# Varley bridge/ Wheatstone bridge problem

Not what you're looking for?

The Varley loop test is a method of fault location in telecom and pilot wire circuits where fairly high circuit resistances are encountered. This solution determines the distance to the fault.

3. A Varley Bridge is connected to a faulty three-core copper cable by two identical copper leads of resistance R1.

(a) Show that for the initial reading (connection to earth);

2Rx = 2R, — Ri (1)

where R, is the resistance of the cable core

Ri is the initial reading of the bridge

Rx is the cable resistance to the fault from the bridge

and for the final reading:

2R, = R f — 2R1 (2)

where R1 is a lead resistance

Rf is the final reading resistance.

Then by substituting (2) in (1) and rearranging the equation, show:

(see the PDF for correct calculations)

(b) By multiplying the rhs brackets and collecting terms, show the effect of the leads is given by:

(see the PDF for correct calculations)

i.e. = effect with no leads — ratio of initial and final readings

x lead resistance

(c) Determine the distance to the fault by modifying the expression in (b)

(see the PDF for correct calculations)

where x is the cable distance to the fault

and L is the length of a cable core.

Derive an expression for x, the distance to the fault.

(d) Using R = pi, A

where p is the resistivity,

L is the length

and A is the cross-sectional area of a cable core

(see the PDF for correct calculations)

and by substituting for R1 show that the distance to the fault is given by:

(see the PDF for correct calculations)

(e) Determine the distance to a fault on a 200 m, 120 mm2 copper cable R.

if copper 10 mm2 test leads of length 10 m are used and = 0.2.

##### Purchase this Solution

##### Solution Summary

This solution addresses the calculations required for determining the effect of leads on the Varley bridge as well as the computation of fault distance.

##### Purchase this Solution

##### Free BrainMass Quizzes

##### Architectural History

This quiz is intended to test the basics of History of Architecture- foundation for all architectural courses.

##### Air Pollution Control - Environmental Science

Working principle of ESP