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GE Multilin
T60 Transformer Protection System
5-113
5 SETTINGS
5.4 SYSTEM SETUP
5
The T60 automatically corrects for CT mismatch errors. All currents are magnitude compensated to be in units of the CTs of
one winding before the calculation of differential and restraint quantities.
The reference winding (
w
ref
) is the winding to which all currents are referred. This means that the differential and restraint
currents will be in per unit of nominal of the CTs on the reference winding. This is important to know, because the settings of
the operate characteristic of the percent differential element (pickup, breakpoints 1 and 2) are entered in terms of the same
per unit of nominal.
The reference winding is chosen by the relay to be the winding which has the smallest margin of CT primary current with
respect to winding rated current, meaning that the CTs on the reference winding will most likely begin to saturate before
those on other windings with heavy through currents. The characteristics of the reference winding CTs determine how the
percent differential element operate characteristic should be set.
The T60 determines the reference winding as follows:
1.
Calculate the rated current (
I
rated
) for each winding:
(EQ 5.9)
Note: enter the self-cooled MVA rating for the
P
rated
setting.
2.
Calculate the CT margin (
I
margin
) for each winding:
(EQ 5.10)
3.
Choose the winding with the lowest CT margin:
In our example, the reference winding is chosen as follows.
1.
Calculate the rated current for windings 1 and 2:
,
(EQ 5.11)
2.
With these rated currents, calculate the CT margin for windings 1 and 2:
,
(EQ 5.12)
3.
Since
, the reference winding
w
ref
is winding 2.
The reference winding is shown in
ACTUAL VALUES
METERING
TRANSFORMER
DIFFERENTIAL AND RESTRAINT
REFERENCE WINDING
.
The unit for calculation of the differential and restraint currents and base for the differential restraint settings is the CT pri-
mary associated with the reference winding. In this example, the unit CT is 1500:5 on winding 2.
Magnitude compensation factors (
M
) are the scaling values by which each winding current is multiplied to refer it to the ref-
erence winding. The T60 calculates magnitude compensation factors for each winding as follows:
(EQ 5.13)
In our example, the magnitude compensation factors are calculated as follows:
(EQ 5.14)
(EQ 5.15)
The maximum allowed magnitude compensation factor (and hence the maximum allowed CT ratio mismatch) is 32.
I
rated
w
[ ]
P
rated
w
[ ]
3
V
nom
w
[ ]
×
-------------------------------------
=
, where
w
1 2
…
w
total
, ,
=
I
margin
CT primary
w
[ ]
I
rated
w
[ ]
---------------------------------------
, where
w
1 2
…
w
total
, ,
=
=
I
rated
1
[ ]
P
rated
1
[ ]
3
V
nom
1
[ ]
×
------------------------------------
100 MVA
3 220 kV
×
--------------------------------
262.4 A
=
=
=
I
rated
2
[ ]
P
rated
2
[ ]
3
V
nom
2
[ ]
×
------------------------------------
100 MVA
3 69 kV
×
-----------------------------
836.7 A
=
=
=
I
margin
1
[ ]
CT primary 1
[ ]
I
rated
1
[ ]
--------------------------------------
500 A
262.4 A
---------------------
1.91
=
=
=
I
margin
2
[ ]
CT primary 2
[ ]
I
rated
2
[ ]
--------------------------------------
1500 A
836.7 A
---------------------
1.79
=
=
=
I
margin
2
[ ]
I
margin
1
[ ]
<
M w
[ ]
I
primary
w
[ ]
V
nom
w
[ ]
×
I
primary
w
ref
[
]
V
nom
w
ref
[
]
×
----------------------------------------------------------------------
, where
w
1 2
…
w
total
, ,
=
=
M
1
[ ]
I
primary
1
[ ]
V
nom
1
[ ]
×
I
primary
2
[ ]
V
nom
2
[ ]
×
--------------------------------------------------------
500 A 220 kV
×
1500 A 69 kV
×
-----------------------------------------
1.0628
=
=
=
M
2
[ ]
I
primary
2
[ ]
V
nom
2
[ ]
×
I
primary
2
[ ]
V
nom
2
[ ]
×
--------------------------------------------------------
1500 A 69 kV
×
1500 A 69 kV
×
-----------------------------------------
1.0000
=
=
=
Summary of Contents for T60
Page 6: ...vi T60 Transformer Protection System GE Multilin TABLE OF CONTENTS ...
Page 14: ...xiv T60 Transformer Protection System GE Multilin TABLE OF CONTENTS ...
Page 34: ...1 20 T60 Transformer Protection System GE Multilin 1 5 USING THE RELAY 1 GETTING STARTED 1 ...
Page 490: ...5 344 T60 Transformer Protection System GE Multilin 5 10 TESTING 5 SETTINGS 5 ...
Page 522: ...6 32 T60 Transformer Protection System GE Multilin 6 5 PRODUCT INFORMATION 6 ACTUAL VALUES 6 ...
Page 536: ...7 14 T60 Transformer Protection System GE Multilin 7 1 COMMANDS 7 COMMANDS AND TARGETS 7 ...
Page 568: ...10 12 T60 Transformer Protection System GE Multilin 10 6 DISPOSAL 10 MAINTENANCE 10 ...
Page 596: ...A 28 T60 Transformer Protection System GE Multilin A 1 PARAMETER LISTS APPENDIX A A ...
Page 716: ...B 120 T60 Transformer Protection System GE Multilin B 4 MEMORY MAPPING APPENDIX B B ...
Page 762: ...E 10 T60 Transformer Protection System GE Multilin E 1 IEC 60870 5 104 PROTOCOL APPENDIX E E ...
Page 774: ...F 12 T60 Transformer Protection System GE Multilin F 2 DNP POINT LISTS APPENDIX F F ...