Power Transformer Protection In General
The typical protective relays and tripping devices of Power Transformer Protection
Hereafter is a listing of transformer concerned protective systems
Symbol graphic | Code ANSI | Designation of device or relay | Comments |
T > | 38 - 49T | Transformer thermal relay | Temperature switch inside transformer |
P > | 63 | Pressure switch | On transformer |
| DGPT and/or Buchholz | Switch(es) on transformer | |
52P | Primary Breaker | In HV with separate TC’s and relays for protections | |
52S | Secondary Breaker | In LV it is generally equipped with independent (autonomous) thermal and magnetic protections for protection of LV network | |
49 | Thermal overload | Equipping breaker or independant | |
I > | 50 | Phase overcurrent relay instant action | Detection on one phase |
I > | 51 | Phase overcurrent relay dependant time action | Detection on one phase – timing can be specified |
I > I >> | Phase overcurrent with 2 setting | Either in 50 or 51 (instant or dependant) | |
IN > | 50N | Earth fault instant action | Current Detection either on 1ary and 2ary Phase to ground or on 3 phases (toroid or zero sequence) |
IN > | 51N | Earth fault dependant time action | Same above, with dependant time |
IG > | 50G | Earth (Ground) fault instant action | Tank to earth (could be identified as well 50N) |
IG > | 51G | Earth (Ground) fault dependant time action | Same above, delayed |
I ¬ | 67 | Directional overcurrent protection | In case of reverse current in phases (short- circuit) |
IN ¬ | 67N | Directional earth fault | Earth fault current associated with a direction of this current |
| 87T | Differential Protection for Transformer | Difference of power between Primary and Secondary |
