symmetrical component of power system

Seminar Topic on:-

SYMMETRICAL COMPONENT OF POWER SYSTEMS

Presented By:- Devendra Mishra

Branch:- EN-1 Roll No:-1401421020

OUTLINE OF THE PRESENTATIONINTRODUCTION

NEED FOR THE SYMMETRICAL COMPONENET METHOD

TECHINQUES USED TO ANALYSIS SYMMETRICAL

CONCLUSION

INTRODUCTIONA three-phase system is said to be symmetrical when the

system viewed from any phase is similar.Thus, in a three-phase symmetrical system the impedances

of all the three phases are equal and the mutual impedances, if any, between the three phases are the same.

The three phase voltages(or currents) are said to be balanced if the magnitude of the three voltages(or currents) are equal and they separated from each other by 120º(electrical) in phase.

When the system is unbalance the voltages, current and the phase impedances are in general unequal. Such a system can be solved by a symmetrical per phase technique known as the method of symmertical component.

This method was proposed by Fortescue in 1981 and is often called the three-component method.

According to Fortescue, An unbalance set of n phasors may be resolved in to (n-1) balanced n-phase system of different phase sequence and one zero-phase sequence system.

A zero-phase sequence system is one in which all phasors are of equal magnitude and identical angle,

PHASE SEQUENCEPhase-Sequence of the phasors is the order in which

they pass through a positive maximum. Thus, a phase sequence a b c implies that the

maxima occur in order a, b, c.If a, b, c is taken as the positive phase sequence then

a, c, b represents the negative phase sequence.It should be noted that for both positive & negative

phase sequence, the direction of rotation of phaser is taken to be anticlockwise

The phasor representation of three phase system

Need for the symmetrical component analysis

Negative sequence relay in generator has helped in protecting the generator from over heating in the event of unbalanced loads.

The positive sequence network is used to supply the sensing voltage to generator voltage regulators

Certain connections of CT and PT develop zero sequence components that are used in protective ground relaying scheme

Method of adopted for symmetrical component analysis

Mathematically:Va= Va0+ Va1+ Va2

Vb= Vb0+ Vb1+ Vb2

Vc= Vc0+ Vc1+ Vc2

Va Vb Vc are unbalance set of phasor

Va1, VbVc1 are set of positive sequence phasor

Va2, Vb2Vc2 are negative sequence phasor Va0 Vb0 Vc0 are zero sequence phasor

Vp=A VsThen Vs=[ adjA÷|A|] Vp

Symmetrical components of generator

Symmetrical components of transformer

Conclusion

Power system analysis using symmetrical component is very helpful in improving the reliability of the power system.

The principle adopted for the analysis of unbalanced fault system is symmetrical component method

Any query

Thank you