Page 369 - Industrial Power Engineering and Applications Handbook

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Table 13.1 Rated voltages and frequencies for metal enclosed List I
bus systems also applicable for switchgear assemblies 1 When the system is not directly connected to an
overhead line, such as when connected through a
~~ ~ ~
Series I Series II transformer.
2 When the neutral of the system is grounded solidly or
Nominal Rated maximum Nominal Rated muximum
system voltage system voltage system voltage system voltage through a small impedance (Section 20.4).
3 When the system is provided with a surge protection.
(ANSI C37-20C)
kV kV kV kV
0.415* 0.44 0.48 0.508 List I1 or List 111
0.6* 0.66 0.60 n.m 1 When the system is connected to an overhead line.
3.3 3.6 4.16 4.76 2 When the neutral of the system is not solidly grounded.
6.6 7.2 7.2 8.25 3 When no surge protection is provided.
11 12 13.8 15.0 4 When the installation demands a high degree of
15 17.5 14.4 15.5 security, such as in a generating station.
22 24 23.0 25.8
33 36 34.5 38.0
44 52 69.0 72.5 Note
66 72.5 - - IS 8084, however, has opted for list I1 for the busbar systems for all
applications.
For higher voltages -refer to Tables 13.2 and 13.3 for series 1 and Although the rated values are based on experience and field
IEC 60694 for series 11. data collected, sometimes these values may be exceeded in actual
operation, due to changed service or weather conditions. It is,
therefore, recommended to take cognisance of this fact and provide
Frequency: 50 or 60 Hz I Frequency: 60 Hz
a surge protection to contain the surge voltages within the rated
values of Tables 13.2 and 13.3. It is recommended that actual site
Based on IEC 60694, BS 159 and ANSI C37-2OC.
tests be conducted on similar installations to ascertain the likely
Notes level of voltage surges that may occur during operation. To be on
Series I: Based on the current practices adopted by India, Europe the safe side, it is recommended for outdoor installations, particularly,
and several other countries. *These voltages have now to contain the severity of the surge voltages, with the help of
been revised from 0.415 kV to 0.4 kV and from 0.6 kV surge arresters, within the maximum assigned impulse voltages
to 0.69 kV as in IEC 60038. (BIL) of the equipment, considered in Tables 13.2 and 13.3, less
Series 11: Based on the current practices adopted in the USA and the protective margins, for range I and range I1 voltage systems
Canada. respectively.
Table 13.2 Standard insulation (impulse) Levels for Series 1 range I voltage systems (1 kV < V,,, 2 245 kV)

Standard one-minute power frequency Standard lightning impulse (1.2/50~)
voltage' v,,, system voltage V,,, withstand voltage withstand voltage phase to ground**
kV(c m.s.) kV(ctn.s.) KV*(r.m.s.) kV* (peak)
List I List I1 List IIl List I List II List IIl
3.3 3.6 20 40 -
6.6 7.2 40 60 -
11 12 60 75 -
15 17.5 75 95 -
22 24 9s 125 -
33 36 145 I70 -
44 ~ 52 250 - -
66 , 72.5 325 - -
- 100 150 185 - 380 450 -
110 123 185 230 - 450 550 -
132 ~ 145 230 275 - 550 650 -
154 1 I70 275 325 - 650 750 -
220 245 360 39s 460 850 950 1050
Notes As in IEC 60071-1 and IEC 60694
* More than one lightning impulse insulation level is indicative of the extent of exposure of equipment to lightning surges. Correspondingly
the power frequency withstand voltage can also he more than one.
** Lightning stress between the phases is not more than the lightning stress between a phase and the ground. For more details refer to IEC
6007 1-1.
'IEC 60071-1 has specified only V,,, values. V,,,,, is indicated based on the practices adopted by various countries.