Medium voltage switchgear application guide

Medium voltage switchgear application guide
Appendix 1:
transformer(cont’d)
6 - SWITCHING CURRENT PEAK
When peaks the are power produced. is switched on, very high signals or switching
Ie
I r
date
11/94
- B•3•2 -
revised
05/2004
transient state of the current during no-load transformer switching
is They very may quickly be 14 absorbed. times greater The time than constant the rated of current. the damp This down switching depends current
the winding resistance and the secondary load. The real values must beon
requested from the manufacturer.
Time constant and peak-switching current values depending on the immersed transformer power
(high voltage switching).
transformer
power
(kVA)
n e = I e peak
I r rms
100 14 0.15
160 12 0.20
250 12 0.22
400 12 0.25
630 11 0.30
800 10 0.30
1000 10 0.35
1250 9 0.35
1600 9 0.40
2000 8 0.45
5000 8 0.50
10000 8 0.50
15000 8 0.50
time
constant
(s)
20000 8 0.50
and In the the event time of constant low voltage divided switching, by 1.5 in the relation ratio neshould to the values be multiplied given in the by 2
table These above.
protection switching is defined. peaks must be taken into account when the type of
The transformer may have its own optional devices.
following: Depending on the type, the transformer’s own protective are the
gas ■the leak, waterproof pressure protection and temperature unit for complete detector. filling transformer:
■Buchholz gaz leak and protection pressure relay detector. for transformer fitted with a conservator:
monitoring. ■thermostat, thermometer for immersed-type transformers: temperature
■thermostatic probes for dry-type transformers: temperature control.
t
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