Murray Loop Bridge

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Murray loop bridge Murray loop bridge is a bridge circuit used for locating faults in underground or underwater cables..[1] It has been used for more than 100 years. [2] cables One end of the faulted cable is connected through a pair of resistors of resistors to the voltage source. Also a null detector is connected. The other end of the cable is shorted. The bridge is brought to balance by changing the values of  R  R B1 and  R B2, which is achieved when:

which is equivalent to:

The value of resistance  R x is proportional the length  L x, thus the location of the fault can be calculated:

where  L is the total length of the cable under test - a value proportional to Rg. The method assumes a single fault exists, of low resistance compared with the undamaged cable insulation resistance, and that the cable conductors have uniform resistance per unit length.

[edit] Varley loop The similar Varley loop uses fixed resistors for RB1 and RB2, and inserts a variable resistor in the faulted leg. Test sets for cable testing can be connected for either bridge technique. If the fault resistance is high, the sensitivity of the Murray bridge is reduced and the Varley loop may be more suitable.

[edit] Answer: Improve A Murray Loop Test is used to locate faults in networks of cables such as three-phase services, groups of underground cables, etc. It works by using the principle equation on which the Wheatstone bridge is based: when the galvanometer is in a null condition, R1/R3=R2/R4. The location of a cable fault within a network can be found by using a process of elimination: good connections are identified and are then excluded from further iterations of the Murray Loop Test.

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