3 phase motor not running to correct speed 1

[robmwa]

Hi all

i have a 3ph star connected smoke extract motor which is meant to run at 2800 rpm but is only running at 1030rpm.i am getting 400v between phases.the motor came pre-wired with 6 tails off the motor.i connected them to suit a star connection,any help greatly appreciated.

 

[DickDV]

How fast does it run with the load disconnected?

 

[sreid]

Y connection is for start only? That would result in a lot of slip driving a "Fan."

 

[Marke]

Being a 400V motor, I suspect that you are in a 50 Hz region.
Usually, 50Hz 400 volt motors below 3KW are star connected for 400 Volts, and greater than 4KW, they are delta connected for 400V. This enables them to be used with a star delta starter.
I suspect that the motor should be connected in delta and it is not producing enough torque in star to get to full speed.
Continuous operation under these conditions will result in rotor failure due to the high slip losses in the rotor.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[robmwa]

i originally had the motor connected in delta and it was tripping the breaker,i even had the supplier out today looking at it,he is lost!!the plate on the motor says to connect the motor in delta for single phase and star for 3 phase.

 

[jraef]

NEVER heard of that! Something is definitely wrong, or that is one special motor (or there is another thing I don't know about IEC motors perhaps).

 

[7anoter4]

Hi robmwa
In my humble opinion as the rated slip of this motor is about 0.06 [3000-2800/3000]
The maximum slip may be[ 5-6 ]*0.06 =0.30-0.36.
In this actual case the slip is be about 0.6 that means in the unstable zone. The rotor should stop.
Since the rotor is moving I think the squirrel_ cage is damaged and so it will rotate as at a reduced frequency.
regards,

 

[robmwa]

hi 7anoter4
i should have mentioned that i actually have 16 of these,5 of which are being controlled by frequency invertors and same happening to them all.so chances of all motors being damaged?would the fact i had them connected in delta first have damaged the windings?

 

[ScottyUK]

This has a familiar feel to it: I've had similar problems with a high inertia fan tripping the breaker or thermal overload.

On one occasion I would have sworn that the motor nameplate was wrong (nameplate said 400D/690Y) after we wiped out a couple of contactors trying to start it ('Telemecanique TeSys', French words meaning 'expensive crap') but the underlying problem was the prolonged acceleration time causing the motor to draw very high current for about 40 seconds. The contactor failed after opening something close to locked rotor current a few times when the thermal relay tripped. It was one of the few occasions where I was pretty much forced to use a soft starter because there was no other way of starting it while maintaining thermal protection.


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If we learn from our mistakes I'm getting a great education!

 

[badservo]

If the fan does not have enough restriction it can be overloaded.

What is the nameplate data? what is the measured amps, measured volts with motor running, measured volts with motor not running? (let's stick with the non inverter version for now)

 

[robmwa]

it's a 2 pole 230d 400Y 3200rpm 1.6A running speed 10A start speed

on run its pulling 1.3A 420 volts with motor running and 400V without

 

[robmwa]

oh and there's no thermal relay as its a fire extract fan.

 

[Marke]

t's a 2 pole 230d 400Y 3200rpm 1.6A running speed

There is a clue!!
It is less than 3KW so it is probably delta 230V and star 400V, and the nameplate says 230d 400y. It should be connected in star for 400Volt!!

I would suggest that perhaps the motor is not capable of starting the motor and running it up to full speed. It is very unusual for a motor of this size to run out of torque on a fan at under half speed. Usually the torque curve of the motor is above 100% right through to full speed on a DOL start. The torque curve of the fan should not be anywhere near 100% until the fan gets to full speed. Is the motor the right size for the fan?? Sounds like it may be way too small.

If you have some on frequency inverters, try connecting one of them in star and slowly increasing the frequency, watching the current as you do so, and see how fast you can get it running without the current going above 1.6A
If you can not get to full speed, then I would say the fan is too large for the motor.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[7anoter4]

May be a Dahlander connection in order to reduce the speed?
see
DAHLANDER-CONNECTION, 750/1500 and 1500/3000 RPM

http://www.nyborgfan.com/manuals/Operation_and_Safety_Manual_Mez_Motors.pdf

 

[jraef]

If it were a two speed motor, his nameplate would have indicated two speeds and two FLC values.

the plate on the motor says to connect the motor in delta for single phase and star for 3 phase

This statement then was a red herring? Because later you said...

it's a 2 pole 230d 400Y 3200rpm 1.6A running speed 10A start speed
on run its pulling 1.3A 420 volts with motor running and 400V without

i originally had the motor connected in delta and it was tripping the breaker,i even had the supplier out today looking at it,he is lost!...

Much about the information you are posting is unclear and somewhat contradictory. Please look at and read the nameplate information ON THE MOTOR.

Here is (probably) why DickDV wanted to know if you had run with the load disconnected. If it was spinning at the correct speed with no load and dropped only when the load is connected, you are connecting the higher line voltage to the lower voltage pattern, in which case the motor will only develop 33% torque. With that low of torque, the motor cannot maintain speed and will go into high slip, which will eventually trip the circuit breaker (it would have tripped the OL relay first if you had one). But it would take a long time for a breaker to trip because even though you were running in high slip, by being in the wrong connection you would have also reduced the current to 33% of normal. So that may fit your scenario first described, you didn't say how long it took for the breaker to trip.

But if you are truly connecting in Star now, and Star is the pattern for the higher voltage, then there s some other serious problem, i.e. a single phase supply or an open winding in the motor. It is possible, although remotely, that because you had them connected in Delta first and without an OL relay, you may indeed have opened up a winding by the time the circuit breaker tripped. But on all 15 motors? Hard to imagine a disaster that pervasive.


Something to consider:
Sometimes when in the midst of a difficult problem, we make an initial simple error that we assume we did not make, and then all observations of problems and attempts to correct them are based on that initial error. Slow down, start all over afresh, assume nothing, forget the past experiences. Connect one motor without a load if possible and observe the running conditions, then connect the load and observe again.

 

[edison123]

I agree with jraef. You have posts contradicting each other.

First post states that the motor is meant to run at 2800 RPM, which indicates 50 Hz. (and a 6.66% slip seems too high).

Then you said "it's a 2 pole 230d 400Y 3200rpm 1.6A running speed 10A start speed" which indicates 60 Hz (and still too high a slip).

Pls post exactly what the nameplate says.

 

[7anoter4]

If the motor is designed for 2 supply system: single phase and 3_phase then is a condenser inserted c/w one of the phase to facilitate the start in single phase system.
If the motor was supplied with 3 phase system while was in single phase connection [delta] then the condenser was supplied with an overvoltage and exploded.
Then may be also a winding of one phase was disconnected by the damage and in the star connection ,only 2 phase winding remain connected.
I think , at least one motor has to be disassembled in order to check the damage.

 

[Marke]

I do not believe that it is a single phase / three phase motor. The motor nameplate says 230D 400Y and it is a small motor. This means that it is 230 volt three phase delta connected and 400 volt star connected three phase.
I think someone has interpreted the 230D to mean that it runs on single phase as the standard single phase voltage is 230 volt, however there are also 230V three phase systems around, plus single phase input VSDs put out 230V three phase.
This is a very standard configuration in the 50Hz world, so I see nothing strange or sinister about this. I believe that there is a simple misinterpretation of the 230 V connections.

What are the markings on the six tails? Are they arranged in a stud pattern, or are they flying leads?
I am wondering if there is a possibility of one winding reversed in star connection?

Best regards,

Mark Empson

http://www.lmphotonics.com