https://www.automationdirect.com/drives/ac-drives (VID-DR-0004)
How to select the right AC Drive
Part 3 of 4
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three steps to selecting the right AC drive this is step two selecting the proper rating in a typical application you can control a 1 horsepower motor with a 1 horsepower drive but there are some cases where the application type and environmental conditions warrant the rating of the drive requiring a drive larger than the typical application we will be using two scenarios for selecting the proper rating scenario 1 will be used in a GS2 series AC Drive scenario 2 will be used in a durapulse AC Drive the motor full-load amperage is required in determining the correct AC Drive size the full-load amp rating can be found on the motor name plate for scenario one we'll be using a 5 horsepower motor rated at 6.5 full Lo amps with the following application and environmental factors for scenario 2 we'll be using a 7.5 horsepower motor rated at 10.7 full load amps in the following factors many applications experience temporary overload conditions due to starting requirements or impact loading most AC drives are designed to operate at 150% overload for 60 seconds if the application requires an overload greater than 150% or longer than 60 seconds the AC Drive must be oversized applications that require replacement of existing motor starters may require up to 600% overload there are three different conditions used to calculate the overload requirements one if the overload is less than 150% for less than 60 seconds divide by its value which should always equal one then multiply by the motor full load amps two which fits scenario one if the overload is greater than 150% for less than 60 seconds divide the overload by 150 which equals 1.33 and multiply by the motor full load amps of 6.5 giving an overload result of 8.66 amps three which fits scenario two if the overload is longer than 60 seconds divide the overload by 100 which equals 1.35 and multiply by the motor full load amps of 10.7 giving an overload result of 14.44% decrease in cooling most AC drives are designed to operate at 100% capacity up to altitudes of 1,000 m above 1,000 M the AC Drive must be derated use the following calculations to adjust for altitude if the altitude is less than 1,000 M enter 1 then multiply by the overload result for scenario 1 the altitude result is 8.66 amp if the altitude is greater than 1,000 but less than 3,000 M enter 1 and add the result of altitude minus 1,000 multiplied by 00001 which is the same as 1% per 100 m over 1,000 multiply the result in this case 1.01 by the overload result for scenario 2 the altitude result is 14.58% significant amount of heating will cause the internal temperature of an enclosure to exceed the rating of the AC Drive even when the ambient temperature is less than 40° C enclosure ventilation and or cooling may be required to maintain a maximum internal temperature of 40° cus or less ambient temperature measurements and calculation should be made for the maximum expected temperature reducing the carrier frequency on AC drives generally lowers the operating temperature which will help prevent overheating use the following calculations to adjust for maximum enclosure internal temperature one if the enclosure temperature is less than 40° C as in scenario 2 and using any series AC Drive multiply the altitude result by one which makes the meit result 14.58% C but less than 50° C and using a GS series AC drive up to 5 horsepower as in scenario 1 multiply the altitude result by one which makes the Mei result 8.66 amps three if the temperature is greater than 40° C but less than 50° C and using a GS series AC Drive greater than 5 horsepower or any Dura pulse AC Drive multiply the altitude result by 1 Point 2 for the GS2 series The adjusted rating is 8.66 amps according to the specification chart a 5 horsepower driv rated output current of 8.2 amps is not sufficient for our application therefore we will use a 7.5 horsepower Drive rated at 13 amps for the durapulse drive the the adjusted rating is 14.58% motor three the installation altitude and four the maximum enclosure internal temperature we're now ready for step three selecting the accessories
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