Motors and Drives for Cold Rolling Steel

I feel the only accurate answer here is maybe.

There are many variables here that need to be properly analyzed by your engineer. What are the mechanical loads your present motors sees? What power consumption do you presently draw to accomplish this? How old are the motors? What is the anticipated power consumption with the VFD motors? How much power is lost by long cable runs between

I recommend doing a single point in production test of one DC motor being driven by a single supply. Measure the VA power entering the supply as the motor runs under all loads. Replace the motor with the new VFD version and compare. This singe point comparison should track reasonably well to the other motors.

The AC motors will not have brushes that can fail. But few motor failures today are from brushes.

You may find, as I suspect, that there is very little difference in power loss between each approach. I suspect you will find that most of your lost power that can be saved is from long low voltage cable runs between driver and motor. Placing the driver close to the motor can save considerable amounts of power and reduce interference from EMI generation from the motor.

Take care of the starting torque if you decide on AC drive.

Surely there is a reason why you ask this question. Is the aim of such a conversion to save money? Will it increase your production and lower the product cost? The usual procedure is to run a thorough and sweeping feasibility evaluation study, to include all relevant parameters. Such conversions are not cheap, therefore the economic benefits of such a conversion must be obvious and assured. And do you really expect anyone in this forum to tell you the "saving percentage" without studying the case?

Hello Guest!

I will share with you the actual facts and figures-

Our plant is a CRD Steel Plant. Here we have a line called CGL Line that has two DC Motors (Pay Off and Tension Reel) both 100 Hp each and with DC Drives.

The running load on each of these motors is 60 KW each, so total 120 KW.

What would be the % savings (eg 5%,6%,10% etc) if i replace these DC Motors with DC Drives with AC Motors with VFDs, considering better efficiency of both AC motors with VFD above DC Motors with DC Drives.

Kindly advice,

Regards,

Rooney

You've given us more but still insufficient information to make a valid assessment. This requires a hands on analysis of the system with pertinent testing before hand. You cannot get accurate advice on efficiency expectations for free.

My only advice that will likely save you some energy is if you are using linear unregulated supplies to power the DC motors, then by switching to an unregulated switching supply you won't be loosing as much power in the supply. You can use a more common regulated switching supply if somebody carefully plans on handling the back EMF from the motors during stopping.

But who told you that DC motors are inefficient? Unlike any squirrel cage inductive motor, a DC motor typically has exceptional starting torque. Moving around the massive loads I would expect a steel plant would need to move, I think that a DC motor is your better option. So you might have to have even larger horse power AC motors to get the starting torque you need to get things moving. Yes commutation by the brushes of a DC motor can put a lifetime limit on the brush and generate EMI that interferes with other circuits. But with the inductive heating that you are likely doing in your plant, EMI is likely not a problem.

It would be safe to assume that your company will purchase VFDS and AC motors from a reputable distributor or manufacturer's rep in your area.

If this is the case, it would make sense to ask the potential supplier of the upgrade equipment to provide the necessary study and analysis required to evaluate your particular plant and equipment and demonstrate the payback expected for your facility BEFORE your company actually spends the money to perform the upgrade.

As was stated in a previous reply, it will cost a considerable amount of money to do the conversion. The supplier of the equipment stands to make a handsome sum selling the parts to your company. It is only reasonable that they provide the expertise up front to justify your company's taking on the conversion project.