Assuming that the insulating media is air bellow 3000 ft of altitude in clean atmosphere and normal humidity level for rigid bus construction for per NEMA SG-6 the clearance requirement for standard nominal voltage rating of 34.5 kV and 200 kV BIL is 3 ft phase-to-phase and 1 ft 3in for phase to ground. For next standard nominal voltage rating of 46 kV and 250 kV BIL the clearance is 4 ft phase-to-phase and 1.5 ft phase-to-ground.
Beware that there are electrical aparatus with clearance varies depending on the construction such as vertical break or center break disconnect switches. Other such as transformers, circuit breakers or switchgears, have a lot less clearances than the values recommended by NEMA for rigid bus.
This clearance could be lowered if the electrical phase are rigidly supported and rigorous dielectric test is performed and verified by independent agency in accordance with acceptable industry procedures.
In general, clearances depend of insulating media, dielectric type test in compliance with code or standard, design overvoltage, environment conditions, construction and size of the conductor among other factors. Notice that there are significant clearances differences between codes such as IEC, IEEE or NEMA and could be additional safety clearances requirement by codes such as NEC, NESC and OSHA.
Dear Sir(s),
Kindly give the IEEE standard no. IEC standard no, which is mentioning these clearances. It would really be very good if someone can help me.
Thanking all,
With Warm Regards,
Nihar S. Raj
For Safety Clearances:
IEEE Standard C2 -National Electrical Safety Code (NESC) 2002
Clearances for equipment/Apparatus:
IEEE Std C37.20.1,2 & 3 TABLE A3 – Metal-Clad & Station Cubicle Switchgear Station Type
IEEE Std C57-19 Dimensions for Outdoor Bushings for Power Apparatus.
Others:?? Check also IEEE C37 40 Fuses,C37.53,
Clearance for Substation Application:
US and Other Countries:
National Electrical Manufacturer Association (NEMA) Standard SG-6
IEEE Std C37-32 -…..Application Guide for HV Air Sw.,Bus Support & Accessories.
IEEE Std P1427 Draft Guide for Recommended Electrical Clearances and Insulation Levels in Air Insulated Electrical Power Substations 1999.
Check the enclose site and associated Tables 4-7 Page 154
