Manual
KVCG202/EN M/H
Example 1:
Application of 2 VRRs (1A rated) with direct paralleling
RL = 50m 2.5mm
2
Cu = 0.37Ω
RLDC = 0.007Ω
X =
R
L
RLDC'
<0.0526 where R
LDC'
= R
LDC
+ R
3
R
LDC
' > 19R
L
R
LDC
' > 7.03
Therefore:
RS > 7.03 – 0.007
> 7.023
Choose a value of Rs = 7Ω.
Required continuous rating = 2In = 2A
Therefore required continuous power rating of RS = 28W.
Allowing a minimum power derating of 50%= 56W, use a resistor rated at 75W.
Therefore use RS = 7 Ω 75W
Note: RS should withstand the maximum main CT secondary rms current for a minimum
of three seconds. The maximum output of the main CTs should not exceed three times
the steady state current through its connected burden and CT resistance to cause
saturation.
Example 2:
Application of two VRRs (5A rated), using 5A: 0.5A interposing transformers to isolate the
individual line CTs, to BEBS T2 standard. The British Electricity Board Specification T2
for transformers and reactors uses LDC circuits paralleled through pilots and 5:0.5 A
interposing CTs.
Assume:
Figure 26:
is equivalent to:
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