ABB Relion 650 Series Applications Manual page 74

Section 6
Differential protection
2000
=
IP
EQUATION1886-ANSI V1 EN-US
Where
IR= 100mA
I = 15mA is the magnetizing current of the CT at the operating voltage
mag
I = 5 mA
res
The magnetizing current is taken from the magnetizing curve for the current transformer cores
which should be available. The value at
Setting of
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 current that the protection function
can detect is 20 mA, if the nominal secondary current of the CT is 1 A. The voltage UR_unb which is
related to IR_unb = 20 mA is:
VR_vnb = R . IR_vnb = 1000 . 0.02 = 20 V
V>Alarm = VR_vnb = 20 V
We suppose that: – the magnetizing current of the CT at UR_unb is 3,7 mA, with an angle of -60°; –
the current that is drawn by the non-linear resistor at UR
primary current is:
(
= ×
IP n
should allow the detection of the open CT on the smallest object in normal load condition.
6.1.3.4 Alarm level operation
The 1Ph High impedance differential protection HZPDIF (87) function has a separate alarm level,
which can be used to give alarm for problems with an involved current transformer circuit. The
setting level is normally selected to be around 10% of the operating voltage
The setting of
sensitivity. The setting example shows the calculation procedure of the setting value of
As seen in the setting examples above the sensitivity of HZPDIF (87) function is normally high,
which means that the function will in many cases operate also for short circuits or open current
transformer secondary circuits. However the stabilizing resistor can be selected to achieve
sensitivity higher than normal load current and/or separate criteria can be added to the operation,
like a check zone. This can be either another IED, with the same HZPDIF (87) function, or be a check
about the fault condition, which is performed by a ground overcurrent function or neutral point
voltage function.
For such cases where operation is not expected during normal service the alarm output should be
used to activate an external shorting of the differential circuit avoiding continuous high voltage in
68
( )
× ° + £
400 0 60 approx
5
is the current drawn by the IED circuit
is the current drawn by the non-linear resistor at the operating voltage
V>Alarm .
2000
)
(
+ = ×
IR I
unb res unb ,
1
V>Alarm is related to the value of the stabilizing resistor and the minimum current
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.140 A
TripPickup is taken.
Ð ° + Ð ° + ×
0, 02 0 0, 0018 0
TripPickup
TripPickup
is about 1.8 mA. So the sensitivity in
unb
)
Ð - ° ;
4 0, 0037 60 58
TripPickup .
Busbar protection REB650
1MRK 505 287-UUS B
(Equation 10)
A
The sensitivity
M16850-196 v5
V> Alarm .
Application manual