GE G30 Instruction Manual page 371

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 thermal inputs
SETTINGS  SYSTEM SETUP  TRANSFORMER  THERMAL INPUTS
 THERMAL INPUTS

The thermal inputs settings are used for computation of hottest-spot winding temperature, aging factor, and accumulated
loss of life.
— Enter a source that represents the true winding load currents.
WINDING CURRENTS
In cases where two or more sets of CTs are associated to the winding and where thermal elements are to be set (for
example, in a breaker-and-a-half scheme), use a spare source for current summation from these CTs to obtain the total
true winding current. Otherwise, select the only source representing the other winding current.
— Select an RTD, DCmA, or remote RTD input if the ambient temperature is to be measured directly.
AMBIENT TEMPERATURE
Otherwise, select "Monthly Average" and enter an average temperature for each month of the year if a directly measured
device output is not available (see the monthly settings that follow).
— Select RTD, DCmA, or remote RTD input for direct measurement of top-oil temperature. If an RTD or
TOP OIL TEMPERATURE
DCmA input is not available, select "Computed."
The following menu displays when
SETTINGS  SYSTEM SETUP  TRANSFORMER  THERMAL INPUTS  AMBIENT TEMPERATURE
AMBIENT TEMPERATURE:
Monthly Average
G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
c c
Id = I [1] + I [2]
A A A
c c
Id = I [1] + I [2]
B B B
c c
Id = I [1] + I [2]
C C C
c
Ir = max (|I [1]|, |I
A A A
c
Ir = max (|I [1]|, |I
B B B
c
Ir = max (|I [1]|, |I
C C C
WINDING CURRENTS:

SRC 1
AMBIENT TEMPERATURE:

RTD Input 1
TOP-OIL TEMPERATURE:

RTD Input 1
is "Monthly Average."
AMBIENT TEMPERATURE
JANUARY AVERAGE:

–20°C
FEBRUARY AVERAGE:

–30°C
MARCH AVERAGE:

–10°C

DECEMBER AVERAGE:

–10°C
c
[2]|)
c
[2]|)
c
[2]|)
Range: SRC 1, SRC 2, SRC 3, SRC 4
(or the user-defined name)
Range: RTD Input 1, RTD Input 2,..., RTD Input 8, dcmA
Input 1, dcmA Input 2,..., dcmA Input 8, RRTD 1,
RRTD2,..., RRTD 12, Monthly Average
Range: RTD Input 1, RTD Input 2,..., RTD Input 8, dcmA
Input 1, dcmA Input 2,..., dcmA Input 8, RRTD 1, RRTD2,...,
RRTD 12, Monthly Average
Range: –60 to 60°C in steps of 1
Range: –60 to 60°C in steps of 1
Range: –60 to 60°C in steps of 1
Range: –60 to 60°C in steps of 1
SYSTEM SETUP
Eq. 5-23
Eq. 5-24
Eq. 5-25
Eq. 5-26
Eq. 5-27
Eq. 5-28
5
5-157