A current transfer type direct current switch and a breaking method thereof

Abstract

The application belongs to the technical field of direct current switch, and discloses a current transfer type direct current switch and a breaking method thereof. When a short circuit fault occurs in the system, the mechanical vacuum switch in the current transfer type direct current switch can quickly respond and move enough opening distance, trigger the thyristor in the pulse current generation branch, and generate a reverse pulse current through the damping branch, so that the current flowing through the mechanical vacuum switch is zero. When the fault is removed, the short circuit current is used to charge the pre-charging capacitor in the pulse current generation branch for the second time, and then the metal oxide surge arrester (MOV) is turned on to dissipate the short circuit energy. The breaking method adopts the pulse current zero crossing technology, has the ability to limit and shut off the short circuit current, realizes the fast response to the short circuit fault, simplifies the driving, reduces the cost of the prototype, improves the reliability, and has the engineering practical value.

Description

Technical Field

[0001] This invention belongs to the field of DC switch technology, specifically relating to a current-transfer type DC switch and its switching method. Background Technology

[0002] With the increasing proportion of renewable energy and the decreasing number of traditional power plants, high-voltage power grids face new challenges. Existing high-voltage AC grids are unsuitable for compensating for the fluctuating nature of renewable energy or for long-distance energy transmission. Currently, large-scale grid-based high-voltage direct current (HVDC) transmission systems can reduce the number of traditional backup power plants and improve system reliability.

[0003] In large-scale mesh-type HVDC transmission systems, developing HVDC switches located at network nodes is essential to reduce the impact of local faults on the entire network. Due to the inherent characteristics of large-scale mesh-type HVDC transmission systems, HVDC switches need to meet requirements for high surge current, miniaturization, low loss, and low cost. Therefore, high-voltage hybrid DC circuit breakers have seen rapid development in recent years. However, existing high-voltage hybrid DC circuit breakers, which use high-voltage mechanical vacuum switches connected in parallel with IGBT modules, still face problems such as slow fault response speed, large size, complex drive mechanisms, and current surge capacity limited by the IGBTs.

[0004] Currently, there is an urgent need to develop a current-transfer type DC switch and its switching method. Summary of the Invention

[0005] One technical problem to be solved by the present invention is to provide a current-transfer type DC switch, and another technical problem to be solved by the present invention is to provide a method for switching on and off a current-transfer type DC switch.

[0006] The current-transfer type DC switch of the present invention consists of a current-carrying branch, a pulse current generating branch, and a damping branch;

[0007] The current-carrying branch includes a power supply U, an inductor L1, a mechanical vacuum switch S1, a mechanical vacuum switch S2, an inductor L2, and a load Load connected in sequence; it also includes a diode D1 connected in parallel with the mechanical vacuum switch S1 and a diode D2 connected in antiparallel with the mechanical vacuum switch S2.

[0008] The pulse current generating branch starts at the midpoint between mechanical vacuum switch S1 and mechanical vacuum switch S2 and ends at the ground wire; the pulse current generating branch includes a diode D, a resistor R, and a pre-charge capacitor C connected sequentially between the start and end points; it also includes an inductor L and a thyristor T, which are connected in series and then in parallel with the pre-charge capacitor C; and it further includes a metal oxide surge arrester MOV, which is connected in parallel with the resistor R and the pre-charge capacitor C.

[0009] The damping branch includes two paths connected in parallel with the pulse current generating branch; one path starts in front of the mechanical vacuum switch S1 and ends at the ground wire, including a diode D3 and a resistor R1 connected in sequence between the start and end points, and also includes a metal oxide surge arrester MOV1 connected in parallel with the resistor R1; the other path starts behind the mechanical vacuum switch S2 and ends at the ground wire, including a diode D4 and a resistor R2 connected in sequence between the start and end points, and also includes a metal oxide surge arrester MOV2 connected in parallel with the resistor R2.

[0010] Furthermore, the thyristor T is a unidirectional semi-controlled device.

[0011] Furthermore, the thyristors T in the pulse current generating branch are multiple sets connected in series, and each set of thyristors is connected in parallel with an RC circuit for voltage equalization.

[0012] Furthermore, the diodes D1 and D2 in the current-carrying branch are replaced with fully controlled IGBT devices.

[0013] The current-transfer type DC switch switching method of the present invention includes the following steps:

[0014] S1. Define the short-circuit current operating threshold as I;

[0015] S2. When the system is working normally, mechanical vacuum switches S1 and S2 are closed, thyristor T is turned off, and current flows through inductors L1 and L2, mechanical vacuum switches S1 and S2 in the current-carrying branch.

[0016] S3. When a short circuit fault occurs in the system and the short circuit current reaches the action threshold I, mechanical vacuum switch S1 and mechanical vacuum switch S2 are disconnected; the contact of the trigger thyristor T moves to a preset distance, and after being subjected to transient recovery voltage, the trigger thyristor T is turned on, and the pre-charge capacitor C discharges through the inductor L to generate a pulse current;

[0017] S4. When the current in inductor L reaches its maximum value, under the negative voltage generated by the pulse current generation branch, a reverse pulse current is generated through the damping branch.

[0018] S5. Under the action of the reverse pulse current, the short-circuit current flowing through the mechanical vacuum switch S2 crosses zero and freewheels through the diode D2;

[0019] S6. When the current in inductor L decreases to 0, the thyristor T is turned off; the short-circuit current charges the pre-charge capacitor C through the pulse current generating branch and the damping branch;

[0020] S7. When the voltage of the pre-charge capacitor C reaches the operating voltage of the metal oxide surge arrester (MOV), the MOV turns on, dissipates the short-circuit current energy, and completes the turn-off, thus clearing the short-circuit fault.

[0021] Furthermore, the inductors L1 and L2 in the current-carrying branch are used to limit the short-circuit current; the metal oxide surge arresters MOV1 and MOV2 in the damping branch are used to limit possible reverse overvoltages.

[0022] The current-transfer type DC switch of this invention uses two medium-voltage switches connected in series, replacing the traditional high-voltage switch. Because the medium-voltage switch itself has smaller moving parts and a smaller contact gap, it responds faster to short-circuit faults and has better robustness. When a short-circuit fault occurs in a large-scale grid-type HVDC transmission system, the mechanical vacuum switch in the current-transfer type DC switch of this invention can quickly respond and move a sufficient opening distance, triggering the thyristor in the pulse current generation branch and generating a reverse pulse current through the damping branch, causing the current flowing through the mechanical vacuum switch to cross zero. When the fault is cleared, the short-circuit current is used to recharge the pre-charge capacitor in the pulse current generation branch, thereby turning on the metal oxide surge arrester (MOV) to dissipate the short-circuit energy.

[0023] The current-transfer type DC switch of the present invention adopts pulse current zero-crossing technology, which has the ability to limit and turn off short-circuit current, realizes rapid response to short-circuit faults, simplifies the drive, reduces the cost and size of the prototype, improves reliability, and has practical engineering value. Attached Figure Description

[0024] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0025] Figure 1 This is a schematic diagram of the current-transfer type DC switch of the present invention;

[0026] Figure 2 This is a schematic diagram of the working process (normal operation) of the current transfer type DC switch of the present invention;

[0027] Figure 3 This is a schematic diagram of the working process of the current-transfer type DC switch of the present invention (short circuit fault).

[0028] Figure 4This is a schematic diagram of the working process of the current-transfer type DC switch of the present invention (the current in inductor L reaches its maximum value).

[0029] Figure 5 This is a schematic diagram of the working process of the current-transfer type DC switch of the present invention (reverse pulse current).

[0030] Figure 6 This is a schematic diagram of the working process of the current-transfer type DC switch of the present invention (the current in inductor L decreases to 0).

[0031] Figure 7 This is a schematic diagram of the working process of the current transfer type DC switch of the present invention (metal oxide surge arrester MOV is turned on). Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] Example: Figure 1 As shown, the current-transfer type DC switch in this embodiment consists of a current-carrying branch, a pulse current generating branch, and a damping branch;

[0034] The current-carrying branch includes a power supply U, an inductor L1, a mechanical vacuum switch S1, a mechanical vacuum switch S2, an inductor L2, and a load Load connected in sequence; it also includes a diode D1 connected in parallel with the mechanical vacuum switch S1 and a diode D2 connected in antiparallel with the mechanical vacuum switch S2.

[0035] The pulse current generating branch starts at the midpoint between mechanical vacuum switch S1 and mechanical vacuum switch S2 and ends at the ground wire; the pulse current generating branch includes a diode D, a resistor R, and a pre-charge capacitor C connected sequentially between the start and end points; it also includes an inductor L and a thyristor T, which are connected in series and then in parallel with the pre-charge capacitor C; and it further includes a metal oxide surge arrester MOV, which is connected in parallel with the resistor R and the pre-charge capacitor C.

[0036] The damping branch includes two paths connected in parallel with the pulse current generating branch; one path starts in front of the mechanical vacuum switch S1 and ends at the ground wire, including a diode D3 and a resistor R1 connected in sequence between the start and end points, and also includes a metal oxide surge arrester MOV1 connected in parallel with the resistor R1; the other path starts behind the mechanical vacuum switch S2 and ends at the ground wire, including a diode D4 and a resistor R2 connected in sequence between the start and end points, and also includes a metal oxide surge arrester MOV2 connected in parallel with the resistor R2.

[0037] Furthermore, the thyristor T is a unidirectional semi-controlled device.

[0038] Furthermore, the thyristors T in the pulse current generating branch are multiple sets connected in series, and each set of thyristors is connected in parallel with an RC circuit for voltage equalization.

[0039] Furthermore, the diodes D1 and D2 in the current-carrying branch are replaced with fully controlled IGBT devices.

[0040] The current-transfer type DC switch switching method of this embodiment includes the following steps:

[0041] S1. Define the short-circuit current operating threshold as I;

[0042] S2. For example Figure 2 As shown, when the system is working normally, mechanical vacuum switches S1 and S2 are closed, thyristor T is turned off, and current flows through inductors L1 and L2, mechanical vacuum switches S1 and S2 in the current-carrying branch.

[0043] S3. For example Figure 3 As shown, when a short circuit fault occurs in the system and the short circuit current reaches the action threshold I, mechanical vacuum switches S1 and S2 are disconnected; the contact of the trigger thyristor T moves to a preset distance, and after being subjected to transient recovery voltage, the trigger thyristor T is turned on, and the pre-charge capacitor C discharges through the inductor L to generate a pulse current;

[0044] S4. For example Figure 4 As shown, when the current in inductor L reaches its maximum value, a reverse pulse current is generated through the damping branch under the negative voltage generated by the pulse current generation branch.

[0045] S5. For example Figure 5 As shown, under the action of the reverse pulse current, the short-circuit current flowing through the mechanical vacuum switch S2 crosses zero and freewheels through the diode D2;

[0046] S6. For example Figure 6 As shown, when the current in inductor L decreases to 0, the thyristor T is turned off; the short-circuit current charges the pre-charge capacitor C through the pulse current generating branch and the damping branch.

[0047] S7. For example Figure 7 As shown, when the voltage of the pre-charge capacitor C reaches the operating voltage of the metal oxide surge arrester (MOV), the MOV turns on, dissipates the short-circuit current energy, and completes the turn-off, thus achieving short-circuit fault isolation.

[0048] Furthermore, the inductors L1 and L2 in the current-carrying branch are used to limit the short-circuit current; the metal oxide surge arresters MOV1 and MOV2 in the damping branch are used to limit possible reverse overvoltages.

[0049] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection of the present invention as defined by the submitted claims.

Claims

1. A current-transfer type DC switch, characterized in that, The current-transfer type DC switch consists of a current-carrying branch, a pulse current generating branch, and a damping branch; The current-carrying branch includes a power supply U, an inductor L1, a mechanical vacuum switch S1, a mechanical vacuum switch S2, an inductor L2, and a load Load connected in sequence; it also includes a diode D1 connected in parallel with the mechanical vacuum switch S1 and a diode D2 connected in antiparallel with the mechanical vacuum switch S2. The pulse current generating branch starts at the midpoint between mechanical vacuum switch S1 and mechanical vacuum switch S2 and ends at the ground wire; the pulse current generating branch includes a diode D, a resistor R, and a pre-charge capacitor C connected sequentially between the start and end points; it also includes an inductor L and a thyristor T, which are connected in series and then in parallel with the pre-charge capacitor C; and it further includes a metal oxide surge arrester MOV, which is connected in parallel with the resistor R and the pre-charge capacitor C. The damping branch includes two paths connected in parallel with the pulse current generating branch; one path starts in front of the mechanical vacuum switch S1 and ends at the ground wire, including a diode D3 and a resistor R1 connected in sequence between the start and end points, and also includes a metal oxide surge arrester MOV1 connected in parallel with the resistor R1; the other path starts behind the mechanical vacuum switch S2 and ends at the ground wire, including a diode D4 and a resistor R2 connected in sequence between the start and end points, and also includes a metal oxide surge arrester MOV2 connected in parallel with the resistor R2. The current-transfer type DC switch uses mechanical vacuum switch S1 and mechanical vacuum switch S2 connected in series to improve the response speed and robustness of short-circuit faults.

2. The current-transfer type DC switch according to claim 1, characterized in that, The thyristor T is a unidirectional semi-controlled device.

3. The current-transfer type DC switch according to claim 1, characterized in that, The thyristors T in the pulse current generating branch are multiple sets connected in series, and each set of thyristors is connected in parallel with an RC circuit for voltage equalization.

4. The current-transfer type DC switch according to claim 1, characterized in that, The diodes D1 and D2 in the current-carrying branch are replaced with fully controlled IGBT devices.

5. A method for interrupting a current-transfer type DC switch, used in any one of the current-transfer type DC switches according to claims 1 to 4, characterized in that, The interruption method includes the following steps: S1. Define the short-circuit current operating threshold as I; S2. When the system is working normally, mechanical vacuum switches S1 and S2 are closed, thyristor T is turned off, and current flows through inductors L1 and L2, mechanical vacuum switches S1 and S2 in the current-carrying branch. S3. When a short circuit fault occurs in the system and the short circuit current reaches the action threshold I, mechanical vacuum switch S1 and mechanical vacuum switch S2 are disconnected; the contact of the trigger thyristor T moves to a preset distance, and after being subjected to transient recovery voltage, the trigger thyristor T is turned on, and the pre-charge capacitor C discharges through the inductor L to generate a pulse current; S4. When the current in inductor L reaches its maximum value, under the negative voltage generated by the pulse current generation branch, a reverse pulse current is generated through the damping branch. S5. Under the action of the reverse pulse current, the short-circuit current flowing through the mechanical vacuum switch S2 crosses zero and freewheels through the diode D2; S6. When the current in inductor L decreases to 0, the thyristor T is cut off; the short-circuit current charges the pre-charge capacitor C through the pulse current generating branch and the damping branch. S7. When the voltage of the pre-charge capacitor C reaches the operating voltage of the metal oxide surge arrester (MOV), the MOV turns on, dissipates the short-circuit current energy, and completes the turn-off, thus achieving short-circuit fault isolation. The current-transfer type DC switch described above employs pulse current zero-crossing technology to limit and shut off short-circuit current, thereby improving the response speed to short-circuit faults.

6. The switching method of the current-transfer type DC switch according to claim 5, characterized in that, The inductors L1 and L2 in the current-carrying branch are used to limit the short-circuit current; the metal oxide surge arresters MOV1 and MOV2 in the damping branch are used to limit possible reverse overvoltages.

Images