Abstract
Increased use of power electronic control
equipment has made it necessary to pay
greater attention to harmonic voltages
and currents in power systems.
Moreover, power electronic control
equipment tends to operate at relatively
low power factor. Since low power
factor leads to poor voltage regulation,
increased line losses and larger plant VA
rating, it is normal practice to install
shunt capacitors either on the customer
service or on the utility system.
Unfortunately, however, in
power systems containing harmonicproducing
equipment, application of
power factor-correcting capacitors may
lead to a resonance condition between
the inductive reactance of the source and
the capacitive reactance of the capacitor
bank. If the resonance frequency occurs
at or near a harmonic current produced
by the load, severe voltage distortion and
harmonic current amplification will
occur. Very often, the increase in
harmonic current is large enough to
cause nuisance fuse blowing, breaker
tripping and overheating of equipment.
The paper begins with a review of the
nature of harmonic currents and voltages
and common sources of harmonicproducing
equipment. This will be
followed by the presentation of results
generated fkom the software developed
by the authors combining the strengths
of Mathcad and Excel spreadsheet. The
output from the program are the parallel
resonant fkequencies and the resulting
voltage distortion due to hannonicproducing
loads. In addition, the
program also determines the value of the
series inductor in the harmonic filter
bank that would shift the parallel
resonant fkequency to a value less than
the lowest-order harmonic term of the
load. Also computed are the bus voltage
distortion and filter harmonic duty.
Work is in progress to extend the scope
of the software fiom traditional passive
filters to active filters.
Introduction
Passive harmonic filters have been in use
on power systems for many years. They
are simple and need very little
maintenance. Two reasons are often
cited as their drawbacks: (i) need for
numerically intensive repetitive
calculations by skilled designers (ii)
sensitivity to topology changes (quite
common in low voltage applications)
and the resulting need for fkequent
update. The goal of this paper is to
address these problems through the
development of computer software
combining the best of a popular numbercrunching
software (Mathcad) and Excel
spreadsheet. Output results generated by
the software for a sample system are
presented below. The topology and
configuration of capacitors and reactors
forming the filters is well known [ 13 and
will not be repeated here.
0-7803-43 14-w981$ io.000 1998 IEEE