Drive

Hello Guest,

<"....Why in AC drive or 3 phase inverter, output voltage is not measurable with respect to earth if output is of pulse width modulation ?....">

Because the output of that AC Drive or 3 phase Inverter does not have a Neutral Point which is connected to Earth, (The Output is totally Isolated, for Safety purposes), there is no Voltage difference, which may be easily measured.

<"....is it possible to draw only singe phase load from 3 phase inverter output ? if yes how?....">

Yes.

It is NOT ADVISABLE to attempt this, as damage to the Inverter, AC Drive, connected equipment or persons may result.

Kind Regards....

One of the most common faults I've seen on ASD/VFD is a ground fault. Motors and entrance bodies where conductors get made up that can get damp, seem to be the culprit sometimes--The drives seem to be able to sense the moisture, because there have been many cases where we got the drive to run without doing much. It is sometimes frustrating that the megohm readings we take may seem good, but the drive doesn't like it. Then other times a motor will meg marginal and the drive will run it. These are open drip motors in hot, damp environments with A/B 1336 plus II drives. Seems like black magic sometimes.

Inverters typically use Residual Current ground fault sensing. The 3 output phase currents are measured and must sum to zero. Any deviation outside of the tolerance level causes a trip. So even if your megohm meter reads high values, if there is enough of a difference in current flow, it will still cause the VFD to trip.

So for that reason, you usually cannot use a single phase load off of the output of a VFD. It's a bad idea anyway, most 1 phase motor loads have capacitors and the PWM output will damage the caps and/or the cap charging current will damage the transistors. It's a race to see which one pops faster.

WHY would you want to derive single phase from a VFD?

Hello noshorts

It seems that "Guest", like so many of that anonymous name, has not bothered to check the replies, after asking the question.

Kind Regards....

the multimeter you used for measurement can measure voltage in 50 Hz or 60Hz. But output of inverter is not 50Hz generally. Because of this you can not read measurement properly at out of 50Hz or 60Hz.

Hello Guest,

The first question is answered by spsrkstation.

This is for 2nd:

It is risky using one of the phase output (that will be two of the phase output actually) for a single phase load. There is already 3-ph. in / single ph. out inverters if the rated power is about 1 kW.

3 Phase PWM Drives are designed to drive closed delta connected systems. Hence phase to ground will not work properly if at all. There is one method to make this work for a limited part of your speed range...i.e. 30 Hz to 90 Hz.......on a 60Hz output...and this is to feed the output of the drive into a Delta-Y connected 1:1 transformer......

Once you have the transformer connected you can then connect your single phase load to the Y connected secondary.....

The limitation is the transformer efficieny curve will be affected by the frequency output due to the fact that the transformer is designed to operate at 60Hz....The loss may be minimal but the transformer manufacturer should be consulted so that you understand both the efficiency curve and the transformer heating curve based on operating frequency.....

`Dear ,

We can not Check votage on the Inverter out put Beacause Inverter out put Frequency is very high (0~650HZ ) .

If we check Voltage with Multimeter it is possible Multimeter OR Inverter damage ( this is espicalt applyable Lenze Inverter ).

We can not use Inverter out put Single Phase motor.