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.