At high altitudes, the properties of air change in ways that have a direct impact on 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 are 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, which can potentially destroy vital components and put 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 cooling ability of the air is governed by the amount of air molecules that encounter hot parts of the motor. At high altitudes, air is less dense, which means that in a given volume of air there are fewer air molecules, 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 maximum allowable temperature rise for the motor is reduced by 1°C. Operators have a variety of 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 outdoors 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 operating temperature of the blower motor, 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 have it operate at a lower percentage of it’s full load, this is known as derating the motor. Because the temperature of the motor 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 option most frequently used in industrial settings, with the motor derating factor incorporated at the design stage. The precise derating factor required depends on the motor and the way 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 protects against this is the insulating capacity of the air. At higher altitude, 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 that are designed specifically for use at high altitude. Unfortunately, there is nothing that 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 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 the total cost of ownership of your equipment.
At eMotors Direct, we offer a wide range of electric motors, speed controls and accessories for every type of application and need.
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