Siemens SIMOSEC - Insulating Capacity and Site Altitude

Description
32 REVISION 02 * DESCRIPTION SIMOSEC * 832-6063.0
9.7 Insulating capacity and site altitude
Insulating capacity
• The insulating capacity is verified by testing the switchgear with rated values of short-
duration power-frequency withstand voltage and lightning impulse withstand voltage
according to IEC 60 694 / VDE 0670 Part 1000, and ANSI/IEEE C37.20.3.
• The rated values are referred to sea level and to normal atmospheric conditions
(14.7 PSI, 68 °F, 0.000687 lb/ft
3
humidity in accordance with IEC 60 071 and VDE 0111)
and ANSI/IEEE Std 4.
• The insulating capacity decreases with increasing altitude.
For site altitudes above 1000 m, the correction factor ’’a“ is recommended, depending
on the actual site altitude above sea level.
Fig. 26: Correction factor ’’a“ as a function of the site altitude in meters above sea level
Rated voltage (r.m.s. value) [kV] 8.25 15 27.6
Rated short-duration (one minute) power-frequency withstand voltage (rms value)
- Across isolating distance [kV] 39.6 39.6 66
- Between phases and to ground 36 36 60
Rated lightning impulse withstand voltage (peak value)
- Across isolating distance [kV] 105 105 138
- Between phases and to ground 95 95 125
Rated short-duration power-frequency withstand voltage to
be selected
Rated lightning impulse withstand voltage to be selected
Rated short-duration power-freq. withstand voltage
W --------------------------------------------------------------------
1.1 * a
Rated lightning impulse withstand voltage
W -------------------------------------------------------------------
1.1 * a
Example:
3000 m site altitude above sea level
15 kV switchgear rated voltage
95.0 kV rated lightning impulse withstand voltage
Rated lightning impulse withstand voltage to be selected
95 kV
-------------------- = 118 kV
1.1 * 0.73
Result: According to the above table, switchgear for a rated voltage of 27.6 kV should be selected.