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Unbalance protection for capacitor banks
(TOCC)
rent of stage IHigh is low compared to the earth fault current in the system. The current
stage I>Low is normally set to give alarm at 50% of the set operate current of stage
I>High.
The calculation of settings for the unbalance protection function must take into consid-
eration how the capacitor bank is built up and it is often made by aids of a computer
program.
6HWWLQJ RI UHOD\ RSHUDWLQJ FXUUHQWV
If Is is the primary setting operating value of the function, then the secondary setting
current (Is
) is:
SEC
I
S EC
⋅
Is
------------- - Is
=
SEC
I
PRIM
where I
is the secondary rated current of the main CT and I
SEC
current of the main CT.
The relay setting value is given in percentage of the secondary base current value, I
associated to the current transformer input I5. The value for I>Low and I>High is given
from the formula:
Is
SEC
⋅
------------- - 100
I
=
set
I
5b
&KDSWHU
&XUUHQW
(Equation 61)
is the primary rated
PRIM
5b
(Equation 62)
135
,
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