WO2013000483A1

WO2013000483A1 - A circuit breaker and method for interrupting large direct currents

Info

Publication number: WO2013000483A1
Application number: PCT/DK2012/050239
Authority: WO
Inventors: Jamie CHAPMAN; Bo Hesselbaek
Original assignee: Vestas Wind Systems A/S
Priority date: 2011-06-30
Filing date: 2012-07-02
Publication date: 2013-01-03

Abstract

A circuit breaker for interrupting an electrical DC current from a power source to an electrical load. The circuit breaker has a first electrical contact, a second electrical contact, and a shunt contact. A diverting device promotes diverting of an electrical arc that extends between the first contact terminal and second the contact terminal to extend between the first contact terminal and the shunt terminal, when the circuit breaker is in a transition mode between a closed and an open mode.

Description

A CIRCUIT BREAKER AND METHOD FOR INTERRUPTING LARGE DIRECT CURRENTS

FIELD OF THE INVENTION

Aspects of the present invention relate to a circuit breaker for interrupting an electrical

DC current from at least one power source to a least one electrical load, and methods for operating the circuit breaker.

BACKGROUND OF THE INVENTION

As grid-connected wind turbine generators increase in power generation capacity and as the size of wind power plants also increase in the number of turbines, turbine designers and operators are considering transitioning from the provision of standardized 50 or 60 Hz

Alternating Current (AC) electricity to Direct Current (DC) power. This is particularly true for turbines installed offshore, motivated by the desire to minimize cable costs and losses in transmission of the power to distant onshore terminals. Another design option under consideration is to increase of the nominal generator output voltage from the customary 690 Vrms or sub 1000 Vrms to thousands and tens of thousands of volts. For such higher- voltage DC wind turbine generator and wind power plant systems, control of the substantial current values presents new challenges. In particular, there is a need for controlled, reliable and repeatable means for interrupting and disconnecting high voltage, high value DC currents from wind farms, wind turbine generators and other controllable DC power sources.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a circuit breaker is disclosed for interrupting an electrical DC current from a power source to an electrical load. The circuit breaker is arranged to operate in a closed mode, an open mode or a transition mode. A first contact terminal and a second contact terminal receives DC current from the first contact terminal when in the closed mode. A shunt terminal receives DC current from the first contact terminal when in the open mode. A diverting device, in the transition mode, promotes diverting of an electrical arc that extends between the first contact terminal and second the contact terminal to extend between the first contact terminal and the shunt terminal. The diverting device may provide technical advantages by reducing the time in which it takes for the circuit to be interrupted. According to some embodiments, a shunt (ZS) connected to the shunt terminal for dissipating electrical energy is less than impedance of the electrical load (ZL), which may advantageously promote movement of the electrical arc to the shunt terminal. Other features may be included in the diverting device to interrupt the circuit more quickly, including but not limited to a nozzle that blows a gas to urge the electrical arc toward the shunt terminal; one or more permanent magnets that provide a magnetic field to urge the electrical arc to the shunt terminal; and an electromagnetic coil that provides a magnetic field to urge the electrical arc to the shunt terminal.

According to some embodiments, a control circuit is arranged to initiate urging the electrical arc to the shunt terminal by activating the diverting device upon receipt of disconnect control signal. A shutdown circuit may be arranged to transmit a control signal to interrupt at least one power source feeding current in the electrical arc.

According to some embodiments, the circuit breaker may be implemented in a distributed renewable power production plant having a plurality of power producing units and a DC distribution grid. In such an embodiment, the circuit breaker may provide a connection between the distributed renewable power production plant and the DC distribution. Each of the power producing units may be arranged to receive an interrupt signal to interrupt the power source feeding the current in the electrical arc, according to some embodiments. The plurality of power producing units may include wind turbine generators.

According to another aspect, a method is disclosed for interrupting an electrical DC current from at least one power source to a least one electrical load with a circuit breaker. The circuit breaker has a first contact terminal, a second contact terminal and a shunt terminal. The method includes mechanically separating the first contact terminal and the second contact terminal. A diverting force diverts any electrical arc formed between the first contact terminal and the second contact terminal to act between the first contact terminal and the shunt terminal, which is advantageous in reducing the time it takes to interrupt the circuit.

According to one embodiment, the electrical arc is diverted to the shunt terminal that is electrically connected to a shunt having a shunt impedance ZS that is less than a load impedance ZL associated with the electrical load. This may prove technically advantageous by promoting movement of the electrical arc to the shunt terminal.

According to some embodiments, diverting includes blowing a gas to direct the electrical arc toward the shunt terminal and/or applying a magnetic field to deflect the electrical arc. Any electromagnetic field may be generated by electromagnetic coil. Such a magnetic field may be controlled in relation to the DC current flowing to second contact terminal.

According to some embodiments, the method includes sending an interrupt signal to the at least one power source feeding the DC current supply to interrupt current flow from the first electrical contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

Figure 1 illustrates the techniques for the interruption and disconnection of currents from controllable DC power sources, with an option 1 showing the known method and option 2 showing the present invention.

Figure 2 shows a normal current path from the DC Power Sources to the Load Impedance

Z_L.

Figure 3 shows the mechanical first contacts terminal and second contact terminal are being retracted with initiation of an electrical arc with continued current flow from the DC Power Sources to the Load Impedance Z_L. Shutdown of the DC Power Sources has been initiated by the Source Shutdown Control Signal.

Figure 4 shows that first Contact terminal is fully retracted with the electrical arc current fully diverted to shunt Terminal and the shunt impedance Zs. The load impedance Z_L is fully disconnected from the DC Power Sources that are in the process of shutting down.

Figure 5 shows the completion of the shutdown and disconnect sequence.

Figure 6 illustrates source shutdown and transfer of source current from the Load impedance Z_L to the Shunt impedance Zs.

Figure 7 shows a flow chart of the method for disconnection

Figure 8 shows a flow chart of the method for disconnection with optional steps. DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be explained in further details. While the invention is susceptible to various modifications and alternative forms, specific embodiments have been disclosed by way of examples. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

In an embodiment of the present invention the DC Disconnect apparatus 29 is

implemented in an energy system where the energy sources are wind turbine generators.

A wind turbine generator is an energy conversion system which converts kinetic wind energy into electrical energy for utility power grids. Specifically, wind is applied to wind turbine blades of the wind turbine generator to rotate a rotor. The mechanical energy of the rotating rotor in turn is converted into electrical energy by an electrical generator. Because wind speed fluctuates, the force applied to the wind blades and hence the rotational speed of the rotor can vary. Power grids however require a constant frequency electrical power to be provided by the wind turbine generator.

One type of wind turbine generator that provides constant frequency electrical power is a fixed-speed wind turbine generator. This type of wind turbine generator requires a generator rotor that rotates at a constant speed. A disadvantage of such fixed-speed wind turbine generator is that it does not harness all of the wind's energy at high speeds and must be disabled at low wind speeds.

Another type of wind turbine generator is a variable speed wind turbine generator. This type of wind turbine generator allows the electrical generator to rotate at variable speeds to accommodate for fluctuating wind speeds. By varying the rotating speed of the generator rotor, energy conversion can be optimized over a broader range of wind speeds.

A variable speed wind turbine generator usually includes a power converter having a generator side converter coupled to a grid side converter via a direct current (DC) link. The generator side converter regulates the power of the generator. This power passes through the DC- link, and is eventually fed to the grid through the grid side converter.

In an embodiment the wind turbine generators feed the produced power to a DC grid without having a grid side converter, which normally would convert the DC link voltage to AC. In another embodiment the wind turbine generators are equipped with grid side converter and then again converted to DC perhaps medium voltage (MV) DC or high voltage DC, also know as HVDC, this may be at wind park level (wind park here means a plurality of wind turbine generators connected at a point of common coupling), or even at a subset of the wind park.

Under normal conditions, the electrical power or energy from the generator is supplied to the grid through the power converter. In other words, the energy captured from the wind by the wind turbine generator is passed to the grid. Therefore, it can be said that there is power balance during normal conditions. However, when there is a sudden wind gust and/or grid fault, this power balance may be disrupted, resulting in more power being generated than power being supplied to the grid.

When there is a grid fault, for example a low voltage event, there is a sudden drop in demand for active power from the grid. Since the pitching of the blades is not able to respond fast enough to reduce power generation, there is an imbalance of power in the wind turbine generator. A crowbar circuit may be used during low voltage events at the grid. The crowbar circuit is coupled to the DC link between the generator side converter and the grid side converter. When the DC link voltage exceeds a predetermined value (due to grid fault), the crowbar circuit is activated to drain the excess generator power, hence lowering the DC link voltage.

The use of a crowbar circuit or a dump load circuit may provide a good way of dissipating excess power during a power imbalance event. The dump load circuit is activated by detecting an abnormal increase in the DC link voltage or a sudden drop in grid voltage.

In an embodiment of the present invention each wind turbine generator supports a fast shutdown when receiving the Source Shutdown Control Signal 22, by diverting the energy normally supplied to the electrical grid, and could be a DC or AC grid, to a dump load and thus reducing the energy dissipation E_Sh_unt in the shunt impedance.

The advantages of this feature is that the power producing unit can dissipate energy into a dump load for a given period of time, during this period of time the wind turbine generator is capable of returning to normal operation within a few milliseconds, as the aerodynamic rotor is still in operation.

Similar behavior can be implemented for other types of distributed power production plants, e.g. solar power, photo voltaic power, wave energy power units etc. Also known as distributed renewable power production plant Described here is a technique for interrupting the DC current flow from such wind turbine generator and wind power plant systems, the use of the present invention is not limited to be used together with wind turbines, it may be used in many application where there is a need for fast interruption DC current flow. More generally, the techniques are applicable to other single and multiple DC power sources whose outputs can be shut down and disconnected in response to a control signal. In addition to describing controlled and coordinated shutdown of the power sources, described also is a specific implementation of electromagnetic apparatus for the disconnect of high- voltage, high-current DC power. Together, the techniques decouple the time required for shutdown and disconnect of the DC sources (which may be variable and excessively long from a grid safety and operational view) from the defined and much shorter time desired for interruption and disconnect of the load current.

Description of the Controlled Power Sources, Controlled Disconnect and Power Sinks

Illustrated in Fig. 1 is an array of DC Power Sources 20 (a,b,c,n) whose outputs are bussed together to a feeder line 25 The feeder combines the power from each source 20 and delivers the power to a load 6. Typically the load 6 would be a converter that transforms the DC power to standardized 50 or 60 Hz utility-grade power. The combined source power is delivered to the load through the DC Disconnect and Source Shutdown Control 29 (the DC Disconnect). The DC Disconnect is responsive to the Disconnect Control Signal 21. Upon receipt of this Disconnect Control Signal 21, the DC feeder circuit is interrupted thus stopping the current flow to the load. At the same time, the DC Disconnect transmits a Source Shutdown Control Signal 22 to each of the DC Power Sources 20. With the sources shut down and disconnected, electrical arcs 10 initiated within the disconnect apparatus are terminated. Load Disconnect Time vs Source Shutdown Times

A factor in the design, reliability and cost of the DC Disconnect apparatus 29 is the time required for complete cessation of current flow to the load 6. To provide maximal protection to downstream loads and components, it is desirable to minimize the disconnect time and to provide time certainty for the cessation of current flow to the load. It is desirable also to have the disconnect time be intrinsic to the DC Disconnect apparatus 29 and be decoupled from the time required for shutdown and disconnect of the ensemble of DC Power Sources 20. The control approach and apparatus described in this present invention meets these objectives. Load Disconnect Options

Consider the operation of the simplest current interrupter or circuit breaker, depicted as Option 1 in Fig. 1 29a. Consider first the use of movable metallic contacts. With the breaker closed, two metallic contacts 1, 2 are in direct contact thus enabling a current flow, e.g. from a source 20 to a load 6. When it is desired to open or break the circuit and interrupt the current flow, an actuator physically separates the contacts 1, 2. Depending on the voltage-current ratings, the separation distance and other construction details, the contacts may separate with arcing 10. For AC current, the zero crossings extinguish any electrical arc 10 that may have been initiated as a result of separating the contacts. However for a DC current, there are no zero crossings of the electrical waveforms. Extinguishing or controlling the arc can prevent destruction or unreliable functioning of the DC breaker. This is particularly the case for the interruption of high values of current and voltage.

There is a further disadvantage to the Option 1 approach: the uncertainty and lack of a known, minimal time for the interruption of current flow to the load, a time that is independent of the shutdown times of the DC Power Sources. With metallic contacts, the Option 1 29a approach typically sustains an electrical arc 10 with continued current flow during the time required for a complete shutdown and disconnect of the DC Power Sources 20. This time may be too long from the perspectives of load/grid operation as well as rapid erosion of the contacts 29. The opening of an Option 1 mechanically-actuated, metallic-contact switch is a necessary but not sufficient condition for interruption of current flow to the load 6.

As indicated in the Option 1 illustration, a semiconductor switch also can interrupt and disconnect the DC current. This may be implemented by a three-terminal semiconductor switch capable of triggered opening with DC current flowing through the switch. An IGBT provides an example of such a switch. However, IGBTs having adequately-high voltage and current ratings may not be economically available or operationally reliable at medium voltages and large currents. The same may be said of other semiconductor switch technologies.

Current Transfer Shunt Switch

The shunt switch arrangement depicted in Fig. 1 as Option 2 29b, an embodiment of the present invention, decouples the time required for load current interruption from that required for a complete shutdown and disconnect of the DC Power Sources 20. A principle of the present invention is that instead of interrupting the DC power source completely, the DC current may be transferred to a Shunt 5 and grounded 4 via a third terminal 3, while the DC current is reduced from the power source 20 by controlling the source 22.

The load current interruption and transfer time x_Sh_Unt depends only on the characteristics of the DC Disconnect apparatus. The DC Disconnect apparatus described below employs a minimum of mechanical moving parts and uses magnetic forces 9 to implement the current shunting action. It is expected that the load current transfer and interruption time x_Shunt can have values of less than five milliseconds.

Upon receipt of the Disconnect Control Signal, the current from the DC Power Sources is diverted from the power delivery load Z_L 6 to the shunt load Zs 5. The time constant x_Sh_Unt for the current transfer operation can be much smaller than the time required for a complete shutdown and disconnect of the DC Power Sources 20. Further, since the triggering of the shunt operation also triggers the shutdown and disconnect of the power sources 20, the shunt impedance 5 need only have power and energy ratings suitable for a time-limited transient.

Suppose that each of the DC Power Sources has an identical shutdown-and-disconnect time

Tshutdown and that they are all triggered to shut down at the same time. Typically, even if simultaneously commanded to shut down and disconnect, differing operating characteristics mean that the time required can be longer than xshutdown- A typical minimum value for the shut down and disconnect of a single utility-scale, multi-megawatt wind turbine generator is a few seconds. Denote the latency (delay) time between the application of the Disconnect Control Signal and the application of the Source Shutdown Control Signal 22 by XLatency- It is expected that xshotdown will be much larger than XLatency and x_Shunt combined. Assuming that the current transfer begins upon receipt of the Disconnect Control Signal 21 and ends with shutdown of the DC Power Sources 20, the shunt impedance Zs must have maximum power (Watts) and energy dissipation (Watt-sec) ratings given by

Pshunt = I² *Re(Z_S) and E_Shunt = I² *Re(Z_S) * ( XShutdown + T_Latency ) where / denotes the initial value of the load current being interrupted and Re(Zs) denotes the resistive component of the shunt impedance Zs.

The size of the impedance value of the shunt impedance effect the ability of the diverting the arc from the second contact terminal to the shunt terminal 3, if the shunt impedance 5 is smaller in value than the impedance of the load the arc is more likely to be diverted to the shunt terminal 3 as the overall impedance for the current flow will be reduced.

Implementation and Operation of the DC Disconnect

Illustrated in the four sequences of Figs. 2 through 5 is the implementation and operation of a mechanically- and magnetically-actuated DC current interrupter and disconnect suitable for large values of voltage and current, from an input 7 to an output 8. The operation takes advantage of the electrical arc that results from separation of the mechanical metallic contacts 1, 2 and 3. The shunt and current transfer operation is effected by magnetic forces 9 acting on the current flow in the electrical arc 10. In this way, during the time interval□ s_hun_t, the source current 7 is diverted from the downstream load impedance Z_L 6 to the shunt impedance Zs 5, thus bringing the load current 8 to zero.

State A Fig. 2 depicts normal operation of the disconnect system wherein the current provided by the DC Power Sources 20 is conveyed through the DC Disconnect to the load impedance Z_L 6. The current 7 is conveyed through the closed metallic first 1 and second contacts 2.

State B In Fig. 3, mechanical separation of the metallic contacts has been initiated by the Disconnect Control Signal 21, starting the x_Shun_t interval (the current transfer time). This in turn results in transmission of the Source Shutdown Control Signal 22 to the DC Power Sources 20, initiating shutdown and disconnect of these sources over the interval xs_hu_tdown- An electrical arc 10 has been formed between the first contact 1 and the second contact 2 in that the distance is not yet great enough that the arc is diverted to the metallic shunt contact 3. Current, although declining, still is being delivered to the load impedance Z_L 6.

State C In Fig. 4, the metallic first contact 1 has been fully retracted. The fully- developed electrical arc 10 has been diverted from the second contact 2 to the metallic shunt contact 3 by the vector J x B magnetic forces 9 acting on the arc current 10. As shown in the embodiment of Fig 2-5 the arc 10 will be diverted downwards, if the magnetic field B 9 had the opposite direction the arc would have been diverted upwards.

In one embodiment the means for diverting the Arc 10 may, additionally or alternatively, be gas blown towards the Arc 10 to urge the arc in the direction of the shunt terminal 3. The source current 7 has been fully diverted to the shunt impedance Zs 5 from the load impedance Z_L 6. The load impedance Z_L 6 is now fully disconnected from the DC Power Sources 20 that are in the process of shutting down.

The current 7 is shown in Fig. 4 as still having the value I indicating that the DC Power Sources 20 have not yet appreciably responded to the Source Shutdown Control signal 22. To the extent that the sources 20 are shutting down, the arc current will be reduced from the original value I.

State D The disconnect sequence is shown as completed in Fig. 5. The DC Power Sources 20 are completely shut down. The electrical arc 10 is extinguished. There is no current flow 7 anywhere.

Provision of the Magnetic Flux Density

The region of magnetic flux density B is indicated by the regions 11 of Figs. 2 through 5. While the magnetic flux density B 9 can be constant within the region 11, there may be advantages to having the flux density value be greater at the top of region 11 between first 1 and second 2 contact terminal and diminishing in value going toward shunt terminal 3. This corresponds to a magnetic pressure gradient that is strongest at the top of the shaded region 11. This can further aid the transfer of the arc 10 from second Contact terminal 2 to shunt terminal 3.

The magnetic field 9 or flux density B 9 may be implemented with permanent magnets either with or without field-shaping pole pieces. Similarly, the field 9 may also be implemented with a separate excitation current flowing through appropriately-shaped and positioned coils. This separate excitation current can be steady-state or, more advantageously, pulsed using the energy stored in a capacitor that is switched by the Disconnect Control Signal 21. The magnetic flux density also could be created using both a permanent magnet assembly together with a current-driven coil-electromagnet source.

In an embodiment there may also be a control circuit for controlling the magnetic field of the magnetic deflecting circuit according to the DC current flow from the first 1 and second 2 contact terminal. The control circuit is not shown in the Figures.

The time x_Shunt for transfer of the arc from second contact to shunt terminal 3 also may be minimized by shaping their ends so as to facilitate the transfer of the arc 10 by shaping the electric field distribution. As a further option, the magnetic forces could be utilized to reduce the distance between first Contact and shunt Terminal with the objective of minimizing the current transfer time.

Illustration of the Current Transfer Timing of the DC Disconnect

Given in Fig. 6 are the time sequences resulting from the two command signals, the

Disconnect Control Signal 21 and the Source Shutdown Control Signal 22. The two graphs (upper and lower) represent the same situation. The top graph has a time scale that shows the complete sequence from application of the Disconnect Control Signal 21 to the shutdown of the DC Sources 20. The lower is an expanded time scale allowing a clearer view of the early time sequences. Shown in the graphs and summarized in the text to the right are the actions resulting from application of the two control signals 21 and 22.

As shown in the lower right-hand side of Fig. 6, the graphs are made for the following values of the three time intervals: TLatency = 0.20 msec

Tshunt = 2 msec

Tshutdown = 10 msec.

These values were chosen to make the graphs more interpretable. They are not believed to be representative of actual realization and operation of the DC Disconnect or the DC Power Sources as represented by an ensemble of megawatt-scale wind turbine generators. For analytic simplicity, the time behavior has been modeled by linear ramps; this may not be the case in real life.

The time sequences in the left part of the graphs illustrate the transfer of source current (the red trace) from the load impedance Z_L to the shunt impedance Zs 5 over the interval x_Sh_Unt- During this interval, the source current 61 is being diverted to the shunt impedance 5. The increasing shunt current 62 increases within the interval x_Shunt, the sum of the declining diverted load current 63 and the increasing shunt current 62 sum to the (declining) value of the source current 61.

After complete transfer of the source current 61 from the load to the shunt impedance

(marked by the end of the interval x_Shunt), the continuing and declining source current is absorbed by the shunt impedance. This is indicated by the overlap of the source current 61 and the shunt current 62 traces. Thus the shunt impedance Zs absorbs source power during the interval x_Shun_t through completion of the source shutdown, indicated by the end of the interval xs_hu_tdown- A Further Consideration about the nature of the load impedance Z_L has not been discussed. For the DC system discussed here, the load might be an electrical apparatus whose purpose is the conversion of the DC power to standardized 50 Hz or 60 Hz power. While the input impedance of the apparatus may be significant, the load impedance may be dominated by the inductance of the transmission line connecting the Power Sources 20 to the load. To the extent that the combination of the transmission line and load impedance are inductive, there is stored magnetic energy associated with the current I. During the disconnect process, the collapse of the magnetic field 9 may result in voltages and voltage transients that could be harmful to one or more parts of the system.

To deal with this possibility, two augmentations may be desirable. The first is an additional command signal 22 sent to the power producing sources or apparatus resulting in a shutdown or other appropriate protective action. In one embodiment such protective action can be a fast shut down of the power production or an interruption of the power flow from the power source, this can for a wind turbines generator be accomplished by triggering the crow bar or the dump load circuit. In yet another embodiment the power production can be interrupted simply by turning of the power converter or even simpler by turning of the gate signals to the converter power switches. This could be the case for PV solar power plants.

The second is the addition of a suitably-rated Transient Voltage Surge Suppressor (TVSS), spark gap or other device that limits the overvoltage arising from collapse of the magnetic field. This may be placed at the DC Disconnect Switch or at more than one location, depending on the length and characteristics of the transmission line. Such a TVSS is not shown in the Figures.

If the energy sources are a Photovoltaic solar panel connected to a power electronic converter system a simple control signal is sufficient to interrupt the converter, and thus stop the current flow.

A more complex situation occurs if the energy sources are wind turbine generators, here a simple shot down is not possible because of mechanical stress on the structure of the wind turbine generator and the use of a dump load may be advantageous.

Figure 7 shows a flow chart of a method according to the invention for operating the circuit breaker. Step 700 includes the initialization of the mechanical separation of the first 1 and second 2 contact terminal, whereby an arc 10 forms between the two terminals 1 and 2. Step 710 includes diverting of the arc 10 from the second contact terminal 2 to the shunt terminal 3.

Figure 8 show a flow chart of a method according to the invention for operating the circuit breaker with number of additional steps. Step 720 includes diverting of the DC current into the shunt impedance 5. Step 730 includes applying a magnetic field 9 to the arc 10, in order to help the diverting of the arc 10. Step 740 includes controlling the magnetic field 9 in the electromagnetic coils which also allows for adjusting the magnetic field 9 depending on the DC current 7 prior to the need for interruption.

In summary the invention relates to, a circuit breaker for interrupting a electrical DC current from a power source to an electrical load, the circuit breaker comprises a first contact terminal, a second contact terminal and a shunt terminal, the circuit breaker is arranged to operate in a closed mode, an open mode or a transition mode, in closed mode the circuit breaker is arranged to conduct DC current from the first contact terminal to the second contact terminal, in open mode the circuit breaker is arranged to block DC current conduction from the first contact terminal to the second contact terminal and from the first contact terminal to the shunt terminal, wherein the circuit breaker comprises a diverting device arranged for, in transition mode, acting on an electrical arc between first and second contact terminal, whereby the electrical arc is diverted to occur between the first contact terminal and the shunt terminal.

The present invention also relates to a method of interrupting a DC current.

Any range or device value given herein may be extended or altered without losing the effect sought, as will be apparent to the skilled person.

It should be understood that aspects of the invention are described herein with reference to the figures, which show illustrative embodiments in accordance with aspects of the invention. The illustrative embodiments described herein are not necessarily intended to show all aspects of the invention, but rather are used to describe a few illustrative embodiments. Thus, aspects of the invention are not intended to be construed narrowly in view of the illustrative embodiments. In addition, it should be understood that aspects of the invention may be used alone or in any suitable combination with other aspects of the invention.

Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

What is claimed is:

Claims

1. A circuit breaker for interrupting an electrical DC current from a power source to an electrical load, the circuit breaker arranged to operate in a closed mode, an open mode or a transition mode and comprising:

a first contact terminal;

a second contact terminal that receives DC current from the first contact terminal when in the closed mode;

a shunt terminal that receives DC current from the first contact terminal when in the open mode; and

a diverting device that, in the transition mode, promotes diverting of an electrical arc that extends between the first contact terminal and second the contact terminal to extend between the first contact terminal and the shunt terminal.

2. The circuit breaker according to claim 1, further comprising:

a shunt (Zs) connected to the shunt terminal for dissipating electrical energy, impedance of the shunt (Zs) being less than an impedance of the electrical load (Z_L).

3. The circuit breaker according to any of the previous claims wherein the diverting device includes a nozzle that blows a gas to urge the electrical arc toward the shunt terminal, at least when in the transition mode.

4. The circuit breaker according to any of the previous claims, wherein the diverting device includes one or more permanent magnets that provide a magnetic field to urge the electrical arc to the shunt terminal, at least when in the transition mode.

5. The circuit breaker according to any of the previous claims, wherein the diverting device includes an electromagnetic coil that provides a magnetic field to urge the electrical arc to the shunt terminal, at least when in the transition mode.

6. The circuit breaker according to any one of claims 3 and 5, further comprising: a control circuit arranged to initiate urging the electrical arc to the shunt terminal by activating the diverting device upon receipt of disconnect control signal.

7. The circuit breaker according to any of the previous claims 6, further comprising:

a shutdown circuit arranged to transmit a control signal to interrupt at least one power source feeding current in the electrical arc.

8. The circuit breaker according to any of the previous claims, in combination with a distributed renewable power production plant having a plurality of power producing units and a DC distribution grid, the circuit breaker providing a connection between the distributed renewable power production plant and the DC distribution.

9. The circuit breaker according to claim 8, wherein each of the power producing units is arranged to receive an interrupt signal to interrupt the power source feeding the current in the electrical arc.

10. The circuit breaker according to any one of claims 9 and 10, wherein the plurality of power producing units include wind turbine generators.

11. A method for interrupting an electrical DC current from at least one power source to a least one electrical load with a circuit breaker having a first contact terminal, a second contact terminal and a shunt terminal, the method comprising:

mechanically separating the first contact terminal and the second contact terminal;

diverting, with a diverting force, any electrical arc formed between the first contact terminal and the second contact terminal to act between the first contact terminal and the shunt terminal.

12. The method according to claim 11, wherein diverting includes diverting the electrical arc to the shut terminal that is electrically connected to a shunt having a shunt impedance Zs that is less than a load impedance Z_L associated with the electrical load.

13. The method according to any one of claims 12 and 13, wherein diverting includes blowing a gas to direct the electrical arc toward the shunt terminal.

14. The method according to any one of claim 12 and 13, wherein diverting includes the applying a magnetic field to deflect the electrical arc.

15. The method according to claim 14, wherein applying includes generating a magnetic field with electromagnetic coil to deflect the electrical arc.

16. The method according to claim 15, further comprising:

controlling the magnetic field of the electromagnetic coil in relation to the DC current flowing to second contact terminal.

17. The method according to any one of claims 13 through 17, wherein the method further comprises:

sending an interrupt signal to the at least one power source feeding the DC current supply to interrupt current flow from the first electrical contact.