What is Transient Disturbance

The term “transient” usually originates from electric circuit theory where it describes voltage and current variation from its present steady state to next steady state.

In the power system, the term transient is usually used in a different way. It denotes abrupt change in voltage and current for short duration.

Usually for duration less than the period of power system voltage and current signal(50-60 Hz).

Why it is considered(Effects)

Previously it was considered that transient disturbances are only because of incorrect operation of circuit breakers and switching of high voltage lines.

Electronic equipment have very less voltage handling capabilities.

Temporal fluctuation produces parity error and interrupts protection system

Causes of Transient disturbance

Switching operation,faults, and other disturbances like lightning.

Shutdown of heavily loaded circuits.

Necessary commutation of a high-powered network (e.g. Pf correction).

Categorization(waveform shape)causes

Oscillatory Impulsive

Oscillatory

Transients which shows damped oscillation with frequency ranging from few kHz to several MHz resulting in overshoot in respective voltage and current from its expected values.

Examples of oscillatory transient

Switching shunt capacitors

Cont..Line Energizing: Energizing of transmission line is

another possible cause of oscillatory transients. Transmission line can be modelled as lumped capacitor

Voltage transient caused by energizing of 160km open ended T-line at source side and at end of line.

ImpulsiveImpulsive transient is abrupt change in

voltage ,current or in both but only on one side (either +ve or –ve )

Normally characterized by their rise and decay times.

Quickly damped by resistive circuit elements and hence do not propagate for from their origin point.

The most common causes of impulsive transients are lightning and electrostatic discharge.

cont..

Impulsive Transient Rise time Duration

Nanosecond 5 ns Less than 50 ns

Microsecond 1 us 50 ns to 1 ms

Millisecond 0.1 ms more than 1 ms

Lightening

How it can be resolved• For better power quality assessment ,we have to define new

indices (other than conventional) based on signal processing technique. As present indices for transient disturbance analysis have limitations.

• Indices can also be defined on basis of time frequency analysis.

• Indices based on time domain analysis are crest factor , peak and RMS value.

• Indices based on frequency domain are THD,Distortion Index ,K-factor. These indices are defined in terms of Fourier series Coefficient.

THANK YOU