ABB RELION 650 SERIES, Applications Manual

Page: 40 / 262

If there is an external fault and CT saturation, as shown in figure 6 , there will be a voltage over the
differential detection. The operation level of the detection must be set higher than this voltage.
The highest wiring resistance shall be considered in the calculation: R
L
= max(R
L
, R
L1
, R
L2
, R
L3
). The
maximum value of V
R
can now be calculated:
( )
max
2
R SC ct L
V I R R
= × + ×
I
SC
is the maximum short circuit current that can flow through one of the bays in case of an
external fault.
With the given data, the following value can be calculated:
( )
max
1
15000 5 2 1.26 188
600
R
V V
= × × + × =
To assure trip in case of an internal fault, it is recommended that the voltage E
al
(600 V as
indicated above) is at least twice the set voltage level. In this case, the operation value 200 V is
recommended.
1. Set Operation to Enabled to activate the function.
2. Adjust the series resistor to a value where the trip level and alarm level is within the setting
range, 20 mA – 1 A.
In the present example a good choice is a series resistor adjusted to 1500 Ω; at the trip
voltage, equal to 200 V, a current of 133 mA flows through that resistor.
3. Set
R series to the physical value of the resistor, 1500 Ω.
The thermal capacity of the resistor is limited to 200 W. A check about the condition: P
loss
<
200 W shall always be done. The condition is fulfilled in the present example:
2
200
27
1500
loss
P W
= =
4. Set
TripPickup to 200 V
The sensitivity (in primary current) at the operating voltage U>Trip is:
m
( (I ))
res ag
IP n IR I
= × + +
å
IECEQUATION2416 V2 EN-US
(Equation 1)
where:
n CT ratio
IR 133 mA: current which is drawn by the IED circuit at the operating voltage;
I
res
20 mA: current which is drawn by the non-linear resistor at the operating voltage
I
mag
35 mA: magnetizing current of the CT at the operating voltage; we suppose that the phase angle is
-60
0
IP 600/1 * ( 0,133 /_0° + 0,02 /_0° + 4* 0,035 /_-60°) = 134 A
i.e. a sensitivity of 22%.
5. Set
AlarmPickup
This setting is related to the detection of an open CT. If the secondary wiring of the CT of
one bay is open, then there is an unbalance condition. The minimum unbalance current which
the protection function can detect is 20 mA, if the rated secondary current of the CT is 1 A.
The voltage VR_vnb which is related to IR_unb = 20 mA is:
VR_unb = R . IR_unb = 1500 . 0,02 = 30 V
So:
Section 3 1MRK 505 287-UUS B
REB650 setting examples
34 Busbar protection REB650
Application manual
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