CONSTRUCTION AND RATINGS OF HIGH VOLTAGE CIRCUIT BREAKERS BASIC INFORMATION



HIGH-VOLTAGE CIRCUIT BREAKER CONSTRUCTION

All high-voltage circuit breakers have

# Contacts that operate at system voltage
# Insulation between main contacts and ground potential (porcelain, oil, or gas)
# Operating and supervisory devices
# Insulated links between the operating devices and the main contacts

Most power circuit breakers are opened and closed automatically by remote control. Various kinds of operating mechanisms are used. Among them are AC or DC solenoids, compressed air, high-pressure oil, springs, or electric motors.

HIGH-VOLTAGE CIRCUIT BREAKER RATINGS

High-voltage circuit breakers are rated by maximum voltage, insulation, maximum continuous and momentary current-carrying capacity, maximum interrupting capacity, transient recovery voltage, interrupting time, and trip delay.

Circuit interruption occurs when a plasma arc with temperatures exceeding 20,000 K appears for a short time interval between the main contacts. This occurs when the current passes zero, and it is determined by the time relationship between the buildup of dielectric strength of the gap between the open contacts and the rise of transient recovery voltage.

The interrupting capacity of a circuit breaker, measured in kilovolt-amperes (kVA), is the product of the phase-to-ground voltage in kilovolts (kV) of the circuit and the interrupting ability, in amperes (A), at stated intervals and for a specific number of operations. The current is the root-mean-square (rms) value existing during the first half-cycle of arc between contacts during the opening stroke.

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