Thermistor Alarm - GE 239 Instruction Manual

CHAPTER 7: TESTING
7.9

Thermistor Alarm

239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
1. Alter the following setpoints:
S4: PROTECTION\TEMPERATURE\THERMISTOR\THERMISTOR FUNCTION: ALARM
S4: PROTECTION\TEMPERATURE\THERMISTOR\THERMISTOR HOT RESISTANCE: 20KW
S4: PROTECTION\TEMPERATURE\THERMISTOR\THERMISTOR COLD RESISTANCE:
0.1KW
2. As shown in FIGURE 7–1: SECONDARY INJECTION TEST SETUP on page 7–96, place a
variable 30 kΩ resistor across thermistor terminals 21/22.
3. With the variable resistor initially set to zero start increasing the resistance until a
thermistor alarm occurs. Verify that the ALARM LED becomes lit and a THERMISTOR
ALARM message is displayed by the 239.
4. Remove the variable resistor and measure its resistance with an ohmmeter to verify
that it agrees with the
S4: PROTECTION\TEMPERATURE\THERMISTOR\HOT
RESISTANCE setpoint.
5. Place the variable resistor back on terminals 21 and 22 and start decreasing its
resistance until the thermistor alarm disappears. This will occur when the input
resistance has decreased below the
PROTECTION\TEMPERATURE\THERMISTOR\COLD RESISTANCE
6. Once again, check by removing the variable resistor and measuring its resistance by
putting an ohmmeter across its terminals to verify that it agrees with the
PROTECTION\TEMPERATURE\THERMISTOR\COLD RESISTANCE
S4:
setpoint.
setpoint.
S4:
7–105