ABB Relion 650 Series Applications Manual page 40

Section 3
REB650 setting examples
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
maximum value of V
I is the maximum short circuit current that can flow through one of the bays in case of an
SC
external fault.
With the given data, the following value can be calculated:
To assure trip in case of an internal fault, it is recommended that the voltage
indicated above) is at least twice the set voltage level. In this case, the operation value 200 V is
recommended.
1. Set
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
The thermal capacity of the resistor is limited to 200 W. A check about the condition: P
200 W shall always be done. The condition is fulfilled in the present example:
P
loss
4. Set
The sensitivity (in primary current) at the operating voltage U>Trip is:
IP
IECEQUATION2416 V2 EN-US
where:
n
IR
I
res
I
mag
IP
i.e. a sensitivity of 22%.
5. Set
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:
34
can now be calculated:
R
Operation to Enabled to activate the function.
R series to the physical value of the resistor, 1500 Ω .
2
200
= =
27 W
1500
TripPickup to 200 V
å
= × + +
n ( IR I (I ))
res m ag
CT ratio
133 mA: current which is drawn by the IED circuit at the operating voltage;
20 mA: current which is drawn by the non-linear resistor at the operating voltage
35 mA: magnetizing current of the CT at the operating voltage; we suppose that the phase angle is
0
-60
600/1 * ( 0,133 /_0° + 0,02 /_0° + 4* 0,035 /_-60°) = 134 A
AlarmPickup
© Copyright 2013 ABB. All rights reserved
(
= × + ×
V I R 2 R
R max SC ct L
=
V 15000
R max
1MRK 505 287-UUS B
= max(R , R , R , R ). The
L L L1 L2 L3
)
1
( )
× × + × =
5 2 1.26 188
600
E (600 V as
al
loss
(Equation 1)
Busbar protection REB650
Application manual
V
<