Ambient Temperature Input - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

10 COMMISSIONING
For the 1 × CT current, the zero-sequence value is 1/3 of 1.0 × CT or 0.333 × CT A. The value for I
fore (1.0 – 0.333) × CT = 0.6667 × CT A. This value must be divided by the CT error correction factor of 0.797
as described above.
Therefore, the value of differential current for phase A, when injecting 1 × CT in Winding 2 only, is:
0.667
I =
---------------------------------- -
( )
A differential
0.797
The action of removing the zero-sequence current results in a current equal to the zero-sequence value intro-
duced into phases B and C. Hence, the differential current for these two elements is:
I = I
( ) (
B differential C differential
Now, applying 1 × CT into phase A Winding 1 and the same current into phase A Winding 2, but 180° out-of-
phase to properly represent CT connections, the total differential current in the A-phase element will be (0.57 –
0.84) × CT = –0.26 × CT. The injection of currents into phase A of Windings 1 and 2 in this manner introduces
a differential current of (–0.57 × CT + 0.42 × CT) = –0.15 × CT into phase B and (0.0 × CT + 0.42 × CT) = 0.42
× CT into phase C.
a) BASIC CALIBRATION OF RTD INPUT
1. Enable ambient temperature sensing through the following setpoint:
SETPOINTS/S2 SYSTEM SETUP/AMBIENT TEMP/ AMBIENT TEMPERATURE SENSING
2. Connect a thermocouple to the relay terminals B10,11,12 and read through actual value:
ACTUAL VALUES/A2 METERING/AMBIENT TEMP/AMBIENT TEMPERATURE
3. Compare the displayed value of temperature against known temperature at the location of the sensor. Use
a thermometer or other means of obtaining actual temperature.
An alternative approach is to perform a more detailed calibration per the procedure outlined below.
b) DETAILED CALIBRATION OF RTD INPUT
1. Alter the following setpoints as shown:
SETPOINT S2: SYSTEM SETUP/AMBIENT TEMP/AMBIENT TEMPERATURE SENSING: Enabled
SETPOINT S2: SYSTEM SETUP/AMBIENT TEMP/AMBIENT RTD TYPE/(select desired type)
2. The measured values should be ±2°C or ±4°F. Alter the resistance applied to the RTD input (note the 3-
input connection must be used for the measurements to be valid) as per the typical table below to simulate
RTDs and verify accuracy of the measured values. View the measured values in:
ACTUAL VALUES A2/METERING/AMBIENT TEMP .
GE Power Management
10.5 DISPLAY, METERING, COMMUNICATIONS, ANALOG OUTPUTS
×
CT A
×
= 0.84 CT A
×
0.333 CT A
= =
---------------------------------- -
)
0.797
745 Transformer Management Relay
×
0.84 CT A

10.5.5 AMBIENT TEMPERATURE INPUT

is there-
W2a'
10
10-11