Reactive Power Compensation - Using Devices

As a switching switch for capacitor banks, the commonly used wiring method is shown in Figure 2. BK in the figure represents a semiconductor device, and C1 represents a capacitor bank. This wiring method uses two sets of switches, and the other phase is directly connected to the power grid without one set of switches, which has many advantages.
The semiconductor devices used as compensation devices generally use thyristors, which have the advantages of convenient material selection, mature and economical circuits. Its drawback is that the components themselves cannot be quickly turned off and are prone to burning out in unexpected situations, so protective measures need to be improved. When the protection issue is solved, it should be an ideal device as a capacitor bank switching device. The compensation effect of dynamic compensation also depends on whether the controller has high performance and parameters. An important requirement is for the controller to have good dynamic response time, accurate power switching, and high self recognition ability in order to achieve the best compensation effect.
When the controller collects the signal that needs to be compensated and issues an instruction (to activate one or more sets of capacitors), the triggering pulse triggers the thyristor to conduct, and the corresponding capacitor group is also connected to the line for operation. It should be emphasized that the condition for thyristor conduction must be that the terminal voltage of the capacitor in its phase is zero to avoid damage to the component caused by inrush current. Semiconductor devices should be switched without inrush current. When the control command is revoked, the trigger pulse immediately disappears and the thyristor zero current naturally shuts off. The voltage of the capacitor after shutdown is the AC peak value of the line voltage, which must be discharged as soon as possible by the discharge resistor in preparation for the capacitor to be put back into operation.
The components can be single-phase thyristors in anti parallel or bidirectional thyristors, or solid-state contactors suitable for capacitive loads can be selected, which can save the pulse circuit triggered by zero and simplify the circuit. The withstand voltage and current of the components should be selected reasonably, and the heat sink and cooling method should also be considered comprehensively.