Differential And Restraint Current Calculations; Transformer Windings Between Two Breakers; Setup Method A (Preferred) - GE T60 Instruction Manual

5 SETTINGS
h) DIFFERENTIAL AND RESTRAINT CURRENT CALCULATIONS
Differential and restraint currents are calculated as follows:
where Id , Id , and Id are the phase differential currents and
A B C
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
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
"1200 A"
PHASE CT F1 PRIMARY:
PHASE CT F1 SECONDARY:
"1 A" (default value)
GROUND CT F1 PRIMARY:
GROUND CT F1 SECONDARY:
"1000 A"
PHASE CT F5 PRIMARY:
PHASE CT F5 SECONDARY:
"1 A" (default value)
GROUND CT F5 PRIMARY:
GROUND CT F5 SECONDARY:
"5000 A"
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(4)
"WDG 1X"
SOURCE 1 NAME:
"F1"
SOURCE 1 PHASE CT:
"None"
SOURCE 1 GROUND CT:
"None"
SOURCE 1 PHASE VT:
"None"
SOURCE 1 AUX VT:
GE Multilin
c c
1   2  
Id I I
= +
A A A
c c
1   2  
Id I I
= +
B B B
c c
1   2  
Id I I
= +
C C C
c c
 1   I  2    I
Ir max I
=
A A A
c c
 1   I  2    I
Ir max I
=
B B B
c c
 1   I 
Ir max I
=
C C C
SYSTEM SETUP
"5 A"
"1 A" (default value)
"5 A"
"1 A" (default value)
"5 A"
"5000 A"
"5 A"
settings menu.
T60 Transformer Protection System
c
  
I w
+ +
A total
c
  
I w
+ +
B total
c
  
I w
+ +
C total
c
    
w
A total
c
    
w
B total
c
2    I     
w
C total
Ir , Ir , and Ir are the phase restraint currents.
A B C
 
AC INPUTS CURRENT BANK
5.4 SYSTEM SETUP
(EQ 5.21)
(EQ 5.22)
(EQ 5.23)
(EQ 5.24)
(EQ 5.25)
(EQ 5.26)
settings menu.

SYSTEM SETUP SIGNAL
5-117
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