GE T35 Instruction Manual page 216

5.4 SYSTEM SETUP
h) DIFFERENTIAL AND RESTRAINT CURRENT CALCULATIONS
Differential and restraint currents are calculated as follows:
where Id , Id , and Id
A B
i) TRANSFORMER WINDINGS BETWEEN TWO BREAKERS
When the relay is to protect a transformer with windings connected between two breakers, such as in a ring bus or breaker-
and-a-half station configuration, one of the methods for configuring currents into the relay presented below should be used
(see the Breaker-and-a-Half Scheme diagram in the Overview section of this chapter).
For this example it is assumed that winding 1 is connected between two breakers and winding 2 is connected to a single
breaker. The CTs associated with winding 1 are CTX, at 1200/5 A and CTY, at 1000/5 A. CTX is connected to current input
channels 1 through 3 inclusive and CTY is connected to current input channels 5 through 7 inclusive on a type 8H CT/VT
5
module in relay slot "F." The CT2 on winding 2 is 5000/5 A and is connected to current input channels 1 through 4 inclusive
on a type 8F CT/VT module in relay slot "M".
SETUP METHOD A (PREFERRED)
This approach is preferred because it provides increased sensitivity as the current from each individual set of CTs partici-
pates directly in the calculation of CT ratio mismatch, phase compensation, zero-sequence removal (if required) and the
differential restraint current. The concept used in this approach is to consider that each set of CTs connected to winding 1
represents a connection to an individual winding. For our example we consider the two-winding transformer to be a three-
winding transformer.
1. Enter the settings for each set of CTs in the
PHASE CT F1 PRIMARY:
PHASE CT F1 SECONDARY:
GROUND CT F1 PRIMARY:
GROUND CT F1 SECONDARY:
PHASE CT F5 PRIMARY:
PHASE CT F5 SECONDARY:
GROUND CT F5 PRIMARY:
GROUND CT F5 SECONDARY:
PHASE CT M1 PRIMARY:
PHASE CT M1 SECONDARY:
GROUND CT M5 PRIMARY:
GROUND CT M5 SECONDARY:
2. Configure source n (source 1 for this example) as the current from CTX in Winding 1 in the

SOURCES SOURCE 1(6)
"WDG 1X"
SOURCE 1 NAME:
SOURCE 1 PHASE CT:
SOURCE 1 GROUND CT:
SOURCE 1 PHASE VT:
SOURCE 1 AUX VT:
5-82
c
1  
Id I
= +
A A
c
1  
Id I
= +
B B
c
1  
Id I
= +
C C
c
 1   I
Ir max I
=
A A
c
 1   I
Ir max I
=
B B
c
 1   I
Ir max I
=
C C
are the phase differential currents and
C
SYSTEM SETUP
"1200 A"
"5 A"
"1 A" (default value)
"1 A" (default value)
"1000 A"
"5 A"
"1 A" (default value)
"1 A" (default value)
"5000 A"
"5 A"
"5000 A"
"5 A"
settings menu.
"F1"
"None"
"None"
"None"
T35 Transformer Protection System
c c
2     
I I w
+ +
A A total
c c
2     
I I w
+ +
B B total
c c
2     
I I w
+ +
C C total
c c
 2    I     
w
A A total
c c
 2    I     
w
B B total
c c
 2    I     
w
C C total
Ir , Ir , and Ir
A B
 
AC INPUTS CURRENT BANK
5 SETTINGS
are the phase restraint currents.
C
settings menu.

SYSTEM SETUP
(EQ 5.20)
(EQ 5.21)
(EQ 5.22)
(EQ 5.23)
(EQ 5.24)
(EQ 5.25)
SIGNAL
GE Multilin