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6 Power Quality - a guide

6 Power Quality - a guide

6.1

Basic Information

The measurement methodology is mostly imposed by the energy quality standards, mainly IEC

61000-4-30.  This standard, introducing precise measurement algorithms, ordered analyzers mar-
ket, allowing customers to easily compare the devices and their results between the analyzers from
different manufacturers. Previously, these devices used different algorithms, and often the results
from measurements  on the same  object  were  completely  different when  tested  with  different  de-
vices.

The factors behind growing interest in these issues have included wide use of electronic power

controllers,  DC/DC  converters  and  switched-mode  power  supplies,  energy-saving  fluorescent
lamps, etc., that is widely understood electrical power conversion. All of these devices had a ten-
dency to significantly deform the supply current waveform.
The design of switched-mode power supplies (widely used in household and industrial applications)
is often based on the principle that the mains alternating voltage is first rectified and smoothed with
the  use  of  capacitors,  meaning  that  it  is  converted  to  direct  voltage  (DC),  and  then  with  a  high
frequency and efficiency is converted to required output voltage. Such a solution, however, has an
undesirable side effect. Smoothing capacitors are recharged by short current pulses at moments
when  the  mains  voltage  is  close  to  peak  value.    From  power  balance  rule  it  is  known  that  if  the
current is taken only at short intervals, its crest value must be much higher than in case it is taken
in a continuous manner.  High ratio of current crest value to RMS value (a so-called crest factor)
and reduction of power factor (PF) will result in a situation in which in order to obtain a given active
power in a receiver (in watts), the power supplier must supply power greater than the receiver active
power (this is a so-called apparent power expressed in volt-amperes, VA).  Low power factor causes
higher load on the transmission cables and higher costs of electricity transfer.  Harmonic current
components accompanying such parameters cause additional problems.  As a result, the electricity
suppliers  have  started  to  impose  financial  penalties  upon  the  customers  who  have  not  provided
sufficiently high power factor.

Among entities that may be potentially interested in power quality analyzers are power utility

companies on one hand, (they may use them to control their customers), and on the other hand the
power consumers who may use the analyzers to detect and possibly improve the low power factor
and solve other problems related to widely understood power quality issues.

The power source quality parameters, as well as the properties of receivers, are described with

many various magnitudes and indicators. This section can shed some light on this area.

As already mentioned, the lack of standardization of measurement methods has caused signif-

icant differences in values of individual mains parameters calculated with various devices. Efforts
of many engineers resulted in IEC 61000-4-30 standard concerning power quality. For the first time,
this standard (and related standards) provided very precise methods, mathematical relations and
required measurement accuracy for power quality analyzers. Compliance with the standard (in par-
ticular, the class A) should be a guarantee of repeatable and almost identical measurement results
of the same magnitudes measured with devices from different manufacturers.