Description
36 9229 0025 176 0E
2021-11-15
Ambient conditions
Occasional condensation may occur under these ambient conditions.
SION
®
Vacuum circuit-breakers are suitable for use in the following climate classes
according to IEC 60721-3-3:2019:
Installation altitudes
Dielectric strength The dielectric strength of insulation in air declines with rising altitude due to the lower
air density. As per IEC 62271-1, the rated lightning impulse withstand voltage values
and rated short-duration power frequency withstand voltage given in Fig. 42 are
valid up to an installation altitude of 1 000 m above sea level.
Above an altitude of 1000 m, the insulation level must be corrected as shown in
Fig. 44:
Class
• Climatic ambient conditions:
3K4
1)
• Biological ambient conditions: 3B1
• Mechanical ambient conditions: 3M2
• Chemically active substances:
3C2
2)
3C3
3)
• Mechanically active substances:
3S2
4)
1) Minimum temperature limit: -5 °C / 23 °F (with addition A40 to
-25 °C / -13 °F)
2) Without occurrence of salt fog and simultaneous condensa-
tion
3) Class 3C3 (H2S < 20 ppm in dry air < 50 % with order suffix
D20)
4) Restriction: Clean insulation parts
5) Average value, measured over 24 hours
6) Average value, measured over 1 month
Fig. 43 Ambient conditions
+55 °C
131 °F
-5 °C
1)
23 °F
1)
95 %
5)
90 %
6)
5%
U U
0
x K
a
U Rated withstand voltage U under standard reference
atmosphere
U
0
required rated withstand voltage for the installation
location
K
a
Altitude correction factor
e e factor (approximately 2.718)
K
a
= e
m
x (H - 1000)/8150
Calculation of the altitude correction factor K
a
:
H = Installation altitude in metres above sea level
m = 1 for AC voltage, lightning impulse withstand volt-
age (between phases, phase-earth, applied longi-
tudinally)
Example
For a required rated withstand voltage of 75 kV at an al-
titude of 2 500 m, an insulation level of at least 90 kV un-
der standard reference atmosphere conditions is
required:
90 kV 75 kV x e
1 x
(2500 - 1000)/8150
75 kV x 1.2
Fig. 44 Altitude correction factor K
a
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