Rockwell Automation 1519 MV DRIVE HARMONIC FILTER PF CORRECTION UNIT - Manual (Page 6)


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1-2 Introduction
Theory of Operation (cont.) These harmonic currents can result in distortion of the voltage waveform. In
rare instances, excessive voltage distortion on the power system can have ill
effects on the system. These effects can include overheating of motors or
transformers, capacitor failure, misoperation of relays, computer system
disruption, and telephone system interference.
The purpose of a harmonic filter is to shunt certain harmonic currents that are
produced by the rectifier away from the power system. The result is a
reduction in distortion of the voltage waveform on the power system and a
reduction in the likelihood of harmonics affecting plant or utility system
components.
Application Considerations Switching with Drive Input Contactor versus Dedicated Harmonic Filter
Contactor
To simplify the system and reduce capital cost, a harmonic filter can be
switched using the same contactor or breaker that feeds the input power to the
associated drive. In this configuration, the harmonic filter is energized as long
as the drive input contactor is closed. The input contactor is usually configured
to close when the Emergency Stop string is completed. The contactor would
then stay closed regardless of whether the drive is running or stopped.
If the system is configured as described above, the user should consider
whether the leading kilovolt-ampere rating (kvar) provided by the filter when
the drive is not running (and thus not drawing any lagging kvar) result in an
acceptable system power factor. In this configuration it is necessary to shut
down the drive in the event of a harmonic filter fault condition since the drive
input contactor is the only means by which the filter can be taken off line. If a
harmonic filter fault were to occur and it was necessary to operate the drive
without the filter it would be necessary to physically disconnect and isolate
power cables from the harmonic filter while the drive system is shut off. It is
necessary to prevent reclosure of the drive input contactor within approximately
five minutes of opening to prevent energizing a harmonic filter capacitor
which may still have a DC charge on it.
Alternatively, a harmonic filter can be switched with a dedicated vacuum
contactor. In general, the vacuum contactor would be configured to energize
the filter when the associated drive receives a start command. The vacuum
contactor would be configured to de-energize the filter when the drive has
stopped. In this way the leading kvar from the filter is only present when the
drive is operating and power factor correction is required.
NOTE:
Re-energization of the harmonic filter should be delayed until the
filter has had adequate time to discharge – typically 5 minutes.