Power System Protection - 2

Evolution of Relays

If we zoom into a relay, we can see three different types of

realization:

• Electromechanical Relays.

• Solid State Relays.

• Numerical Relays.

Electromechanical Relays

• First generation of relays.

• Uses the principle of electromechanical energy conversion.

•  Immune to electromagnetic interference and rugged

                                         

Solid State Relays

These   relays were developed  with the advent of transistors, operational amplifiers   etc. Their  functionality  is through  various  operations  like comparators etc. Their advantages are

• More flexible.

• Self checking facility.

• Less power consumption and low burden.

• Improved dynamic perfomance characteristics.

• High seismic withstand capacity.

• Reduced panel space. 

Numerical Relays 

Operation of a numerical relay involves analog to digital conversion of voltage and  currents  obtained  from  VT  and  CTs.  These  samples  are  fed to  the microprocessor  or  DSP where the protection algorithms process these signals and necessary decisions are taken.

              

Its advantages are

• Maximum flexibility.

• Provides multiple functionality.

• Self checking and communication facility.

• It can be made adaptive.

What is a Circuit Breaker?

A circuit breaker is basically a switch to interrupt the flow of current.

• It opens on relay command.

• It has to handle large voltages and currents.

• The inductive nature of power system results in arcing between the terminals of a CB.

• CBs are categorized based on the interrupting medium used.

Summary

• Necessity of a protection system.

• Types of Protection.

• Three generations of relays.

• Role of circuit breakers.