Question

KES 1215 : MESUREMENT AND INSTRUMENTATION Wheatstone bridge Application: (Varley Loop Test) A Varley loop test is an application for Wheatstone bridge. The test is one of the most accurate tests of locating faults in sheathed cables or finding a short circuit in multi-core cables. It is a modification of the Murray loop test. It consists of two fixed ratio arms R1 and R2 and a rheostat R3 in the third arm. Figure below shows commonly used test set up for Varley Loop R E Ra Terminator Rb Rx Ground fault A healthy cable is connected to the defective cable at the termination. This healthy cable is represented by resistance Ra. The ground fault has occurred in the cable represented by resistance Rb, which the distance is Lx from the test set up. In order to locate the fault (short to ground), first switch is set to position a. Then, the circuit is balance by adjusting R3. At balance condition, the value of (Ra+Rb) is obtained. R₂ RatRb R3 R, Rg R Ra+R, Rb R, CRat Ro) R₂ R2 Rat Ro R, R3 R.

measurement and instrumentation exercise plz read and answer .

Answer 1

Qustions Vorley loof test Condition It Switch at a w un Ra Q YE Rb S k 1 Ru I Circuit R equation balance Rot Ro ,R₂ R3 = R, Rat R, Rb R (Rat Ry R₂ R3 RI

Condition 2 to fosition b Switch is moved the circuit now becomes like this. -Saffase new balance value of Rz is Re RI R2 Ra Ra G Ra Ku Ro Rx bround & fault Rb New balance equation R₂ Rat (Ry - Px) Ri R3'+ Rx R₂ R₂ + R₂ R₂ = R, Ra + R, Rb - R, Rx Rx = R2 R3 R, Rat R, Ry R,+ R2