Concepts of transients:
ü Transient
over voltages in electrical transmission and distribution networks result from
the unavoidable effects of lightning strike and network switching operations.\
ü Response
of an electrical network to a sudden change in network conditions.
ü Oscillation
is an effect caused by a transient response of a circuit or system. It
is a momentary event preceding the steady state (electronics) during a
sudden change of a circuit.
ü An
example of transient oscillation can be found in digital (pulse) signals in
computer networks. Each pulse produces two transients, an oscillation resulting
from the sudden rise in voltage and another oscillation from the sudden drop in
voltage. This is generally considered an undesirable effect as it introduces
variations in the high and low voltages of a signal, causing instability.
ü Types of
transient:
o Impulsive transient
o
Oscillatory transient
1. Impulse transient:
A sudden, non power frequency change in the steady state condition of
voltage or current that is unidirectional in polarity.
2. Oscillatory transient:
A sudden, non power frequency change in the steady state condition of
voltage or current that is bidirectional in polarity.
3. Short duration variations –
Interruption
The
complete loss of voltage on one or more phase conductors for a time less than 1
min.
3.1 Types of Short Duration interruption:
ü Momentary
Interruption < 1 min , <0.1 pu
ü Temporary
Interruption < 1 min , <0.1 pu
4. Long duration variations –
Sustained interruption
The complete loss of voltage on one or more phase conductors for a time greater than 1 min.
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