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Power Quality ProblemsPower quality is a vital attribute of any
distribution andtransmission system. It is the duty
of the utility to deliver power to the consumer that is reliable
and consistent at apredeterminedvoltage and frequency. However, the
quality of power is affected bynumerous issues such as sags,
swells, over voltage, etc. The following are some of theproblems
that affect power quality.
Voltage SagsThey are also known as voltage dips. These are
voltage drops which last for a shortperiod, from 8milliseconds to
60 seconds. They are caused by momentary faults inthe transmission
lineswhich get cleared quickly. The drop in voltage may range from
10to 90 percent.
Voltage SwellsThese are momentary increases in the voltage
exceeding 110% which last less than aminute. They can be caused by
phase to ground faults.
UndervoltagesThese are caused by a drop in the voltage to less
than 90% of thevoltage for more than1 minute. They are also
referred to asbrownouts. Overloading of the distribution systemcan
cause undervoltage.
OvervoltagesThey are similar to voltage swells except that they
can last for more than a minute.The voltage exceeds 110%.
Overvoltages are caused by poor voltage regulation. Theycan also be
caused by switching of capacitors or by sudden load reduction.
Wrongsetting of transformer taps can also lead to overvoltages.
InterruptionsInterruptions are defined as the drop of voltage to
10%. Interruptions are furtherclassified into momentary
interruptions lasting from 8 milliseconds to 3 seconds,temporary
interruptions lasting from 3 seconds to 1 minute and sustained
interruptionsor long duration interruptions which last for more
than a minute.Power interruptions cancause loss to production lines
in industries. Some of the ways of mitigating the effects
ofinterruptions are by installing a UPS, an emergency genset or by
having power fed fromtwo different feeders.
TransientsSeeArticle on Transients
Unbalanced VoltagesWhen the voltages in all the three phases are
not balanced, this situation occurs. This iscaused by single phase
overloading of one phase. Loads such as arc furnaces alsolead to
unbalanced loading. Unbalanced loading can be harmful for loads
such
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