Power distribution line non-outage loop closing relay protection method and device

Abstract

The invention discloses a power distribution line non-outage loop closing relay protection method and device. The method comprises the following steps: S1, acquiring short-circuit current distribution characteristics and voltage characteristics of a loop closing line; s2, designing loop closing device protection logic for the phase-shifting transformer according to the acquired short-circuit current distribution characteristics and voltage characteristics; and S3, performing short-circuit protection on the distribution line in the loop closing operation process according to the configured loop closing device protection logic. According to the method, the problems that the protection setting value needs to be adjusted due to protection misoperation or operation refusal caused by the fact that the original distribution line protection setting value cannot adapt to the current distribution change in the loop closing process are solved, the safety and the reliability of the loop closing operation are ensured, and the complexity and the workload of the loop closing operation are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power system operation, and in particular to a non-stop closing relay protection method and device for distribution lines. Background Art

[0002] The direct connection of the distribution network to the load is the key to ensuring the quality of power supply to users, and usually follows the basic principles of closed-loop design and open-loop operation. If the load can be reversed without power outage, that is, the closing operation without power outage, the reliability of the distribution system operation can be greatly improved. The closing operation of the distribution line refers to the operation of closing the network composed of distribution lines, transformers or circuit breakers in the electrical operation of the power system. In the event of a fault, overload, power outage for maintenance, etc., the closing operation is performed in a first-on-then-off manner, which can realize load transfer and avoid power outages for users. Due to factors such as the continuous adjustment of the power grid structure, the imperfect protection configuration and design, the closing of the distribution network may generate a large closing current, which will cause the misoperation of the line protection. After the closing, the existing line protection cannot accurately distinguish between the short circuit of the line and the short circuit of the opposite line, causing a short circuit on either side of the line, and the protection of the two lines is simultaneously removed, which expands the scope of the fault. At present, the commonly used solution is to install current protection on the contact switch, modify the protection settings of the two lines, and coordinate with the protection at the contact switch through delay. Although this method can solve the fault location problem, it prolongs the fault removal time and requires modifying the protection setting value, which is cumbersome and increases the probability of human error. In addition, when a single-phase grounding fault occurs on one of the lines, the outgoing line switch does not trip because the 10kV distribution network can operate with the fault. If the closing operation is performed at this time, it will not only cause the fault to spread, but also increase the difficulty of single-phase grounding and distance measurement of the distribution network.

[0003] Therefore, the conventional protection used in existing distribution lines can no longer meet the requirements of protection selectivity, speed and reliability when performing fault protection on distribution lines in closed-loop operation. In addition, the operation is cumbersome and cannot meet the requirements of fast and flexible actual operation of the distribution network. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method and device for non-stop closing-loop relay protection of distribution lines, which can ensure that the current protection of distribution lines can meet the requirements of protection selectivity and speed in the closed-loop state, and can accurately monitor and locate single-phase grounding faults.

[0005] Technical solution: A non-stop closing relay protection method for distribution lines, comprising the following steps: S1, obtaining the short-circuit current distribution characteristics and voltage characteristics of the closed-loop line; S2, designing the protection logic of the closing device for the phase-shifting transformer according to the acquired short-circuit current distribution characteristics and voltage characteristics; S3, according to the configured protection logic, short-circuit protection is performed on the distribution line during the ring closing operation.

[0006] Furthermore, by configuring current detection elements, zero-sequence voltage and low voltage detection elements in the circuit breakers on both sides of the phase-shifting transformer in the closing device, the current characteristics, three-phase voltage and zero-sequence voltage characteristics of the closing lines on both sides are detected.

[0007] Furthermore, in the closing device, the circuit breakers on both sides of the phase-shifting transformer are equipped with quick-break protection, overcurrent protection, single-phase grounding protection based on zero-sequence voltage startup, and low voltage protection. The protection logic of the closing device of the phase-shifting transformer is as follows: Before the closing operation, the single-phase grounding protection action or low voltage protection action initiated by the zero-sequence voltage on either side of the circuit breaker on both sides should terminate the closing operation; When the line on the left side of the closing switch is short-circuited, the current protection of the left distribution line is activated, the current protection at the left circuit breaker of the phase-shifting transformer is activated, the left distribution line is cut off, and the protection of the outgoing line switch of the right closing line does not operate; when the line on the right side of the closing switch is short-circuited, the current protection of the right distribution line is activated, the current protection at the right circuit breaker of the phase-shifting transformer is activated, the right distribution line is cut off, and the protection of the outgoing line switch of the left closing line does not operate; When single-phase grounding occurs in the line on the left side of the closing switch, the zero-sequence voltage single-phase grounding protection on the left side of the phase-shifting transformer is activated, and the single-phase grounding fault alarm signal on the left side is sent, the circuit breaker on the left side of the phase-shifting transformer is tripped, and the protection of the outgoing switch of the right closing line does not operate; when single-phase grounding occurs in the line on the right side of the closing switch, the zero-sequence voltage single-phase grounding protection on the right side of the phase-shifting transformer is activated, and the single-phase grounding fault alarm signal on the right side is sent, the circuit breaker on the right side of the phase-shifting transformer is tripped, and the protection of the outgoing switch of the left closing line does not operate.

[0008] Furthermore, the current protection action value of the circuit breaker on the left side of the phase-shifting transformer is adjusted according to the short-circuit current flowing through the left circuit breaker when the line is closed due to a short circuit at the right outlet of the phase-shifting transformer; the current protection action value of the circuit breaker on the right side of the phase-shifting transformer in the closing device is adjusted according to the short-circuit current flowing through the right circuit breaker when the line is closed due to a short circuit at the left outlet of the phase-shifting transformer.

[0009] Furthermore, trip acceleration logic is configured on the circuit breakers on both sides of the phase-shifting transformer. When a short circuit or single-phase grounding occurs in one line, if the circuit breakers on both sides of the phase-shifting transformer are in the closed state, the circuit breaker adjustment acceleration circuit is connected and the circuit breaker is accelerated to trip.

[0010] Furthermore, when the distribution line is closed, the relay protection action logic and each protection action setting value of the closing device of the phase-shifting transformer are designed according to the short-circuit current distribution characteristics and the zero-sequence voltage and low-voltage characteristics: When a short circuit occurs in the left line after the loop is closed, the short-circuit current distribution characteristics in the closed line are that the left line outgoing circuit breaker and the left circuit breaker of the phase-shifting transformer of the closing device flow through the same large short-circuit current, and the right line outgoing circuit breaker and the right circuit breaker of the phase-shifting transformer of the closing device flow through the same small short-circuit current. The setting value of the quick-break protection of the right circuit breaker of the phase-shifting transformer is less than the quick-break protection action value of the right line outgoing circuit breaker. The current protection of the left line and the current protection on the closing device are activated. Under the action of the acceleration logic, the circuit breaker in the closing device is accelerated to trip, the fault is cut off and the closing device is locked. The right line has been cut off due to the fault, and the overcurrent protection returns without tripping. When a single-phase grounding fault occurs in the left line after the loop is closed, the zero-sequence voltage distribution characteristic in the closed line is that the zero-sequence voltage is detected on the left side of the phase-shifting transformer, and there is no zero-sequence voltage on the right side of the phase-shifting transformer. At this time, the single-phase grounding protection in the closing device is activated, and a single-phase grounding alarm signal occurs on the left line; When a short circuit occurs in the left line before closing the loop, the low voltage feature in the closing line is that a low voltage is detected on the left side of the phase-shifting transformer. At this time, the low voltage protection in the closing device is activated and the closing device is locked; When a single-phase grounding fault occurs in the left line before closing the loop, the zero-sequence voltage distribution characteristic in the closing line is that the zero-sequence voltage is detected on the left side of the phase-shifting transformer. At this time, the single-phase grounding protection in the closing device based on the zero-sequence voltage is activated and the closing device is locked.

[0011] A non-stop power-on and power-off relay protection device for a power distribution line, used to implement the non-stop power-on and power-off relay protection method for a power distribution line, comprising: An acquisition module is used to acquire the short-circuit current distribution characteristics and voltage characteristics of the closed-loop line before and after the closed-loop; A setting module, connected to the acquisition module, for configuring the current protection, single-phase grounding protection and low voltage protection action logic on the circuit breakers on both sides of the loop closing device; A protection module, connected to the setting module, for protecting the closed-loop line according to the configured protection logic; The closing lockout circuit is used to lock the closing device if a short circuit or single-phase grounding is detected on either side of the line before and after the closing operation; after closing, if a short circuit or single-phase grounding occurs on either side of the line, the circuit breakers on both sides of the phase-shifting transformer in the closing device are accelerated to open and close, and then the closing device is locked.

[0012] Compared with the prior art, the present invention has the following significant effects: The present invention configures current detection elements, zero-sequence voltage and low-voltage detection elements in the circuit breakers on both sides of the phase-shifting transformer in the closing device, detects the current characteristics, three-phase voltage and zero-sequence voltage characteristics of the closing lines on both sides, and designs the closing device protection logic for the phase-shifting transformer according to the acquired short-circuit current distribution characteristics and voltage characteristics; when protecting the closing line, it is possible to accurately determine on which side the fault occurs, thereby avoiding the need for both sides of the line to trip and causing the power outage to expand. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a flow chart of the protection method of the present invention; Figure 2 is a schematic diagram of a ring closing device; Figure 3 It is a schematic diagram of the protection device of the present invention. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0015] like Figure 1 As shown, it is a flow chart of the non-stop closing relay protection method of the present invention, which comprises the following steps: Step 1, obtaining short-circuit current distribution characteristics, low voltage and zero-sequence voltage characteristics of the closed-loop line; In the closing device, the circuit breakers on both sides of the phase-shifting transformer are equipped with current detection elements, zero-sequence voltage and low-voltage detection elements to detect the current characteristics, three-phase voltage and zero-sequence voltage characteristics of the closing lines on both sides.

[0016] Step 2: designing a protection logic of a loop closing device for a phase-shifting transformer according to the acquired short-circuit current distribution characteristics and voltage characteristics; In the loop closing device, the circuit breakers on both sides of the phase-shifting transformer are equipped with quick-break protection and overcurrent protection, such as Figure 2 As shown, when the left line is short-circuited, the current protection of the left distribution line is activated, the current protection at the left circuit breaker of the phase-shifting transformer is activated, the left distribution line is cut off, and the protection of the outgoing switch of the right closing line does not operate; when the right line of the closing switch is short-circuited, the current protection of the right distribution line is activated, the current protection at the right circuit breaker of the phase-shifting transformer is activated, the right distribution line is cut off, and the protection of the outgoing switch of the left closing line does not operate.

[0017] In the closing device, the circuit breakers on both sides of the phase-shifting transformer are equipped with single-phase grounding protection based on zero-sequence voltage startup. Figure 2As shown, when single-phase grounding occurs in the left line, the zero-sequence voltage single-phase grounding protection on the left side of the phase-shifting transformer is activated, and the single-phase grounding fault alarm signal on the left side is sent, the circuit breaker on the left side of the phase-shifting transformer is tripped, and the protection of the outgoing line switch on the right side of the closed-loop line does not operate; when single-phase grounding occurs in the line on the right side of the closing switch, the zero-sequence voltage single-phase grounding protection on the right side of the phase-shifting transformer is activated, and the single-phase grounding fault alarm signal on the right side is sent, the circuit breaker on the right side of the phase-shifting transformer is tripped, and the protection of the outgoing line switch on the left side of the closed-loop line does not operate.

[0018] In the loop closing device, the circuit breakers on both sides of the phase-shifting transformer are configured with trip acceleration logic. Figure 2 As shown, when a short circuit or single-phase grounding occurs on one side of the line, if the circuit breakers on both sides of the phase-shifting transformer are in the closed state, the circuit breaker adjustment acceleration circuit is connected and the circuit breaker is accelerated to trip.

[0019] In the closing device, the circuit breakers on both sides of the phase-shifting transformer are provided with closing and locking circuits. Figure 2 As shown, it is used to lock the closing device before and after the closing operation when a short circuit or single-phase grounding is detected on either side of the line. Before closing the loop, if a short circuit or single-phase grounding occurs on either side of the line, the closing device is locked; after closing the loop, if a short circuit or single-phase grounding occurs on either side of the line, the circuit breakers on both sides of the phase-shifting transformer in the closing device are accelerated to open and close, and then the closing device is locked.

[0020] Step 3: According to the configured protection logic, the distribution line is short-circuited during the ring closing operation.

[0021] According to the short-circuit current distribution characteristics of the closed-loop line and the low voltage and zero-sequence voltage characteristics, the relay protection action logic for the phase-shifting transformer closing device is designed; and according to the optimized protection action logic and setting value, the closed-loop line is protected by relay, so that the fault line can be accurately judged and the fault can be quickly isolated without modifying the original line protection setting value. At the same time, when a fault is found in the line before or after the closing, the closing device is locked in time to avoid closing the faulty line. This solves the problem that when using traditional current protection to protect the closed-loop line, it is impossible to accurately judge which side the fault occurs, so that both sides of the line need to trip, causing the power outage to expand.

[0022] When the distribution line is closed, short circuit or single-phase grounding fault occurs at different locations, and different short-circuit current distribution characteristics and zero-sequence voltage and low-voltage characteristics will appear. According to the short-circuit current distribution characteristics and zero-sequence voltage and low-voltage characteristics, the relay protection action logic and each protection action setting value of the phase-shifting transformer closing device are designed.

[0023] The following takes the case where a short circuit and a single-phase grounding fault occur in the left line after the ring is closed and the case where a short circuit and a single-phase grounding fault occur in the left line before the ring is closed as examples to explain respectively.

[0024] For example, after the loop is closed, a short circuit occurs in the left line. Generally, the distribution line outgoing circuit breaker is equipped with current quick-break protection. Because the line has been closed, the short-circuit current is provided to the short-circuit point from both sides of the line at the same time. Therefore, the current protection on both sides of the line is activated. The reasonable logic should be that the current protection of the left line is activated, the current protection on the connecting switch is activated, and the current protection of the right line should not be activated.

[0025] Therefore, when the short-circuit point is in the left line after closing the loop, the short-circuit current distribution characteristics in the closed-loop line are that the left-side line outgoing circuit breaker and the left-side circuit breaker of the phase-shifting transformer of the closing device flow through the same large short-circuit current. Due to the current limiting effect of the phase-shifting transformer, the right-side line outgoing circuit breaker and the right-side circuit breaker of the phase-shifting transformer of the closing device flow through the same small short-circuit current. The setting value of the quick-break protection of the right-side circuit breaker of the phase-shifting transformer is less than the quick-break protection action value of the right-side line outgoing circuit breaker. Therefore, the current protection of the left line and the current protection on the closing device are activated. Under the action of the acceleration logic, the circuit breaker in the closing device is accelerated to trip, the fault is cut off and the closing device is locked. The right-side line has been cut off due to the fault, and the overcurrent protection returns without tripping.

[0026] For example, after the loop is closed, a single-phase grounding fault occurs on the left line. Under normal circumstances, after a single-phase grounding occurs on a 10kV distribution line, the insulation monitoring device based on zero-sequence voltage monitoring on the bus will sound an alarm, but it will not trip. Therefore, the interconnecting switch will not automatically open the loop at this time. The reasonable logic should be to disconnect the closing device to prevent the fault from spreading.

[0027] Therefore, when a single-phase grounding fault occurs in the left line after closing the loop, the zero-sequence voltage distribution characteristic in the closed-loop line is that the zero-sequence voltage is detected on the left side of the phase-shifting transformer. Because the phase-shifting transformer adopts Y / Z connection, there is no zero-sequence voltage on the right side of the phase-shifting transformer. At this time, the single-phase grounding protection in the closing device is activated, and a single-phase grounding alarm signal occurs in the left line.

[0028] For example, a short circuit occurs in the left line before closing the loop. Under normal circumstances, because the connecting switch is not closed, the current protection at the connecting switch does not detect the short-circuit current and will not operate, and the connecting switch will not be locked. After closing, the current protection will operate. The reasonable logic is to lock the closing device to prevent the equipment from being subjected to the short-circuit current shock and the expansion of the short-circuit fault range.

[0029] Therefore, when a short circuit occurs in the left line before closing the loop, the low voltage feature in the closing line is that a low voltage is detected on the left side of the phase-shifting transformer. At this time, the low voltage protection in the closing device is activated and the closing device is locked.

[0030] For example, before closing the loop, a single-phase grounding fault occurs in the left line. Under normal circumstances, the interconnecting switch will not be locked and the closing operation can be performed. After closing, because the interconnecting switch has no single-phase grounding protection, it will neither adjust nor alarm. The reasonable logic is that the closing device should be locked to avoid closing on a fault and causing a safety hazard.

[0031] Therefore, when a single-phase grounding fault occurs in the left line before closing the loop, the zero-sequence voltage distribution characteristic in the closed loop line is that the zero-sequence voltage is detected on the left side of the phase-shifting transformer. At this time, the single-phase grounding protection in the closing device based on the zero-sequence voltage is activated and the closing device is locked.

[0032] like Figure 3 As shown, the present invention also provides a non-stop closing protection device for distribution lines, which includes: an acquisition module, a setting module and a protection module. The device is described below.

[0033] An acquisition module is used to acquire the short-circuit current distribution characteristics and the zero-sequence voltage and low voltage distribution characteristics in the closed-loop line; A setting module, connected to the acquisition module, configured to configure the action logic and setting value of the overall protection scheme according to the acquired short-circuit current distribution characteristics and voltage characteristics; The protection module is connected to the setting module and is used to protect the closed-loop line according to the protection logic and action value of the setting configuration.

[0034] The acquisition module includes a current detection circuit, a low voltage detection circuit and a zero-sequence voltage detection circuit; the current detection circuit is used to detect the short-circuit current distribution in the closed-loop line; the low voltage detection circuit is used to detect the low voltage caused by a short circuit in the closed-loop line; the zero-sequence voltage detection circuit is used to detect the zero-sequence voltage that appears after a single-phase grounding fault occurs in the closed-loop line.

[0035] The protection module includes a protection action acceleration circuit, which is used to accelerate the short circuit tripping of both sides of the phase-shifting transformer in the closing device when a short circuit occurs on either side of the closing line.

[0036] The protection device also includes a closing device locking circuit, which is used to lock the closing device if a line short-circuit or single-phase grounding occurs on either side before the closing of the loop; after the closing of the loop, if a line short-circuit or single-phase grounding occurs on either side, the circuit breakers on both sides of the phase-shifting transformer in the closing device are accelerated to open and close, and then the closing device is locked.

[0037] The present invention can solve the technical problems that the existing distribution line current protection cannot meet the protection selectivity and quickness requirements in the closed loop state and cannot accurately monitor and locate single-phase grounding faults.

Claims

1. A non-stop closing relay protection method for distribution lines, characterized in that: Includes steps: S1, obtaining the short-circuit current distribution characteristics and voltage characteristics of the closed-loop line; S2, designing the protection logic of the closing device for the phase-shifting transformer according to the acquired short-circuit current distribution characteristics and voltage characteristics; S3, according to the configured closing device protection logic, short-circuit protection is performed on the distribution line during the closing operation.

2. The non-stop closing relay protection method for distribution lines according to claim 1 is characterized in that: By configuring current detection elements, zero-sequence voltage and low-voltage detection elements in the circuit breakers on both sides of the phase-shifting transformer in the closing device, the current characteristics, three-phase voltage and zero-sequence voltage characteristics of the closing lines on both sides are detected.

3. The non-stop closing relay protection method for distribution lines according to claim 1 is characterized in that: In the closing device, the circuit breakers on both sides of the phase-shifting transformer are equipped with quick-break protection, overcurrent protection, single-phase grounding protection based on zero-sequence voltage startup, and low voltage protection. The protection logic of the closing device of the phase-shifting transformer is as follows: Before the closing operation, the single-phase grounding protection action or low voltage protection action initiated by the zero-sequence voltage on either side of the circuit breaker on both sides should terminate the closing operation; When the line on the left side of the closing switch is short-circuited, the current protection of the left distribution line is activated, the current protection at the circuit breaker on the left side of the phase-shifting transformer is activated, the left distribution line is cut off, and the protection of the outgoing line switch of the right closing line does not operate; When the line on the right side of the closing switch is short-circuited, the current protection of the right distribution line is activated, the current protection at the circuit breaker on the right side of the phase-shifting transformer is activated, the right distribution line is cut off, and the protection of the outgoing line switch of the left closing line does not operate; When single-phase grounding occurs in the line on the left side of the closing switch, the zero-sequence voltage single-phase grounding protection on the left side of the phase-shifting transformer is activated, and a single-phase grounding fault alarm signal is sent on the left side, the circuit breaker on the left side of the phase-shifting transformer is tripped, and the outgoing line switch protection on the right side of the closing switch does not operate; When single-phase grounding occurs in the line on the right side of the closing switch, the zero-sequence voltage single-phase grounding protection on the right side of the phase-shifting transformer is activated, and a single-phase grounding fault alarm signal on the right side is sent, the circuit breaker on the right side of the phase-shifting transformer is tripped, and the protection of the outgoing switch of the left closing line does not operate.

4. The non-stop closing relay protection method for distribution lines according to claim 3 is characterized in that: The current protection action value of the circuit breaker on the left side of the phase-shifting transformer is set according to the short-circuit current flowing through the circuit breaker on the left side when the line is closed; The current protection action value of the circuit breaker on the right side of the phase-shifting transformer in the closing device is set according to the short-circuit current flowing through the right circuit breaker at the left outlet of the phase-shifting transformer when the line is closed.

5. The non-stop closing relay protection method for distribution lines according to claim 3 is characterized in that: The circuit breakers on both sides of the phase-shifting transformer are configured with tripping acceleration logic. When a short circuit or single-phase grounding occurs on one side of the line, if the circuit breakers on both sides of the phase-shifting transformer are in the closed state, the circuit breaker adjustment acceleration circuit is connected and the circuit breaker is accelerated to trip.

6. The non-stop closing relay protection method for distribution lines according to claim 3 is characterized in that: When the distribution line is closed, the relay protection action logic and each protection action setting value of the closing device of the phase-shifting transformer are designed according to the short-circuit current distribution characteristics and zero-sequence voltage and low voltage characteristics: When a short circuit occurs in the left line after the loop is closed, the short-circuit current distribution characteristics in the closed line are that the left line outgoing circuit breaker and the left circuit breaker of the phase-shifting transformer of the closing device flow through the same large short-circuit current, and the right line outgoing circuit breaker and the right circuit breaker of the phase-shifting transformer of the closing device flow through the same small short-circuit current. The setting value of the quick-break protection of the right circuit breaker of the phase-shifting transformer is less than the quick-break protection action value of the right line outgoing circuit breaker. The current protection of the left line and the current protection on the closing device are activated. Under the action of the acceleration logic, the circuit breaker in the closing device is accelerated to trip, the fault is cut off and the closing device is locked. The right line has been cut off due to the fault, and the overcurrent protection returns without tripping. When a single-phase grounding fault occurs in the left line after the loop is closed, the zero-sequence voltage distribution characteristic in the closed line is that the zero-sequence voltage is detected on the left side of the phase-shifting transformer, and there is no zero-sequence voltage on the right side of the phase-shifting transformer. At this time, the single-phase grounding protection in the closing device is activated, and a single-phase grounding alarm signal occurs on the left line; When a short circuit occurs in the left line before closing the loop, the low voltage feature in the closing line is that a low voltage is detected on the left side of the phase-shifting transformer. At this time, the low voltage protection in the closing device is activated and the closing device is locked; When a single-phase grounding fault occurs in the left line before closing the loop, the zero-sequence voltage distribution characteristic in the closing line is that the zero-sequence voltage is detected on the left side of the phase-shifting transformer. At this time, the single-phase grounding protection in the closing device based on the zero-sequence voltage is activated and the closing device is locked.

7. A non-stop closing relay protection device for distribution lines, characterized in that: Used to execute the non-stop closing relay protection method for distribution lines as claimed in any one of claims 1 to 6, comprising: An acquisition module is used to acquire the short-circuit current distribution characteristics and voltage characteristics of the closed-loop line before and after the closed-loop; A setting module, connected to the acquisition module, for configuring the current protection, single-phase grounding protection and low voltage protection action logic on the circuit breakers on both sides of the loop closing device; A protection module, connected to the setting module, for protecting the closed-loop line according to the configured protection logic; The closing lockout circuit is used to lock the closing device if a short circuit or single-phase grounding is detected on either side of the line before and after the closing operation; after closing, if a short circuit or single-phase grounding occurs on either side of the line, the circuit breakers on both sides of the phase-shifting transformer in the closing device are accelerated to open and close, and then the closing device is locked.

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