In short. An air-cooled stabiliser rejects heat to room air through natural or fan-assisted flow. It is lighter, cleaner and simpler than oil-cooled units and suits most indoor commercial and light industrial sites. Ambient temperature, dust and ventilation decide whether it is enough.
Heat path
Copper and core losses → winding and core heat → air passing over surfaces → room → ventilation or air conditioning. If the room cannot remove that heat, temperature rises and rating falls.
Advantages and limits
| Aspect | Air-cooled |
|---|---|
| Weight and size | Lower for small and medium ratings |
| Fire and leak risk | No oil to leak |
| Maintenance | Clean filters and fans; no oil checks |
| Dusty or hot sites | Limited; dust clogs and heat reduces rating |
| Overload tolerance | Lower thermal mass than oil-filled designs |
Site checks
- Ambient temperature range, including the hottest hours.
- Ventilation: inlet and outlet clearance, room air exchange.
- Dust, humidity and corrosive air.
- Heat released into the room: losses in kW.
Heat to remove (kW) ≈ rated kVA × losses fraction
Ask the maker for losses at full load, then size room ventilation to carry that heat.
Derating
High ambient reduces permitted loading. Check the maker’s curve. Similar principles apply to generators. See ambient derating and altitude derating.
Maintenance
- Clean filters and vents on schedule.
- Check fan operation and noise.
- Inspect brushes and terminals with thermography.
- Log temperatures to see trends.
Compare with oil-cooled units.
Illustrative example
A 60 kVA unit with a few percent losses releases a couple of kW into a small closed room. Without ventilation, room temperature climbs through the afternoon and the unit trips on thermal protection. A louvre and exhaust fan solve the problem with no change to the stabiliser.
Ventilation sizing: a worked example
Assume a 100 kVA air-cooled stabiliser with losses of about 2 percent at full load. Heat released is about 2 kW. To remove that heat while holding the room rise to 5 degrees Celsius, the air flow needed is roughly:
Air flow (m³/s) ≈ Heat (kW) ÷ (1.2 × 1.0 × temperature rise in °C)
For 2 kW and a 5 °C rise, this gives about 0.33 m³/s, or roughly 1,200 m³/h. The figure is illustrative; use the maker’s loss data and the room’s actual conditions. In a closed room without such air flow, temperature climbs until the thermal trip acts.
Air quality and filters
| Condition | Effect | Response |
|---|---|---|
| Dust | Blocks vents, insulates windings | Filters and cleaning schedule |
| Humidity | Lowers insulation resistance | Dry location, heaters if needed |
| Corrosive air | Attacks contacts and terminals | Sealed enclosure or different design |
| High ambient | Cuts allowable loading | Derate or cool the room |
Routine inspection list
- Inlet and outlet clear of obstruction.
- Filter condition; clean or replace on schedule.
- Fan rotation, noise and current.
- Winding and terminal temperature with an infrared camera at load.
- Control and protection test.
Fault diagnosis
| Symptom | First check |
|---|---|
| Thermal trip at midday | Room temperature and airflow |
| Rising trip frequency over weeks | Clogged filters |
| Hot terminal | Tightness and contact condition |
| Fan noise | Bearings or obstruction |
Siting advice for Hyderabad conditions
Summer ambient temperatures in the region can be high and electrical rooms often have limited ventilation. Place the unit where hot exhaust air does not recirculate to the inlet, and avoid sharing a small room with other heat sources such as UPS units or transformers unless the combined heat has been calculated.
The master engineering question
Where does the heat go at the hottest hour, and does the unit still carry full load there?
What to send us
Send site temperature, room size and load. Send your application details.
Questions engineers ask
Can I place it in a closed room?
Only with enough ventilation or cooling for its losses.
Is air cooling suitable above a certain rating?
Maker-specific; large ratings often use oil cooling.
Do filters matter?
Yes, clogged filters raise temperature.
What about noise?
Fans add noise; check site limits.
Values are illustrative. Use manufacturer data.