4E Electrical Services
Short Circuit Studies ( Power System Fault Studies)
The steady state operating mode of a power system is balanced 3 phase alternating current. However due to sudden external or internal changes in the system, this condition is disrupted.When the insulation of the system fails at one or more points or a conducting object comes in contact with a live point, a short circuit or fault occurs.The causes of faults are numerous, for example, lightning, heavy winds, trees falling across lines, vehicles colliding with lines, towers or poles, birds, line breaks etc. A fault involving all the three phases is known as symmetrical fault ( balanced fault) while one involving only one or two phases is known as unsymmetrical fault ( unbalanced fault). Single line to ground, line to line and two line to ground faults are unsymmetrical faults. Majority of the faults are unsymmetrical. A symmetrical fault occurs infrequently, as for example, when a line which has been made safe for maintenance by clamping all the three phases to earth, is accidently made alive or when, due to slow fault clearance, an earth fault spreads across to the other two phases or when a mechanical excavator cuts quickly through a whole cable
Fault calculations involve finding the voltage and current distribution throughout the system during the fault. It is important to determine the values of system voltages and currents during fault conditions so that the protective devices may be set to detect the fault and isolate the faulty portion of the system so as to minimize the harmful effects of such contingencies.When a fault occurs at a point in a power system, the corresponding MVA is referred to as the fault level at that point. Protections settings and fault clearance times are determined using fault study results.
We have recently conducted a short ciruit study on the 22KV and LV distribution system at Cheetham Salt, Bajool, Queensland, Australia.The study results were used to determine the protection settings on the LV distribution system and in turn were used for determining the arc flash levels on the Switchboards. Please contact us for your power system fault study needs on 0423087897.
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