GE Multilin T60 Transformer Protection System 5-117
5 SETTINGS 5.4 SYSTEM SETUP
5
h) DIFFERENTIAL AND RESTRAINT CURRENT CALCULATIONS
Differential and restraint currents are calculated as follows:
(EQ 5.21)
(EQ 5.22)
(EQ 5.23)
(EQ 5.24)
(EQ 5.25)
(EQ 5.26)
where , , and are the phase differential currents and , , and are the phase restraint currents.
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
SYSTEM SETUP AC INPUTS CURRENT BANK settings menu.
PHASE CT F1 PRIMARY: “1200 A”
PHASE CT F1 SECONDARY: “5 A”
GROUND CT F1 PRIMARY: “1 A” (default value)
GROUND CT F1 SECONDARY: “1 A” (default value)
PHASE CT F5 PRIMARY: “1000 A”
PHASE CT F5 SECONDARY: “5 A”
GROUND CT F5 PRIMARY: “1 A” (default value)
GROUND CT F5 SECONDARY: “1 A” (default value)
PHASE CT M1 PRIMARY: “5000 A”
PHASE CT M1 SECONDARY: “5 A”
GROUND CT M5 PRIMARY: “5000 A”
GROUND CT M5 SECONDARY: “5 A”
2. Configure source n (source 1 for this example) as the current from CTX in Winding 1 in the
SYSTEM SETUP SIGNAL
SOURCES
SOURCE 1(4) settings menu.
SOURCE 1 NAME: “WDG 1X”
SOURCE 1 PHASE CT: “F1”
SOURCE 1 GROUND CT: “None”
SOURCE 1 PHASE VT: “None”
SOURCE 1 AUX VT: “None”
Id
A
I
A
c
1 I
A
c
2 I
A
c
w
total
+++=
Id
B
I
B
c
1 I
B
c
2 I
B
c
w
total
+++=
Id
C
I
C
c
1 I
C
c
2 I
C
c
w
total
+++=
Ir
A
max I
A
c
1 I
A
c
2I
A
c
w
total
=
Ir
B
max I
B
c
1 I
B
c
2I
B
c
w
total
=
Ir
C
max I
C
c
1 I
C
c
2I
C
c
w
total
=
To Next Page
Loading...
Need help?
General
