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CHAPTER 6: SETPOINTS
Thermal protection
setpoints
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 17: Thermal Protection Cooling Following a Trip at t = 0
THERMAL PROTECTION RESET
Thermal Protection operation is a serious event, and it consequently results in a lockout
that cannot be reset until the motor has cooled, unless an Emergency Restart or a Lockout
Reset is used. An Emergency Restart will reset the motor Thermal Capacity Used from its
current value to 0% so that a hot motor may be restarted. Note that a Lockout Reset does
not reset the Thermal Capacity Used register; if the motor is re-started it may re-trip
quickly. Should process interruption concerns overweigh the probable damage to the
motor that early starting would create, an Emergency Restart can be issued.
A setpoint AUTO RESET TCU≤15% is available to control whether once the motor has
cooled until the Thermal Capacity Used reaches 15% (approximately twice the Cool Time
Constant Stopped setting), the lockout is replaced with a trip that can be manually reset, or
alternatively the condition is fully reset, allowing immediate re-start.
THERMAL CAPACITY ALARM
A Thermal Capacity Alarm will occur when the Thermal Capacity rises above the
programmed THERMAL ALARM PKP level.
PATH:
SETPOINTS > S3 PROTECTION > THERMAL PROTECTION
THERMAL O/L FUNC
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
The selection of the Latched Alarm, Alarm, or Trip setting enables the Thermal Overload
function. If the operating condition is satisfied when Trip is selected as the function, the
TRIP output relay will operate, and the "TRIP" LED will be turned on. If Alarm is selected,
the "ALARM" LED will flash upon Thermal Overload operation, and will automatically
reset when the activating condition clears. If Latched Alarm is selected, the "ALARM"
LED will flash upon Thermal Overload operation, and will stay "ON" after the condition
clears, until a reset command is initiated. The TRIP output relay will not operate if the
Latched Alarm or Alarm function is selected. Any assignable output relays can be
selected to operate when the Thermal Overload Function is selected as Latched Alarm,
Alarm, or Trip.
S3 PROTECTION
6–67
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