Over Voltages
Introduction:
ü Transient
over voltages in electrical transmission and distribution networks result from
the unavoidable effects of lightning strikes and network switching operations.
ü These
over voltages have the potential to result in large financial losses each year
due to damaged equipment and lost production.
ü They are
also known as surges or spikes.
ü Transient
over voltages can be classified as
o Impulsive
transient
o
Oscillatory transient
ü A
transient is a natural part of the process by which the power system moves from
one steady state to another.
ü Its
duration is in the range of microseconds to milliseconds.
ü Low
frequency transients are caused by network switching.
ü High
frequency transients are caused by lightning and by inductive loads turning
off.
ü Surge
suppressors are devices that conduct across the power line when some voltage
threshold is exceeded.
ü Typically
they are used to absorb the energy in high frequency transients.
ü The
devices are used for over voltage protection is,
o
Surge arrester(crowbar & clamping device)
o Transient
over voltage Surge suppresser
o Isolation
transformer
o Low pass
filter
o Low impedance power conditioners
o Pre-insertion
resistors (transmission and distribution)
o Pre-insertion
inductors (transmission)
o
Synchronous closing (transmission and distribution)
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