With the help of Murray loop test, we can easily locate the earth fault and short circuit fault in the underground cable. At first, we describe how does locate earth fault in underground cable:
In this test, the sound cable is used to connect in between test end and far end of the faulty conductor.
Lets, AB is sound cable, CD is faulty cable, The Earth fault occurs a point F Far end D point of the faulty cable is connected to far end sound cable point B through a low resistance. Two variable resistance ( i.e P. Q ) is connected to the end A point of sound cable and C point of faulty cable respectively.
A battery is connected to point O and Earth point E through a switch K1. And a galvanometer G is connected in between point A and C through a switch K2.
Let, R = Resistance of the conductor loop upto fault point F from the test end point A, i.e resistance of portion AF. X= Resistance in between two points C and F. note that, P, Q,R and X are the four arms of the Wheatstone bridge.
Now, the switch K1 and K2 are closed respectively. Then the variable resistance P & Q are varied till the galvanometer shows zero deflection. In the balance position of the bridge, we get
If r is the resistance of each cable, then R + X = 2r
Let, total length of the cable is l meter, so the resistance per meter will be = r/l, Therefore , we can easily measure the fault point from the faulty point is
Note that the fault resistance Rf is not in the bridge circuit. So, the fault resistance does not affect the balancing of the bridge. But, if the fault resistance is high, the sensitivity of the bridge is reduced.
It is the same procedure as earth fault test. For short circuit test, battery terminal is connected to the point O and the other point is connected to another faulty cable.
Let, R = Resistance of the conductor loop upto fault point F from the test end point A, i.e resistance of portion AF. X= Resistance in between two points Cand F.
note that , P,Q,R and X are the four arms of the Wheatstone bridge. Now, the switch K1 and K2 are closed respectively. Then the variable resistance P & Q are varied till the galvanometer shows zero deflection. In the balance position of the bridge, we get
If r is the resistance of each cable, then R + X = 2r
Putting the value of resistance and loop length of the cable, we can easily calculate the fault location.
![]() Multiple Choice Question (MCQ) of Electronics page-17:241. Which of the following statement is true? a) The saturation voltage VCF of silicon transistor is more than germanium transistor. b) The saturation voltage VCE for germanium transistor is more than silicon transistor. c) The saturation voltage VCE for silicon transistor is same as that for germanium. d) The saturation voltage VCE for silicon transistor is lower than germanium transistor. |
![]() Multiple Choice Question (MCQ) of Electronics page-16:226. Which of the following statement is correct? a) Inner electrons are always present in the semiconductor. b) Bound electrons are always present in the semiconductor. c) Free electrons are always present in the semiconductor. d) Inner and bound electrons are always present in the semiconductor. |
![]() Multiple Choice Question (MCQ) of Electronics page-15:211. The materials whose electrical conductivity is usually less than 1 × 106 mho/m are a) Semiconductors b) Conductors c) Insulators d) Alloys |
![]() Multiple Choice Question (MCQ) of Electronics page-14:196. In which of the following device the base resistors are not added in the package but added externally? a) UJT b) CUJT c) PUT d) None of the above |
![]() Multiple Choice Question (MCQ) of Electronics page-13:181. The conduction in JEFT is always by the a) Majority carriers b) Minority carriers c) Holes d) Electrons e) Holes and electrons simultaneously |