Solid State relays for Engineering Students

Solid State Relays and Numerical relays

1. UNIT – IV Static Relays and Numerical Protection

2. Unit-IV Static relays and Numerical Protection Static relays – Phase, Amplitude Comparators – Synthesis of various relays using Static comparators– Block diagram of Numerical relays – Over current protection, transformer differential protection, distance protection of transmission lines.

3. Static Relays The relays which do not use moving parts and use the solid state electronic components such as diodes, transistors etc. are called static relays. Static relay response circuit does not have moving parts and made up of electronic components but its tripping circuit may be electronic or electromagnetic.

4. Block Diagram of a Static Relays

5. Comparison of Static and Electromagnetic Relays Static relays Electromagnetic relays Moving parts are absent Moving parts are present Response is very quick Response is slower compared to static relay Power consumption is small Power consumption is more Characteristics of components depend on temperature Characteristics of components are not dependent on temperature Testing and servicing is easy Testing and servicing is complicated Low short time overload capacity Higher short time overload capacity Additional d.c. supply is required for electronic components Additional d.c. supply is not required Less robust More robust in nature Susceptible to the voltage fluctuations and transients Not susceptible to the voltage fluctuations and transients Wiring errors are less Possibility of wiring errors Resetting time and overshoots are reduced Resetting time and overshoots are more due to inertia of the mechanical parts Single relay can perform various functions and can be programmable Programming facility is not available and single relay cannot perform several functions

6. Advantages of Static Relays The moving parts are absent. The moving parts are present only in the actual tripping circuit and not in the control circuit. The burden on C.T. gets considerably reduced thus smaller C.T.s can be used The power consumption is very low as most of the circuit are electronic The response is very quick As moving parts are absent, the minimum maintenance is required. No bearing friction or contact troubles exist.

7. Advantages of Static Relays The resetting time can be reduced and overshoots can be reduced due to absence of mechanical inertia and thermal storage The sensitivity is high as signal amplification can be achieved very easily The use of printed circuits eliminates the wiring errors and mass production is possible As electronic circuits can be used to perform number of functions, the wide range of operating characteristics can be obtained, which almost approach to ideal requirements

8. Advantages of Static Relays The low energy levels required in the measuring circuits make the relays smaller and compact in size The testing and servicing is simplified Smaller and compact in size No gravity effect on operation of static relays. Hence can be used in ships, aircrafts etc. A single relay can perform several functions like overcurrent, under voltage single phasing protection by incorporating respective functional blocks. This is not possible in electromagnetic relays.

9. limitations of Static Relays The characteristics of electronic components such as transistors, diodes etc. are temperature dependent. Hence relay characteristics vary with temperature and ageing The reliability is unpredictable as it depends on a large number of small components and their electrical connections These relays have low short time overload capacity compared to electromagnetic relays Additional d.c. supply is required for various transistors circuits Susceptible to the voltage fluctuations and transients Less robust compared to electromagnetic relays

10. Comparators Many relays operate based on the resultant of the comparison of the two quantities. The comparator is that part of relay, which receives two input and it produces the output based on the comparison of the two inputs. In some relays the amplitude of the two quantities, entering and leaving a protected zone are compared. While in some relays the phase angle between the sending end quantities and receiving end quantities are compared. Thus the phase and amplitude comparators are necessary for the relay opeartion

11. Comparators

12. Amplitude Comparators

13. Rectifier Bridge Comparator

14. Integrating Amplitude Comparator

15. Integrating Amplitude Comparator

16. Phase Comparator

17. Sine type Phase Comparator

18. Cosine type Phase Comparator

19. Duality in Comparators

20. Duality in Comparators

21. Hybrid Comparators

22. Semiconductor Devices used in Static Relays Semiconductor diodes – p-n junction diode, zener diode, avalanche diode, rectifiers, regulators Transistors – BJT, FET – amplifiers, switches UJT – relaxation oscillator, to trigger SCR Thyristor family – SCR, traic , diac , Silicon controlled switch Logic circuits – ON and OFF Filter circuits – RC and LC Multivibrators – square waveform, diode clipper Time delay circuits – delay lines, RC circuits, timer circuits, resonant circuits using transistors, thyristors and ICs. Level detector – diodes, rectifiers and RC elements Analog circuits – op-amp, adder, subtractor , differentiator, integrator, inverting amplifier, zero crossing detector, Schmitt trigger.

23. Static Over Current Relay

24. Static Time-Current Characteristics

25. Static Time-Current Characteristics

26. Static Instantaneous Overcurrent Relay

27. Inverse Time-Current Relay

28. Directional Static Overcurrent Relay

29. Static Differential Relay

30. Static Distance Relay

31. Static Distance Relay

32. Synthesis of Mho Relay using Static Comparator

33. Synthesis of Mho Relay using Static Comparator

34. Synthesis of Reactance Relay using Static Comparator

35. Synthesis of Reactance Relay using Static Comparator

36. Synthesis of Reactance Relay using Static Comparator

37. Synthesis of Impedance Relay using Static Comparator

38. Block Diagram of Numerical Relay

39. Advantages of Numerical Relay It uses electronic circuits for functioning and hence is compact in size The numerical relay can be made multifunctional with suitable modifications in software or with slight modification in hardware It uses fewer components resulting in less inter connections and reduced component failures. Hence it is more reliable Relay characteristics are stored in memory of microprocessor. Hence it provides better matching of protection characteristics

40. Advantages of Numerical Relay Numerical relay can be easily interfaced with digital communication equipments (like fibre optical communication) Numerical relay imposes less burden on CTs and PTs It has high pick up ratio and greater sensitivity Tripping time of ½ cycle or less can be achieved with the use of numerical relay It has least resetting time It can provide data history for future reference One unit can perform relaying of several systems Very economical for large power systems Useful for centrally co-ordinated back up protection

41. Limitations of Numerical Relay The microprocessor unit needs to be properly shielded as gets affected by external interferences and environment Proper care of earthing must be taken If it is multifunctional, then failure of one element affects all the systems It has risk of hacking The relay can be faster but of no use if circuit breaker operation is not as fast as relay.

42. Numerical Overcurrent Protection

43. Numerical Differential Protection of Transformer

44. Numerical Differential Protection of Transformer

45. Numerical Distance Protection