CLOSING OPERATION OF POWER CIRCUIT BREAKERS BASIC INFORMATION



How Power Circuit Breaker Closing Operation Works?

Circuit breakers are designed to perform the closing and reclosing operations as per standard requirements. When operated to close on long lines, extra-high-voltage circuit breakers require special measures to keep switching overvoltages within specified limits.

Such measures may be single or multiple step closing resistors, synchronously closing at the moment of voltage zero, or polarity-controlled-closing, which means closing during the period of equal polarity at the line and source side of the breaker. When operated to close on capacitor banks special measures may be taken to limit transient currents and voltages.

Such measures may be closing resistors; controlled closing at the moment of voltage zero for grounded wye capacitor banks; or controlled closing on ungrounded wye capacitor banks where the first phase is closed at the moment of voltage zero and the other two phases are closed at a point where the voltage difference between the two phases is zero.

When operated to close on power transformers or shunt reactors special measures may be taken to limit inrush transient currents and transient voltages. Such measures may be single or multiple step closing resistors, or controlled closing at the moment of voltage peak.

The magnitude of overvoltages on energizing and reenergizing is influenced by the nature and variables of the power system. Parameters of supply side and line must be taken into account in order to compute the overvoltages or to determine them using transient network analyzers or transient analysis software, such as electromagnetic transients programs (EMTP), power systems computer aided designs (PSCAD), or alternative transient program. (ATP).

For a summary of the magnitude of overvoltages occurring when energizing high-voltage lines, based on numerous studies and measurements in high-voltage networks, see Table 10-9. Surge arresters may also be used to limit switching overvoltages.

Overvoltages Occurring When Energizing High-Voltage Lines

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