GE 339

CHAPTER 6: SETPOINTS S3 PROTECTION
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL 6–43
TCU
used_start
: the TCU caused by an overload condition
TCU
used_end
: the TCU dictated by the hot/cold safe stall ratio when the motor is
running (=0 when the motor is stopped)
t: time in minutes
τ: Cool Time Constant (running or stopped)
I
eq
: equivalent motor heating current
O/L
_PKP
: overload pickup setting as a multiple of FLA
HCR: hot/cold safe stall ratio
Figure 6-18: 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.