100/133% INSULATION LEVEL
100/133% INSULATION LEVEL
(OP)
Can anybody explain, what is the idea behind having 100% insulation level and 133% insulation level in testing XLPE, EPR medium voltage cables?
Thank you
Thank you
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100/133% INSULATION LEVEL
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RE: 100/133% INSULATION LEVEL
100% insulation is perfectly suitable for solidly grounded systems.
Rafiq Bulsara
http://www.srengineersct.com
RE: 100/133% INSULATION LEVEL
RE: 100/133% INSULATION LEVEL
Therefore, depending of the system grounding (solidly, impedance grounded or ungrounded) the stresses in the insulation with respect to ground should be designed accordingly for 100%, 133% or larger. For larger cable insulation, it is common to use the next standard voltage level.
RE: 100/133% INSULATION LEVEL
Single conductor 5-15KV, 100% &133% insulation level.
My questions is
1- Do i have to order the insulation level depending on the status of grounding? Any standard for that?
2- Any explanations Why 33% and 73% more insulation, any calculations?
Thanks again
RE: 100/133% INSULATION LEVEL
Hopefully that is obvious.
For high-resistance ground, I think the neutral grounding resistor is sized at Xc0 / 3. Solid line to ground fault on then leads to max steady state overvoltage to ground (ignoring transients) of 1.33 = 1 + 33%. That's not as obvious to me before my morning coffee, but I know it's true.
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(2B)+(2B)' ?
RE: 100/133% INSULATION LEVEL
And I'm not so sure where the 133% comes from. Maybe someone can explain it.
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(2B)+(2B)' ?
RE: 100/133% INSULATION LEVEL
thread238-232606: Cable Insulation Level Selection
[quote IEEE-141/1993]"There are three levels of conductor insulation for MEDIUM-VOLTAGE CABLES: 100, 133, and 173% levels. The solidly grounded system permits the use of 100% insulation level. When the fault on the other system will raise the system voltage above normal during the time of the fault, 133% insulation level should be specified if the fault is cleared within one hour. When the fault will remain on the system for an indefinite time, 173% voltage level insulation[quote]
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(2B)+(2B)' ?
RE: 100/133% INSULATION LEVEL
2- Any standard for that? IEEE Std 141 (7.2.5) & IEEE Std C62.92.1
3- Any explanations :
a)Why 33% and 73% more insulation: During SLG fault, the faulted phase voltage approaches to zero while the unfaulted phase voltage rise. (See the enclosed file for additional information)
CALC. GUIDELINE:
In the absence of the sequence impedance parameters (reactances & resistances)at the cable connection, the following general assumptions may be used:
• Effectively grounded system: the phase-to ground voltage (VLg) typically could rise up to 80% of the max VLL (phase-to-phase maximum operating nominal voltage): Vcable ~ 0.8(max VLL)
• Ungrounded system: Vcable ~ VLL
• Impedance Grounded: 0.8(max VLL)< Vcable < max VLL = 1.05xVLL
b) Any calculations?: The above calculation guideline could be sufficient for most MV applications. However, if more accurate information is required, the withstand cable temporary overvoltage (TOV) could be determined using EMTP or similar transient software. An acceptable practical approach to determine the TOV could be as follows:
Min Cable voltage withstand rating > 1.05xCOGxVLL
NOTE: The COG (Coefficient of grounding) could be estimated considering the sequence impedance parameters. For details about estimate the COG, refer to IEEE Std C62.92.1 or the enclosed link. htt