5-16
Applications
Date Code 20010515
SEL-2BFR, -2/BFR Instruction Manual
secondary
J
1.09
26CF
•
75%
26CP
secondary
J
45
.
1
TS
•
85%
26CF
secondary
J
71
.
1
PTR
•
CTR
primary
MJ
.41
4
TS
pole
breaker
per
primary
MJ
41
.
4
TS
cm
/
J
700
•
cm
225
•
disks
28
TS
SEC
SEC
MAX
3
3
MAX
=
=
=
=
=
=
=
=
47Q Negative-Sequence Overvoltage Element Setting
When the breaker is closed and a potential fuse blows, the relay measures voltage across the
breaker pole. Because current is flowing and voltage is measured, the relay could begin to
accumulate energy in a resistor that is not in service. To prevent this, the negative-sequence
overvoltage element 47Q supervises close resistor thermal models. When the 47Q element
asserts, the relay disables the close resistor thermal model. Set the 47Q element to assert when
negative-sequence voltage is great enough to indicate a potential fuse operation.
While the 47Q element asserts during single-pole open intervals in single-pole trip installations,
single-pole trip operations do not adversely affect the thermal models because current does not
flow in the open pole.
Calculate the magnitude of negative-sequence voltage for given phase voltages using the
following equation.
(
)
o
o
240
1
a
and
120
1
a
:
where
aVC
VB
a
VA
3
1
2
V
2
2
∠
≡
∠
≡
+
+
=
When the A-phase potential fuse blows, the magnitude and angle of negative-sequence voltage
presented to the relay is:
(
)
(
)
[
]
[
]
o
o
o
o
o
o
o
o
0
V
22.3
120
V
0
120
V
0
0
V
67
3
1
120
0
V
0
240
0
V
0
0
V
67
3
1
2
V
∠
=
∠
+
−
∠
+
∠
=
+
∠
+
+
∠
+
∠
=
The magnitude of V2 is the same when two potential fuses operate. The accuracy specification of
47Q is ±0.27 V secondary ±15% of setting, yielding a maximum error of 3.62 V for a 22.3 V
setting, so:
47Q = 22.3 V – 3.62 V = 18.69 V secondary.
Do not make the 47Q setting too sensitive. After issuing the close signal, the relay continues to
measure negative-sequence voltage until all three breaker poles close. If a single-pole close
resistor remains in service, the relay measures a small amount of negative-sequence voltage. This
amount should not be greater than the 47Q element setting or close resistor thermal elements may
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