuit breaker 100 according to the present invention is applied.
When the fault current is interrupted in the vacuum circuit breaker 110 as described above, the voltage at the B side rapidly increased to be larger than that at the A side. In this case, the gas circuit breaker 110 starts operating after a predetermined time elapses from the beginning of the operation of the vacuum circuit breaker 110 to provide a dielectric strength to withstand the increased voltage at the B side. That is, the vacuum circuit breaker 110 primarily operates such that the two contacts are separated from each other to interrupt a fault current, and then the gas circuit breaker 120 operates after a predetermined time elapsed from the beginning of the operation of the vacuum circuit breaker 110 to block the DC transmission line. In this way, the gas circuit breaker 120 functions to withstand the high voltage at the B side.
Even in this case, preferably the gas circuit breaker 120 starts operating before an operation period of the vacuum circuit breaker 110 terminates, thereby providing an operation overlap period during which both of the circuit breakers 110 and 120 operate together. In this case, since the vacuum circuit breaker 110 primarily interrupts a fault current, the gas circuit breaker 120 needs not include various parts for arc extinguishment, for example, an arc contact, a nozzle, etc., thereby simplifying the structure of the circuit breaker and reducing the manufacturing cost thereof.
With reference to
As illustrated in
In this way, the present invention reduces a high burden to a circuit breaker, which was required in conventional arts in which a single circuit breaker needs to have a function of interrupting a fault current attributable to a high voltage and to have a high dielectric strength to withstand a high voltage of 80 kV. According to the present invention, the vacuum circuit breaker 110 and the gas circuit breaker 120 perform a fault current interruption function and a high voltage withstanding function, respectively. Therefore, the present invention can provide a high voltage DC circuit breaker that can effectively interrupt a fault current and can be manufactured at low cost.
As described above, the high voltage DC circuit breaker 100 according to the embodiment of the present invention is characterized in that the resonance current attributable to the LC resonance is not formed by the main switch CB as in the conventional art illustrated in
Although the present invention has been described above in connection with the preferred embodiments, the present invention is not limited to the above embodiments. Those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the appended claims, and all of those modifications, additions, and substitutions also fall within the technical scope of the present invention. Accordingly, the substantial technical protection scope of the present invention should be defined by the technical spirit of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0192740 | Dec 2014 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2015/014286 | 12/24/2015 | WO | 00 |
