IEEE Std C37.012-2014 pdf download – IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1 000 V.
4. Capacitor bank switching 4.1 General Because the use of capacitor banks for compensation purposes is increasing, it is common that more than one capacitor bank is connected to the same bus. This practice has no influence on the conditions at interruption. The current at closing (i.e., inrush current), however, is affected to a high degree. To describe the phenomena associated with capacitor bank switching, a general single-phase equivalent circuit is shown in Figure 1. The figure shows a single-line diagram of the case in which two capacitor banks (C 1 and C 2 ) are connected in back-to-back to a busbar. L 1 and L 2 represent the stray inductance (or stray inductance plus additional damping inductance). The inductance L s of the source network will be several orders of magnitude higher than that of L 1 or L 2
5.2.2 Recovery voltage In the case of a screened cable (Figure 9), the recovery voltage is similar to that of a capacitor bank with grounded neutral (see 4.2.2). In the case of a belted cable (Figure 10), the recovery voltage is similar to that of an uncompensated transmission line (see 6.1.2). 5.3 Energizing unloaded cables 5.3.1 General A circuit breaker may be required to energize a no-load cable during its normal operating duties. Prior to energization the cable is usually at ground potential, but can have a trapped charge from a previous switching operation. A cable may be switched from a bus that does not have other cables energized (single or single cable) or against a bus that has one or more cables energized (i.e., back-to-back cable). The energization of a cable by the closing of a circuit breaker will result in a transient inrush current. The magnitude and rate of change of this inrush current is a function of the following: ¾ Applied voltage (including the point on the voltage wave at closing) ¾ Cable surge impedance ¾ Cable capacitive reactance ¾ Inductance in the circuit (amount and location) ¾ Any charges on the cable at the instant of closing ¾ Any damping of the circuit because of closing resistors or other resistance in the circuit