Rockwell Automation 20A PowerFlex 70 Adjustable Frequency AC Drive - Manual (Page 7)

Rockwell Automation Publication 20A-IN009D-EN-P - June 2013 7
PowerFlex 70 Adjustable Frequency AC Drive
Output Contactor Precaution
ATTENTION: The “adjust freq” portion of the bus regulator function is
extremely useful for preventing nuisance overvoltage faults resulting from
aggressive decelerations, overhauling loads, and eccentric loads. It forces the
output frequency to be greater than commanded frequency while the drive’s
bus voltage is increasing towards levels that can cause a fault; however, it can
also cause either of the following two conditions to occur.
• Fast positive changes in input voltage (more than a 10% increase within 6
minutes) can cause uncommanded positive speed changes; however an F25
“OverSpeed Limit” fault occurs if the speed reaches P82 [Max Speed] + P83
[Overspeed Limit]. If this condition is unacceptable. Take action to 1) limit
supply voltages within the specification of the drive and, 2) limit fast positive
input voltage changes to less than 10%. Without taking such actions, if this
operation is unacceptable, the “adjust freq” portion of the bus regulator
function must be disabled (see parameters 161 [Bus Reg Mode A] and 162 [Bus
Reg Mode B]).
• Actual deceleration times can be longer than commanded deceleration times;
however, a “Decel Inhibit” fault is generated if the drive stops decelerating
altogether. If this condition is unacceptable, the “adjust freq” portion of the bus
regulator must be disabled (see parameters 161 [Bus Reg Mode A] and 162
[Bus Reg Mode B]). In addition, installing a properly sized dynamic brake
resistor provides equal or better performance in most cases.
Note: These faults are not instantaneous and have shown test results that take
between 2 and 12 seconds to occur.
ATTENTION: To guard against drive damage when using output contactors, the
following information must be read and understood. One or more output
contactors can be installed between the drive and motor(s) for the purpose of
disconnecting or isolating certain motors/loads. If a contactor is opened while
the drive is operating, power is removed from the respective motor, but the drive
continues to produce voltage at the output terminals. In addition, reconnecting
a motor to an active drive (by closing the contactor) could produce excessive
current that can cause the drive to fault. If any of these conditions are
determined to be undesirable or unsafe, wire an auxiliary contact on the output
contactor to a drive digital input that is programmed as “Enable.” This causes the
drive to execute a coast-to-stop (cease output) whenever an output contactor is
opened.