Power Quality:
A Case Study
When
a customer
was experiencing high neutral currents, BEST was called
out to check and record temperatures on a 150kVA zig zag
type
transformer. A power quality analyzer was used to determine
harmonic amplitudes and waveform distortions. The transformer
temperature
was 249.5F with a 3rd harmonic RMS 401.6 amps. and a 9th
harmonic RMS 124.0 amps.
It
was recommended that a 3rd harmonic filter/blocker be installed
to reduce the RMS neutral current at the power
source, thus reducing
the entire systems harmonic load.
After the harmonic blocker was installed the transformer
was retested 6 days later. Temperature were reduced by
15.0 degrees
F, but most importantly the 3rd harmonic was reduced by
393.6 Amps RMS current to a total of 8 Amps RMS current.
With the
same loads we saw a reduction in the phase current by 7
to 12% with
an increase in power factor and improved current waveform.
The
installation will allow the customer to add additional
loads without up sizing the electrical system and should
see a
return on investment in less than 24 months with an increase
in transformer life.
Annual
savings due to reduction of harmonic current losses: $8,278
Annual
savings due to reduce need for heat removal: $2,030
Total
Annual Savings: $10,308 |
In
the last 20 years, there has been a marked increase in the use
of non-linear products, such as switched-mode power supplies,
uninterruptible power systems, variable frequency drives, electronic
ballasts, personal computers and copiers. These non-linear products
plague electrical systems with a condition called harmonics.