Siemens 3AH37, Operating Instructions Manual

Page: 36 / 64

Description
36 9229 9992 176 0D
2013-07-08
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. 45 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. 48:
3AH37/38vacuum 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 means: +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. 47 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 metres
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. 48 Altitude correction factor K
a