4-4 1000 Series / Guide to Installation, Troubleshooting, and Maintenance
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Attention
High voltage may be present even when all electrical power supplies are
disconnected. After switching off electrical power, wait at least 15 minutes
for bus circuit capacitors to discharge before working on the drive or
associated equipment. Use an appropriate voltmeter to further verify that
capacitors are discharged before beginning work. Do not rely exclusively on
the bus voltage indicator. Dangerous voltage levels may remain even when
the indicator is off.
4.5.1
Power Source Conditioning
The use of an AC line reactor and/or isolation transformer is recommended under certain
circumstances. The drive is designed for direct connection to AC lines of the correct
voltage and impedance. Use the guidelines that follow to determine whether an isolation
transformer or line reactor is required. Refer to Table 4-13 for isolation transformer
sizing specifications and to Table 4-14 through Table 4-16 for line reactor sizing
specifications for three-phase connections. When using a single-phase input, select a line
reactor based upon the input current requirements of the 1110 drive as specified in Table
4-12. You may purchase isolation transformers and line reactors directly from Unico.
Contact the factory for more information.
Impedance mismatch
Input lines must have a minimum impedance of 1% relative to the rated input kVA of the
drive (assume the drive’s horsepower rating is approximately equal to its kVA rating). If
the line has a lower impedance, a line reactor or isolation transformer must be added
ahead of the drive to increase line impedance. If line impedance is too low, transient
voltage spikes or interruptions can create excessive current spikes that may cause
nuisance input fuse blowing and may damage the drive. Generally, if the kVA capacity of
the AC line is greater than four times the rated power of the motor (in horsepower), an
isolation transformer or AC line reactor should be used.
No neutral or referenced phase
If the AC input power system does not have a neutral or one phase referenced to ground,
an isolation transformer with the neutral of the secondary grounded is highly
recommended. If the line-to-ground voltages on any phase exceed 125% of the nominal
line-to-line voltage, an isolation transformer with the neutral of the secondary grounded
is always required.
Transient power interruptions or voltage spikes
If the AC line frequency experiences transient power interruptions or significant voltage
spikes, an isolation transformer or AC line reactor must be installed. The drive can be
damaged by extreme voltage and current spikes.
Power factor correction capacitors
If the AC line supplying the drive has power factor correction capacitors that are
switched in and out, an isolation transformer or AC line reactor must be installed between
the drive and the capacitors. The drive can be damaged by the extreme voltage and
current spikes caused by capacitor switching. If the capacitors are permanently connected
and not switched, the guideline for impedance mismatch applies.
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