AC Loco Protective Equipment
by Lakshman Thodla
Below are the main items of protective equipment found on AC electric locos of Indian Railways with the abbreviations commonly used for them.
| Abbreviation | Name | Function |
|---|---|---|
| DJ | Main air blast circuit breaker | Opens under the control of various protection devices. From 'disjoncteur', French term for circuit breaker. |
| QLM | Main overload relay | Main overload protection in case of failure of main transformer |
| Q1, Q2, etc. | Traction motor overload relays | Overload for the traction motors main rectifiers |
| QOP | Main earth fault relay | Voltage operatted relay for earth faults in main traction circuit and DJ |
| QOA | Earth fault relay for auxilaries | Earth fault protection of auxilaries and opens the DJ |
| Q30 | No voltage relay | Opens DJ if catenary loses power |
| Q118 | Auxilary protection relay | A time delay which opens the DJ in the event of auxiliary failure |
| Q52 | Tap changer notching relay | Trips DJ if incorrect notching occurs in tap changer |
| SMGR | Main tap changer shaft | Used for increasing or decreasing the notches as it moves along a cylinder from botom to top with contacts for each notch; the even contacts from the bottom are for progressive notches and the odd ones are regressive notches. It can traverse 40 notches in 10 seconds. |
| QPDJ | Air blast circuit breaker lockout relay | Trips DJ if air pressure drops to 4.5 kg/cm^2 and recloses only on pressure reaching 5.00 kg/cm^2 |
| Q20 | Traction motor overload relay. | Only in YAM-1 - Sounds a buzzer if voltage for traction motors is exceeded |
| QSI, QRSI | Silicon rectifier overload relay | Prevents overload of main silicon rectifier and trips the DJ |
| ET1, ET2 | Roof spark gap | HT surge protection |
| ETF | Surge arrestor | Prevents surges from affecting the main silicon rectifier |
| CAPF, RCAPF | Surge arrestors | Surge absorber and series resistor for silcon rectifier |
| LTBA | Surge arrestor | For the battery circuits |
| Q130, C130 | Dc voltage relay | Trips DJ if generator fails |
| QPH | Oil flow relay | Trips DJ if oil flow in main transformer fails |
| QVM1, QVM2 | Blower motor relays | Detects failure of traction motor blowers and trips DJ |
| QTSI | Over temperature relay for silcon rectifier | Detects overheating of the silicon rectifier and trips DJ |
| Q44 | Time delay | Time delay for certain other relays like Q30, QTSI, etc. |