Murray Loop Test and Locating Faults

Q.1 (a) Using the Murray Loop test, determine the distance to an earth fault on one of the cores of a uniform three-core underground cable. Ra = 2 ohms, Rb = 1 ohm and the cable length is 300 m.

(b) If the cable measurement is accurate to ±1% what length of excavation would be required to locate the fault?

Q.2 A cable run consists of 100 m of 120 mm2 three-core cable jointed to 100 m of 240 mm2 cable. The ratio of the potentiometer resistances in a Murray Loop test, Rb/(Rb + Ra), is 1/3 For an earth on one core of the cables, determine the location of the fault.