I.D Fan Problem

Depending on the starting current code letter of the motor, the DOL starting current would be around 6-8 times FLC, or 852-1136 A. If the acceleration time is long, it seems more likely that the 100%O/L setting is tripping the CB. Keeping the inlet damper closed until the fan comes up to speed should help; it will still be dealing with acceleration but will not yet be pumping air. I doubt that Y-Δ will help much.

How are you measuring that 1350A? That would be very unusual / abnormal if it s the "starting" current, i.e. a sustained peak as the motor accelerates. But if you had a digital ammeter and had t set to "Peak" recording, you may have just picked up the instantaneous inrush current as the motor windings are energized, something that happens for no more than a second. 10X FLC is not that unusual for a modern energy efficient motor design now. If your MCCB is tripping immediately when you close the DOL contactor, that would mean it is the instantaneous inrush current.

But I hope you are not saying that you have a 1000A MCCB trying to protect a 142A load are you? Something is wrong there. Either you have mis-stated the values, you are leaving out some other details or someone has no clue on how to coordinate electrical protection equipment and you need to hire a professional engineer RIGHT NOW before your burn down your factory!

Normal starting conditions for a DOL ID fan should include a damper closed interlock. Is that working correctly?

Which overload is tripping, the panel MCCB or the motor protection? If it's the incoming MCCB it should be rated at 7 times inrush current.

Dear sir

The ID fan motors will take more time for starting and to come to normal speed. say 8 seconds,this means that starting current of say 1350 amps will prevail for 8 seconds.since the MCCB is set 1000 Amps,it is bound to trip,however the MCCB character curves to be checked.

Further it should be noted that the 1000 Amps MCCB will not protect the motor for over load

You can provide 250 Amps MCCB ,205 A contactor and a heavy duty thermal over load relay of range 115-180 A.This is as per type 2 coordination

You can also bye pass the Over load relay during starting by suitable circuitary

For ID fan application star- delta method of starting will have problems

I've heard some drivel in my time but this takes the biscuit!

Dear sir

I do not understand your comment.Can you please elaborate in simple English.

I think we need a better description of the MCCB, such as thermal rating vs magnetic rating, if it is a combination. My earlier estimate of 6-8 x FLC should also be updated in light of JRaef's note about higher-efficient motors.

@All Motor Having MCCB 250 Amps With Thermal Protection(O/L & S/C,E/F) and its panel MCC incomer having 1000Ams MCCB having microprocessor based Tripping(O/L & S/C,E/F)and motor also have a Digital motor protection relay.but tripping always happen in MCC incomer MCCB (1000Amps).and we are measuring current from Digital Motor protection relay having recording facility for max.current.

I am not surprised. The Incomer MCCB has a micro-processor based protection release. In such a release, the earth fault current calculation is normally by finding & summing the zero sequence components in the phase currents and if the sum is above the E/F setting, the MCCB will trip on earth fault. During the switching-ON of a motor, there will definitely be zero sequence components in the phase currents - due to the magnetising in-rush phenomenon. This could be wrongly construed by the microprocessor release as an earthfault and thus the MCCB is tripping. This will not happen in conventional thremo-magnetic releases.

General practice, to avoid such nuisance tripping is by introducing a time delay in the earth fault element, typically about 100 milliseconds or by providing a stabilising resistor in series with the earth fault element current coil.

Before starting this motor current what was the load current in the 1000A MCCB?. Give maximum not minimum information to find a solution.

What is the brand,Amp rating,frame size of motor MCCB?. How many motors(and kw)are connected to 1000A MCCB?. Is this a new MCC or it was functioning without tripping for a long period of time? Is it tripping when you start a particular motor and not tripping when starting similar(kW)motors connected to same incomer(1000A)?. You can write to the designer of MCC as well as to the manufacturer of MCCB and get their advice.

Install a VFD and soft start the motor. Base the drives output to the motor on the damper position, VIA feed back from the actuator to the speed reference on the drive. Or if it is to maintain some sort of building or supply static base it on the static requirements. You can set the ramp time on the VFD and it now becomes your device protection.

I think electricalexpert65 and pnaban are getting you towards the right track now, but it seems like it has been a lot of labor to extract useful information from you. That indicates to me that you are in over your head. This issue needs the attention of a professional electrical engineer that can visit the equipment and assess all of the contributing issues involved, not some best guesses from people 3,000 - 12,000 kM away.

I faced similar problem while commissioning a boiler. The ID outlet damper was leaky and the fan impeller torque requirement doesn'r match with the motor speed characteristic. Check the two points. In my case it was reaveled that the fan impeller improperly designed and motor rating was wrongly selected.

@panban The load a 1000Amps MCCB HAVE ONLY 50Amps.