If there is a "momentary Powerloss Ride Through" parameter in the VFD, please enable it.

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Bear in mind that, on a 50Hz supply, the distance between the +peak of a cycle and the -peak is 10 milliseconds. If the undervoltage trip is set to these sorts of values, then expect it to nuisance-trip.

Thanx a lot for your precious reply.

I'ld like to add some more info. & let me clear some of your doubts.

For Mr. electricalexpert65-The VFDs has a function of "Flying Restart" with 06 objectives but it doesn't work due to "Ramp up" & "Ramp down" time functions. (We'd tried for that one too but ...... no use). This function works exactly same that you've suggested about "Momentatry powerloss ride through".

For Mr. pwslack - The question arises about measurement of +peak of a cycle
and the -peak of the cycle. If I'm not wrong then in my knowledge, undervoltage tripping depends on the time that DC Bus voltage remains low below the Undervoltage tripping voltage level (i.e. if it remains low below 530V for about some seconds then it trips). If there's any error pl. make me correct.

For Mr. Guest - You are right that operating voltage is from 380 - 15%. Let me clarify you, sometimes it is also observed undervoltage tripping at a voltage upto 394V which is observed on our digital recorder too.

1). Undervoltage measurement is of mains supply of VFD & not of the DC link voltage.

2). There is a pure power dip problem & no power loss. We'd tried whatever you've suggested. Pl. refer my very first answer.

3). Other drives MM440 & others (Master/Sinamics) lies within a range from 1.1 KW to 315 KW with different applications.

Pl. note that, We also have 02 nos. of MicroMaster 430 drives 132KW capacity for fan application, but they aren't tripping on undervoltage.

4). Whatever you've suggested in your answer about adding of additional capacitors to avoid undervoltage, will it solve it? Because in my knowledge capacitor & inductor used in the VFD after rectifier section used for smoothning the DC o/p voltage.

This problem can be solved by not adding the capacitors but adding a huge no. of DC volt. batteries (say around 100 nos.) to the DC link but which could cost a lot. We've seen this impleted in another company.

The main thing is that this problem is also referred with Siemens itself but they also'd given up.