Measurement of Resistivity by Wheatstone Bridge Method (For Liquid Insulators)
For liquid insulators the measuring unit (cell) has the following construction.
Procedure to find resistivity of a liquid insulator
- As explained in the previous case of solid insulation, the experimental set up w the same i.e. H.V stable supply voltage to the circuit of Wheatstone bridge connected with amplifier and an null detector ammeter.
- R = The above numbered 3-electrodes 1, 2 and 3 are connected to the Wheatstone bridge circuit and by varying RA a nut point is obtained by balancing the bridge. (see the figure in solid insulation case).
- In this case following calculation are done.
ρ = 2 πRℓ / loge d2/d1
where
ρ = volume resistivity in Ω cm
R = measured resistance in Ω
ℓ = effective length of the guarded electrode in meter
Known values outer
d1 = diameter of guarded electrode
d2 = inner diameter of unguarded electrode