Working Principle of Murray Loop Test

Working Principle of Murray Loop Test Points : working principle of murray loop test This test employ the principle of wheatstone bridge. The connection diagrams to locate earth fault and short-circuit fault by Murray loop test method are shown in figs respectively. In the circuit P and Q are the two ratio arms consisting of step resistors or slide wire, G is a galvanometer, B is a battery, K_B is a battery key and K_G is a galvanometer key. The faulty cable is connected to a sound cable through low resistance link at the far end. Bridge is balanced by adjusting the resistances of ratio arms P and Q until the galvanometer indicates zero.

Under balanced condition of bridge

In this test since the fault resistance is in the battery circuit (not in bridge circuit) so balancing is not affected by it. Unless it is very high and reduce the sensitivity. The connections for short circuit test are practically the same as in earth fault test except, that a portion of one of the short-circuiting cables is used instead of earth as return path in the battery circuit. Balance is obtained as before.

At balance