CN111934290A - A kind of multi-terminal DC circuit breaker and its control method - Google Patents

Abstract

The invention belongs to the field of direct current transmission of a power system and discloses a multi-terminal direct current circuit breaker, which comprises n ports, wherein a port x is connected with a bidirectional thyristor BTx and a quick mechanical switch MSx through a residual current switch RCBx; one end of the MSx is connected with the BTx, and the other end of the MSx is connected with the 1 st bus; one end of the BTx is connected with the MSx, and the other end of the BTx is connected with the 2 nd bus through a residual current switch RCB2_ x; the reverse conducting thyristor RT, the inductor and the capacitor form a series branch which is connected with the lightning arrester in parallel, one end of the series branch is connected with the 1 st bus through a residual current switch RCB1_0, and the other end of the series branch is connected with the 2 nd bus through a residual current switch RCB2_ 0. The multi-terminal direct current breaker has the advantages of extremely low conduction loss and high breaking reliability, and also has the capability of isolating direct current bus faults. The invention also provides a control method of the multi-terminal direct current breaker.

Description

A kind of multi-terminal DC circuit breaker and its control method

technical field

The invention relates to the field of direct current transmission in power systems, in particular to a multi-terminal direct current circuit breaker and a control method thereof.

Background technique

In a large-scale flexible HVDC grid, a DC bus has multiple DC outlets. In order to selectively cut off the faulty line, each DC line port needs to be equipped with a DC circuit breaker, but the construction cost of this configuration scheme is too high. Using a single multi-terminal DC circuit breaker to replace multiple DC circuit breakers enables multiple ports to share expensive breaking equipment, which can effectively reduce construction costs.

For most of the existing multi-terminal DC circuit breakers, the load current will flow through multiple load commutation switches LCS composed of IGBT (Insulated Gate Bipolar Transistor) during normal operation of the system, and each LCS will bring dozens of kilowatts conduction loss. Some existing multi-terminal DC circuit breakers do not include LCS, the load current only flows through the mechanical switch, and the conduction loss is only tens of watts, which is almost negligible. However, the existing multi-terminal DC circuit breakers that do not include LCS need to open multiple mechanical switches during the current breaking period. The failure of any one mechanical switch will lead to breaking failure, and the breaking reliability is low. The failure of the multi-terminal DC circuit breaker will seriously affect the normal operation of the flexible HVDC grid.

Therefore, it is necessary to study a new type of multi-terminal DC circuit breaker without LCS, so that it has higher breaking reliability.

SUMMARY OF THE INVENTION

Aiming at the shortcomings and deficiencies of the prior art, the present invention provides a novel multi-terminal DC circuit breaker. During the failure of the breaking port, the multi-terminal DC circuit breaker of the present invention only needs to open one mechanical switch, and can provide backup protection when the mechanical switch fails, thereby effectively improving the breaking reliability.

The invention also provides a control method for a multi-terminal DC circuit breaker.

The multi-terminal DC circuit breaker of the present invention is realized by the following technical solutions:

A multi-terminal DC circuit breaker, characterized in that the multi-terminal DC circuit breaker includes n ports, and the port x is connected to the triac BTx and the fast mechanical switch MSx through the residual current switch RCBx, wherein n is a natural number not less than 3, x It is a natural number not less than 1 and not greater than n; one end of MSx is connected to BTx, and the other end is connected to the first bus; one end of BTx is connected to MSx, and the other end is connected to the second bus through the residual current switch RCB2_x; reverse conduction thyristor RT, inductor and capacitor form a series branch connected in parallel with the arrester. One end of the series branch is connected to the first busbar through the residual current switch RCB1_0, and the other end is connected to the second busbar through the residual current switch RCB2_0.

Preferably, the residual current switch interrupts the residual current of no more than 10A within tens of milliseconds.

Preferably, the fast mechanical switch completes opening within milliseconds.

Preferably, the capacitor has an initial voltage U0 in a normal state.

The multi-terminal DC circuit breaker control method of the present invention is realized by the following technical solutions:

A control method of a multi-terminal DC circuit breaker is used to control the multi-terminal DC circuit breaker of the present invention, including: a control method when a disconnecting port is faulty, a control method when a fast switch fails, and a control method when the disconnecting bus is faulty.

Preferably, the control method when the disconnection port is faulty includes the following steps:

Step 1. During the normal operation of the system, the reverse thyristor and all triacs are in the off state, all the residual current switches are in the on state, and the capacitor is charged to the initial voltage U0; the multi-terminal DC circuit breaker passes through the fast mechanical switch MS1 ～MSn conducts the system current, and the conduction loss is extremely small;

Step 2. Port x fails at time t1; at time t2, the multi-terminal DC circuit breaker detects the fault and immediately arcs and opens MSx;

Step 3. At time t3, MSx completes the opening, and BTx and RT are turned on at this time, and the capacitor begins to discharge through the following loop: capacitor – BTx – MSx – RT – inductance; at time t4, MSx extinguishes the arc and restores the insulation capacity;

Step 4. At t5, the fault current charges the capacitor voltage to the arrester reference voltage, and the fault current begins to transfer to the arrester; once the fault current drops below 10A, the multi-terminal DC circuit breaker opens the RCBx, thereby isolating port x.

Preferably, the control method when the quick switch fails includes the following steps:

Step 1. When the breaking port x fails, the MSx fails; at t'2 time, the multi-terminal DC circuit breaker recognizes the MSx failure and immediately arcs to open all the fast mechanical switches except the MSx;

Step 2. At t'3 time, all fast mechanical switches except MSx have completed the opening, at this time the multi-terminal DC circuit breaker turns on RT and all triacs except BTx, after which the capacitor begins to discharge; at t'4 At the moment, all fast mechanical switches except MSx extinguish the arc and restore the insulating ability;

Step 3. At t'5, the fault current charges the capacitor voltage to the arrester reference voltage, and the fault current begins to transfer to the arrester; once the fault current drops below 10A, the multi-terminal DC circuit breaker opens the RCBx, thereby isolating port x.

Preferably, the control method for breaking the busbar failure includes: a control method for breaking the first busbar failure and a control method for breaking the second busbar failure.

Preferably, the control method for breaking the first busbar fault includes the following steps:

Step 1. After the multi-terminal DC circuit breaker detects the fault of the first busbar, it immediately fires off all the fast mechanical switches;

Step 2. After all the fast mechanical switches are opened, turn on the RT and all the triacs; then the capacitor starts to discharge, and the discharge current of the capacitor causes all the fast mechanical switches to extinguish the arc and restore the insulation capacity;

Step 3. After the fault current charges the capacitor voltage to the arrester reference voltage, the fault current begins to transfer to the arrester; once the fault current drops below 10A, the multi-terminal DC circuit breaker opens RCB1_0 to isolate the first bus.

Preferably, the control method for breaking the second busbar fault includes the following steps: after the second busbar fault, since the RT and all triacs are in the off state, the current injected into the fault point is very small, no more than 10A; multi-terminal DC After the circuit breaker detects the fault of the second bus, it can isolate the second bus by opening all residual current switches connected to the second bus.

Compared with the prior art, the present invention includes the following beneficial effects:

1. The normal load current path of some existing multi-terminal DC circuit breakers contains a load commutator switch LCS composed of IGBTs, and the LCS will bring about tens of kilowatts of conduction loss; and the normal load current path of the multi-terminal DC circuit breaker of the present invention The load current path contains only fast mechanical switches with minimal conduction losses.

2. The existing multi-terminal DC circuit breaker without LCS needs to open a plurality of fast mechanical switches during the fault of the breaking port. The failure of any one of the fast mechanical switches will lead to the failure of breaking, and the breaking reliability is low; and the present invention The multi-terminal DC circuit breaker only needs to open one fast mechanical switch during the disconnection port fault, and when the fast mechanical switch fails, other fast mechanical switches can still be used to disconnect the port fault; therefore, the multi-terminal DC circuit breaker of the present invention DC circuit breakers have high breaking reliability.

3. Some existing multi-terminal DC circuit breakers need to use a main circuit breaker composed of a large number of IGBTs to break the current, and the cost of IGBTs is high and the capacity is low. Low, high capacity thyristor.

4. The multi-terminal DC circuit breaker of the present invention has the advantages of low cost, extremely small conduction loss, and high breaking reliability, and also has the ability to isolate the fault of the DC bus.

Description of drawings

FIG. 1 is a topology diagram of a multi-terminal DC circuit breaker in an embodiment of the present invention.

Detailed ways

The present invention will be described in further detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

A multi-terminal DC circuit breaker includes n ports, and port x is connected with a triac BTx and a fast mechanical switch MSx through a residual current switch RCBx, wherein n is a natural number not less than 3, and x is a natural number not less than 1 and not greater than n; One end of MSx is connected to BTx, and the other end is connected to the first bus bar; one end of BTx is connected to MSx, and the other end is connected to the second bus bar through the residual current switch RCB2_x; the reverse conducting thyristor RT, inductor and capacitor form a series branch, the One end of the series branch is connected to the first busbar through the residual current switch RCB1_0, and the other end is connected to the second busbar through the residual current switch RCB2_0; RT, inductors and capacitors form a series branch and are connected in parallel with the arrester.

In a preferred embodiment, the residual current switch can interrupt the residual current not exceeding 10A within tens of milliseconds.

In a preferred embodiment, the fast mechanical switch can be opened in milliseconds.

In a preferred embodiment, the capacitor has an initial voltage U0 in a normal state.

A control method of a multi-terminal DC circuit breaker includes: a control method when a disconnecting port fails, a control method when a fast switch fails, and a control method when a busbar is disconnected, wherein:

The control method for disconnecting the port failure includes the following steps:

Step 1. During the normal operation of the system, the reverse thyristor and all triacs are in the off state, all the residual current switches are in the on state, and the capacitor is charged to the initial voltage U0; the multi-terminal DC circuit breaker passes through the fast mechanical switch MS1 ～MSn conducts the system current, and the conduction loss is extremely small;

Step 2. Port x fails at time t1; at time t2, the multi-terminal DC circuit breaker detects the fault and immediately arcs and opens MSx;

Step 3. At time t3, MSx completes opening, and BTx and RT are turned on at this time. The capacitor begins to discharge through the following loops: Capacitance – BTx – MSx – RT – Inductance; at time t4, MSx extinguishes the arc and restores insulation;

Step 4. At t5, the fault current charges the capacitor voltage to the arrester reference voltage, and the fault current begins to transfer to the arrester; once the fault current drops below 10A, the multi-terminal DC circuit breaker opens the RCBx, thereby isolating port x.

The control method when the quick switch fails includes the following steps:

Step 1. When the breaking port x fails, the MSx fails; at t'2 time, the multi-terminal DC circuit breaker recognizes the MSx failure and immediately arcs to open all the fast mechanical switches except the MSx;

Step 2. At t'3 time, all fast mechanical switches except MSx have completed the opening, at this time the multi-terminal DC circuit breaker turns on RT and all triacs except BTx, after which the capacitor begins to discharge; at t'4 At the moment, all fast mechanical switches except MSx extinguish the arc and restore the insulating ability;

Step 3. At t'5, the fault current charges the capacitor voltage to the arrester reference voltage, and the fault current begins to transfer to the arrester; once the fault current drops below 10A, the multi-terminal DC circuit breaker opens the RCBx, thereby isolating port x.

The control method for breaking the busbar fault includes: a control method for breaking the first busbar fault and a control method for breaking the second busbar fault, wherein:

The control method for breaking the first busbar fault includes the following steps:

Step 1. After the multi-terminal DC circuit breaker detects the fault of the first busbar, it immediately fires off all the fast mechanical switches;

Step 2. After all the fast mechanical switches are opened, turn on the RT and all the triacs; then the capacitor starts to discharge, and the discharge current of the capacitor causes all the fast mechanical switches to extinguish the arc and restore the insulation capacity;

Step 3. After the fault current charges the capacitor voltage to the arrester reference voltage, the fault current begins to transfer to the arrester; once the fault current drops below 10A, the multi-terminal DC circuit breaker opens RCB1_0 to isolate the first bus.

The control method for breaking the second busbar fault includes the following steps: after the second busbar fault, since the RT and all triacs are in the off state, the current injected into the fault point is very small, no more than 10A; the multi-terminal DC circuit breaker detects After the second busbar fails, open all residual current switches connected to the second busbar to isolate the second busbar.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (10)

1. A multi-terminal direct current circuit breaker is characterized by comprising n ports, wherein a port x is connected with a bidirectional thyristor BTx and a quick mechanical switch MSx through a residual current switch RCBx, wherein n is a natural number not less than 3, and x is a natural number not less than 1 and not more than n; one end of the MSx is connected with the BTx, and the other end of the MSx is connected with the 1 st bus; one end of the BTx is connected with the MSx, and the other end of the BTx is connected with the 2 nd bus through a residual current switch RCB2_ x; the reverse conducting thyristor RT, the inductor and the capacitor form a series branch which is connected with the lightning arrester in parallel, one end of the series branch is connected with the 1 st bus through a residual current switch RCB1_0, and the other end of the series branch is connected with the 2 nd bus through a residual current switch RCB2_ 0.

2. The multi-terminal dc circuit breaker according to claim 1, characterized in that the residual current switch opens a residual current of not more than 10A within tens of milliseconds.

3. The multi-terminal dc circuit breaker according to claim 1, characterized in that the fast mechanical switch completes the opening within milliseconds.

4. The multi-terminal dc circuit breaker according to claim 1, wherein the capacitor has an initial voltage U0 in a normal state.

5. A method for controlling a multi-terminal DC circuit breaker, characterized in that it is used to control the multi-terminal DC circuit breaker according to any of claims 1-4, comprising: a control method when an open port fails, a control method when a quick switch fails, and a control method when an open bus fails.

6. The control method according to claim 5, wherein the control method in the event of a failure of an open port comprises the steps of:

step 1, during the normal operation of the system, the inverse thyristors and all the bidirectional thyristors are in a turn-off state, all the residual current switches are in a turn-on state, and the capacitor is charged to an initial voltage U0; the multi-terminal direct current breaker conducts system current through the rapid mechanical switches MS 1-MSn, and conduction loss is extremely low;

step 2, the port x fails at the time t 1; at the time t2, the multi-terminal direct-current circuit breaker detects a fault and immediately burns an arc opening MSx;

step 3, at the time t3, MSx completes the opening, BTx and RT are turned on, and the capacitor starts to discharge through the following loops: a capacitor-BTx-MSx-RT-inductor; at time t4, MSx arcs out and restores the insulation capability;

step 4, at the moment of t5, the fault current charges the capacitor voltage to the reference voltage of the lightning arrester, and the fault current starts to be transferred to the lightning arrester; once the fault current drops below 10A, the multi-terminal dc breaker opens RCBx, isolating port x.

7. The control method according to claim 5, wherein the control method in the event of a rapid switch failure comprises the steps of:

step 1, when a cut-off port x fails, MSx fails; at the time of t' 2, the multi-end direct-current circuit breaker identifies MSx failure and immediately arcs and opens all the quick mechanical switches except MSx;

step 2, at the time of t' 3, all the quick mechanical switches except the MSx complete brake opening, at the moment, the multi-terminal direct current circuit breaker conducts the RT and all the bidirectional thyristors except the BTx, and then the capacitor starts to discharge; at the time t' 4, all the quick mechanical switches except the MSx are quenched and the insulating capability is recovered;

step 3, at the moment of t' 5, the fault current charges the capacitor voltage to the reference voltage of the lightning arrester, and the fault current starts to be transferred to the lightning arrester; once the fault current drops below 10A, the multi-terminal dc breaker opens RCBx, isolating port x.

8. The control method according to claim 5, wherein the control method in the event of a fault of an open bus includes: the control method for the 1 st bus fault and the control method for the 2 nd bus fault.

9. The control method according to claim 8, wherein the control method when the 1 st bus is disconnected in a fault includes the steps of:

step 1, after the multi-terminal direct current breaker detects a fault of a 1 st bus, all fast mechanical switches of an arc opening brake are immediately burnt;

step 2, after all the quick mechanical switches complete opening, the RT and all the bidirectional thyristors are conducted; then the capacitor starts to discharge, and the discharge current of the capacitor enables all the quick mechanical switches to extinguish arcs and recover the insulating capability;

step 3, after the fault current charges the capacitor voltage to the reference voltage of the lightning arrester, the fault current starts to be transferred to the lightning arrester; once the fault current drops below 10A, the multi-terminal dc breaker opens the RCB1_0, isolating the 1 st bus.

10. The control method according to claim 8, wherein the control method when the 2 nd bus is disconnected in a fault includes the steps of: after the 2 nd bus fails, because the RT and all the bidirectional thyristors are in a turn-off state, the current injected into a failure point is very small and does not exceed 10A; after the multi-terminal direct current circuit breaker detects the 2 nd bus fault, all residual current switches connected with the 2 nd bus are opened, and the 2 nd bus can be isolated.

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