Rockwell Automation 1336E IMPACT Adjustable Frequency AC Drive User Manual V 1-4.XX - Manual (Page 371)

Control Block Diagrams B-33
For both the temperature tests and the current over time tests, the
internal reference Is is scaled in terms of percent rated motor current.
It is also scaled to the inverter. For these conversions, Nameplate
Amps (parameter 4) and Inverter Amps (parameter 11) are also used.
Understanding the NTC Foldback Protection
The NTC foldback protection test measures for excessive
temperatures within the device. To do this:
1. The value of I
s
, which has been converted to inverter units, is
multiplied by 30
°C.
2. This value represents a temperature rise that is added to the actual
inverter heatsink temperature.
3. From the result of this sum, 120
°C is subtracted.
4. The result is an error value that is integrated and limited.
If NTC foldback predicts that the temperature within the device has
exceeded 120
°C, then the motor current is limited (causing a foldback
condition).
If the motor current has been limited in the positive direction due to
excessive temperature, bit 1 is set in Torque Limit Sts (parameter 87).
Bit 9 indicates a current limit in the negative direction due to
excessive inverter temperature.
Understanding the IT Inverter Protection
The IT inverter protection test measures for excessive current over
time. To do this for most drives, the test uses both 100% and 150%
times the rated inverter current in motor per unit. (For the 460/800 HP
H-frame drives, the test uses 100% and 135%.) If the current stays at
or above 150% times the rated inverter current for 60 seconds, the test
limits the current to 100% times the rated inverter current. When a
drive limits the current, either bit 2 (positive values) or bit 10
(negative values) in Torque Limit Sts (parameter 87) is set.
You can also decide if you want to be notified when the drive limits
the current.
The following is the inverter overload curve for frames A – G This
inverter overload curve also applies to the frame H, with the exception
of the 460V/800 HP.
file: Monitor
group: Drive/Inv Status
To: You need to:
Receive a fault Set bit 13 in Fault Select 2 (parameter 22).
Receive a warning
Set bit 13 in Warning Select 2 (parameter 23) and clear
bit 13 in Fault Select 2.
Ignore the limit condition Clear bit 13 in both Fault Select 2 and Warning Select 2.