GE T35 Instruction Manual page 359

CHAPTER 5: SETTINGS
5.5.4.8 Differential and restraint current calculations
Differential and restraint currents are calculated as follows:
where
Id , Id , and Id are the phase differential currents
A B C
Ir , Ir , and Ir are the phase restraint currents
A B c
5.5.4.9 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 as follows
should be used (see the Breaker-and-a-Half Scheme diagram in the Overview section of this chapter).
For this example, 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
participates 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, 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: "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
SOURCES  SOURCE 1(6)
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"
T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
c c
Id = I [1] + I [2] + ... + I
A A A
c c
Id = I [1] + I [2] + ... + I
B B B
c c
Id = I [1] + I [2] + ... + I
C C C
c c
Ir = max (|I [1]|, |I [2]|, ... , I
A A A
c c
Ir = max (|I [1]|, |I [2]|, ... , I
B B B
c c
Ir = max (|I [1]|, |I [2]|, ... , I
C C C
SYSTEM SETUP  AC INPUTS  CURRENT BANK
settings menu.
c
[w ]
A total
c
[w ]
B total
c
[w ]
C total
c
[w ])
A total
c
[w ])
B total
c
[w ])
C total
settings menu.
SYSTEM SETUP
Eq. 5-24
Eq. 5-25
Eq. 5-26
Eq. 5-27
Eq. 5-28
Eq. 5-29
SYSTEM SETUP  SIGNAL
5-157
5