High continuous current levels:
GCB s must be able to carry high continuous current levels for extended periods of time.Then require some form of a continuous cooling system for the conductors.
Unique fault current conditions:
- System-source (transformer-fed faults)
- Generator-source (generator-fed) faults
For Item 1: can be very high because the full energy of the power system feeds the To clear these kinds of faults, GCB must be tested and capable of interrupting not only the high symmetrical fault current.
For Item 2: while usually lower in magnitude, are subject to much higher degrees of asymmetry, sometimes resulting in another type of very demanding condition called “Delayed Current Zeroes”.
Unique voltage conditions:
- Very fast RRRV
- Out-of-phase switching
For item 3: Consequently, the resistance and stray capacitance of the generator circuit is typically much less than in a normal distribution circuit.Then very high natural frequencies of the circuit and in turn result in extreme TRV with high RRRV.
For Item 4: which can occur during normal startup. Initially, the generator is GCB off and the is in the open position with the power system operating at normal voltage.