| Characteristic |
Electro Mechanical 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 r 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 Signal Processors |
Microprocessor s,Digital ICs, DigitalSignal processors |
| Measuring method |
Electrical Qtysconverted intomechanical force, torque |
Level detects,comparison withreference value in analogue Comparator |
A/D conversion,Numericalalgorithmtechniques |
A/D conversion,Numericalalgorithmtechniques |
| Surrounding Environment |
Depend upon gravitation and the value changes to the surrounding magnetic fields also. |
There value may vary with respect to temperature also. |
|
|
| 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 |
| 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 |
| 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 |
