In short. Rail and metro backup power serves station services, depots, signalling and telecommunications, and emergency systems, not traction. Each subsystem has its own consequence of loss and its own authority-defined requirement, so the generator must be engineered within the approved system interfaces rather than added as a general-purpose set. Tunnel ventilation and drainage set the motor-starting demand, signalling and communications sit on UPS with the generator behind, and all work happens in short non-revenue windows with formal acceptance.
Our railway work. In May 2010 South Central Railway hired a 100 kVA generator from us for Bellampalli railway station. We transported it from Secunderabad and back, made the earth pits and installed the changeover switch and cabling; the Railway supplied the diesel and the operators. It is listed in our Project Register.
State exactly what the generator serves
A generator inside a rail project does not establish its suitability for every railway system. Traction power, whether 25 kV AC overhead or 750 V DC third rail, is a specialist discipline with its own substations, protection and authority approval, and should never be grouped with standby distribution. What a diesel generator properly serves is the auxiliary and emergency supply of stations, depots, operations control centres and wayside installations, and the first step of any enquiry is to name those loads and the authority specification that governs them.
Metro systems in Indian cities, including the elevated and underground sections that Hyderabad’s commuters use, are normally fed from two independent grid sources with automatic changeover, and standby generators are provided for essential station and tunnel services in case both fail. Mainline stations, maintenance depots and freight terminals vary more widely, and some rely on a single DISCOM feed with a generator as the only alternative. In every case the responsible infrastructure authority or its consultant sets the loads, the autonomy, the transfer time and the acceptance method, and the generator supplier’s job is to meet them with evidence.
Subsystems and their consequence of loss
| Subsystem | Typical loads | Consequence of loss | Support arrangement |
|---|---|---|---|
| Signalling and telecommunications | Interlocking, train control, radio, CCTV, PA, passenger information | Service suspension, safety | UPS with generator behind, often dual-fed |
| Tunnel and station ventilation | Tunnel ventilation fans, smoke extraction, staircase pressurisation | Life safety in an incident | Generator, first in sequence, large motor starts |
| Drainage | Sump pumps in underground sections and subways | Flooding of track and equipment rooms | Generator, early priority, duty and standby pumps |
| Vertical transport | Lifts, escalators | Evacuation and accessibility | Lifts on generator; escalators selectively |
| Passenger systems | Automatic fare collection gates, platform screen doors, lighting | Crowding, safety | Emergency lighting immediately; gates and doors on UPS or generator |
| Fire systems | Fire pumps, detection, suppression in equipment rooms | Statutory, life safety | Generator by design |
| Depots and workshops | Cranes, lifting jacks, compressors, washing plants, pit lighting | Maintenance delay | Partial generator, often rental during works |
| Operations control centre | Servers, consoles, displays, cooling | Network-wide loss of control | UPS plus N+1 generators |
The table shows why the generator for an underground station is sized by ventilation and drainage rather than by lighting, and why the operations control centre looks like a data centre in its power architecture. The general principles of continuity architecture are on source hierarchy and the continuity chain.
Sizing around ventilation fans and pumps
Tunnel ventilation fans in the hundreds of kilowatts, reversible for smoke control, are the largest standby loads on an underground line. They are increasingly on inverter drives, which makes their start gentle, but older installations and many station exhaust fans start direct-on-line or star-delta. Drainage pumps and fire pumps are also direct-on-line motors that must be available during the same incident. The generator must therefore be sized for the emergency operating mode defined by the authority, in which specific fans run at specific speeds together with pumps, lighting and UPS input, and its step-load capability must be checked against the start sequence.
S_gen = (P_emergency-mode / PF) + S_largest-fan-start
In this expression S_gen is the indicative generator kVA, P_emergency-mode is the running kW of the fans, pumps, lighting and UPS input that operate together in the defined emergency mode, PF is the power factor and S_largest-fan-start is the transient kVA of the largest fan start after the base load is connected. For a station whose emergency mode requires 320 kW of fans on inverter drives, 60 kW of pumps, 40 kW of lighting and a 100 kVA UPS at a 1.2 ratio, with the largest direct-on-line start a 45 kW exhaust fan, S_gen is about 615 kVA plus about 350 kVA of transient, pointing to a 750 to 800 kVA class set or a pair in N+1 where the authority requires redundancy (illustrative). The step-load analysis is covered on large motor starting on diesel generators and the redundancy question on N+1 generator sizing.
Interfaces, earthing and protection within the approved system
A rail installation has approved distribution, control and monitoring interfaces, and the generator must work within them. Transfer logic is usually part of the station’s auxiliary switchboard automation and SCADA, not a standalone AMF panel; the generator controller provides status and accepts commands through the approved protocol. Earthing and bonding near traction systems are governed by stray-current and touch-voltage requirements, so the generator’s neutral earthing and the bonding of its enclosure must follow the project earthing design rather than a generic electrode arrangement. Protection must remain selective on the lower generator fault level, so relay settings for generator mode need to be studied and recorded. Any requirement specific to rail, such as electromagnetic compatibility with signalling, needs the appropriate competent review and supporting evidence from the equipment supplier. Earthing principles are on earthing and neutral grounding.
Access windows, testing and restoration
Everything on an operating railway happens in a window. Installation, cable pulling, load testing and the annual service of a station generator are done in the non-revenue hours after the last train and before the first, often three to four hours including the time to obtain and surrender the possession. Work must be planned to fit, with equipment staged in advance, lifting and access arranged, and a fall-back if the window is cut short. Testing is witnessed and documented to the authority’s acceptance format, including transfer time, voltage and frequency behaviour during fan starts, and UPS synchronisation. Restoration of the normal configuration at the end of the window is formally confirmed by the authority’s nominated person before the possession is returned. Depot works and temporary supplies during station construction follow the same discipline with more generous windows; rental practice for such projects is described on rental power for construction, and the testing method on load-bank testing.
Common mistakes
- Describing the requirement as “a generator for the metro station” without the authority’s load schedule. The set is sized for lighting and cannot start the ventilation fans in the emergency mode.
- Supplying a standalone AMF panel where the station automation already controls transfer. Two controllers fight for the changeover and the acceptance test fails.
- Earthing the generator with a generic electrode near traction return paths. Stray current and touch-voltage requirements are breached and the installation is rejected.
- Planning a load test without a possession. The team arrives, the window is refused, and the set remains untested for another quarter.
- Treating the operations control centre like an ordinary office. A single set without N+1 leaves the whole line’s control dependent on one engine.
What to send us
Send the authority’s specification or load schedule for the station or depot, the single-line diagram showing the auxiliary switchboard and the generator interface, the emergency operating mode with fan and pump ratings and starter types, the UPS ratings for signalling and telecommunications, the earthing design requirements, and the access windows available for installation and testing. Where an existing set is being replaced, include nameplate and controller photographs. Send your rail or metro power requirement.
Questions engineers ask
Can a diesel generator supply traction power?
Not in normal practice. Traction supply is a specialist high-voltage or DC system designed and approved separately. Diesel generators serve station auxiliaries, depots, signalling UPS input and emergency systems.
What decides the generator size for an underground station?
The emergency operating mode defined by the authority, in which tunnel ventilation fans, smoke extraction, drainage pumps, emergency lighting and UPS input run together, plus the largest fan or pump start. Lighting alone is a small part of it.
Do signalling systems run directly on the generator?
No. Signalling and telecommunications run on UPS, often with dual feeds, and the generator keeps the UPS input alive during a long outage. The generator’s voltage and frequency must stay within the UPS synchronisation window.
How is generator work carried out on an operating line?
In non-revenue possessions of a few hours, with equipment staged in advance, work planned to the window, formal testing witnessed by the authority, and the normal configuration confirmed restored before the possession is returned.
Does a metro depot need the same arrangement as a station?
No. Depots have workshop loads such as cranes, jacks and compressors that can usually pause, with a smaller essential set for lighting, security, pits and control rooms. During depot construction or upgrades, rental power with temporary distribution is common.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.