Cable Insulation for 24.9kV Service

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bdm5066

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Pittsburgh, PA
I'm working on a project where the utility is providing a 24.9kV (nominal) service (primary metering). From a cable insulation standpoint, will I need to specify 35kV cable (e.g. 35kV MV-105)? My concern is that 25kV cable would be too low of a rating if the utility's voltage were to fluctuate above nominal.

Thanks in advance for any input!
 
bdm5066 said:
I'm working on a project where the utility is providing a 24.9kV (nominal) service (primary metering). From a cable insulation standpoint, will I need to specify 35kV cable (e.g. 35kV MV-105)? My concern is that 25kV cable would be too low of a rating if the utility's voltage were to fluctuate above nominal.

Thanks in advance for any input!
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If the voltage gets to 25001 volts will the cable explode?
 
I'm assuming your question is rhetorical, but the answer is no.

With that said, my understanding is that utility voltages can fluctuate +/- 5% from nominal, so the upper maximum would be 26.1kV. Sorry if this is a dumb question, but couldn't the insulation fail if the cable is exposed to this voltage for an extended period of time?
 
bdm5066 said:
I'm assuming your question is rhetorical, but the answer is no.

With that said, my understanding is that utility voltages can fluctuate +/- 5% from nominal, so the upper maximum would be 26.1kV. Sorry if this is a dumb question, but couldn't the insulation fail if the cable is exposed to this voltage for an extended period of time?
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I think your question is best answered by looking at the specs for the cable. It is likely you will find that the voltage rating of the cable is nominal and includes allowances for normal fluctuations.
 
bdm5066 said:
I'm working on a project where the utility is providing a 24.9kV (nominal) service (primary metering). From a cable insulation standpoint, will I need to specify 35kV cable (e.g. 35kV MV-105)? My concern is that 25kV cable would be too low of a rating if the utility's voltage were to fluctuate above nominal.

Thanks in advance for any input!
Click to expand...

You are confused. 35 kV is tested to 71 kV (DC). Absent any additional info it might go up to 140% (TOV) but that’s why you use surge arresters.
 
UL 1072 Table 13.1 presents the required XLPE or EP insulation thickness. Then the thickness for 133% for 25 kV it is 100% for 35 kV.

The voltage level state actually the maximum electric field [voltage gradient] and the insulation losses will accelerate the ageing of cable.

According to IEC 60502-2 the rated voltage of a cable depends on how long this cable will works if a phase is grounded. If it is less than 1 hour you may use at the rated voltage for more you have to jump to the next rated voltage and according to EPRI-EL-5036-V4/1998 [presenting ICEA -USA] recommendations [see attached file]
 

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