p-4 Overview
!
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 would otherwise cause a fault.
However, it can also cause either of the following two conditions
to occur.
1. Fast positive changes in input voltage can cause
uncommanded positive speed changes.
A.PowerFlex 700H An “OverSpeed Limit” fault will occur if
the speed reaches [Max Speed] + [Overspeed Limit]. If this
condition is unacceptable, action should be taken 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 and 162).
B.PowerFlex 700S An “Abs Overspd Det” fault will occur if
the speed reaches [Rev Speed Limit] - [Overspeed Limit] or
[Fwd Speed Limit] + [Abs Overspd Lim]. If this condition is
unacceptable, action should be taken to 1) limit supply
voltages within the specification of the drive and, 2) limit fast
positive input voltage changes. Without taking such actions,
if this operation is unacceptable, disable the bus regulator by
setting parameter 414 [Brake/Bus Cnfg], bit 2 (Bus Reg En)
to zero (0).
2. Actual deceleration times can be longer than commanded
deceleration times.
A.PowerFlex 700H 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 and 162). The “Decel
Inhibit” fault can be disabled by setting parameter 238 [Fault
Config 1] bit 6 (Decel Inhibit) to zero (0).
B.PowerFlex 700S A “Vref Decel Fail” fault is generated if the
drive stops decelerating altogether. If this operation is
unacceptable, disable the bus regulator by setting parameter
414 [Brake/Bus Cnfg], bit 2 (Bus Reg En) to zero (0). This
fault cannot be disabled in the PowerFlex 700S.
Note: For both drives, installing a properly sized dynamic
brake resistor or external dynamic brake will provide equal or
better performance in most cases.
Important: These faults are not instantaneous. Test results
show they can take 2-12 seconds to occur.
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