Unidrive Regen Installation Guide
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Issue Number: 2
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Sizing of a Regen system
Refer to Appendix E Unidrive Regen specifications on page 44, for the specifications of the Unidrive Regen.
The sizing of a Regen system must take into account the following factors:
•
Line voltage
•
Motor rated current, rated voltage and power factor
•
Maximum load power and overload conditions
In general, when designing a Regen system, equal Regen and motoring drive rated currents will work correctly. However, care must be taken to
ensure that under worst case supply conditions the Regen drive is able to supply or absorb all the required power. In multi-drive configurations, the
Regen drive must be of a sufficient size to supply the net peak power demanded by the combined load of all the motoring drives and the drive losses.
If the Regen drive is unable to supply the full power required by the motoring drive, the DC bus voltage will drop and in severe cases may lose
synchronisation with the mains and trip. If the Regen drive is unable to regenerate the full power from the motoring drive into the DC bus, then the
Regen/motoring drive will trip on over-voltage.
The following are two examples of how the required ratings of a Regen drive can be calculated.
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The Regen drive’s current limits are set at 150% and are not adjustable.
In the case of a 25A, UNI2403 operating in Regen mode from a 400V supply, and a UNI2403 driving a 400V rated, 0.85 pf motor:
The rated power of the Regen drive is
=
√
3 x Rated current x Supply voltage
= 1.73 x 25 x 400
= 17.3kW
The motoring drive can supply power
=
√
3 x Rated current x Motor voltage x Power factor
= 1.73 x 25 x 400 x 0.85
= 14.7kW
When the motoring drive is supplying rated current to the motor, the Regen drive only needs to provide 14.7kW, plus drive losses. The Regen drive
can supply 17.3kW at rated current, which is ample, in this case.
Conversely, in some cases, a Regen drive of the same rating as the motoring drive, may not be able to supply enough power, as the following
example shows:
Example
In the case of a 156A, UNI4403 operating in Regen mode, and a UNI4403 driving a 75kW, 400V, 0.95pf motor:
If the motoring drive is supplying 175% maximum current and the Regen drive has its 380V supply at the lower limits of -10% (342Vac), then, at the
Regen current limit of 150%:
The Regen drive max. available power is
=
√
3 x 150% x Rated current x Supply voltage
= 1.73 x 1.5 x 156 x 342
= 138.6kW
The motoring drive max. power is
=
√
3 x 175% x Rated current x Motor voltage x Power factor
= 1.73 x 1.75 x 156 x 400 x 0.95
= 179.7kW
The Regen drive is also required to supply the Regen and motoring drive losses. However, this Regen drive is only capable of supplying
approximately 138.6kW and therefore a drive of a larger current rating is required.
Due to the effects of increased DC bus capacitance, there is a limit to the number of motoring drives that can be supplied from a Regen drive. This is
true irrespective of the balance of power between the motoring drives and the Regen drive.
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If the system consists of one Regen Unidrive and more than three motoring drives, Control Techniques Technical Support MUST be consulted about
the design of the system.
NOTE
NOTE
