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EP-4736208-A1 - ARRANGEMENT, SYSTEM, AND METHOD FOR DETECTING A FAULT IN AN ELECTRIC CIRCUIT BREAKER

EP4736208A1EP 4736208 A1EP4736208 A1EP 4736208A1EP-4736208-A1

Abstract

An arrangement for interrupting current 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 is provided with a mechanical circuit breaker (1 ), which, during normal operation, carries current, and a resonant circuit (3) adapted be excited to achieve a zero-crossing the current through the mechanical circuit breaker (1 ). By providing an excitation circuit (40) adapted to initiate excitation of the resonant circuit (3) for the purpose of determining whether the mechanical circuit breaker (1) can carry a current as intended, a faulty circuit breaker module can be identified.

Inventors

  • NORRGA, STAFFAN

Assignees

  • Scibreak AB

Dates

Publication Date
20260506
Application Date
20240627

Claims (16)

  1. 1 . An arrangement for interrupting current 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, where the circuit breaker module is provided with a mechanical circuit breaker (1 ), which, during normal operation, carries current, and a resonant circuit (3) adapted be excited to achieve a zero-crossing the current through the mechanical circuit breaker (1), characterized by an excitation circuit (40) adapted to initiate excitation of the resonant circuit (3) for the purpose of determining whether the mechanical circuit breaker (1) is properly operable.
  2. 2. The arrangement according to claim 1 , comprising a voltage source converter (4) connected in series with the resonant circuit (3), wherein the excitation circuit (40) is connected to the voltage source converter (4), and wherein the excitation of the resonant circuit (3) is achieved by means of the voltage source converter (4).
  3. 3. The arrangement according to claim 1 or 2, comprising a current sensor (41 ) adapted to sense current (Io) that flows in a loop containing the mechanical circuit breaker (1) and the resonant circuit (3).
  4. 4. The arrangement according to any one of claims 1-3, comprising a disconnecting switch (5) connected in series with the circuit breaker module (10).
  5. 5. A system for interrupting current comprising at least two arrangements for interrupting current according to any of claims 1-3, wherein said at least two arrangements for interrupting current are connected in series.
  6. 6. A system according to claim 5, comprising a disconnecting switch (5) connected in series with the circuit breaker modules (10).
  7. 7. A method of detecting a fault in a mechanical circuit breaker (1 ), the method comprising the following steps: - exciting a current (Io) through the mechanical circuit breaker (1 ), - determining the behaviour of the current (Io), and - depending on the behaviour of the current (Io), determining the currentcarrying capability of the mechanical circuit breaker (1 ).
  8. 8. The method according to claim 7, comprising a step of sensing the current (Io) before determining the behaviour of the current (Io),
  9. 9. The method according to claim 7 or 8, wherein a resonant current (Io) is excited through the mechanical circuit breaker (1 ), and the transient behaviour of the resonant current is observed, for the purpose of determining the currentcarrying capability the mechanical circuit breaker (1 ).
  10. 10. The method according to claim 9, comprising a step of sensing and comparing the peak amplitude of at least two subsequent oscillation cycles of the resonant current (Io).
  11. 11 . The method according to claim 8 or 9, comprising the step of detecting no current (Io).
  12. 12. The method according to any one of claims 7-11 , wherein the current (Io) is sensed by means of a current sensor (41 ).
  13. 13. The method according to any one of claims 7-12, wherein the current (Io) is excited by means of a voltage source converter (4) forming part of a loop in which the current (Io) flows.
  14. 14. The method according to claim 13 wherein the current (Io) is sensed by observing a voltage across a DC link capacitor of the voltage source converter (4).
  15. 15. The method according to any one of claims 7-14, comprising a step of operating a disconnecting switch (5), before the step of exciting a current (Io) through the mechanical circuit breaker (1 ).
  16. 16. The method according to any one of claims 7-15, comprising a step of synchronizing the excitation to the resonance frequency, preferably by sensing the current, providing an open loop, measuring the voltage, and measuring magnetic fields.

Description

ARRANGEMENT, SYSTEM, AND METHOD FOR DETECTING A FAULT IN AN ELECTRIC CIRCUIT BREAKER Technical 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 I 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 refer to patent EP3398198 and EP3161846. This 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 said circuit breaker is opened, preferably using a fast actuator. The current keeps flowing by way of an arc inside the breaker. Next, an alternating 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. Fig. 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 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 metallic separation when in the open state, since an energy absorbing device 2 is connected in parallel to the mechanical circuit 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 path of the main current. The residual current breaker only needs very limited current interruption capability. [0007] It is often beneficial to use the mentioned switch 5 for closing the current circuit and allow the line current I to flow. By this method of closing the circuit, the circuit breaker is normally in the closed state, or in case it consists of several series connected breaker submodules 10 all of these are closed, and thus conducting. The voltage is then