WO2012045360A1

WO2012045360A1 - Direct current circuit breaker

Info

Publication number: WO2012045360A1
Application number: PCT/EP2010/065035
Authority: WO
Inventors: Magnus Backman; Lars Liljestrand; Magnus Öhrström; Per Skarby
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2010-10-07
Filing date: 2010-10-07
Publication date: 2012-04-12
Anticipated expiration: 2013-04-07

Abstract

A direct current (DC) circuit breaker module (100) is provided. The module comprises a DC circuit (101), a mechanically operated vacuum interrupter (104) for interrupting the DC circuit, a repulsive force actuator for operating the interrupter in response to receiving a trip signal (111), an active resonance circuit (105) connected in parallel with the interrupter, and a surge arrester (106) connected in parallel with the interrupter. Preferably, the actuator is arranged inside the vacuum chamber of the interrupter. Further, a DC circuit breaker is provided, the circuit breaker comprising a plurality of circuit breaker modules connected in series. By series-connecting a plurality of circuit breaker modules, a circuit breaker may be constructed having a desired operating voltage higher than the operating voltage of a single circuit breaker module.

Description

DIRECT CURRENT CIRCUIT BREAKER

Field of the invention

The invention relates in general to high voltage direct current (HVDC) power transmission, and more specifically to direct current (DC) circuit breakers.

Background of the invention HVDC power transmission is becoming increasingly important due to the steadily rising need for bulk power delivery and interconnected power transmission and distribution systems.

An HVDC grid typically comprises multiple terminals for converting an alternating current (AC) power source for transmission over transmission lines, i.e., underground cables and/or overhead lines, or vice versa. Within the grid, a terminal may be connected to multiple terminals resulting in different types of topologies. Such a multiple terminal grid enables efficient congestion management and has an improved stability against disturbances.

DC circuit breakers are commonly used for isolating faulty

components, such as transmission lines, in HVDC grids. Due to the lack of current-zeros, in contrary to AC circuit breakers, special attention has to be given to the design of HVDC circuit breakers. Further, due to the low inductance of DC transmission lines, as compared to AC systems, HVDC systems suffer from a high rate of rise of fault induced currents. Thus, the tripping of DC breakers has to be effected quickly, before the rising current exceeds the interrupting capacity of the breakers.

Summary of the invention It is an object of the present invention to provide a more efficient alternative to the above techniques and prior art. More specifically, it is an object of the present invention to provide an improved direct current (DC) circuit breaker.

These and other objects of the present invention are achieved by means of a DC circuit breaker module having the features defined in independent claim 1 . Embodiments of the invention are characterized by the dependent claims.

According to an aspect of the invention, a DC circuit breaker module is provided. The module comprises a DC circuit, an interrupter, a repulsive force actuator, an active resonance circuit, and a surge arrester. The interrupter is mechanically operated and is arranged for interrupting the DC circuit. The repulsive force actuator, which may, e.g., be based on Thomson coils, is arranged for operating the interrupter in response to receiving a trip signal. The active resonance circuit is connected in parallel with the interrupter. The surge arrester is connected in parallel with the interrupter.

For the purpose of describing the present invention, a DC circuit is an electrical connection for carrying a direct current between two terminals at which the circuit breaker module is electrically connected to an external circuit. An embodiment of the invention may be arranged in series with a pole of a transmission line.

The present invention makes use of an understanding that a circuit breaker having a short opening time may be realized by utilizing an operating mechanism based on Thomson coils. This is advantageous since short opening times are required in HVDC power transmission systems due to the high rate of rise of fault induced currents.

According to an embodiment of the invention, the active resonance circuit comprises a capacitor, an inductance, and a switch. The switch is arranged for activating the resonance circuit. The resonance circuit is activated in response to determining that the interrupter has opened, such that the fault current can be interrupted. Using an active resonance circuit in a DC circuit breaker is advantageous since it provides the lacking current- zeros. More specifically, when the contacts of the interrupter are in an open position, the closing switch is closed and the pre-charged capacitor is discharged through the interrupter. The discharge current is of AC character and is superimposed on the direct current, resulting in a current-zero so that the interrupter may interrupt the resulting current. The closing switch may, e.g., be a mechanical switch, a triggered spark gap, or a power electronics device, such as a thyristor.

According to an embodiment of the invention, the interrupter is a vacuum interrupter.

According to an embodiment of the invention, the actuator is arranged inside a vacuum chamber of the interrupter. This is advantageous since it mitigates problems typically encountered in known circuit breakers, which problems frequently relate to the use of bellows and flexible contacts in such circuit breakers. Thus, by integrating the actuating mechanism inside a the vacuum chamber of the interrupter, i.e., together with the contacts of the interrupter, the need for a bellow and flexible contacts is eliminated. In particular, integrating a Thomson-type actuator inside the vacuum chamber is advantageous in that only electric leads, used for activating the actuator, need to cross the vacuum barrier, thereby increasing the reliability of the circuit breaker module. Further, other mechanical components, such as mechanical springs for providing a bi-stable contact position, damping means, and sliding contacts, may also be integrated inside the vacuum chamber.

According to an embodiment of the invention, the vacuum interrupter is arranged inside a gas enclosure. In this way, a gas insulated switch (GIS) may be achieved.

According to another embodiment of the invention, the interrupter is a gas insulated interrupter.

According to an embodiment of the invention, a DC circuit breaker is provided. The circuit breaker comprises a plurality of DC circuit breaker modules. The plurality of DC circuit breaker modules are connected in series. By series-connecting a plurality of circuit breaker modules, a circuit breaker may be constructed having a desired operating voltage higher than the operating voltage of a single circuit breaker module. The circuit breaker modules may be configured for tripping simultaneously in response to receiving a trip signal. Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of embodiments of the present invention, with reference to the appended drawings, in which:

Fig. 1 is a circuit diagram of a DC circuit breaker module, in

accordance with an embodiment of the invention.

Fig. 2 shows a vacuum interrupter, in accordance with an embodiment of the invention.

Fig. 3 illustrates a DC circuit breaker, in accordance with an

embodiment of the invention.

Fig. 4 illustrates DC circuit breakers, in accordance with embodiments of the invention

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested. Detailed description

In Fig. 1 , a DC circuit breaker module according to an embodiment of the invention is shown.

Circuit breaker module 100 comprises a DC circuit 101 for carrying a direct current between terminals 102 and 103, an interrupter 104 for breaking the direct current being carried by circuit 101 , an active resonance circuit 105 connected in parallel with the interrupter 104, and a surge arrester 106 connected in parallel with the interrupter 104. The interrupter 104 is a mechanical interrupter comprising contacts which are maneuvered, using an actuator, between a closed and an open position.

The resonance circuit 105 comprises a capacitor 107, an

inductance 108, and a closing switch 109 for activating the resonance circuit when the interrupter 104 has opened, such that the fault current can be interrupted.

In the following, the operation of the DC circuit breaker module 100 is described with reference to Fig. 1 .

During normal operation, the interrupter 104 is closed, the

capacitor 107 is charged, and the closing switch 109 is open. Upon reception of a trip signal 1 1 1 , received, e.g., from an external controlling entity of an HVDC power transmission system, the interrupter 104 starts opening by moving its contacts apart. An arc is built up between the interrupter contacts, which can only be extinguished by forcing the current to zero. This is accomplished by the active resonance circuit 105. More specifically, when the contacts of interrupter 104 have reached an open position, such that the fault current may be interrupted, closing switch 109, which is initially in an open position, is closed. As a consequence, the capacitor 107 is discharged through the interrupter 104. Since the discharge current is of oscillating character and is superimposed on the direct current carried on circuit 101 , a zero-crossing of the current is achieved and the arc current through

interrupter 104 is cleared.

Once the interrupter 104 has cleared the arc current, the direct current is commutated to the active resonance circuit 105. The capacitor 107 will start charging and the voltage across the capacitor 107 will increase. Once the voltage has reached the clamping voltage of the surge arrester 106, the latter will change to a conducting state, and, consequently, the direct current will start to decrease and the remaining inductive energy stored in the DC circuit 101 , and in a transmission line connected to the DC circuit 101 , will be dissipated in the surge arrester 106. Finally, the direct current will decrease to zero and the breaking operation is completed.

The values of the capacitor 107 and the inductance 108 comprised in the active resonance circuit 105 are chosen such that a suitable resonance frequency is achieved. A higher resonance frequency will result in a shorter time until the first zero-crossing of the current occurs and an interruption attempt can be made. There is a trade-off between the resonance frequency and the interrupter's capability to interrupt high-frequency currents. Suitable resonance frequencies are in the kHz range. If the self-inductance of the resonance circuit 105 is in a suitable range, no additional electrical

component, such as a reactor, is required for the inductance 108.

The clamping voltage of the surge arrester 106 is chosen to be of a suitable level. The difference between the clamping voltage and the

operational voltage of the power transmission system determines the time it takes for the direct current to decrease to zero. A higher clamping voltage results in a shorter fault clearing time, but stresses the system more. Thus, there is a trade-off between the clamping voltage of the surge arrester 106 and the insulation requirements of the power transmission system.

With reference to Fig. 2, a vacuum interrupter according to an embodiment of the invention is described.

Vacuum interrupter 200 comprises a vacuum chamber 201 , a fixed contact 202, and a movable contact 203 which is operated by an

actuator 204. The contacts 202 and 203, as well as actuator 204, are integrated inside the vacuum chamber 201 . The interrupter 200 further comprises terminals 205 and 206 for electrically connecting the interrupter. Terminal 206 is arranged with a sliding contact for maintaining an electrical contact with the movable contact 203.

The actuator 204 shown in Fig. 2 comprises two Thomson coils 207 and 208, i.e., flat-wound helical coils, and a moveable metallic disc 209 arranged in-between the two coils 207 and 208. The disc 209 is in mechanical contact with the moveable contact 203. Further, actuator 204 is arranged with electrical leads 210 for supplying current to either of the coils 207 and 208. The actuator 204 is activated by forcing current through either of the coils 207 and 208, thereby forming a variable magnetic field. The variable magnetic field induces eddy currents in the adjacent metallic disc 209, which, in turn, create a variable magnetic field of opposite direction. Thus, for sufficiently large current pulses through either of the coils 207 and 208, a repulsive force is formed between the coil and the disc 209, resulting in an acceleration of the disc, and with it, the moveable contact 203. In other words, current is passed through coil 207 for opening the contacts 202 and 203, whereas current is passed through coil 208 for closing the contacts 202 and 203.

In Fig. 3 a DC circuit breaker according to an embodiment of the invention is illustrated.

Circuit breaker 300 comprises a plurality of DC circuit breaker modules 301 ¹-301 ^N. Each of the modules 301 ¹-301 ^N may, e.g., be an embodiment of the circuit breaker module 100 described with reference to Fig. 1 . The modules 301 — 301 ^N are connected in series at their respective terminals (102 and 103 in Fig. 1 ). The resulting circuit breaker may be electrically connected to an external circuit using terminals 302 and 303. The modules 301 — 301 ^N are arranged for tripping simultaneously in response to receiving a trip signal 304 originating, e.g., from an external controlling entity of a power transmission system. By combining several circuit breaker modules 301 — 301 ^N, a circuit breaker having a higher operating voltage than the operating voltage of the individual modules may be obtained. For instance, if a circuit breaker having an operating voltage of 300 kV is required, such a circuit breaker may be constructed from ten circuit breaker modules having a 30 kV voltage rating.

In Fig. 4, different alternatives for arranging the components comprised in a circuit breaker according to an embodiment of the invention are illustrated schematically.

Circuit breaker 410 comprises two circuit breaker modules, the first module comprising an interrupter 41 1 , a resonance circuit 413, and a surge arrester 415, and the second module comprising an interrupter 412, a resonance circuit 414, and a surge arrester 416. As an alternative, the combined modules may share some of the components. Circuit breaker 420, e.g., comprises two interrupters 421 and 422, two resonance circuits 423 and 424, and one surge arrester 425 which is shared by the two

interrupter/resonance circuit combinations 421 /423 and 422/424. As a further alternative, circuit breaker 430 employs only one resonance circuit 433, and one surge arrester 434, both of which are shared by interrupters 431 and 432. Finally, it will be appreciated that a circuit breaker may be constructed using more than two interrupters or modules. This is illustrated by circuit

breaker 440, which comprises three interrupters 441-443, one common resonance circuit 444 and one common surge arrester 445.

An embodiment of a circuit breaker according to the invention, such as the circuit breakers 300 and 410^140 described with reference to Figs. 3 and 4, may comprise circuit breaker modules of different types. For instance, a circuit breaker may comprise a combination of circuit breaker modules based on vacuum interrupters, and circuit breaker modules based on gas insulated interrupters. Circuit breaker 410, described with reference to Fig. 4, may, e.g., comprise one vacuum interrupter 41 1 and one SF6 interrupter 412. Combining different types of interrupters in a circuit breaker benefits from the distinct advantages of the respective interrupter types. A vacuum interrupter, e.g., exhibits excellent thermal interruption capabilities, whereas an SF6 interrupter has a higher dielectric withstand capability.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the interrupter comprised in a circuit breaker module may be operated using any type of actuator and is not limited to an actuator based on Thomson coils.

In conclusion, a DC circuit breaker module is provided. The module comprises a DC circuit, a mechanically operated vacuum interrupter for interrupting the DC circuit, a repulsive force actuator for operating the interrupter in response to receiving a trip signal, an active resonance circuit connected in parallel with the interrupter, and a surge arrester connected in parallel with the interrupter. Preferably, the actuator is arranged inside the vacuum chamber of the interrupter. Further, a DC circuit breaker is provided, the circuit breaker comprising a plurality of circuit breaker modules connected in series. By series-connecting a plurality of circuit breaker modules, a circuit breaker may be constructed having a desired operating voltage higher than the operating voltage of a single circuit breaker module.

Claims

1 . A direct current, DC, circuit breaker module (100) comprising: a DC circuit (101 ),

a mechanically operated interrupter (104, 200) being arranged for interrupting the DC circuit,

a repulsive force actuator (204) being arranged for operating the interrupter in response to receiving a trip signal (1 1 1 ),

an active resonance circuit (105) connected in parallel with the interrupter, and

a surge arrester (106) connected in parallel with the interrupter.

2. The DC circuit breaker module according to claim 1 , wherein the active resonance circuit comprises:

a capacitor (107),

an inductance (108), and

a switch (109) being arranged for activating the resonance circuit in response to determining that the interrupter has opened.

3. The DC circuit breaker module according to claim 1 , wherein the interrupter is a vacuum interrupter.

4. The DC circuit breaker module according to claim 3, wherein the actuator (204) is arranged inside a vacuum chamber (201 ) of the interrupter (200).

5. The DC circuit breaker module according to claim 4, wherein the vacuum interrupter is arranged inside a gas enclosure.

6. The DC circuit breaker module according to claim 1 , wherein the interrupter is a gas insulated interrupter.

7. A DC circuit breaker (300) comprising a plurality of DC circuit breaker modules (301 — 301 ^N) according to any one of the claims 1 to 6, the plurality of DC circuit breaker modules being connected in series.