Most motors are designed with the assumption that they will be operating in air conditions similar to those found at sea level. When motors are installed at higher altitudes, where air density is lower, this assumption can lead to challenges, particularly with temperature management. In this article, we’ll explore why these issues occur and what you can do to mitigate them.
Changes in Air Quality
As you move from sea level to higher elevations, the air quality undergoes significant changes. At higher altitudes, you will encounter lower air pressure and reduced air density, along with lower humidity and greater temperature fluctuations. Electric motors, especially induction motors, depend on ambient air to dissipate the heat generated by energy losses during operation. However, the reduced air pressure and density at higher altitudes make it harder for motors to cool down, which can lead to higher operating temperatures.
Effects on Motor Efficiency
The thinning of the air at higher elevations affects a motor’s ability to effectively dissipate heat. The combination of altitude, ambient temperature, and your motor’s specific temperature rise characteristics may necessitate de-rating your motor to keep it within the safe temperature limits of its insulation class. Key impacts of high altitude on motor performance include:
- Reduction in thermal capacity
- Decrease in combustion efficiency
- Reduced efficiency in heat dissipation, leading to overheating
- A temperature increase of about 1% per 100 feet of altitude gain
Allowing your motor to run as normal at high altitudes without adjustment can result in these problems and more, potentially shortening your motor’s lifespan.
Compensating for Altitude
According to NEMA MG-1 standards, it is recommended to de-rate your motor by 3% for every 500 meters (1,640 feet) of altitude above 1,000 meters (3,280 feet) above sea level. While more precise calculations can be done to determine the exact de-rating required for your specific motor and elevation, the following table provides general guidelines for de-rating based on altitude:
| Altitude (Feet) | HP De-rating Factor |
|---|---|
| 3,301 – 5,000 | 0.97 |
| 5,001 – 6,600 | 0.94 |
| 6,601 – 8,300 | 0.90 |
| 8,301 – 9,900 | 0.86 |
| 9,901 – 11,500 | 0.82 |
| 11,501 – 13,100 | 0.78 |
| 13,101 – 14,700 | 0.74 |
| 14,701 – 16,300 | 0.70 |
In addition to de-rating, you can compensate for the effects of high altitude by maintaining a lower ambient temperature around the motor, using a higher insulation class, or opting for a motor with a service factor rating. These measures can help keep your motor operating efficiently and extend its operational life in high-altitude conditions.
