24-07-2012, 11:12 AM
Power Quality in Electric Networks: Monitoring, and Standards
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Abstract :
Power Quality in electric networks is one of today's most
discussed topic in Electrical Engineering but also one of the
most problematic subject as it is only quite recently that it
became one of the main devastating problem in the supply
network. It is also considered as one of the most expensive and
wasteful parameter in the supply network.
Since the beginning of the use of electricity Power Quality has
always been one of the major points of concern for all
professionals involved in Electrical Engineering. In this paper
common practices in monitoring and standards in power quality
in electric networks are reviewed.
Introduction
What exactly is power quality? This is a question with no
fully accepted answer, but surely the response involves
the waveforms of current and voltage in an ac system, the
presence of harmonic signals in bus voltages and load
currents, the presence of spikes and momentary low
voltages, and other issues of distortion. Perhaps the best
definition of power quality is the provision of voltages
and system design so that the user of electric power can
utilize electric energy from the distribution system
successfully, without interference or interruption. A
broad definition of power quality borders on system
reliability, dielectric selection on equipment and
conductors, long-term outages, voltage unbalance in
three-phase systems, power electronics and their interface
with the electric power supply, and many other areas. A
narrower definition focuses on issues of waveform
distortion.
Monitoring Power Quality and Harmonics
Today, power quality monitoring is an essential service
many utilities perform for their industrial and other key
commercial customers. Because of the technology and
software now available this monitoring is highly
effective. Not only can a monitoring system provide
information about the quality of the power and the causes
of power system disturbances, but it can identify problem
condition throughout the system before they cause
widespread customer complaints, equipment
malfunction, and even equipment failures. Many surveys
have shown that the majority of problems are localized
within customer facilities. Given this fact, monitoring
provides a key opportunity for a utility to protect its
reputation and improve its relationship with customers.
Conclusions
The main point with which all the professionals involved
in power Quality and harmonics in the supply network
deal is that the problem is here to stay: the Electric Power
Research Institute (EPRI) estimates that in 1992 , 15 to
20% of the total load has been nonlinear, while by the
year 2,000 ,50 to 70% of all loads are expected to be
nonlinear.
There is at least one concept hat must change fast, i.e.
traditional measuring equipment is not useful in
monitoring Electric Network Variables in networks the
contains nonlinear loads but only equipment that is able
to measure true RMS parameters (it is necessary for the
user to check up to which level of Harmonics it can
measure to be sure that it covers the Power Quality and
harmonic deviations present in the local supply network
to be monitored).