(A) Megger
(B) Murray loop test
(C) Electro-dynamometer
(D) Ohm-meter
Answer: (B) Murray loop test
Explanation:
Murray loop test:
It is the common method to determine location of earth or short circuit fault in underground cable.
It operates on the principle of the Wheatstone bridge.
The material commonly used for insulation in high voltage cables is
(A) Teflon
(B) impregnated paper
(C) rubber
(D) PVC
Answer: (B) impregnated paper
Explanation:
Generally, insulation of cables is required to have high dielectric strength, to provide the necessary withstand against normal operating and impulse voltages.
There are mainly two types of cable insulating materials.
- Impregnated Paper
- Polymer.
Impregnated paper is the most popular insulating material, especially for the land installations in the H.V and EHV lines.
Polymer insulation is preferably used in new installations like DC and the submarine system.
Around 83% of HV cables are paper insulated.
Solid paper insulated cables are suitable for application up to the MV range. At higher voltage, there is some operation problem with them due to high dielectric losses and pressure of voids.
In oil-filled cables at high voltage, the formation of voids is prevented by maintaining a flow of oil under pressure.
The impregnation of paper improves the dielectric properties of paper insulation.
Polymer insulation is immune to thermal degradation and must not be prone to defects such as voids, protrusions, or contaminants.
For extra-high voltage (400 kV and higher) new types of types mode up of PPLP (Poly propylite laminated paper) are used.
PPLP has the advantage of combining the technical traditional technology used for impregnated paper cables with the excellent electrical and dielectric properties of synthetic insulators.
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