Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 53)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 53
Drive Configuration Chapter 1
Droop Feature Droop is used to shed load and is usually used when a soft coupling of two motors
is present in an application. The master drive speed regulates and the follower
uses droop so it does not oppose the master. The input to the droop block is the
commanded motor torque. The output of the droop block reduces the speed
reference. P620 [Droop RPM at FLA] sets the amount of speed, in RPM, that
the speed reference is reduced when at full load torque. For example, when P620
[Droop RPM at FLA] is set to 50 RPM and the drive is running at 100% rated
motor torque, the droop block subtracts 50 RPM from the speed reference.
Duty Rating Applications require different amounts of overload current.
Normal Duty
Sizing the drive for Normal Duty enables the use of the highest continuous
output current rating of the drive and an overload rating of 110% for 60 seconds
(every 10 minutes) and 150% for 3 seconds (every minute).
Heavy Duty
For heavy duty applications, a drive one size larger than is required for the motor
is used in the application and therefore provides a larger amount of overload
current in comparison to the motor rating. Heavy Duty sizing provides at least
150% for 60 seconds (every 10 minutes) and 180% for 3 seconds (every minute).
Light Duty
The light duty setting, for a given normal duty rated drive, provides a higher
continuous output current but with limited overload capability. When in light
duty, the drive provides 110% for 60 seconds (every 10 minutes). The light duty
setting is only available on PowerFlex 755 drives, frame 8 and larger.
The overload percentages are with respect to the connected motor rating.
The duty rating is programmed in P306 [Duty Rating]. This parameter is reset to
the default setting if a Set Defaults “ALL” is executed. For drives rated under 7.5
kW (10 Hp) the normal duty and heavy duty continuous current ratings are the
same, and have the heavy duty overload settings.
When changing the [Duty Rating], review P422 [Current Limit 1] and P423
[Current Limit 2].
Refer to the PowerFlex 750-Series AC Drives Technical Data, publication 750-
TD001 , for continuous and overload current ratings for each catalog number.