Rockwell Automation 20D PowerFlex 700S AC Drives with Phase II Control Reference Manual - Manual (Page 45)

Rockwell Automation Publication PFLEX-RM003E-EN-E - January 2011 45
Detailed Drive Operation Chapter 1
• During Flash mode, host stops ping, but still supports status/command
messages at a 1…5 second rate. drive will use 1 second rate. Data transfer
occurs via explicit message as fast as possible (i.e. peripheral request, host
response, peripheral request, etc.) but only between two devices.
The MUT, is based on the message type only. A standard command and Datalink
command could be transmitted from the same peripheral faster than the MUT
and still be O.K. However, two successive Datalink commands will have to be
separated by the MUT.
DriveLogix See the DriveLogix 5730 Controller User Manual, publication 20D-UM003 .
Drive Overload Theory of Operation
The following discussion assumes that the IT curve does not change with Pulse
Width Modulated (PWM) carrier frequency or drive output frequency.
A drive has three rated current values; a continuous current rating, a 1 minute
current rating, and a 3 second current rating. Typically, the 1 minute rating will be
close to 110% of the continuous rating, and the 3 second rating will be close to
150% of the continuous rating. This may vary from drive to drive to optimize the
performance of each frame size. In the following examples the one minute rating
is 110% and the three second rating is 150%.
Open Loop Current Limit
The drive can thermally allow 102.5%.
The 1 minute current rating assumes a duty cycle of 1 minute on, followed by 3
minutes at 100%. This results in an average current of 102.5%.
The 3 second current rating assumes a duty cycle of 3 seconds on, followed by 57
seconds at 100%. This results in an average current of 102.5%.
Typically the drive will have a 60 second rating of 110% of continuous current
and a 3 second rating at 150% of the continuous current. Under normal operating
conditions, the open loop function sets this current limit to the short term (3
second) rating. If the function detects an overload, it lowers the limit to the
continuous level. If the function is in the continuous level limit, this can be lower
110% x 60 sec + 100% x 180 sec
average current = ------------------------------------------- = 102.5%
150% x 3 sec + 100% x 57 sec
average current = ------------------------------------------- = 102.5%