Transients in Back-to-Back Capacitor Switching using MATLAB

[tush_8600]

Investigation & Mitigation of Transients in Back-to-Back Capacitor Switching using MATLAB

Capacitors are commonly found in distribution circuits. They increase the performance of distribution systems by reducing losses and reducing voltage drop. Utilities typically employ them to improve voltage regulation and reduce losses. Customers may use them for power factor correction.

However, the switching operations are frequently required in order to energize and de-energize these capacitor banks occur frequently because of system load variation or voltage fluctuation. These switching operations lead to transient overvoltage, which could probably damage the switching device. The energization of capacitor bank causes the high inrush current and transient voltage oscillation at the capacitor bank terminal. For de-energization, the trapped charge on the switched-off capacitor would probably cause restriking at the switching device contact. Due to load growth and higher requirement in power quality, a large number of capacitor banks have been increasingly installed in substation. As a result, capacitor banks switching must be carefully investigated.



The magnitude and frequency of the inrush current is a function of the following:
— Applied voltage
— Capacitance of the circuit
— Inductance in the circuit
— Any charge on the capacitor bank at the instant of closing
— Any damping of the circuit due to closing resistors or other resistances in the circuit


Methods of reducing transients:
1) Pre-inserted resistors and/or reactors
2) Synchronous Switching – most effective

The attached file contains simulation of above experiment using MATLAB.