Series resonance (also known as variable frequency series resonance) capacitor position
The position of the series resonant capacitor depends on the economic and technical considerations of the circuit. Series resonant capacitors can be located at the transmitting end, receiving end, or line center. Sometimes they are located at two or more positions along the line.
The degree of compensation and the characteristics of the circuit determine the position of the capacitor. Installing them on the terminals can simplify maintenance, but in the event of a fault, overvoltage on the capacitor terminals can cause the capacitor to overload.
Capacitors are installed in longer line switching stations. The position of the line center also reduces the nominal capacitor capacity. The size of a series resonant capacitor is given by the following equation
I am the line current. A capacitor bank is composed of small units connected in series, parallel, or simultaneously in series and connected to obtain the required voltage and Var rating.
Protection system for series resonant capacitors
When a fault or overload occurs, a large current will flow through the series resonant capacitor of the line. Therefore, excessive voltage drop occurs on the transmission line. To protect the capacitor from such abnormal voltages, spark gaps and overvoltage inverters are connected to the terminals of the capacitor. The circuit breaker is also connected in parallel with it. The following introduces some methods of series resonant capacitors.
Issues related to series resonant capacitors
The following provides a detailed introduction to some issues related to the series application of capacitors.
The series compensation line resonates in series at frequencies lower than the power frequency. This is called subsynchronous resonance. The secondary synchronization generates mechanical stress, which causes high torsional stress in the rotor shaft. The problem of sub synchronous resonance mainly occurs during faults or switch operations. The following methods solve the problem of sub synchronous lines with compensation line series connection. Use filters.
Connect capacitors in series under resonance conditions.
By triggering the generator under resonance conditions.
The series connected capacitors generate high recovery voltage through the circuit breaker contacts.
If the compensation level and the position of the capacitor are not appropriate, the distance relay used for line protection may not function properly.
Connecting an unloaded transformer at the end of the line compensation will generate nonlinear resonance or ferromagnetic resonance. This can lead to uninterrupted oscillation, which can be reduced by using a shunt reactor on the capacitor or temporarily short circuiting the capacitor to lower the oscillation frequency. Low load synchronous motors tend to drive.
Series resonant capacitors will generate more net voltage rise, resulting in greater voltage drop.