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Variable Frequency Drive Induction Motor

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vikash23

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Hi,

I am planning to use a 5 horse power induction motor for hydraulic press.

Every 4 minutes the press will be switched ON and there will be load.

It is then switched off to replace the load.

I would like to know if using a variable frequency drive will lower the power consumption of the induction motor ?

Also the function of the press is just to press the load. So do i really need a variable frequency drive?

can i just use a ON , OFF switch to run the motor only when I need ?
 

Direct or star-delta switching are the usual motor start methods in this power range. I don't see particular advantage of VFD drive for this application. If the motor is run at rated speed and voltage, there's no power consumption reduction with VFD.
 

Variable frequency drive is the best option for induction motor. It will improve power factor hence savings of energy.
Your application is not a continues operation so you can drive motor without variable frequency control

Hope your operation time of the press is less than 4minuts. So duty cycle will be 50% or less. In this scenario heating problems dur to low efficacy will eliminate.
You can’t drive induction motor directly from mains using on of switch because of high inrush current

I am recommending a current limiting resistive switching array using relay (Soft start).
When switching on the motor the current should flow through resistor, after few milliseconds the resistor array should disconnect , and current should pass through conductor. This arrangement can be made using 555 timer circuit and relay.
 

You can’t drive induction motor directly from mains using on of switch because of high inrush current

I am recommending a current limiting resistive switching array using relay (Soft start).
When switching on the motor the current should flow through resistor, after few milliseconds the resistor array should disconnect , and current should pass through conductor. This arrangement can be made using 555 timer circuit and relay.
Click to expand...
Nice idea, but quite far from industrial practice.
 

FvM said:
Nice idea, but quite far from industrial practice.
Click to expand...

Hi,
Can in please know how do I drive the induction motor and reduce the power consumption .

Also as mentioned earlier a on off switch cannot be implemented directly to mains , how do I implement a switch for driving my motor ?

My aim is to reduce the power consumption by any method.
 

It will improve power factor hence savings of energy.
Click to expand...

Power factor 0.7 - 0.9 of induction motors involves reactive current and thus some additional losses in power lines, but no higher power consumption as such. Using an industry standard inverter, you are trading displacement power factor of the induction motor against distortion power factor of the input rectifier. RMS input current may be even higher.

- - - Updated - - -

Can in please know how do I drive the induction motor and reduce the power consumption.
Click to expand...
What are you exactly talking about? Motor inrush current, as addressed by smijesh, or consumed real power in operation?

As for the inrush current, you should try if star-delta switching gives acceptable results. If you need to avoid current peaks by any means, VFD might be necessary.

Power consumption is given by the motor operation conditions. As previously mentioned, if the application requires the motor to run at rated speed and voltage, there's no chance to reduce power consumption. If the hydraulic press runs idle for a larger part of the operation cycle, it may be possible to switch to pressure controlled operation, probably requiring a redesign of the hydraulic system.
 

Hi,

It will improve power factor hence savings of energy.
Click to expand...
If your motor has a power factor of 0.7 and the power factor of the VFD is 0.95..
Then you lower the losses in power distribution (good for the power provider)
But your electricity bill will also increase, due to losses in the VFD. (again good for the power provider)
(apparent power will decrease, but real power will increase)

Mind: You don´t pay for apparent power, but you pay for real power.

Klaus
 

KlausST said:
Hi,

Mind: You don´t pay for apparent power, but you pay for real power.


I should pay for real power if i operate any equipment otherwise it will become illegal !:lol:


For PFC application, capacitors are being used. in VFD, the capacitors are used in DC bus to perform PFC. So without adding extra equipment this power factor correction can be made. These attributes of variable frequency drive tempt the industries to choose it and enjoy extra savings in terms of energy and fewer losses
Click to expand...
 

Industry standard VFD inverters handle reactive motor currents but don't implement PFC. Respectively you need to account for harmonic currents.
 

Technically I don't have anything useful to add. But as a safety feature you might consider a 2 switch startup system. The switches would be far enough part to where the operator would have to use both hands to start press. This might prevent and accidental start while his hands are in harms way.
 

One little clarification: The utility company does not sell you power (watts). it sells you energy (watt-hours).

The scenario where a VFD will save energy consumption is if the load is a variable load.....induction motors become inefficient at lower loads and thus a VFD by lowering the speed to match the optimal torque curve.

However, if your load is constant, a VFD will not save ANY energy. On the contrary the VFD's losses will add and you will have a higher energy consumption.
 

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