2.2kw motor overload setting

[ajay34]

hai all..

recently i had facing problem with sew euro drive motor(2.2kw rated amp 4.95
415 voltage.

this motor c/w gear motor to drive screw conveyor ..

problem is the motor get Burn and overload didnt trip. where by the overload
is set to 7.5amp..as i told to MCC supplier this motor overload is to big to trip
but than they argue saying it correct..i had try calculate as the rated amp X 115% also didnt reach to 7.5amp. that why it didnt trip ..they say i m wrong
and it should trip .but the fact it didnt ..

had i make mistake on calculation using 115%.. i been using this formulation for many years.
freeload this motor running is 3.1amp.

i had check mechincal part such bearing .gearbox and even screw conveyor .
all seem okay and no damage ..

 

[Liam Moran]

I think your MCC supplier is incorrect for this application.
Most 4 pole 2.2Kw squirrel cage motors connected to 415v would draw around 5 amps.
Motors with more than 4 poles would draw more. From where does he get his figures?
Is he perhaps using a motor supplied by 230/240V in his calculations?

In any case, if the motor nameplate states 4.95 amps,
then your protection equipment must match, regardless of
who does the calculation.

 

[Gil47]

A motor of the rating 2.2 kw on a 50Hz system
will normally have a name plate with two voltage ratings
SEW motors do

The voltages will be 230 volt / 400 volt or values close to this

If the supply is 230 volts the motor is connected in
Delta configuration and will draw about 7.8 amps
If the supply is 400 volts the motor is connected in
Star configuration and will draw about 4.5 amps

The square root of three for the voltage ........ 400 volts is 230 volts
Multiply by the square root of three, the amps 4.5 amps is 7.8 amps

A rough rule of thumb for 400 volt motors on 400 volt is 2 amps per Kw
Smaller motors are x2 plus a little
Larger motors are x2 - a small amount
As bigger motors have a smaller percentage of the power driving the cooling fan

Your SEW motor should be on 400 volts at 4.5 amps
and be connected in Star in the motor terminal box.

 

[ajay34]

thanks guys

least i know that i m correct about it

 

[jraef]

In addition, most overload relays ALREADY have the 115% for determining the trip curve pick-up point built-in to the design of the relay. So you do NOT add ANOTHER 15% on top of that, or else you are effectively setting your OL trip curve pick-up point at 115% of 115%, so 133%, which is going to already be above the damage curve of the motor.

When in doubt, READ THE FACTORY MANUAL. The setting instructions for your OL relay will tell you if you need to ADD a pick-up point percentage to the motor FLA. But again, MOST DO NOT, they will tell you to set the dial at the EXACT motor FLA value from the nameplate.

I know, lots of people do this and have been for years, but it doesn't make it right. However it does keep the motor rewind industry in business... that's probably who started the trend!