The calculations of these currents are made by Symmetrical Component method. Unbalanced fault analysis is important for Relay setting, single phase switch and system stability studies. Please log in to add an answer. Continue reading The best way to discover useful content is by searching it. Engineering in your pocket Now study on-the-go. For switchgear, interrupting rating may also be specified as short circuit MVA. Why you may ask?
The operating voltage of the power system fluctuates based on load. Also the fault current a device can interrupt is inversely proportional to the operating voltage. So regardless of what the operating voltage is, the product of pre-fault voltage and interrupting current rating is constant. This term refers to fault current magnitude at the 8th cycle and beyond.
In 8 or more cycles typically 15 , the fault current will decay to a symmetrical waveform which, ofcourse , would have no DC offset. Slow operating devices like molded case breakers typically used in low voltage systems V and below use symmetrical RMS rating. The spec sheets implicitly list their ratings in symmetrical amps. In other words, the equipment exposure to the asymmetry is prolonged.
Fault current rating is only one piece of information that defines a protective device. RMS is not a phantom quantity. The interrupting rating is the short-circuit duty as the equipment contacts part, and is expressed in symmetrical amperes or MVA. Medium-voltage fuses have interrupting ratings expressed in symmetrical amperes. Email This BlogThis! Power Systems Switchgear Generators Electrical. Upvote 0 Views Followers 1. Write an Answer Register now or log in to answer.
Low voltage panels too are rated by their symmetrical current rating. Most modern circuit breakers implicitly list their ratings in symmetrical amps.
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