At high altitudes, the properties of air change in ways that directly impact the way electric motors must be operated to maximize service life and productivity. Because air is less dense at high altitude, its capacity to carry heat away from the motor and keep it cool is significantly reduced. There is a range of approaches to combat this and maintain proper cooling of the motor. In addition, one of the altitude effects on electric motors that many operators are not aware of is that its insulating ability is reduced. In electronics with tightly packed components, this can lead to a phenomenon known as flashover, potentially destroying vital components and putting motor controls out of action.
Almost every electric motor is cooled by passing air over the body or through the inside of the motor, carrying heat away from the stator and rotor windings. The air's cooling ability is governed by the amount of air molecules that encounter hot parts of the motor. At high altitudes, the air is less dense, which means that there are fewer air molecules in a given volume of air, and therefore the air has less ability to cool the motor, and it runs hotter.
Most motors are designed to operate up to 1000 meters above sea level without requiring any special attention to cooling. Some of the highest elevation cities in Canada include:
- Canmore, AB (1,428 m)
- Elkford, BC (1,300 m)
- Cochrane, AB (1,159 m)
- Airdrie, AB (1,098 m)
- Okotoks, AB (1,051 m)
- Calgary, AB (1,045 m)
As a general rule of thumb, for every 100m above 1000 meters, the motor's maximum allowable temperature rise is reduced by 1°C. Operators have various options for achieving this and keeping the motor cool so that it provides long-lasting, trouble-free service.
If the motor is operated in an outdoor environment, it may not be necessary to do any more to keep the motor properly cooled, depending on the environment. However, many applications involve operating the motor indoors, in hot or climate-controlled environments. This means that additional measures will have to be taken to keep the operating temperature at an acceptable level.
A second option involves blowing air over the motor so that more heat can be carried away. For standard TEFC motors, this is not an option since the fan speed cannot be controlled independently of the motor. For a blower-cooled motor, increasing the speed of the blower will improve motor cooling. However, this may introduce additional problems, such as increasing the blower motor's operating temperature, which is also affected by altitude. Check with the equipment manual or manufacturer to determine safe speeds for your blower fan.
A third way to reduce the heat generated within a motor is to choose a larger motor and operate at a lower percentage of its full load; this is known as derating the motor. Because the motor's temperature is roughly proportional to the square of the current, operating a motor at a lower current than it is rated for means that the motor will remain cooler. This is the most frequently used option in industrial settings, with the motor derating factor incorporated at the design stage. The precise derating factor required depends on the motor and how it is cooled and should be checked with the manufacturer.
No matter which option is right for you, ensure that your motor is operating efficiently, with a minimum of stops and starts and changes in speed and torque. This will greatly reduce the heat stress and heat build-up inside your motor and reduce the need to address cooling issues.
When operating electronics at high voltages, two conductors that come close together can experience flashover, where the electricity jumps across the air gap between them and creates a short circuit. This can destroy components and put vital electronics out of action, incurring high repair and replacement costs. One of the things that protect against this is the insulating capacity of the air. At higher altitudes, less-dense air has a reduced capacity to insulate against flashover.
Most electronics are designed to operate at altitudes up to 1000-2000 metres. Above this, it may be necessary to purchase electronics such as speed controls designed specifically for use at high altitudes. Unfortunately, nothing can be done to modify existing electronics to operate at higher altitudes than they are rated for. It is necessary to take the risk of flashover into account at the design stage to ensure the right electronics are installed and the maximum service life is achieved.
The effects of altitude on electric motors can result in heat-stressed motors and damaged electronics unless careful planning is carried out at the design stage. By choosing the right motor and controls for your high-altitude application, you can save money and reduce your equipment's total cost of ownership.
At eMotors Direct, we offer a wide range of electric motors, speed controls and accessoriesfor every type of application and need.