Answer / deepak tyagi

a.c is non-uniformly distributed on the surface of the
conductor.this means that skin effect comes into play.this
mean that actual resistance increse in case of a.c, while
the d.c is uniformly distributed on surface of the
conductor.

Answer / mega

Cable Hi-pot test is done with D.C voltage because, if we
do the test in A.C voltage the capacitance effect of the
cable will be charged and will not get the exact value.
That's we are using D.C test instead of A.C

Answer / udhaya shankar

DC alone is used because we need to measure only the resistance of the winding (or) cable insulation. If we use AC to conduct the insulation test, we will be measuring impedance instead of the resistance as the insulation has a substantial capacitive reactance.

The health of the winding (or) cable is best indicated by its resistance and not its impedance. This is why only DC is used to measure the insulation resistance

Answer / vineeth kumar c g

in the case of insulation tester (megger) we need to take care of cable insulation resistance not insulation impedance, so we choose DC rather than AC.
In hipot test we give high voltage to the cable and if cable is twisted type then AC will induce an emf due to flux and this will change the value of impedence... (if you only need to measure resistance only)
skin effect may occurs if the frequency is higher than 50 and long length cables.
normally in site DC voltages are used for testing but in manufacturing industry they also use AC tester to calculate impedence also...

Answer / hashir

Insulation tests, known as megger tests, are carried out using DC because AC introduces reactance, mainly capacitive (AC resistance), into the readings.

The high voltage DC, usually twice the operating voltage, will break down any defective resistance in the insulation.

Answer / malik

Power cables testing is 2 types IR and Hipot.
1. megger normally D.C, we required the resistance value of
the insulation. AC megger till not to use.
2. Hi pot test, we apply the AC voltage low Frequency(VLF),
we measure the leakage current value. this kit we cannot
measure for the resistance value if the insulation.
so we use AC supply and DC supply for the different
application.

Answer / guest

because no continuity in a.c. Power supply that y we r tested a cable with d.c. Supply

Answer / abdul malick

AC supply having frequency

dc supply Fq=0 ...

Answer / chalapathi

Compartivley DC testing equipment is more cheap than AC, and
it is more easy to produce required test voltage with DC
comparitively AC

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