GE 745 Instruction Manual page 251

CHAPTER 7: COMMISSIONING
7.4.5 Ambient Temperature Input
7.4.5.1 Basic Calibration of RTD Input
7.4.5.2 Detailed Calibration of RTD Input
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Now, applying 1 × CT into Winding 1 Phase A 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 Phase A 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.
 Enable ambient temperature sensing with the
AMBIENT TEMP
 Connect a thermocouple to the relay terminals B10, B11, and B12 and
read through the
TEMPERATURE
 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.
1. Alter the following setpoints. Set
TEMPERATURE SENSING
AMBIENT RTD TYPE to the desired type.
The measured values should be ±2°C or ±4°F.
2. 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.
3. View the measured values in
TEMPERATURE.
Refer to RTD tables included in this manual for calibration of resistance versus
temperature.
Table 7–1: Measured RTD temperature
Ω
RTD type 100 Platinum
resistance
100 Ω Platinum 80.31
100.00
119.39
138.50
157.32
175.84
194.08
AMBIENT TEMPERATURE SENSING

A2 METERING

actual value.
S2 SYSTEM SETUP
to Enabled and set
S2 SYSTEM SETUP
A2 METERING AMBIENT TEMP

Expected RTD reading
°C °F
–50 –58
0 32
50 122
100 212
150 302
200 392
250 482
METERING
S2 SYSTEM SETUP
setpoint.
AMBIENT TEMP AMBIENT

AMBIENT TEMP AMBIENT
 
AMBIENT TEMP

AMBIENT

Measured RTD temperature
____°C ____°F (select one)


7–13