The circuit breaker is the terminal equipment for power system relay protection, and its intelligent level will have a profound impact on the stability and automation of the power system. The synchronous closing technology discussed in this paper is an important direction of circuit breaker intelligence. At present, the circuit breaker in the system is connected to the power equipment instantaneously. The initial phase angle of the system voltage is usually random and uncertain. When the no-load transformer, capacitor bank and no-load line are closed, the amplitude is often generated. Very high inrush current and over voltage.

This is only detrimental to the equipment in the system, and can also cause protection malfunctions and affect the stability of the power system. Synchronous closing technology means that the dynamic and static contacts of the circuit breaker are closed at the specified phase angle of the system voltage waveform, so that the power equipment such as the no-load transformer, capacitor bank and no-load line is put into the minimum impact on itself and the system. Power Systems. The synchronous closing technology greatly reduces the overcurrent and overvoltage during the transient operation of the closing operation, thereby greatly improving the life of the power equipment and the stability of the system.

Describes the action process of synchronization closure. Assume that the system voltage is selected to be synchronously closed when the initial phase angle is °. Where z is the target closing time; K is the delay time; 7; is the operating time of the circuit breaker. After receiving the closing command, the circuit breaker calculates 7 from the specified closing phase angle (in this example, °); and, after the delay of 7;, controls the operating mechanism of the circuit breaker to perform the closing operation.

In the following, the necessity of the synchronous closing technique and the selection principle of the synchronous closing moment are explained by analyzing the inrush current generated when the no-load transformer and the capacitor are closed. u Simulation of the no-load transformer The analysis of the no-load closing process of a transformer with a rated current of 165A/917A is carried out as an example. When the low-voltage side of the transformer is unloaded, the high-voltage side receives a 35kV sinusoidal power supply at time <=! After / after, the rolling side loop equation is as follows: full flux; the initial phase angle of the power supply when the transformer is just turned on; A and n are the excitation current and resistance of the high voltage side winding.

Equation (1) is a nonlinear differential equation due to the saturation of the transformer core. In this paper, the Simu-link component of Matlab software is used to dynamically model and simulate the no-load closing process of the transformer. By changing the time of the circuit breaker to change the initial phase angle, the waveform of the inrush current at different phase angles can be obtained. As shown, (a) to (c) are the inrush current waveforms when a is 0°, 45°, and 90°, respectively, and (d) is the relationship between the multiple of the inrush current and the rated current and a.

It can be seen that when it is 0°, the maximum value of the inrush current is the highest, reaching 11.4 times of the rated current; when a is 45°, the maximum value of the inrush current is 7.3 times of the rated current; when it is 90°, Ideally, no inrush current will occur and the transformer will go directly into steady state operation. When ct is in the range of 0° to 90°, the magnitude of the inrush current decreases as it increases. When in the range of 90° to 180°, the magnitude of the inrush current increases as the amplitude increases. Therefore, if the circuit breaker can be controlled to close the no-load transformer at a temperature of 90° or 270°, the multiple of the inrush current will be greatly reduced.

1.2 Simulation Analysis of Closed Capacitor The principle of circuit breaker closing capacitor is as shown. Where / is a 10kV voltage source; C5 is a circuit breaker; is a line resistance of 0.2Q; L is a line inductance of 1.5mH; C is a load capacitor of 355垆; is the frequency of the power supply.

Circuit Breaker Closing Capacitor Schematic When the circuit breaker is closed at /=, the line resistance, inductance, and capacitor resonate, producing a high inrush current with high amplitude and frequency. The equation of the loop is as follows: idt=Usin(cona)(2) Simultaneously integrate the two sides of the above equation: The process described by time (S) equation (3) can be dynamically simulated by Sinmlink. By changing the time when the circuit breaker is closed, the initial phase angle of the power supply when the capacitor is just turned on is changed, and the waveform of the inrush current at different phase angles is obtained. As shown, (a) and (c) are the inrush current waveforms when a is 0°, 45°, and 90°, respectively, and (d) is the relationship between the multiple of the inrush current and the steady-state current and a.

It can be seen that when ct is 0°, the amplitude of the inrush current is only 1.6 times of the steady state value, and the transient process is shorter; when a is 45°, the amplitude of the inrush current rises to the steady state value of 3 When it is 90°, the amplitude of the inrush current reaches 4.3 times of the steady state value, and the transient process is long, which is very harmful to the power equipment. When a is in the range of 0° to 90°, the magnitude of the inrush current increases with increasing; when in the range of 90° to 180°, the magnitude of the inrush current decreases as it increases. Therefore, if the circuit breaker can be controlled to close the capacitor at or near 180°, the multiple of the inrush current will be greatly reduced.

Inrush current analysis of closed capacitors under different phase angles 1.3 Necessity of synchronous closing According to the above mathematical analysis, the circuit breaker will generate a high frequency and amplitude inrush current when it is connected to power equipment such as no-load transformers and capacitors. A very high amplitude inrush current will cause damage to the circuit breaker contacts, mechanical stresses in the transformer windings, and protection device malfunction. Overvoltage can cause partial discharge of the device. The use of synchronous closing technology can greatly reduce the amplitude and voltage disturbance of the inrush current.

Transient processes of switching operations can cause various disturbances to the power distribution system, including severe power quality degradation caused by untimely action and unacceptable overvoltages and early failures. When a current transient occurs locally in the switch, the transient overvoltage propagates to a remote location, sometimes affecting other users and developing to different voltage levels. The synchronous closing technology can greatly reduce the overcurrent and overvoltage that the grid equipment is subjected to when the load is closed, which will effectively improve the power quality and improve the stability of the system.

2The realization of synchronous closing technology 2.1 Permanent magnet mechanism and synchronous closing technology Since the operating mechanism of the traditional vacuum circuit breaker is a mechanical system consisting of a connecting rod and a lock and an energy supply system, there are many links and many mechanical parts. The motion tolerance is large and the response is slow, the controllability is poor, and the efficiency is low. Therefore, the dispersion and uncontrollability of the action time determine that it is difficult for the traditional operating mechanism to achieve synchronous closing control. In recent years, permanent magnet operating mechanisms have been developed in the field of medium voltage at home and abroad, creating material conditions for the realization of synchronous closing technology. The permanent magnet operating mechanism adopts a new working principle and structure. By combining the electromagnet and the permanent magnet, it not only realizes all the functions of the traditional circuit breaker operating mechanism, but also realizes without the need of the disengagement and locking device. The retention function of the organization's terminal location. The advantage of the permanent magnet mechanism is that there are few mechanical parts and fewer moving parts during operation, thereby greatly reducing the dispersion of the action time. At the same time, the operating energy required for the permanent magnet mechanism to operate is very small, enabling maintenance-free operation.

The operating function of the permanent magnet operating mechanism is provided by the charging and voltage-stabilizing capacitor splitting and closing coil discharge. By controlling the speed at which the capacitors are divided and closed by the high-power turn-off transistor, the speed and time of the circuit breaker can be adjusted, and the motion characteristics of the circuit breaker can be controlled.

The difficulty of the synchronous closing technique is that the time during which the circuit breaker operating mechanism operates is dispersive, and the dispersion of the operating time comes from the dispersion of the operating time inherent in the mechanism itself and the dispersion of the operating time caused by the difference in environmental conditions. For the permanent magnet mechanism, the dispersion of the action time is negligible relative to the latter, and the influence of the latter on the action time must be compensated by the software or hardware of the control system. The environmental conditions affecting the action time mainly include the ambient temperature and the capacitor. Charging voltage, mechanical wear and aging of the contacts, etc. There are two methods of compensation: one is to control the motion characteristics by closed-loop control by changing the current of the split and closing coils during operation, and keep the action time constant; the other is to perform real-time online detection of each god influence factor. And calculate their values ​​for the change of the action time to determine the moment when the action signal is sent. The design of the synchronous closing control on the vacuum circuit breaker is explained below based on the second method.

2.2 Implementation Scheme As mentioned above, factors affecting the operating time include mechanical wear and aging of the contacts, ambient temperature, capacitor charging voltage, and the like. The three-phase voltage and current waveforms, as well as the ambient temperature and control voltage are sent to the MCU through A/D conversion for real-time uninterrupted sampling. After receiving the manual or remote-action closing signal, the voltage zero-crossing point is calculated. And the time to compensate for ambient temperature, control voltage, and mechanical wear and aging to determine when to send an action signal. The action signal drives the power electronics to turn on the closing coil circuit to generate a corresponding closing action. The control structure is as shown.

The compensation control principle of the action time is as shown. Where T is the inherent operating time of the circuit breaker; it is time compensation for the ambient temperature and control voltage change; A7/ is the time compensation for mechanical wear and aging.

Large but known operating times due to operational changes can be adjusted accordingly. The two most critical operational changes are the temperature and the voltage applied to the operating coil, the capacitor charging voltage. Multiple tests can be performed to determine the effects of this operational change, and the results of the test need to cover a wide range of operating temperatures and control voltages. In the actual control process, interpolation can be used to determine the time to be compensated.

3 Summary Synchronous closure technology is one of the important signs of intelligent circuit breakers, which plays an important role in the stability of power systems and the quality of power supply. Through the simulation analysis of the inrush current of the capacitor and the no-load transformer, the following conclusions are drawn: (1) Synchronously closing the air-loaded transformer when the initial phase angle of the system voltage is 90° will reduce the multiple of the closing inrush current by more than ten times. Several times, even no inrush current.

(2) When the initial phase angle of the system voltage is °, the capacitor is synchronously closed, which will reduce the multiple of the closing inrush current from 4.3 times to 1.6 times.

(3) Synchronous closing technology greatly reduces overcurrent and overvoltage, reduces the impact on power equipment, and improves the stability of the power system.

(4) The difficulty of the synchronous closing technique is that the time during which the circuit breaker operating mechanism operates is dispersive. There are two ways to compensate for the influence of operating conditions on the action time; one is to use real-time closed-loop control to ensure the stability of the action time; the other is to superimpose the compensation time on the intrinsic action time.

With the continuous improvement of the operating mechanism and its control technology, the synchronous closing technology will be further developed and will generate huge economic benefits.

2.2.2 Compensation for mechanical wear and aging Mechanical wear and aging is a long-term process. The actual time of the previous action is measured, and the error between it and the calculated action time is calculated. If after several actions, the error remains at a fixed planting, indicating a certain mechanical wear and aging. Match this error to a certain relative gain to adjust the action time of the next operation. Different gains are compensated from 0 and 2.2.3 for temperature and control voltage. At the same time, the synchronous closing operation must have a compensation part.

(Finish)

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