If we zoom into a relay, we can see three different types of
realization:
- Electromechanical Relays.
- Solid State Relays.
- Numerical Relays.
- First generation of relays.
- Uses the principle of electromechanical energy conversion.
- Immune to electromagnetic interference and rugged
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.
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.
- Maximum flexibility.
- Provides multiple functionality.
- Self checking and communication facility.
- It can be made adaptive.
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.
- Necessity of a protection system.
- Types of Protection.
- Three generations of relays.
- Role of circuit breakers.
