motor overcurrent

[HARRY 7]

I installed a new 3phase motor 1hp.The old one had burnt.The new one is not the same brandt with the old one.The electrical connection of the new one is 380v star connection 2,02A,220v delta connection 3.6A.I connect in star and begin the motor.I measured the current and found 3.7A in each phase!What could be the problem??
I forgot to say the motor is in a water coil clima unit.

[Brian_UK]

Is the motor driving the fan?

If so then check the airflow, if the fan is handling more air than design then the amperage will increase.

Where you testing the amperage with the plant access door open?

[HARRY 7]

Hello Brian.The motor is driving the fan but it has the same strength with the old one.I don't know if it has the same rpm.The unit supplies air from the enviroment,to the floor..

[NoNickName]

Actual voltage?
Are the terminals correct for a star connection?

[Yuri B.]

Or maybe frequencies of the motor and the net not corresponding.

[chilliwilly]

This might sound like a stupid question but is the motor invertor driven or contactor driven? If its invertor driven make sure that the motor decal plate spec matches the parameters in the invertor programme. Especially the voltage.

Its unusual for a motor to be connected in star these days when invertor driven motors have the torque and inrush current controlled externally by the invertor.

I bet your going to tell me that the old motor is connected in star now aren't you :o.

[NoNickName]

What an inverter has to do with all of this? There is no clue any inverter is used here.
Now, will the OP answer please to the questions?

[chilliwilly]

What an inverter has to do with all of this? There is no clue any inverter is used here.
Now, will the OP answer please to the questions?

Thats right, thats why I asked the question.

[HARRY 7]

It is not an inverter motor guys.The star connection is the correct.The voltage is 400V.

[HARRY 7]

I forgot to say that the motor moves the fan with a belt.

[Peter_1]

Belt tightened too much?
Motor overloaded, too small for your application.
One phase wrongly connected in factory, have you measured all 3 phases separately?
Is the star connection with plates?

[HARRY 7]

Hi Peter 1.The star connection is with plates.I have measured the 3 phases separately.The motor has the same power with the old one.I am not sure about the rpm.Can an overtightened belt or a smaller motor increase the amperage?

[Peter_1]

If the kW on the motor are the same as you said, then your present motor isn't smaller.
Over-tightening the belt can give such a big differences in AMP reading. (3.7 instead of 2 A)
This can be the reason why the old one failed, capacity too small.
Isn't the coil completely clogged. The motor is driving a fan of what?

[HARRY 7]

The motor is driving a fan in a ducted water climatism unit which brings fresh air and distibutes in offices.The coil and the filters of the unit are clean.

[NoNickName]

When one says the voltage is 400V, it means he didn't measure it.
Besides, is the number of motor poles the same than before? 2-4 and 6 poles motors are quite frequent, but their speed is approx 2950, 1450 and 950 rpm respectively.
The current absorbed is proportional to speed, if you dont' adjust the ratio of pulleys.

[DTLarca]

When one says the voltage is 400V, it means he didn't measure it.
Besides, is the number of motor poles the same than before? 2-4 and 6 poles motors are quite frequent, but their speed is approx 2950, 1450 and 950 rpm respectively.
The current absorbed is proportional to speed, if you dont' adjust the ratio of pulleys.

The power is proportional to speed change ratio cubed.

½mv² = mgh

h = ½v²/g

The height the air column rises to is proportional to the speed of the impellar squared. That means throw the air up at twice the initial speed and it will climb four times as high. A column of air four times as high will exert a gravitational pressure downward four times greater. So the pressure the fan creates on account of doubling the speed is quadrupled.

The volume of air pumped is doubled if the fan speed is doubled.

Power = PV/µ = 2² x 2 = 2³.

Thus the amps should increase by a factor of 8, from just over 2A to 16A if the fan speed is doubled when half as many poles are used.

[NoNickName]

The power is proportional to speed change ratio cubed.


Not in the real world, because motor slip and pressure drops play a role.

[DTLarca]

Testing...

[DTLarca]

NNN - you are wrong.

[DTLarca]

I can't post a full reply in one post - I shall try stretch it over a number of posts...

[DTLarca]

v = √(2gh) meaning velocity is proportional to the square root of the height.

[DTLarca]

I give up - posts not working - but you are very wrong.

[NoNickName]

posts not working

:D

Try again next time.

[DTLarca]

Your ignorance astounds me :p

[DTLarca]

Slippage = higher amps. Pressure changes negligible = amps will still be over 8 times higher :)

[nike123]

I installed a new 3phase motor 1hp.The old one had burnt.The new one is not the same brandt with the old one.The electrical connection of the new one is 380v star connection 2,02A,220v delta connection 3.6A.I connect in star and begin the motor.I measured the current and found 3.7A in each phase!What could be the problem??
I forgot to say the motor is in a water coil clima unit.

What is old motor make and model number?
What is new motor make and model number?

[HARRY 7]

I don't have the old motor Nike,somebody else removed it.I installed the new one which they said had the same power with the old one but different brandt.The new one is a Stanfam ms 902-4.
1HP power

[DTLarca]

Are the fan blades forward curved?

You may need to adjust the inlet vanes or the discharge damper or some such to increase the system pressure drop to reduce the fan motor power requirements.

Fan Power = Pressure x Volume

If you close the discharge damper you raise the pressure but the volume reduces at a greater rate than the pressure rises and thus power requirements drop.

Forward curved fans easily overload if their is not enough system restriction.

Brian alluded to this.

There could also be system effect taking place - if the inlet ducting is configured such that air is being pre-whirled against the fan direction then performance of the fan will go up but so will amps. You may need to reconfigure the inlet ducting.

Close off the pre-diffuser dampers if you have no other means. Otherwise slap a bigger motor on their.

[DTLarca]

Why am I spelling there as their? Age?

[HARRY 7]

Thanks DTLarca.The fan blades are forward curved.I will check for damper to reduce the volume of the fan,but i was curious, because the new one had the same power with the old one but the amberage too high!

[DTLarca]

A piece on forward curved fans attached...

[HARRY 7]

You are very informative DTLarca:).

[chilliwilly]

When one says the voltage is 400V, it means he didn't measure it.


20 volts more than 380 volts :eek:

My words what are the supply authoroties thinking of not feeding at 380 volts? :rolleyes:

Hey NNN what you do if you came across a slightly higher voltage than what was stated on the decal?

Let me guess... disconnect it and make a complaint to that shower of sh!te in Brussells.

[DTLarca]

20 volts more than 380 volts :eek:

My words what are the supply authoroties thinking of not feeding at 380 volts? :rolleyes:

Hey NNN what you do if you came across a slightly higher voltage than what was stated on the decal?

Let me guess... disconnect it and make a complaint to that shower of sh!te in Brussells.

380 ±38 (10%) is fine?

[mad fridgie]

NNN and DT,
changing the poles.
Increasing the speed will as DT says increase amps proportially to the reduction in poles, BUT the blade speed can only be achieved, if you have the moter power available, in this case clearly not.
The moter is likely to a LRA of 16amps, no rotation. No airflow
As this is a fan and not apositive displacment, it will rotate. As the speed increases so does the load, as the load increases, the moter slows (slippage If i understand how NNN is applying it) to a point where mechinical/electrical equalibrium is reached

[chilliwilly]

380 ±38 (10%) is fine?


Yes more than fine.

[NoNickName]

20 volts more than 380 volts :eek:

My words what are the supply authoroties thinking of not feeding at 380 volts? :rolleyes:
I don't know what you're talking about. 380 doesn't exist anymore in most of european countries
What I meant is that perfectly 400V is a mere wishful thinking, as it's more the case with e.g. 397/395/399.
When one says 400V clearly hasn't measured the voltage.

Think before puking on your keyboard.

[nike123]

I don't have the old motor Nike,somebody else removed it.I installed the new one which they said had the same power with the old one but different brandt.The new one is a Stanfam ms 902-4.
1HP power

Then, you are acting on behalf of someones statement without possibility to check for yourself if the motors are matching.

Now, what is unit make and model?

[HARRY 7]

When i said 400V i meant that this is the voltage that should be given from the electricity company.The exact voltage is 399V-401V-398V.Do you beleive that this makes difference?Nike it is a trane unit,i do not have the exact model,i will try to find out.

[nike123]

Stanfam doesn't give any result in Google.
Are you sure that is correct name?

[HARRY 7]

Yes Nike,i searched in google too.

[nike123]

Does motor overheat on housing if you let him work for 10-15 min? Overheat would be if housing is hotter than 90°C or more. Check with IC thermometer.
If not, monitor it for hour or more for temperature rise. If everything is OK, and you have satisfactory air Δt, leave it as is. It probably have wrong nameplate.

What was old setting of thermal relay?

[HARRY 7]

No thermal relay nike.The motor starts directly from the fuse.I checked that it was overheated:).

[HARRY 7]

I think the mystery solved.I went to find the old one motor that the other technician removed and it was 1.5HP!So they gave me a smaller motor..

[nike123]

I think the mystery solved.I went to find the old one motor that the other technician removed and it was 1.5HP!So they gave me a smaller motor..

I don't know why I am not surprised?;)

[DTLarca]

Damn - that simple - well, it was good while it lasted :)

[HARRY 7]

Thanks all of you guys for your help:).

[mad fridgie]

Thanks all of you guys for your help:).
Thank you for being honest with your solution, simple, when you have all the info you needed:D