How to Size Overcurrent Protection for Frequency Inverter (1)
Frequency inverters (variable frequency drives, VFDs, frequency converters) are electronic controllers, used on electrical alternating current (AC) motors. Variable frequency drives (VFDs, frequency converters) adjust the speed of ac electric motors by modulating the power being delivered.
These AC drives control the speed of AC motors in a very accurate fashion. In most all applications the adjustable frequency drives provide overcurrent protection for the motors. The main feed of electrical power to the frequency drive must still have some form of overcurrent protection to safely power the drive unit. Sizing the overcurrent protection, regardless of the specifications provided with the drive unit, may still require calculation.
How to size overcurrent protection for frequency inverter? Let's follow these 4 steps:
1. Obtain the electrical specifications from the electrical alternating current (AC) motor's nameplate tag. The nameplate data tag is generally placed on the motor, near the topside of the exterior frame. The operational voltage, the full load amperage, the horsepower and the power factor rating are recorded on the motor nameplate.
As a particular example, an ac motor may have the operational specifications of 480 v at a 20-ampere full load capacity with a horsepower (hp) of 12 hp. The power factor rating of this ac motor is 1.0. (To be continued)
