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A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) [a] is an electrical safety device that interrupts an electrical circuit when the current passing through a conductor is not equal and opposite in both directions, therefore indicating leakage current to ground or current flowing to another powered conductor.
Transmission and distribution systems use an automatic re-close function which is commonly used on overhead lines to attempt to restore power in the event of a transient fault. This functionality is not as common on underground systems as faults there are typically of a persistent nature. Transient faults may still cause damage both at the site ...
A problem arises if the electricity supply is upgraded, by adding new generation capacity or by adding cross-connections. Because these increase the amount of power that can be supplied, all of the branch circuits must have their bus bars and circuit breakers upgraded to handle the new higher fault current limit. [citation needed]
A shunt-trip unit appears similar to a normal breaker and the moving actuators are ganged to a normal breaker mechanism to operate together in a similar way, but the shunt trip is a solenoid intended to be operated by an external constant-voltage signal, rather than a current, commonly the local mains voltage or DC. These are often used to cut ...
Calculation of the required breaking capacity involves determining the supply impedance and voltage. Supply impedance is calculated from the impedance of the elements making up the supply system. Customers of an electrical supply utility can request the maximum value of prospective short-circuit current available at their point of supply.
The hold current is the maximum current at which the device is guaranteed not to trip. The trip current is the current at which the device is guaranteed to trip. [7] When power is removed, the heating due to the leakage current will stop and the PPTC device will cool.
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Examples of TRV waveshapes. A transient recovery voltage (TRV) for high-voltage circuit breakers is the voltage that appears across the terminals after current interruption. It is a critical parameter for fault interruption by a high-voltage circuit breaker, its characteristics (amplitude, rate of rise) can lead either to a successful current interruption or to a failure (called reignition or ...