Arrangement, system, and method for bypassing faulty submodules in an electric circuit breaker

Abstract

An arrangement for interrupting current (1 ) comprises a first and a second terminal (11,12) being adapted to electrically connect two sections (100,200) of a power system, the arrangement comprising a circuit breaker module (10) adapted to interrupt current The circuit breaker module (10) is provided between the first and second terminals (11, 12), forming a first current path between the first and second terminals (11, 12). By providing a bypass device (50) connected in parallel with the first current path, thereby forming a second current path between the first and second terminals (11, 12), wherein the bypass device (50) comprises a switch, preferably a mechanical switch, a faulty circuit breaker module does not impede the operation of the arrangement.

Description

ARRANGEMENT, SYSTEM, AND METHOD FOR BYPASSING FAULTY SUBMODULES IN AN ELECTRIC CIRCUIT BREAKERTechnical field

[0001] This invention relates to electric circuit breakers. In particular, it relates to circuit breakers employing resonant circuits to achieve an artificial zero-crossing in the current through a mechanical circuit breaker whereby a current interruption can be made absent any zero-crossings in the primary current to be interrupted.Background art

[0002] It is known that a circuit breaker for interrupting current when there are no zero crossings (such as in a DC current, for instance) can be designed by using a resonant circuit to impose a resonant current in a mechanical circuit breaker, such as a vacuum interrupter, carrying the line current, see Fig. 1 and Fig. 2. Opening the mechanical circuit breaker by itself will generally not eliminate the current; instead an arc will form inside the mechanical circuit breaker by which the current continues to flow. However, if the resonant current exceeds the line current a zerocrossing occurs whereby the current though the mechanical switch is interrupted. The current is then commutated into an energy absorbing device such as a metal- oxide surge arrester. As this device starts conducting the current it will provide a counter voltage that drives the line current to zero, whereby the current extinction process is completed.

[0003] One variety of such an active resonant circuit breaker uses a power- electronic voltage source converter to excite the resonant circuit, see Fig. 3 and with reference to patent publications EP3398198B1 and EP3161846B1. This variety offers several benefits. A high resonance frequency can be used, which implies smaller components in the resonant circuit. Furthermore, the resonant process can be precisely controlled by the voltage source converter. The typical procedure for interrupting current using such a circuit breaker is as follows. Initially, the line current I current flows through a mechanical circuit breaker 1. To start the interruption process, the circuit breaker is opened, preferably using a fast actuator. The current keeps flowing by way of an arc inside the breaker. Next, analternating voltage llo is produced by the voltage source converter 4 at the resonance frequency of the resonant circuit 3. This leads to a resonant current Io flowing through the resonant circuit with increasing amplitude. Notably, the resonant current also flows through the mechanical breaker. When the amplitude eventually exceeds the magnitude of the line current I a zero crossing will occur in the current though the mechanical circuit breaker Isw. This causes the arc to be quenched whereby Isw will stop flowing. As there is no other path for the line current I to flow it will be forced into a surge arrestor 2. The surge arrestor will generally be chosen so as to provide a counter voltage that is significantly higher than the driving voltage in the grid when a current flows through it. Thereby, the line current is forced to zero and the current interruption process is completed.

[0004] An alternative embodiment of the mentioned circuit breaker using a voltage source to excite the resonant circuit is seen in Fig. 4. In this case the placement of the surge arrester has been altered to be connected in series with the inductor of the resonant circuit. Figure 4 also indicates how several sets of voltage source converters and resonant circuits can be connected in parallel to achieve a higher resonant current.

[0005] It is also known that a circuit breaker for high voltage can be designed by series-connecting several circuit breaker modules 10 of the described kinds, designed for lower voltage, see Fig. 5. This brings the important benefit that the current interruption is still possible even if one of the circuit breaker modules fail to interrupt the current properly, as long as the combined voltage provided by the other modules is sufficient to bring the line current to zero.

[0006] The mentioned types of circuit breaker do not provide a contact separation when in the open state since an energy absorbing device 2 is connected in parallel with the mechanical breaker 1 . This implies that a low current may flow even when the breaker is in the open state. It is therefore common practice to connect a switch in the form of a residual current breaker 5 in series with the main circuit breaker. The residual current breaker is then used to eliminate the current flowing though the energy absorption device and provide a galvanic separation in the pathof the main current. The residual current breaker generally only needs very limited current interruption capability.

[0007] It is often beneficial to use the mentioned residual current breaker for closing the current circuit. By this method of closing the circuit, the circuit breaker modulelO is normally in the closed state, or in case it consists of several series connected breaker modules all of these are closed, and thus conducting. The voltage is then supported by the residual current breaker, which is in the off-state. When the command to close the current circuit is given the residual current breaker is closed and a path for the current is formed. The residual current breaker thus needs current making capability (i.e. turn-on capability).

[0008] A possible fault case when using such a modular high-voltage circuit breaker occurs when one or several of the circuit breaker modules 10 have failed to turn on properly. If the modular high-voltage circuit breaker is commanded to turn on, and one or several of the modules fail to start conducting current as intended in the on-state, this or these modules will still be forced to carry current which may result in their destruction. Therefore, it is desirable to minimize the probability of this fault case occurring.Summary of the invention

[0009] An object of the invention is therefore to provide an arrangement and a method for interrupting current wherein a faulty circuit breaker module does not impede the operation of the arrangement. Another object is to provide an arrangement and a method for interrupting current wherein the risk of destruction of a faulty circuit breaker module is minimized.

[0010] The invention is based on the insight that an individual circuit breaker module can be shorted and thus does not impede the flow of current. This is made by providing an alternative path for the current through a breaker submodule by means of a bypass element connected in parallel with the circuit breaker module.

[0011] According to a first aspect of the invention, an arrangement for interrupting current is provided comprising a first and a second terminal being adapted toelectrically connect two sections of a power system, the arrangement comprising a circuit breaker module adapted to interrupt current, wherein the circuit breaker module is provided between the first and second terminals, forming a first current path between the first and second terminals, the arrangement being characterized by a bypass device connected in parallel with the first current path, thereby forming a second current path between the first and second terminals, wherein the bypass device comprises a switch, preferably a mechanical switch.

[0012] In a preferred embodiment, the bypass device comprises a first and a second contact, wherein the first contact is movable so that a stable short-circuit can be formed by joining the first and second contacts together.

[0013] In a preferred embodiment, the first and second contacts form part of a vacuum interrupter.

[0014] In a preferred embodiment, the first contact is displaceable into contact with the second contact by means of an electromechanical actuator, preferably a solenoid or a Thomson coil.

[0015] In a preferred embodiment, the first contact is displaceable into contact with the second contact by means of a pyro-electric actuator.

[0016] In a preferred embodiment, a thrusting actuator is provided, which is adapted to directly push the first contact into contact with the second contact.

[0017] In a preferred embodiment, a bi-stable mechanism is provided, which is adapted to uphold sufficient contact pressure in the bypass device after the switch has been closed.

[0018] In a preferred embodiment, a pin puller, preferably a pyrotechnical pin puller, is provided for operating the switch.

[0019] In a preferred embodiment, a spring-loaded mechanism with a spring is provided and adapted to move the first contact into contact with the second contact, whereby the spring maintains a required contact pressure between thefirst and second contacts in the closed position, and an actuator adapted to release the spring-loaded mechanism.

[0020] In a preferred embodiment, the circuit breaker module is provided with a mechanical circuit breaker, normally carrying current between the first and second terminals, and a resonant circuit adapted to be excited to achieve a zero-crossing of the current through said mechanical circuit breaker. Preferably, a voltage source converter is provided to excite the resonant circuit to achieve a zero-crossing of the current through the mechanical circuit breaker.

[0021] According to a second aspect of the invention a system for interrupting current is provided comprising at least two arrangements for interrupting current according to the invention, wherein the at least two arrangements for interrupting current are connected in series.

[0022] According to a third aspect of the invention, a method of operating a system for interrupting current according to the invention is provided, the method comprising the following steps: identifying that a circuit breaker module is faulty, and subsequently, activating an associated bypass device.Brief description of drawings

[0023] The invention is now described, by way of example, with reference to the accompanying drawings, in which:Figs. 1-5 show prior art arrangements for interrupting current;Figs. 6-7 show diagrams of a general embodiment of an arrangement for interrupting current according to the invention; andFigs. 8-9 show various embodiments for implementing a bypass element according to the invention.Description of embodiments

[0024] An arrangement for interrupting current according to the invention will now be described, particularly with reference to Figs. 6 and 7.

[0025] The invention ensures that a faulty circuit breaker module is in the shorted state and thus does not impede the flow of current. This is made by providing an alternative path for the current through a circuit breaker module by means of a bypass element connected in parallel with the circuit breaker module. Thus, an embodiment of an arrangement for interrupting current according to the invention, comprises a first and a second terminal 11 , 12 which are adapted to electrically connect two sections 100, 200 of a power system. A circuit breaker module 10 adapted to interrupt current is provided between the first and second terminals 11 , 12 forming a first current path between the first and second terminals 11 , 12. A bypass device 50 is connected in parallel with the first current path, thereby forming a second current path between the first and second terminals 11 , 12 wherein the bypass device 50 comprises a switch. This bypass element is thereby adapted to turn on by command and carry the full line current indefinitely or at least until the next maintenance event, when the faulty circuit breaker module 10 can be replaced or repaired. In a preferred embodiment, the bypass device 50 requires no capability to return to the non-conducting state and is possibly provided without such capability.

[0026] The bypass device 50 is preferably provided as a mechanical switch comprising at least one fixed contact 53 and one movable contact 52 normally separated by a distance large enough so as to be able to block the voltage that appears across the breaker module 10 when open. The bypass device 50 is activated by forcing the movable contact into contact with the fixed contact.

[0027] Such a bypass device 50 can be implemented in different ways. In one embodiment, the same type of mechanical circuit breaker and associated actuator is used as for interrupting current in the circuit breaker module 10. However, this may be an unnecessarily expensive solution, particularly as the bypass element does not need any circuit breaking capability or even the ability to return to the non-conducting state.

[0028] One embodiment of the mentioned mechanical switch to be used in the bypass element is the use of a vacuum interrupter. Thereby, the contact separation in the normal state (open contact) can be short, preferably less than 20millimeters, even more preferably less than 10 millimeters, which simplifies the design of the actuator since only a short actuator stroke is required. Using a vacuum interrupter also ensures the integrity of the contact surfaces since there is no air or other gases inside the vacuum chamber that can contribute to oxidation of the contact surfaces.

[0029] One embodiment for realizing the said actuator involves a pyrotechnical actuator 56, see Fig. 8. Such an actuator has the advantage that it requires only a relatively low-power electrical signal to operate and it can exert significant force. Such a pyrotechnical actuator can either be used for directly moving the moving contact 52 of the bypass device so that a closed circuit is established. In such case, the bypass element may also favorably be equipped with a bi-stable mechanism 57 for ensuring that the movable contact 52 is pressed towards the fixed contact 53 with sufficient force after closing to ensure that a stable electrical contact is established and maintained.

[0030] Alternatively, see Fig. 9, a pyrotechnical actuator capable of exerting a tractive force, also known as a pyrotechnical pin puller 58, can be used to release a spring-loaded mechanism 59 that forces the movable contact 52 towards the fixed contact 53, by pulling out a pin that initially holds the movable contact in the open position. The spring mechanism 59 can be designed to establish and uphold a sufficient contact force after the closing operation to ensure that a stable electrical contact is established and maintained.

[0031] In addition, other forms of actuation of the moving contact of the mechanical switch into the closed position are possible. These include, but are not limited to, the use of an electromagnetic actuator, such as a solenoid or a Thomson coil. Importantly, the operation speed requirements of the bypass element are considerably lower than a bypass element intended for a submodule in a converter made from semiconductor modules.

[0032] The bypass device 50 can be activated by the overall circuit breaker control system, which is advantageous since the control system receives the necessary measurement signals to determine whether a fault in the main circuitbreaker has occurred. There can also be a separate controller for the bypass device 50. This way, the by-pass of a faulty module is not reliant on the correct function of the overall control system.

[0033] As in the prior art design described above with reference to Fig. 5, a circuit breaker for high voltage can be designed by series-connecting a plurality of N circuit breaker modules 10 designed for lower voltage, see Fig. 7. This brings the important benefit that the current interruption is still possible even if one of the circuit breaker modules fail to interrupt the current properly, as long as the combined voltage provided by the other modules is sufficient to bring the line current to zero.

[0034] In the case a plurality of circuit breaker modules 10 for interrupting current are connected in series, one or more of the bypass devices 50 can be activated, thereby bypassing a respective faulty circuit breaker module 10, as long as the functioning circuit breaker modules 10 can take up the voltage across the plurality N of modules 10. Thus, in one embodiment, 16 circuit breaker modules Ware serially connected, each module 10 being designed for taking up a voltage of 50 kilovolts. In such a system, it is sufficient that 14 circuit breaker modules 10operate properly.

[0035] During operation of the arrangement for interrupting current, the different steps involving the by-passing are as follows. Initially, it is identified that a circuit breaker module 10 is faulty, i.e., it fails to conduct current properly. Subsequently, the associated bypass device 50 is activated, thereby forming a second current path bypassing the circuit breaker module 10. Meanwhile, other circuit breaker modules 10 connected in series with the faulty circuit breaker module 10 conduct the current flowing between the first and second terminals 11 , 12.

[0036] Preferred embodiments of an arrangement, a system, and a method of interrupting current have been described. These may be varied within the scope of the appended claims without departing from the inventive idea. Thus, each circuit breaker module 10 has been described as comprising one movable contact and one fixed contact. It will be appreciated that other configurations are possible, aslong as you have a contact arrangement adapted for interrupting a current flowing between the contacts. Thus, it is possible to have more than one movable contact and / or more than one fixed contact. It is also possible to only have movable contacts.

Claims

CLAIMS1 . An arrangement for interrupting current (1 ) comprising a first and a second terminal (11 ,12) being adapted to electrically connect two sections (100,200) of a power system, the arrangement comprising a circuit breaker module (10) adapted to interrupt current, wherein the circuit breaker module (10) is provided between the first and second terminals (11 , 12), forming a first current path between the first and second terminals (11 , 12), c h aracteri zed by a bypass device (50) connected in parallel with the first current path, thereby forming a second current path between the first and second terminals (11 , 12), wherein the bypass device (50) comprises a switch, preferably a mechanical switch.

2. The arrangement according to claim 1 , wherein the bypass device (50) comprises a first and a second contact (52, 53), wherein the first contact (52) is movable so that a stable short-circuit can be formed by joining the first and second contacts together.

3. An arrangement according to claim 2, 2. wherein the first and second contacts (52, 53) form part of a vacuum interrupter.

4. An arrangement according to claim 2 or 3, wherein the first contact (52) is displaceable into contact with the second contact (53) by means of an electromechanical actuator, preferably a solenoid or a Thomson coil.

5. An arrangement according to claim 2 or 3, wherein the first contact (52) displaceable into contact with the second contact (53) by means of a pyro-electric actuator.

6. An arrangement according to claim 4 and 5, comprising a thrusting actuator adapted to directly push the first contact (52) into contact with the second contact (53).

7. An arrangement according to any one of claims 2-6, comprising a bistable mechanism (57) adapted to uphold sufficient contact pressure in the bypass device (50) after the switch has been closed.

8. An arrangement according to any one of claims 2-5, comprising a pin puller 58, preferably a pyrotechnical pin puller, for operating the switch.

9. An arrangement according to claim 2 or 8, comprising a spring-loaded mechanism (59) with a spring adapted to move the first contact into contact with the second contact, whereby the spring maintains a required contact pressure between the first and second contacts in the closed position, and an actuator adapted to release the spring-loaded mechanism.

10. An arrangement according to any one of claims 1 -9. where the circuit breaker module (10) is provided with a mechanical circuit breaker, normally carrying current between the first and second terminals (11 , 12), and a resonant circuit adapted to be excited to achieve a zero-crossing of the current through said mechanical circuit breaker.

11. An arrangement according to claim 1 -10, comprising a voltage source converter adapted to excite the resonant circuit to achieve a zero-crossing of the current through the mechanical circuit breaker.

12. A system for interrupting current comprising at least two arrangements for interrupting current according to any of the preceding claims, wherein the at least two arrangements for interrupting current are connected in series.

13. A method of operating a system for interrupting current according to any claims 1-10, comprising the following steps: identifying that a circuit breaker module (10) is faulty, and subsequently, activating an associated bypass device (50). —

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