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Where:
V
= RMS voltage in the differential circuit.
D
V
= RMS voltage in the restraint circuit.
F
V
= Threshold voltage in the level detector.
O
I
= RMS current in the differential circuit.
D
I
= RMS current in the restraint circuit.
F
K= Restraint percent in unit value.
T= Detector time (in ms.).
We will have the following values' ratio:
=
=
V
I
*
N
*
R
D
D
ED
D
=
=
V
I
*
N
*
R
F
F
EF
F
On the other hand, the differential unit will produce an output when the VA value is above the V
when:
−
2
( *
V
K
*
V
* )
sen(
D
F
or what is the same when:
−
≥
I
K
*
I
V
*
1 (
2 /
D
F
O
The circuit design values are:
V
= 0.137 V
o
T = 1.5 ms.
N = 0.01
R = 100 ÿ
With these values the equation is reduced to:
−
≥
I
K
*
I
0
1 .
D
F
For an internal fault I
= I
D
≥
−
I
0
1 .
1 /(
K
)
D
From this equation we obtain the relay's sensitivity in amperes for the different values of K.
GEK-98514B
I
*
N
*
R
D
I
*
N
*
R
F
−
≥
90
9
T
)
V
O
−
*
sen(
90
9
T
))
*
1 (
N
, so:
F
BUS1000 Busbar Protection
*
R
)
3. OPERATION PRINCIPLES
one, that is,
O
[5]
[6]
[7]
[8]
3-3
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