Overview

Where does the term power quality stands for?!

Power quality is the set of limits of electrical properties that allows electrical systems to function
in their 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 properly
with that electric power. Without the proper power, an electrical device (or load) may malfunction,
fail 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
to an 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 complexity of
the system to move electric energy from the point of production to the point of consumption combined
with 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.
Power 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 voltages
(as illustrated in the diagram below) and currents, harmonic content in the waveforms, etc.




It 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:


Sags: 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.





Surges
:  are short duration increases in the mains supply voltage which generally last several cycles.
When surges 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 lasting only
a few milliseconds. When transients or Transient screen occur equipment can lock or hang, crash and
even suffer damage which inevitably causes data loss and corruption. Large transients can occur from
local or worst case a direct lightning strike.





Electrical Noise:  this is a high frequency noise either common or normal mode which can
cause severe disruption and damage to computer-based equipment.





Over voltage: That happens when the RMS voltage exceeds 10% of the nominal voltage for
longer than 60 seconds. Over voltage conditions cause electronic component heating with the
potential for immediate 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 seconds up
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 total
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 or voice
processing IP network, such as PC, terminal, console, server, PBX, printer, modem, hub or
router.





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
power sources. For sensitive equipment, the results can be data loss, program failure, equipment
lock-up or complete shutdown.





Harmonic distortions: is deformation of the normal waveform, generally transmitted by nonlinear
loads like switched mode power supplies, variable speed motors and drives, copiers and fax
machines, 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
electronic devices, seems to be more sensitive to power quality variations than was equipment used in the past? The answer is
simply due to the following factors:



   
     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
            (even at 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 mode noise
            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 sensitive to
            electromagnetic interferences.


   
    The increasing emphasis on overall power system efficiency the last two decades has resulted in continued growth
            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 manipulate
            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",
            amongst many other negative results. These disturbances affect not only your personal computer, but also any
            industrial or 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
AC commercial 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 cases
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 highly
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.