In short. A textile mill is a drive-dense, humidity-dependent, continuous process, so its generator must be sized on the restart sequence and the humidification plant, not on the connected load. Spinning and weaving tolerate a short break if machines restart in a controlled order; dyeing and finishing often cannot. Classify departments by consequence, size for the largest motor start on top of the running load, and allow for harmonic current from inverter drives.
Why a textile load is different from a factory load
A spinning mill in Telangana or Andhra Pradesh runs around the clock, and electricity is usually its second largest cost after fibre. The load is made up of hundreds of small and medium motors on blow room, cards, draw frames, speed frames, ring frames, autoconers and looms, plus a humidification plant that can be a fifth of the whole demand. Very little of it is resistive, much of it is on variable-frequency drives, and almost none of it can simply be switched back on together after an outage.
The consequence of an interruption is also unusual. On a ring frame an outage breaks ends across the whole machine, and the piecing work that follows costs more production than the outage itself. In a dye house a stopped jet or soft-flow machine mid-cycle can mean shade variation and a re-dye. On a stenter, a stop with fabric in the chamber can scorch the cloth. These are process losses, not just lost minutes, and they decide what the generator must protect.
Classify departments by consequence, not by kW
The useful first step is a department-by-department table that records what happens one second, one minute and one hour after supply is lost, and what must be running before that department can restart. The pattern below is typical of composite mills, although the numbers belong to each site.
| Department | Consequence of a short outage | Must be live before restart | Usual backup class |
|---|---|---|---|
| Blow room and cards | Lap and sliver breaks, cleaning time | Filtration and waste suction | Short break, staged restart |
| Ring frames and autoconers | End breaks across the frame, piecing labour | Humidification, compressed air | Short break, one frame at a time |
| Looms (air-jet, rapier) | Stop marks, weft breaks | Compressed air at pressure | Short break, compressor first |
| Dyeing and finishing | Shade variation, scorching, re-processing | Thermic fluid or boiler auxiliaries | Essential, short break |
| Humidification plant | RH drift, yarn breakage rises within minutes | None, it is the enabler | Essential, first on the bus |
| Offices, lighting, canteen | Inconvenience | None | Shed or restore last |
Two points usually surprise mill owners. The humidification plant and the air compressor are production enablers and belong at the top of the restoration list. And the processes that look least electrical, such as dyeing, often have the least tolerance for a break. A structured approach is described in critical-load classification and prioritisation.
Sizing: running load, starting steps and harmonics
Three things set the generator rating in a textile mill. The first is the running load of the departments to be backed up, measured rather than taken from nameplates, because textile motors run well below rated output most of the time. The second is the largest load step that will be applied during restart, which is normally a humidification fan bank, a chiller or an air compressor started direct-on-line. The third is the harmonic current drawn by inverter drives, which heats the alternator and distorts voltage for every other machine on the bus.
S = P / PF
Here S is apparent power in kVA, P is the real running load in kW and PF is the power factor at the generator terminals, typically 0.8 for sizing. For a spinning unit with a measured running load of 900 kW on the protected departments, S is 1,125 kVA at 0.8 PF (illustrative). If the largest single start is a 110 kW humidification fan on a star-delta starter, the step is manageable on a set of that size, but if a 160 kW screw compressor must start direct-on-line, the transient dip should be checked using the method on motor starting on generators. Where more than a third of the load is on variable-frequency drives, many engineers specify the alternator one frame size larger or request the manufacturer’s nonlinear load rating; see harmonics and THD.
One large set or several smaller sets
Mills that need the whole process on backup often do better with two or three sets in parallel than with one large unit. Partial load is then carried by fewer engines at better efficiency, one set can be serviced without losing backup, and the controller can add sets as departments restart. The trade-offs are covered under generator paralleling.
Restart sequencing is where the plan succeeds or fails
A generator that is correctly sized can still trip on restart if the operators or the AMF panel reconnect everything at once. A workable sequence for a spinning unit looks like this.
- Humidification plant fans and pumps first, so relative humidity recovers while machines are being prepared.
- Air compressors next, run up to pressure before autoconers and air-jet looms are touched.
- Preparatory machines in process order, blow room before cards before draw frames, so material flow is re-established.
- Ring frames one or two at a time, with a short pause for the inrush of each frame’s main motor and spindle drive.
- Lighting, offices and the canteen only after production is stable.
Where the mill has a load management system, these priorities should be programmed as timed steps; where restart is manual, they should be printed and posted at the PCC. Either way the sequence has to be rehearsed on a planned test, not discovered during a monsoon outage. Guidance is on restart sequencing.
Keeping the plan aligned with the mill
Textile demand changes with count, blend and machine replacement. A move to compact spinning, the addition of autoconers, or a new humidification plant can shift the running load by a quarter without anyone updating the generator file. Record the assumptions used when the set was sized, including which departments were included and the measured load that day, and review them whenever machinery changes. Note planned expansions so that generator room space, cable routes and fuel storage are not boxed in. The general method for this is set out on generator sizing, and the wider industrial context on industry power solutions.
Common mistakes
- Sizing from the connected load of every motor in the mill. The set is far too large, runs lightly loaded, and suffers wet stacking and high fuel cost per unit.
- Treating the humidification plant as a comfort load and leaving it off the standby bus. Relative humidity falls, end breaks climb, and production on generator is worse than production stopped.
- Ignoring harmonic loading from inverter drives when selecting the alternator. Voltage distortion trips drives and overheats the alternator windings over time.
- Restarting ring frames in bulk after transfer. The combined inrush trips the generator breaker and the whole sequence starts again.
- Never reviewing the sizing after machinery changes. The backup that was adequate at commissioning silently becomes undersized.
What to send us
Send a department-wise load list with measured running kW where you have it, the single-line diagram of the mill, the rating and starter type of the humidification fans, compressors and chillers, and a note on which departments must stay in production on backup. Photographs of the existing generator nameplate and the AMF or PCC panel help if a replacement or an addition is being considered. Send your textile power requirement.
Questions engineers ask
What size generator does a spinning mill need?
There is no rule of thumb per spindle that survives contact with a real mill. Measure the running load of the departments you intend to back up, add the largest motor start, and allow for the nonlinear load from drives. A unit with 900 kW measured running load typically lands in the 1,000 to 1,250 kVA range (illustrative), but the sequencing plan matters as much as the rating.
Should the humidification plant be on the generator?
Yes, and it should be among the first loads restored. Without controlled humidity, yarn breakage rises within minutes and the production you are trying to protect is lost anyway.
Do inverter drives on ring frames and looms affect generator selection?
They do. Drives draw non-sinusoidal current, which raises alternator heating and voltage distortion. Ask the generator manufacturer for the nonlinear load rating, or select the alternator one size up when drives make up a large share of the load.
Is it better to back up the whole mill or only critical departments?
That depends on how long outages last and what a stopped department costs. Many mills protect humidification, compressed air, dyeing and a subset of spinning or weaving, and shed the rest. The decision should be written down with the reasons, so it can be revisited.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.