Comparison Table
This comparison summarize characteristics of all protection relay types described in previously published technical articles:
- Using Protective Relay For Fighting Against Faults
- The Good Old Electromechanical Protective Relay
- The Solid State Relay (Static Relay) Overview
- Few Words About Digital Protection Relay
- Flexibility and Reliability of Numerical Protection Relay
| Characteristic | El. Mech. Relay | Static Relay | Digital Relay | Numerical Relay |
| Technology Standard | 1st generation relays. | 2nd generation relays. | Present generation relays. | Present generation relays. |
| Operating Principle | They use principle of electromagnetic principle. | In this relays transistors and IC’s been used | They use microprocessor. Within built software with predefined values | They use microprocessor. Within built software with predefined values |
| Measuring elements/ Hardware | Induction disc, electromagnets, induction cup, balance beam | R, L, C, transistors, analogue ICs comparators | Microprocessors, digital ICs, digital dignal processors | Microprocessors, digital ICs, digital signal processors |
| Measuring method | Electrical qtys converted intomechanical force, torque | Level detects,comparison withreference value in analogue comparator | A/D conversion, numerical algorithm techniques | A/D conversion, numerical algorithm techniques |
| Surrounding Environment | Depend upon gravitation and the value changes to the surrounding magnetic fields also. | There value may vary with respect to temperature also. | ||
| Characteristic | El. Mech. Relay | Static Relay | Digital Relay | Numerical Relay |
| Relay Size | Bulky | Small | Small | Compact |
| Speed of Response | Slow | Fast | Fast | Very fast |
| Timing function | Mechanical clock works, dashpot | Static timers | Counter | Counter |
| Time of Accuracy | Temp. dependant | Temp. dependant | Stable | Stable |
| Reliability | High | Low | High | High |
| Vibration Proof | No | Yes | Yes | Yes |
| Characteristics | Limited | Wide | Wide | Wide |
| Requirement of Draw Out | Required | Required | Not required | Not required |
| CT Burden | High | Low | Low | Low |
| CT Burden | 8 to 10 VA | 1 VA | < 0.5 VA | < 0.5 VA |
| Characteristic | El. Mech. Relay | Static Relay | Digital Relay | Numerical Relay |
| Reset Time | Very High | Less | Less | Less |
| Auxiliary supply | Required | Required | Required | Required |
| Range of settings | Limited | Wide | Wide | Wide |
| Isolation Voltage | Low | High | High | High |
| Function | Single function | Single function | Multi function | Single function |
| Maintenance | Frequent | Frequent | Low | Very Low |
| Resistance | 100 mille ohms | 10 Ohms | 10 Ohms | 10 Ohms |
| Output Capacitance | < 1 Pico Farad | > 20 Pico Farads | > 20 Pico Farads | > 20 Pico Farads |
| Characteristic | El. Mech. Relay | Static Relay | Digital Relay | Numerical Relay |
| Deterioration due to Operation | Yes | No | No | No |
| Relay Programming | No | Partially | Programmable | Programmable |
| SCADA Compatibility | No | No | Possible | Yes |
| Operational value indication | Not Possible | Possible | Possible | Possible |
| Visual indication | Flags, targets | LEDs | LEDs, LCD | LEDs, LCD |
| Self monitoring | No | Yes | Yes | Yes |
| Parameter setting | Plug setting, dial setting | Thumb wheel, dual in line switches | Keypad for numeric values, through computer | Keypad for numeric values, through computer |
| Fault Disturbance Recording | Not possible | Not possible | Possible | Possible |
Relay’s Nomenclature as per ANSI
| No | Type of Relay |
| 2 | Time delay relay |
| 3 | 3 Checking or Interlocking relay |
| 21 | 21 Distance relay |
| 25 | Check synchronizing relay |
| 27 | Under voltage relay |
| 30 | Annunciation relay |
| 32 | Directional power (Reverse power) relay |
| 37 | Low forward power relay |
| 40 | Field failure (loss of excitation) |
| 46 | Negative phase sequence relay |
| 49 | Machine or Transformer Thermal relay |
| 50 | Instantaneous Over current relay |
| 51 | A.C. IDMT Over current relay |
| 52 | Circuit breaker |
| 52a | Circuit breaker Auxiliary switch “Normally open” (‘a’ contact) |
| 52b | Circuit breaker Auxiliary switch “Normally closed” (‘b’ contact) |
| 55 | Power Factor relay |
| 56 | Field Application relay |
| 59 | Overvoltage relay |
| 64 | Earth fault relay |
| 67 | Directional relay |
| 68 | Locking relay |
| 74 | Alarm relay |
| 76 | D.C Over current relay |
| 78 | Phase angle measuring or out of step relay |
| 79 | AC Auto reclose relay |
| 80 | Monitoring loss of DC supply |
| 81 | Frequency relay |
| 81 U | Under frequency relay |
| 81 O | Over frequency relay |
| 83 | Automatic selective control or transfer relay |
| 85 | Carrier or pilot wire receive relay |
| 86 | Tripping Relay |
| 87 | Differential relay |
| 87G | Generator differential relay |
| 87G | T Overall differential relay |
| 87U | UAT differential relay |
| 87NT | Restricted earth fault relay |
| 95 | Trip circuit supervision relay |
| 99 | Over flux relay |
| 186A | Auto reclose lockout relay |
| 186B | Auto reclose lockout relay |
Relays for Transmission and Distribution Lines protection
| No | Line | Protection |
| 1 | 400 KV Transmission Line | Main-I: Non switched or Numerical Distance Scheme |
| Main-II: Non switched or Numerical Distance Scheme | ||
| 2 | 220 KV Transmission Line | Main-I : Non switched distance scheme (Fed from Bus PTs) |
| Main-II: Switched distance scheme (Fed from line CVTs) With a changeover facility from bus PT to line CVT and vice-versa | ||
| 3 | 132 KV Transmission Line | Main Protection: Switched distance scheme (fed from bus PT). |
| Backup Protection: 3 Nos. directional IDMT O/L Relays and 1 No. Directional IDMT E/L relay. | ||
| 4 | 33 KV Lines | Non-directional IDMT 3 Over Current and 1 Earth Fault relays |
| 5 | 11KV Line | Non-directional IDMT 2 Over Current and 1 Earth Fault relays |
References:
– Handbook of Switchgear – Bhel – Digital/Numerical Relays – T.S.M. Rao
Related electrical guides & articles
Jignesh Parmar
Electrical Middle management professional having more than 22 years rich and dynamic experience in Project Execution / Project Management / Designing / Maintenance diversifies from Electrical Power Transmission (400KV/220KV/66KV)- Distribution(11KV/220V) to Lifts-HVAC-Ventilation-Fire Fighting-Fire Alarm-Lifts-CCTV-Stack Parking Works (High Rise Buildings, Townships, Shopping Complex, Commercial Complex, School, Temple).Profile: Jignesh Parmar
Best Information sir,
We have China made Microprocessor based relay in hydro power projets, now we are finding alternative to same in Indian manufacturing relays. can you advice the indian componies?
Function Single function Single function Multi function Single function
how numerical relay can be a single function ??
please explain
Its very informative artical.thank you sir
Dear Jignesh
A very well compiled work. Hats off.
A very important things that needs to be noted is that all the three types of these Relays(Considering Digital & Numerical to be one) are SCADA Compatible. However you will need different types of Interfaces at the RTUs. A different interface port for the Hot signals (with varying voltages) for the E&M and Static Relays while as a different Communication port for the Soft signals from the Numerical Relays.
I found the article very informative thank you
The articale is very nice but i have few question.
1.what is difference between numerical relay & digital relay?(many literature say both are same-Digital/Numerical Relays – T.S.M. Rao)
2.why In comparison table relay resistance are different unit? (for EM relay 100 mile ohm,other relay are 10 ohm)
Thank you , IT IS VERY HELFULL AND HELP TO IMPROOVE ELECTRICAL IND.
This portal is very useful for Electrical Engineers.
Why the numerical relay is single function type? I think it is multi-function type?
Good work Jignesh, But for El Mechanical Relay like CDD21 (Alstom) Aux. Supply is not required and all the Numerical Relay are Multi function relays.
very good information
this portal is very helpful to all the electrical engineering student as well as professor and technical engineer.It’s very nice and helpful for all in electrical engineering to get practical knowledge & idea very easily.