How Added Service Factor Benefits You
Having a higher service factor is like having extra power in your back pocket that you can spend any way you want – whether you need it to overcome frequent overloads, high ambient temperatures and altitudes, bad environments or poor supply conditions. Think of it as your built-in reserve capacity to use as-needed. Even at no stress, the added service factor can lower the motor operating temperature and increase its overall life expectancy.
Elektrim Motors have some of the highest service factors in the marketplace – up to 1.4 – making it more capable than other brands to endure a variety of conditions at nameplate values (i.e. without having to derate the motor). Let's find out how and why:
According to NEMA Standard MG1-1.42: "The service factor of an ac motor is a multiplier which, when applied to the rated horsepower, indicates a permissible horsepower loading which may be carried under the conditions specified." The usual service factor for most motors in the marketplace from 1-200 horsepower is 1.15, although some manufacturers list only 1.0.
This means that during intermittent overload conditions, a typical 5 HP motor on the marketplace with a 1.15 SF is capable of operating at 5.75 HP (5 HP x 1.15 SF = 5.75 HP) before damage to the motor can occur. On the other hand, an Elektrim 5HP motor rated with a 1.4 service factor can operate as a 7 HP motor (5 HP x 1.4 SF = 7 HP) under the same conditions as a competing motor with only a 1.15 SF. Similarly, an Elektrim 50HP motor with a 1.3 service factor has the ability to operate as a 65HP motor. This gives Elektrim users more added power to overcome overload situations caused by intermittent variations in plant operations, materials and conditions.
Service Factor can also be “spent,” so to speak, to withstand intermittent or continuous high ambient temperatures found in a variety of locations from ship engine rooms to casting houses and more. Due to the high service factor of Elektrim Motors, many motors can operate at nameplate values under these conditions without having to de-rate the motor, and impact power.
For example, a motor needing to operate at 60°C would have a de-rating factor of .82 at 3300’. A standard motor starting with 1.15 SF would need to be de-rated to 47 HP. (50 HP x 1.15 SF x .82 = 47.15 Max HP). An Elektrim motor starting with 1.3 SF could operate as a 50 HP or higher. (50 HP x 1.3 SF x .82 = 53.3 Max HP)
Service factor can also be used to determine if a motor can be operated continuously at altitudes higher than 3300 feet satisfactorily. At altitudes greater than 3300 feet, the lower density of air reduces the motor's cooling ability thereby causing the temperature of the motor to be higher. This higher temperature is compensated for by reducing the effective service factor to 1.0 on motors nameplated with a 1.15 service factor or greater. Having a higher service factor to start with, as with an Elektrim motor, ensures that your motor can run at higher ambient temperatures and altitudes without being overly stressed.
You can also “spend” your motor’s service factor to compensate for low or unbalanced line voltage, for temporary ventilation restrictions caused by dirt buildup, or to allow for an increased power demand caused by process expansion or a higher production rate.
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Posted on: May 19, 2015
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