Which of the following cable insulation resistance can be measured by the direct deflection method?
Right Answer is:
Both 1 and 2
SOLUTION
The direct deflection method is used for the measurement of the insulation resistance of the cable. The cable can be of two types
- Cable with sheath
- Cable without sheath
(a) Direct deflection method for Cable with Sheath
Fig. shows the direct deflection method for measuring the insulation resistance of a cable with a sheath. The galvanometer measures the current Ix between the conductor and the metal sheath. The leakage current IL, over the insulating material is carried by the guard wire wound on the insulation and therefore does not flow through the galvanometer.
(b) Cable without Sheath:- Cables without metal sheaths can be tested in a similar way like in cable with sheath. The direct deflection method for measuring the insulation resistance is shown in Fig. First, the cable is immersed in slightly saline water for about 24 hours and the temperature is kept constant at about 20°C. The water enters the pores of the cable and the temperature of the cable attains the temperature of the water. The water and tank then form the return path for the current.
