Answer / c.satheeshkumar

1.For earthed and un earthed XLPE cables, the IS 7098 part2
1985 does not give any difference in specification. The
insulation level for cable for unearthed system has to be
more. In simple statement the manufacturers states that 11
KV earthed cable is suitable for use in 6.6 KV unearthed
system.The process of manufacture of cable is same. The
size of cable will depend on current rating and voltage
level.

what IS specifies and I quote below:

" b) Voltage Grade (Uo/U)

1) Earthed System - 1.9/3.3 kV, 3.8/6.6 kV, 6.35/11 kV,
12.7/22 kV and 19/33 kV.

2) Unearthed System - 3.3/3.3 kV and 11/11 kV.

Note 1 - Cables of 6.35/11 kV grade (earthed system) are
suitable for use on 6.6/6.6 kV (unearthed system) also.

Answer / ajay patel

Basically, Power Systems are defined as Earthed System,
Resistive Earthed or Un-Earthed System.

Hence, Cables are designed for Earthed & Unearthed Power
System. For Example, 11 kV (E) cable is used for 11 kV
Earthed System & 11 kv (UE) cables are uded for 11 kV not
effectively Earthed System. Insulation Thickness is more of
11 kV (UE) cables compare to 11kV (E) cables.

Answer / ashim sarkar

I fully agree with the comments of Mr. C. Satheeshkumar.
Insulation level for Unearthed system is root over 3 times
the insulation level for Earthed system.
Earthed system - Insulation of 19 KV for 33 KV system
Unearthed system - Insulation of 33KV for 33 KV system

Answer / karthikeyan.s

For an earthed power system, phase to phase voltage is
equal to line voltage and phase to earth voltage shall be
VL/1.732. But for an unearthed power system, phase to earth
voltage shall be equal to line voltage (VL). Hence for an
unearthed system the cable insultation should be very high
to withstand the abnormal voltage during fault.
That is why it has been widely said that 6.6kV unearthed
cable shall be used in 11kV earthed application, since the
insulation level for an unearthed cable is very high
compared to earthed cable.

Answer / b. ramachandra rao

Cables of 6.35/11 kV grade (earthed system) are
suitable for use on 6.6/6.6 kV (unearthed system) also.

But is it true other way as well?

Can Cables of 6.6/6.6 kV grade (unearthed system) are
suitable for use on 6.35/11 kV (earthed system) also.

Answer / kalyan chekuri

I have a system which had 400kV 100 MVA/11 kV 50 MVA/11kV 50
MVA transformer whose secondary is earthed with NGR of 300
Amps. I have bought 18000 Km of 11 kV earthed cable to lay
on 11 kV side of it. If the phase to earth voltage is 6.4kV
and root 3 times is the voltage expected to go up i.e 11kV,
why cant it be used if the power frequency withstood for
17kV for 5 minutes

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