Disclaimer: The information presented here is neither complete nor accurate. Complete details on the topics here are available only from Indian Railways and other official organizations. The material here is not a substitute for the official documentation or official training procedures, which are provided to duly authorized personnel. Do not use the information here to design, build, operate, repair, or maintain any equipment.
This article is based on information provided by Ashish Kuvelkar and other IRFCA members.
Auto-Emergency Brakes (AEB) refers to a special system of braking employed on some ghat sections with steep gradients, notably the Braganza ghat between Kulem and Castle Rock. With this system, the loco's speed is limited to 30km/h and the brakes are automatically applied if the loco moves faster than that at any time on the AEB section.
The AEB system is activated by means of a key obtained at the top of the descending grade (at Castle Rock for the Braganza ghat). The key, which is specific to each loco, is engaged and turned in the loco, and then removed and handed to the guard of the train (except for light locos where there is no guard). While the AEB system is activated, the loco cannot run faster than 30km/h; the brakes are applied immediately if the speed rises above that.
When the loco reaches the bottom of the down grade (Kulem at the foothills of the Braganza ghat), the AEB system is deactivated and the key is handed over to the Station Master of the station at the bottom of the ghat section (Kulem). From there onwards, the loco can proceed at normal permissible speeds.
The AEB key specific to a loco is handed over to the loco pilot by the Station Master of the station at the bottom (Kulem) when the loco is above to ascend the ghat section.
The AEB system depends on a speed sensor attached to the axle generator (tachometer generator) of the locomotive. The speed sensor controls the Emergency Brake Relay (EBR). The EBR gets energized when the speed sensor detects that the loco is moving faster than 30km/h (or other programmed speed limit).
When the EBR is energized, two emergency brake valves, EBV1 and EBV2 get activated.
The first emergency brake valve EBV1 cuts off pilot air from A9 to C2, with the additional C2 relay then causing the Brake Pipe to exhaust, while the second emergency brake valve EBV2 also exhausts the Brake Pipe pressure and causes application of the brakes.