GE T35 UR Series, Инструкция по эксплуатации

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5-94 T35 Transformer Protection System GE Multilin
5.4 SYSTEM SETUP 5 SETTINGS
5
The T35 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 T35 determines the reference winding as follows:
1. Calculate the rated current ( I
rated
) for each winding:
(EQ 5.8)
Note: enter the self-cooled MVA rating for the P
rated
setting.
2. Calculate the CT margin ( I
margin
) for each winding:
(EQ 5.9)
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 5.10)
2. With these rated currents, calculate the CT margin for windings 1 and 2:
, (EQ 5.11)
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 T35 calculates magnitude compensation factors for each winding as follows:
(EQ 5.12)
In our example, the magnitude compensation factors are calculated as follows:
(EQ 5.13)
(EQ 5.14)
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
= = =