Question

Some models of Hitachi inverters will accept either single phase or three-phase power input. How do I know which input power type to use? Can the drive power a single phase motor?

Answer

If three-phase power is conveniently available for your application, we recommend using that (the inverter can develop its three-phase output power most efficiently from three-phase input power). In the absence of three-phase power, you can use a single-phase power source with slightly less efficiency but the power output rating is the same for N models (single or three-phase).

All Hitachi inverters develop a variable three-phase output, requiring the use of a three-phase AC induction motors.

Sizing single phase drives:

1) Higher motor current for single vs. 3 phase - this is about double (x 1.732 to be exact, but double for selection purposes). You must also account for peak motor current (application dependent), and select the proper drive size based on its output current capacity, rather than hp rating.

2) The fact that one input phase is missing means that part of the input bridge is carrying higher current than it normally would. You must make sure that the input current does not exceed the rating of the drive.

3) Since we are only rectifying single phase, the harmonic content is higher, and different in frequency composition. This means that an input line reactor is a definite requirement. Also this impacts on the DC Link, and the higher harmonic content may adversely affect the life expectancy of the DC Link capacitors. There is no easy way to calculate this, but if the drive is sized adequately, this is not a major issue.

Standard practice is to double the size of a 3-phase rated SJ300 drive when using single-phase input. Connect power (L1)to "R" and (L2) to "T" terminal, and jumper "S" and "T" together. Under no circumstances can the output be used on a single-phase motor.

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FAQ Subcategory: None

This item was last updated on 2008-12-22
Document ID: 291

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