The thyristor electronic non-contact switch not only has the advantages of zero-crossing, small inrush current and no over-voltage, but also can solve the problem of heat dissipation during work. In practical work, its operating life is almost unlimited, it can be switched frequently, and the timing of switching can be precisely controlled. Therefore, smooth input and removal without transition process can be realized, and the dynamic response time is only 0.01-0.02 s. This is an ideal switch for switching capacitors.

1 Capacitive compensation switching device switching and characteristics

Capacitor compensation switching devices include AC common contactors, special contactors with preset resistance, and thyristor electronic switches.

1.1 Ordinary AC contactor AC contactor is low in price and versatility, but it will generate large surges and pulse overvoltages when used for capacitor switching, sometimes it may cause insulation breakdown or contactor contact burning. It is easy to cause damage to the contactor and thus affect the use of the compensation device.

1.2 Capacitor switching dedicated contactor Capacitor switching dedicated contactor is installed on the main contact of the ordinary AC contactor current limiting impedance device, this improvement can play a role in the capacitor switching is not frequent, but its The effect of suppressing the inrush current of the capacitor is not ideal. When the current is large, the current limiting resistor and the main contact are often burned. Especially when the reactive power load fluctuates frequently and the capacitor is switched frequently, the actual service life is often only about one year. Therefore, this special contactor is only suitable for ideal operating conditions that are basically balanced and the basic balance of three-phase voltages.

1.3 Thyristor Electronic Switch Module The thyristor electronic switch makes full use of the thyristor characteristics of voltage zero-crossing triggering, current zero-crossing cut-off, switch non-contact, and fast response speed, enabling the voltage on the capacitor to rapidly rise from zero to the rated operating voltage. When disconnected, the zero-crossing current on the thyristor is cut off. The capacitor can be used for no-inrush current, no over-voltage cut off, and no-arc fast dynamic compensation function is switched on, which can better solve the transient when the capacitor is switched. Impact problem. However, the thyristor has a large pipe voltage drop (about 1 V) in the on-state, so during operation, the power consumption and the large amount of heat generated and dissipated should be taken into account, which increases the cost of operation and maintenance.

1.4 Contactor and Thyristor Control Compensation Device Performance Comparison 2 Thyristor Electronic Switch Module Internal Functions

The thyristor electronic switch module mainly includes an anti-parallel thyristor, a zero-crossing detection trigger module, a resistance-capacitance absorption device that suppresses overvoltage, and a heat dissipation device.

2.1 Zero-crossing trigger module Since the removed capacitor generally has a residual voltage, the voltage across the capacitor cannot be mutated. Therefore, when the difference between the system voltage and the residual voltage of the capacitor is large, the trigger thyristor will generate a large inrush current. It may damage the thyristor directly. In order to realize the rapid response of the dynamic reactive power compensation device, and at the same time guarantee that the switching does not have inrush current, it is necessary to detect the capacitor voltage and the grid voltage. Only when the two are equal in size and polarity are the same, can the capacitor be input instantaneously. Therefore, it is necessary to install a zero-crossing trigger module. At present, a typical trigger circuit that obtains a zero-crossing signal from both ends of a thyristor is the MOC3083. The MOC3083 chip has a zero-crossing trigger judging circuit. It is a special chip designed for 220V power grid voltage, and its chip bidirectional thyristor voltage is 800V.

2.2 Inhibition of over-voltage resistance and capacitance absorption device Overvoltage protection of the device can also be generally used RC method. For short duration and low energy over-voltage, generally the RC circuit can be connected in parallel across the module to absorb the electromagnetic energy of the overvoltage into electrostatic energy. The use of an absorption resistor not only prevents the circuit from oscillating, but also limits the turn-on losses and di/dt values ​​that occur when the thyristor turns on.

2.3 Heat sink thyristor switch module during operation, the thyristor chip junction temperature will increase. In order to maintain the junction temperature below the maximum 125°C rating, a heat sink must be used. Moreover, the quality of heat dissipation conditions also directly affects the safe, stable, and reliable operation of the module. At present, there are methods of cooling such as water cooling, air cooling (forced and natural air cooling), and heat pipe cooling.

Reactive power compensation is the basic requirement for power system operation. In order to perform reactive power balancing in the power system operation, it is necessary to compensate for the reactive power required for various power loads. The methods of reactive power compensation include camera compensation and capacitor bank compensation. Among them, the most effective and easy to implement method is local reactive power compensation near the load point. Since the reactive power compensation is connected to the power grid mainly through automatic input and removal of the power capacitor to achieve the compensation effect, the performance of the switching element controlling the switching of the capacitor plays a key role in the quality and stability of the entire device. At present, domestic reactive power compensation product controllers generally use AC contactors or thyristors as switching elements to control the on and off of capacitors.