Description
32
9229 9947 176 0C
2013-03-28
Ambient conditions
Installation altitudes
Insulating capacity
The insulating capacity of insulation in air decreases with rising altitude due to the
lower air density. In conformity with IEC 62271-102, the rated lightning impulse
withstand voltage values given in Fig. 41 are valid up to an installation altitude of
1,000 m above sea level.
As from an altitude of 1,000 m, the insulation level must be corrected as shown in
Fig. 43:
3AH47 vacuum circuit-breakers are suitable for use in
the following climate classes in accordance with
IEC 60721, Part 3-3:
Class
• Climatic ambient conditions:
3K4
1)
,
3K6
2)
,
3Z2,
3Z5
• Biological ambient conditions:
3B1
• Mechanical ambient conditions:
3M2
• Chemically active substances:
3C2
3)
• Mechanically active substances:
3S2
4)
1) peak value of the 24-hour mean: +35 °C
2) Without ice formation and wind-driven precipitation
3) Without occurrence of salt fog and simultaneous condensation
4) Restriction: clean insulating parts
5) Average value, measured over 24 hours
6) Average value, measured over 1 month
Fig. 42
Ambient conditions
U
U
0
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
K
a
= e
m
(H – 1000)/8150
Calculating the altitude correction factor
K
a
:
H
=
Installation altitude in meters
m = 1 for AC voltage, lightning impulse withstand
voltage (between phases, phase-to-earth, applied
longitudinally)
Example
For a required rated withstand voltage of 75 kV at an
altitude of 2,500 m, an insulation level of at least 90 kV
under standard reference atmosphere conditions is
required:
90 kV
75 kV
e
1
(2500 – 1000)/8150
75 kV
1.2
Fig. 43
Altitude correction factor
K
a
