Where does the term
power quality stands for?!
Power quality is the set of limits of electrical
properties that allows electrical systems to function
intended manner without significant loss of performance or
life span. The term is used to
describe electric power that
drives an electrical load and the load's ability to function
with that electric power. Without the proper power, an
electrical device (or load) may malfunction,
prematurely or not operate at all. There are many ways in which
electric power can beof poor
quality and many more causes of
such poor quality power. The electric power industry comprises
electricity generation (AC power), electric power
transmission and ultimately electricity distribution
electricity meter located at the premises of the end user of
the electric power. The electricity
then moves through the
wiring system of the end user until it reaches the load. The
the system to move electric energy from the point
of production to the point of consumption combined
variations in weather, generation, demand and other factors
provide many opportunities for the
quality of supply to be
compromised. While "power quality" is a convenient term for
many, it is the
quality of the voltage rather than power or
electric current that is actually described by the term.
is simply the flow of energy and the current demanded by a
load is largely uncontrollable.
The quality of electrical power
may be described as a set of values of parameters, such as:
continuity of service, variation in voltage magnitude, transient
(as illustrated in the diagram below) and currents,
harmonic content in the waveforms, etc.
is often useful to think of power quality as a
compatibility problem: is the equipment connected to the
grid compatible with the events
on the grid, and is the power
delivered by the grid, including the events, compatible with the
equipment that is connected?
Compatibility problems always have
at least two solutions: in this case,
either clean up the power, or make the equipment tougher. The
tolerance of data-processing equipment to voltage variations has
limits, once those limits are
exceeded; premature defect or software
disruption is inevitable.
Power quality problems have a different cause. Some problems are
a result of the shared infrastructure.
For example, a fault on the network may cause a dip that will
affect some customers; the higher the level
of the fault, the greater the number affected. A problem on one
customer's site may cause a transient that
affects all other customers sharing the same MV/LV substation.
Problems, such as harmonics, arise within
the customer's own installation and may propagate onto the
network and affect other customers.
Regardless of the cause of the problem, the result will include
one or more of the following
types of power problems:
are short duration decreases in the mains supply voltage which
generally last for several cycles.
They are one of the more common forms of disturbances. When sags
occur sensitive equipment
can lock or hang causing data loss and system resets.
short duration increases in the mains supply voltage
which generally last several cycles.
occur equipment can suffer from premature failure. The
high voltage causes wear and
tear and general
component degradation. This may not be noticeable until
failure, though heat out is
a good sign.
Transients and Transient screen:
these are very fast low energy surges up to 6000 volt
milliseconds. When transients or
Transient screen occur equipment can lock or hang, crash and
damage which inevitably
causes data loss and corruption. Large transients can
or worst case a direct lightning
Electrical Noise: this is
a high frequency noise either common or normal mode
disruption and damage to computer-based equipment.
Over voltage: That happens
when the RMS voltage exceeds 10% of the nominal voltage
longer than 60 seconds. Over voltage conditions
cause electronic component heating with the
or future component failure through overstressing. If
this heating effect
causes enclosure temperature to
raise above the safe limit the system may shut down.
Brownouts: are long term
sags in the mains supply voltage which can last from 60
to several days. During a brownout
equipment can reset or even shutdown.
Blackouts (Mains Failures): when the mains supply fails completely this is known as a
mains failure or blackout. A break in the
mains supply of only several milliseconds is sufficient
enough to crash, lock or
reset many of the components that make up a typical data
processing IP network, such as PC,
terminal, console, server, PBX, printer, modem, hub or
Frequency deviation: involves a change in frequency from the normally stable
utility frequency of
50 Hz. This may be caused by erratic operation of
emergency generators or unstable frequency
sources. For sensitive equipment, the results can be
data loss, program failure, equipment
is deformation of the normal waveform, generally
transmitted by nonlinear
loads like switched mode power supplies, variable speed
motors and drives, copiers and fax
etc. The effects are overheating, equipment damage, and
communication errors, etc.
If you haven't experienced any
of the aforementioned 9 common power quality problems
yet, you might will !!.
The question can be asked now, why
new-generation load equipment, with high speed
microprocessor-based controls and power
devices, seems to be more sensitive to power quality variations than was equipment
used in the past? The answer is
simply due to the
♣ Footprint of the new products became a hot issue,
and there is a market need for a product with smaller
size, less weight, etc.
That means less space between adjacent conductors on the printed circuit board,
which increase susceptibility for over voltage
low level), and increasing adjacent-channel
interferences. The microprocessor chips become
smaller and smaller and
more densely packed (more
solid-sate components). This decreases heat
dissipations, and makes them less robust.
♣ The operating voltage has and continuous to
decrease. For instance, in the digital system (0 & 1), a
digital "1" maybe in the
vicinity of 3.5-5.0 volts or
less, while "0" in the range of 0-1.5 volts. So
smaller over voltages from transient conditions maybe
result in operating errors.
♣ Zero voltage reference ground is very critical for
proper operations of computer-based equipment. Common
represents direct threat for the reference voltage, especially when the immunity against the
common mode noise has been
compromised in the super
speed new generation of microprocessors.
♣ Operating speeds have been increased in the radio
frequency spectrum, making the circuit boards more
♣ The increasing emphasis on overall power system
efficiency the last two decades has resulted in
in the application of devices such as high-efficiency, adjustable-speed motor drives and
shunt capacitors for power
factor correction to reduce
losses. This is resulting in increasing harmonic levels injected back on the power lines.
♣ computers use the ON and OFF voltages and the
timing provided by their power supply to store and
data in the microprocessor. Therefore, any deviations, as a result of electrical noise, from
the voltage specified by
the processor can cause the
data to be corrupted or erased. This is what often causes your computer to "freeze up",
other negative results. These disturbances affect not
only your personal computer, but also any
commercial office processes .
Electrical disruptive & destructive events are nothing
more than invisible low energy events in an unusable or undesirable form.
Those events lurking your systems 24 hours and able at any moment to cause data loss,
system lockups, aborted tests,
premature defect, or even
direct damage in some scenario's. Therefore, plugging your sensitive equipment directly to the
power, without protection, expose it to all kinds of
damaging events. For instance, Transient screen, sag, swell,
harmonic distortion, normal & common mode noise, EMI, RFI, etc.
Terefore, don't blame the software always; you
could suffer from polluted power, especially that recent Studies have shown that "80% of the hardware damage
are due to power quality related problems". And
"that Power problems caused by Transient screen, swells, sags and ground loops in
the electricity supply cause 15 times more software problems today than viruses".
Therefore, once your equipment suffers
power supply damage, burned PCB, communication errors, system lockup,
automatic reboot, shrinking screen, delay in process
(especially in local area network), then the chance is
very big that has to do with power quality related problem. t's
recommended in that case to do site survey by
power quality expert to identify source of problem by means of the right
power quality measuring instrument.