Altitude derating is not one fixed percentage applied to the whole genset. Engine air and combustion, radiator heat rejection, fan duty, alternator temperature rise and installation each have limits; the first limit governs usable output.
Engineering scope
Teams selecting, expanding or troubleshooting generation at high-altitude, hot or dusty mine sites.
Separate engine, cooling, alternator and installation limits instead of applying a generic derating percentage.
Obtain component confirmations, usable continuous output, starting boundary and site-test conditions.
Fix the altitude, maximum intake temperature and installation first. Obtain limits for the exact engine, radiator and alternator configuration; the genset rating cannot exceed the lowest available component boundary.
01
Define the actual site environment
At the same altitude, intake temperature, solar load, recirculation, dust and fouling create different results. Use the adverse continuous condition, not a nearby city average.
- Record elevation and pressure data
- Provide maximum ambient and intake temperature
- State indoor, container or outdoor installation
- Describe dust, wind, solar and recirculation risk
02
Review engine air and combustion limits
Lower air density affects combustion air. Use the exact engine, turbocharging, fuel setting and speed to obtain manufacturer correction data.
- Confirm complete engine model and calibration
- Obtain continuous power at combined altitude and temperature
- Check intake and exhaust restriction
- Confirm transient loading and smoke limits
03
Confirm site heat-rejection capability
Available engine power does not prove that heat can be rejected. Radiator, fan, ducting, louvers and recirculation determine cooling margin.
- Confirm radiator ambient design rating
- Check airflow, static pressure and louver loss
- Prevent hot-air recirculation
- Allow for dust fouling and cleaning interval
04
Review alternator temperature rise and load
Altitude and temperature also reduce electrical cooling. Confirm kVA against insulation, temperature rise, power factor, harmonics and unbalance.
- Confirm alternator model and temperature-rise class
- State power factor and reactive demand
- Identify VFD and rectifier harmonic loads
- Review starting dip, fault duty and unbalance
05
Close with a system limit and site test
Place component limits in one capability table and use the lowest boundary. Compare it with continuous load, largest starting step and reserve, then validate through staged loading.
- Compare standard and site conditions
- Record component source and data revision
- Define loading steps and stabilization time
- Retain hot-period temperatures, voltage, frequency and alarms
Data required for derating review
| Environment | Altitude, pressure, maximum temperature, solar, dust and installation |
|---|---|
| Engine | Model, calibration, restrictions, continuous and transient limits |
| Cooling | Radiator rating, airflow, pressure, louvers, ducting and recirculation |
| Alternator | Model, rise, insulation, power factor, harmonics and unbalance |
| Load | Continuous kW/kVA, largest start, combinations and expansion |
| Validation | Load steps, temperatures, smoke, voltage, frequency and alarms |
Three common errors
Applying one fixed percentage
Component limits vary; a generic value cannot replace configuration confirmation.
Checking engine power only
Cooling or alternator limits may prevent continuous genset output.
Testing only in cool weather
A cool test does not prove hot-season or fouled-radiator capability.
Package required for manufacturer review
- Altitude and maximum intake temperature are confirmed
- Complete engine, radiator and alternator models are available
- Continuous load and largest starting step are provided
- Airflow, louvers and recirculation are documented
- Manufacturer limits show revision and conditions
- Staged load and hot-condition retest are defined