Question

A building takes a three-phase supply at 400 V with a declared prospective short circuit current of 30 kA at the intake switchboard. The cable installed between the intake switchboard and a remote distribution board has a circuit length of 100 m. The cable is PVC-insulated and has the following characteristics at 20 °C: 12.4 Phase conductor resistance 0.095 ma/m Phase conductor reactance 0.075 mO/m Conductor temperature coefficient of resistance 0.004 per c Connected to the remote distribution board is a balanced three-phase load of 250 kVA, non-distorting, but with a power factor of 0.8. Calculate: (a) the percentage volt drop at the remote distribution board; and (b) the minimum breaking capacity for the protective devices installed in [2.1%, 12.8 kA] the remote distribution board.

Answer 1

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