Electrical power 2

[fshah]

Forthe underground Medium Voltage specification I have seen the term used, 100% or 133 % insuation and full neutral or 1/3rd neutral.
Can someone help me to understand these terms and applications of it.
Any read up available to understand for these type of the cable details?

 

[fshah]

Sorry, I mean Underground Medium Voltage Cable specification (Specifically used in the utility)

Thanks.
FJS

 

[davidbeach]

Try

http://www.okonite.com,

http://www.kerite.com

or

http://www.southwire.com.

You should find lots of information about what each is for and how you might want to specify a cable.

 

[cuky2000]

This refer to the insulation capacity of power cables used more often in the Ansi/IEEE marketplaces. Its is also related with the fault clearing time of the protective devices. For instance, if the fault is cleared within 1 min, 100% insulation may be appropiated. However, if the clearing time is long or undetected such as in a ungrounded system, the insulation should be rated for 173%.
As higher is the percent of insulation, higher is the cable insulation thickness.

 

[magoo2]

The other part of your question relates to the neutral size.

For single-phase circuits, all the current returns over the neutral so a full neutral, one equivalent to the current carrying capacity of the phase is generally used.

On three-phase circuits, the 4-wire multi-grounded neutral predominates in North America. In this case, the neutral can be sized smaller than the phase conductor since it normally just carries the imbalance. It is common to have a half neutral or one that is smaller than the phase conductor. Remember that if you are using single phase cables, a 1/3 neutral on each phase cable gives a resultant full sized neutral for the three phase circuit. Individual cables with 1/6 neutrals results in a 1/2 neutral circuit.

If you deal with 3-wire circuits, the shield is mostly used to grade the voltage stress so it doesn't have to be that large.