MCB OK and MPCB not OK for VFD

http://cr4.globalspec.com/thread/25466

Check this.

On VFDs I would size your breakers for the conductors and leave the motor protection to the drive and possibly add a line filter between the drive and motor.

Thankyou

How to calculate the Line reactor for my 30HP motor

Hire a competent electrical engineer or a qualified electrician.

The Line reactor will reduce earth leakage peak currents caused by the inverter switching pulses charging the motor cable capacitance. This can cause inverter 'overcurrent' trips (nuisance). Unless you have 100m+ of armoured cable you may not really need this, but, if required, a value of 1mH and a current rating to cover the motor FLC will suffice and set inverter switching frequency to a lower level, say 3 - 4kHz to stop choke core overheating. However, I think the MPCB is unlikely to be affected by the inverter output to the motor.

The MPCB is likely affected by the 'rectifier' current shape at the inverter supply, so it may be unsuitable for an inverter load as opposed to a sinusoidal motor load. You can improve the waveform by adding an input choke or a DC choke if this isn't included in the inverter already. Normally though, select cable for inverter input (RMS) current and protect accordingly with fuses or CB. The motor overload should be taken care of in the inverter but not all offer good single phasing proection. Better would be thermistor protection in the motor if the plant operation is critical.

Likely questions:

What is the inverter rated input current? (On the nameplate)

What is the MPCB / MCB rating? (Current and type)

What RMS current are you drawing in operation?

we have the frequent problem in drives because of power serge.

this 3 phase line reactor will help us or not?

how much it cost?

please inform me

What kind of problem does the power surge give your drives?

Overvoltage trips?

Input bridge failure?

Transistor failure?

An input reactor and varistors will definitely offer some protection from surge but it will depend on the total energy and duration of surge as to exactly how much this helps. You can configure some drives to disconnect from supply before the voltage goes too high if you use choke to slow down the charging rate. An input choke coupled with a DC choke for AC drives is a near best scenario if you have severe problems and failure of semi-conductors.

I would need more details (supply V, Hz, kW, type of drive etc, type of surge cause)to be able to recommend some options if you want some parts recommendations - not sure how you do this via this forum??

I believe one advantage that we targeted with the filters was to subside the voltage spikes created in remaking the alternating wave and protect the motors from breakdown voltage and keep the drive from piercing the motor insulation.

<...how much it cost?...>

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A company called MTE has a good tables for industor sizing.

http://www.mtecorp.com/index.html