Motor Drawing Excessive Current?

what is the supply ? 50Hz or 60Hz

you have written the transformer is 50Hz but the supply ?

Check the powerfactor and if required compensate.

Aren't you supposed to run the motor at delta connection at full load ?

Note that 72√3 = 124.7 A

Note also that if your supply voltage is lower than your rated motor voltage, you will have to draw additional current to make up for the lower voltage.

Also be aware that power to only two of the three phases will run the motor but at a higher than rated current. At 110 amps you will surely destroy the remaining windings within a short time.

Voltage, Frequency and connections of the motor are not in line.

1. What is the Speed of the Motor.? Lower and Lower the Speed of the motor- Higher and Higher of the Inductance effect which means Lesser and Lesser Power factor which is directly linked to Line current drawn by the Motor. Improving the Power factor is one possible solution.

2. The installed capacity interms of H.P required for the motor may be more than the H.P of the motor installed. Please check this also.

DHAYANANDHAN,S,

INDIA.

motors normally designed for 60 hertz will underflux at 50 hz.

the magnetic circuit being designed at 60 hz will have lesser reactance at 50 hz thus drawing excessive current

you may try running it with VFD

I would like to ask one common question here because I am not a electrical engg. How can I calculate electrical power consumtion of one machine. Then how can I calculate electrical unit. Then whatever (or 'X') is the Unit charges. So that I will come to know the power and money consumtion of that perticular machine.

What is this terms power factor and underflux.

May be this subject already discuss before but I am not aware. Is there any way so that I can directly go that forum.

Please guide me.

When a machine is run (I will assume you are a mechanical engineer) -

consider a spring + a flywheel+ an agitator

when is enrgy given - the spring is compressed- but an ideal spring does not absorb (or wastes energy) similar is the fly wheel.

But the agitator (or any thing like that) uses the energy to do an useful work. When the input energy is not there it is supplied by the spring/flywheel etc.

But these spring/flywheel takes energy from the prime mover and then passes it on to the sink (or load)

Electrical system also is like this - the Inductors, capacitors are the energy storage devices.

These do need input current - but supply power to load when input is absent.

Since there is no energy dissipated in them, these are called reactive power (or imaginary power) and the load takes active power.

The ratio of the active to the total power (square and add) is called the power factor.

It has an effect in the current drawn - the imaginary one also draws current and that has an effect in the supply ratings as well as on the line losses - where the loss is I²R and the I increase increases losses.

So we always like the pf to be as near 1 as possible - to have the total useful current. But the loads are bound to have some inductances and capacitances (can you make a machine with zero spring effect or zero flywheel effect ?)

What we do is to compensate inductances wth capacitances (they are opposite- ie when one demandes other supply).

The second portion is the load

The load = V *I*pf (in single phase)

=√3 V*i*pf (in 3 phases)

this is instantaneous (being power)

energy consumed = power * time

for usual unit rates (universally used) it is KW Hrs or KWH

ie 1 KW load run for 1 hrs

and from that you calculate your $s

reduce the voltage according to frequency

Reactance is resistance to AC current. At 50hz the motors Reactance is different than at 60hz. Remember the formula for inductive reactance is 2*PI*F*Inductance. As the frequency goes up the increased reactance causes the motor to draw less amps because for lack of a better word is more resistive to the AC current.