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Chapter: Power Quality : Over Voltages

Over Voltages

Transient over voltages in electrical transmission and distribution networks result from the unavoidable effects of lightning strikes and network switching operations.

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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