TOSHIBA- 7
TX Series 48 - 1250A
Run Mode overload protection is initiated when the TX Series determines
that the motor is At-Speed. Overload Protection is initiated when the motor
RMS current rises above a “pick-up point” (as determined by the motor
nameplate FLA and service factor). Run mode protection is provided by the
CPU monitoring the Dynamic Thermal Register. Data for the Dynamic
Thermal Register is accumulated from I
2
t calculations and cooling rates. A
trip occurs when the register reaches 100% as determined by the selected
Overload Protection Curve (NEMA Class 5-30 standard curves) and is based
on the programmed Locked Rotor Current indicated on the motor nameplate.
The Dynamic Thermal Register is altered, or “biased”, by the following condi-
tions:
· Current Imbalance: will bias the register higher to add protection from
additional motor heating during a current imbalance condition.
· Normal Cooling: provided when the motor current drops below the pick-up
point or the motor is off line. The cooling rate is lower for motors that are off-
line (such as after a trip) since cooling fans are also inoperative.
· RTD Input: (requires the optional RTD monitor card): will bias the register in
either direction based on real-time input of the motor, bearing and even
ambient temperature conditions.
· Dynamic Reset is another feature that adds reliability and consistency to the
performance of the TX Series soft starter. If a motor overload condition
occurs and the soft starter trips, it cannot be reset until sufficient cool down
time has elapsed. This cool down time is determined by the thermal state of
the motor when it tripped (i.e. hot motors cool more quickly due to additional
convection). The cool down time is also biased by RTD measurements when
used.
Retentive Thermal Memory provides continuous overload protection and real
time reset even if power is lost. Upon restoration of power, the TX Series will
read the Real Time Clock and restore the thermal register to what it should be
given the elapsed time.
· Learned Reset Capacity is a feature that is unique to the TX Series. By
sampling the amount of thermal capacity used in the previous three successful
starts, the TX Series will not allow a reset until a sufficient amount of
thermal capacity has been regained in the motor. This prevents nuisance
tripping and insures that unsuccessful start attempts (which would otherwise
use up the starts-per-hour capacity of the motor) are not allowed.
