In short. Since 2018 Reddy Generators has maintained the standby diesel generators and fire-fighting pump engines at nearly 50 substations in three O&M divisions of Transmission Corporation of Telangana (TS TRANSCO), among them Yeddumailaram and Chandulapur, including the 400 kV substation at Narsapur. The work covers sets from 15 kVA to 250 kVA across four engine makes, Kirloskar, Cummins, Eicher and Greaves Cotton, under work orders from the utility’s O&M divisions. It includes repairs as well as servicing: at the Sadashivpet substation, a burnt alternator was rewound and the set returned to duty rather than replaced.
| Customer | Transmission Corporation of Telangana Ltd (TS TRANSCO), O&M divisions |
|---|---|
| Sites | Nearly 50 substations across three O&M divisions, including Yeddumailaram and Chandulapur, with sites such as 400 kV Narsapur and Sadashivpet |
| Since | 2018, continuing |
| Equipment | Standby DG sets 15–250 kVA; fire-fighting pump engines |
| Engine makes | Kirloskar, Cummins, Eicher, Greaves Cotton |
| Contract basis | Work orders issued by the utility’s O&M divisions |
| Scope | Preventive maintenance, breakdown repair, AVR servicing, alternator rewinding, fire-pump engine upkeep |
Why a substation depends on its diesel engines
A transmission substation must keep its protection, control and communications alive when the grid around it fails, because that is exactly when it is needed to isolate faults and restore supply. Station batteries carry the protection relays and breaker tripping, but battery chargers, control-room cooling, lighting, oil and gas handling, and many auxiliaries rely on the station’s AC supply. When both incoming auxiliary sources are lost, the standby DG set carries them. The fire-fighting system is just as critical: large power transformers hold thousands of litres of oil, and the diesel-driven fire pump must start on demand even with no electricity at all.
The challenge: many sites, mixed fleets, rarely run
| Challenge | Why it matters at substations |
|---|---|
| Sets run only in emergencies or tests | Low running hours hide problems: stale fuel, weak batteries, sticky governors, damp windings. The first real demand is often the first true test. |
| Four engine makes, sizes from 15 to 250 kVA | Each make has its own spares, settings and service intervals; one team must know them all. |
| Nearly 50 sites across three divisions | Response time and spares logistics decide how long a site stays unprotected after a fault. |
| Fire-pump engines must start without mains power | Battery, fuel and starter condition are life-safety items, not routine maintenance. |
What the work involves
- Preventive servicing of DG sets and fire-fighting pump engines: oil, filters, coolant, belts, batteries, fuel system
- Start and run checks so each set is proven, not assumed, to be ready
- Breakdown attendance and repair across all four engine makes
- Alternator rewinding and refurbishment instead of replacement where the machine is otherwise sound
- Automatic voltage regulator (AVR) servicing, testing and replacement on the generator alternators
Example: rewinding a burnt alternator at Sadashivpet
At TS TRANSCO’s Sadashivpet substation, the alternator of the 15 kVA standby set had burnt out. Replacing the whole set would have meant a new procurement cycle and weeks without standby power. Instead the alternator was taken out and overhauled: the main rotor was rewound with class F insulation and dual-coated copper wire, double-sleeved and double-varnished; the slip ring unit, cooling fan and bearings were replaced; the shaft was machined and refitted; and the stator was cleaned, varnished and baked to restore its insulation resistance before the alternator was refitted. Rewinding a sound machine typically costs a fraction of a new set and avoids the procurement delay entirely. See alternator rewinding.
Example: annual maintenance orders, Narsapur division (2023)
In November 2023 the O&M division of the 400 kV Narsapur substation issued letters of award for annual maintenance, with supply of materials, of the standby sets at four substations in Medak district. The scope covered B-check kits, filters, engine oil, fan belts and servicing, plus parts found necessary during service.
| Substation | Standby set | Additional items |
|---|---|---|
| 132 kV Kowdipally | 15 kVA, Kirloskar | Routine service kit |
| 132 kV Chinnashankrampet | 15 kVA, Eicher | New 100 Ah starting battery |
| 132 kV Yeldurthy | 15 kVA, Eicher | Routine service kit |
| 220 kV Minpur | 25 kVA, Kirloskar | Ignition switch and stop-solenoid coil |
Outcome and limits
A single contractor maintaining a mixed fleet of standby engines across nearly 50 substations since 2018 gives the utility one accountable point of contact for every make and size. Readiness still depends on regular test runs by station staff between visits, and on fuel being kept fresh.
Questions engineers ask about this work
What size DG set does an electrical substation need?
It depends on the auxiliary load the set must carry, not on the substation’s transmission capacity. In this fleet, sets range from 15 kVA at smaller substations to 250 kVA at the 400 kV Narsapur substation, where auxiliary loads such as cooling, lighting and battery charging are much larger.
Why rewind an alternator instead of replacing it?
If the stator core, shaft and frame are sound, a rewind with modern insulation restores the machine for much less than a new alternator, and far faster than procuring a new set. A failed insulation test after the rewind would change that decision.
How often should a standby fire-pump engine be run?
Fire-pump engines are normally run on a fixed weekly schedule under the site’s fire-safety procedure, so that batteries, fuel and starting are proven regularly. Follow the site’s applicable fire code and the engine maker’s instructions.
Engineering record reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Source: TS TRANSCO work orders since 2018 and Sadashivpet substation repair records, 2021, and letters of award from the 400 kV Narsapur O&M division, November 2023. Last reviewed: 20 October 2026.
Related: all verified projects · preventive maintenance · alternator rewinding · fire and site safety · discuss a maintenance contract