4–77
System Setup and Setpoints – 4
87 Phase Differential
NOTE
: See Section 4.6,
Transformer Con-
nections
for detailed discussion on
transformer connection applications for
87 function differential.
87T Phase Differential Restrained Overcurrent
The 87T Phase Differential function is a percentage
differential function with dual adjustable slope char
-
acteristics (see Figure 4-50). This function provides
protection for the transformer from internal wind
-
ing faults. This function offers sensitive differential
protection at low fault currents and tolerates larger
mismatch of currents that can occur during high
through fault current for greater security.
The 87T minimum pickup setting should be set to
prevent operation of the 87T function due to trans-
former excitation current. Typical setting is 0.2 to
0.4 PU of tap setting.
Slope 1
The setting of Slope #1 should be set according to
various possible errors:
1.
Tapchanger operations in the power
transformer (worst case
10%).
2.
CT mismatch due to ratio errors. Errors
can be as high as
10%.
A typical Slope #1 setting of 30 to 40% prevents
misoperation due to above errors.
Slope 2
For heavy faults outside the differential zone, CT
saturation can occur. Factors such as residual mag
-
netism in the CT core, CT characteristic mismatch
and burden mismatch can contribute large differential
currents during this condition. Slope #2 should be set
higher than Slope #1. It can provide security against
misoperation during high through fault currents.
A typical Slope #2 setting is 60 to 100%.
Even Harmonic Restraint
Transformer magnetizing inrush currents contain
significant amounts of 2
nd
and some 4
th
harmonic
currents. This inrush can cause undesirable trips
and delay putting a transformer into service. The
even harmonic restraint keeps it from operating
during a magnetizing inrush condition. Magnetizing
inrush current is distinguishable from fault current by
harmonic components. The M-3311A Transformer
Protection Relay can be set to restrain if the level
of even harmonic current is above a set percentage
of fundamental.
The harmonic currents are calculated from the
differential current in the windings. The amount of
even harmonic current (
I
d
24
) in PU can be found by
using the formula:
Id
24
=
Id
2
2
+
Id
4
2
Where
I
d
2
and
I
d
4
are second and fourth harmonic
currents in PU, respectively.
The percentage of even harmonics is found by the
ratio
I
d24
I
d1
. If this ratio is greater than the even
harmonic restraint setpoint then 87T is restrained
from operating. The equation below illustrates how
the restraint works for A-Phase:
I
d24
> Even Harmonic Restraint Setpoint
I
I
AW1
+
I
AW2
+
I
AW3
+
I
AW4
I
The amount of even harmonics present in the
transformer inrush currents depends upon the mag-
netizing characteristics of the transformer core and
residual magnetism present in the core. A setting in
the range of 10 to 15% can provide security against
misoperations during magnetizing inrush conditions.
Modern transformers tend to have low core losses
and very steep magnetizing characteristics. When
the relay is applied to this type of transformers, the
even harmonic setting should be set around 10% (in
some cases, the setting may be lower than 10%).
Older transformer designs tend to have higher
amounts of even harmonics, where a setting of 15%
or greater can provide security against misoperation
during magnetizing inrush conditions.
The setting of the even harmonic restraint should be
set to a low enough value to provide security against
misoperation during transformer magnetizing inrush
current and it should not be lower than the amount of
even harmonics generated during internal fault con-
ditions with CT saturation so as not to compromise
reliability for heavy internal fault detection.
Fifth Harmonic Restraint
Transformer over-excitation produces a high
amount of excitation current, which will appear as
a differential current to the 87T function. The Fifth
Harmonic restraint function can prevent misopera
-
tion of the 87T function by shifting the minimum
pickup to a higher value (typically set at 150 to
200% of 87T minimum pickup), during transformer
over-excitation conditions.
The over-excitation condition is detected by the
presence of Fifth Harmonic component as a per
-
centage of fundamental component of differential
current above a set value.
The amount of Fifth Harmonic depends on the
transformer core magnetizing characteristics.
A setting of 30% is adequate to discriminate
over-excitation from other conditions.
Содержание M?3311A
Страница 1: ...Instruction Book M 3311A Transformer Protection Relay ...
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Страница 67: ...M 3311A Instruction Book 2 12 Path Monitor Metering ll Figure 2 9 Metering II Screen 4 Winding ...
Страница 87: ...M 3311A Instruction Book 2 32 This Page Left Intentionally Blank ...
Страница 89: ...M 3311A Instruction Book 3 2 Figure 3 2 IPScom Main Screen ...
Страница 93: ...M 3311A Instruction Book 3 6 Figure 3 8 Terminal Window Figure 3 7 IPScom Modem Communication Dialog Screen ...
Страница 99: ...M 3311A Instruction Book 3 12 Path Monitor Metering ll Figure 3 14 Metering II Screen 4 Winding ...
Страница 103: ...M 3311A Instruction Book 3 16 Path Monitor Phasor Diagram F87T Figure 3 18 Phasor Diagram F87T 4 Winding ...
Страница 107: ...M 3311A Instruction Book 3 20 Figure 3 22 Setup System Dialog Screen 2 3 Winding ...
Страница 108: ...IPScom 3 3 21 Figure 3 23 Setup System Dialog Screen 4 Winding ...
Страница 112: ...IPScom 3 3 25 Figure 3 29 I O Map Screen 4 Winding ...
Страница 114: ...IPScom 3 3 27 Figure 3 31 Display All Setpoints Screen 4 Winding ...
Страница 119: ...M 3311A Instruction Book 3 32 Figure 3 38 View Sequence of Events Recorder Screen ...
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Страница 150: ...4 23 System Setup and Setpoints 4 Figure 4 14 Setup Sequence of Events Recorder Dialog Screen ...
Страница 163: ...4 36 M 3311A Instruction Book Figure 4 15 IPScom Relay Setup System Dialog Screen 2 3 Winding ...
Страница 164: ...4 37 System Setup and Setpoints 4 Figure 4 16 IPScom Relay Setup System Dialog Screen 4 Winding ...
Страница 166: ...4 39 System Setup and Setpoints 4 Figure 4 18 IPScom Selection Screen for Input Settings ...
Страница 179: ...4 52 M 3311A Instruction Book Figure 4 28 Example of V Hz Capability and Protection Curves ...
Страница 187: ...4 60 M 3311A Instruction Book Figure 4 33 49 Function Overload Curves ...
Страница 229: ...4 102 M 3311A Instruction Book Table 4 5 Transformer Connections ...
Страница 231: ...4 104 M 3311A Instruction Book Table 4 7 Custom Transformer and CT Configuration ...
Страница 233: ...4 106 M 3311A Instruction Book CONNECTION EXAMPLES Figure 4 72 Typical Transformer Differential Application ...
Страница 234: ...4 107 System Setup and Setpoints 4 AUXILIARY TRANSFORMER EXAMPLE Figure 4 73 Delta ac Wye Wye CT Connection Diagram ...
Страница 236: ...4 109 System Setup and Setpoints 4 GSU TRANSFORMER EXAMPLE Figure 4 75 Wye Delta ac Delta ac CT Connection Diagram ...
Страница 243: ...M 3311A Instruction Book 5 6 Figure 5 5 Mounting Dimensions for GE L 2 Cabinet H3 and H4 ...
Страница 275: ...M 3311A Instruction Book 5 38 Dip Switch J46 J60 J61 J5 J20 J21 J22 J18 Figure 5 34 M 3311A Circuit Board Standard I O ...
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Страница 389: ...M 3311A Instruction Book B 6 This Page Left Intentionally Blank ...
Страница 393: ...D 2 M 3311A Instruction Book Figure D 1 Volts Hz 24IT Inverse Curve Family 1 Inverse Square ...
Страница 394: ...Inverse Time Curves Appendix D D 3 Figure D 2 Volts Hz 24IT Inverse Family Curve 2 ...
Страница 395: ...D 4 M 3311A Instruction Book Figure D 3 Volts Hz 24IT Inverse Time Curve Family 3 ...
Страница 396: ...Inverse Time Curves Appendix D D 5 Figure D 4 Volts Hz 24IT Inverse Curve Family 4 ...
Страница 399: ...D 8 M 3311A Instruction Book Figure D 5 Definite Time Overcurrent Curve ...
Страница 400: ...Inverse Time Curves Appendix D D 9 Figure D 6 Inverse Time Overcurrent Curve ...
Страница 401: ...D 10 M 3311A Instruction Book Figure D 7 Very Inverse Time Overcurrent Curve ...
Страница 402: ...Inverse Time Curves Appendix D D 11 Figure D 8 Extremely Inverse Time Overcurrent Curve ...
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