Replacing a Dc Shuntwound motor

[Feg]

Hi Guys,

I am wondering what to look out for when replacing a DC Shunt wound motor. We have an application where we have a 150Hp Fincor Imo Motor 950-1700 Rpm 508ATZ Field V 150-300V Arm Volts 500. This is lifting a product from ground to roof similar to an elevator. It does not have re-gen as far as I am aware. This motor failed after 15 years and the spare is now gone in and working but we need to come up with cover as it is critical. I cannot find any info on the web on this motor an we are considering replacing this with an AC sq frame motor and drive from SIEMENS or ABB but we have not done anything like this before and I would like some pointer on what to look out for when speaking to the motor/drives sales guys as we can only get one shot at this so I need to cover all bases. I would consider DC again but it looks like SIEMENS and ABB don't have shunt wound.

The original nameplate is very poor and this is about all I can get unless the OEM can get back with more info this is all I have at the moment.

Thanks in advance
F.E.G

 

[Skogsgurra]

There are DC motors and also thyristor rectifiers from ABB and Siemens.
The important thing is that you are aware of the special needs that a lifting application has.
The Siemens 6RA70 (there may be newer numbers) is a very good digital thyristor rectifier that usually has regen as a standard. Application programs for hoisting is available and brake control is built in.

But I think that I would use AC. More robust motors and it is being more and more difficult to get good engineers that take care of the problems when you have DC.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[mikekilroy]

If you do go Ac, ask the potentiall supplier applications people about emergency braking. It may be significantly different on ac motor.

If your mechanical drive is back drivable, it can fall if power is lost; the dc could too but was cspable of self braking if required and circuitry installed (might be built in your old Fincor).

 

[waross]

Check with a motor shop as to the possibility of rewinding the old motor??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Bogz]

Remeber this a dc shunt motor is commonly used for good speed regulation, that being said todays ac hz drives will do the same!

 

[waross]

Check the starting torque of the replacement motor. It will be embarrassing if the new motor won't start the hoist.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iceworm]

I'm guessing the old motor took out the stator/rotor iron when it failed - or you would be looking at rewinding it. So you have to replace it.

All the above are good comments. I'll add my experience.

I was involved with one of these about 25 years ago. One of the poorer jobs I was ever associated with. We replaced a 25 year old MG set and 30hp DC series motor with an 1800rpm, 50hp Design B and a 50hp VFD. It as a disaster. We hit most every problem noted so far.

The 50 hp motor did not have anywhere near the starting torque of the 30hp DC. Unless the operators started out real slow the motor would stall - or the drive would shut down on overload. Dropped the grapple the first time that happened - the brake did not come on. Fixed it so the brake would come on if the motor pulled out or if the drive shutdown on overload. Slowed the drive acceleration to where it wouldn't overload no matter what the operator called for.

It worked eventually. Operators got to where they could coax the best performance being very gentle with the control joystick. Lack-luster performance at best. And the operators never took me out back - it wasn't my design, however, that still would likely have been considered justifiable.

Couldn't get a bigger frame motor. The 50hp was the biggest that would fit in the space. Couldn't get a Design D motor. That would have helped some.

As mentioned - really, really check the worst case required starting torque. Your existing is a shunt motor, so it likely does not have the starting torque of a series wound motor. Still, I would not be surprised if it took a 300hp+ Design B motor to get the same starting torque available from the 150hp DC motor.

The AC drives have excellent speed regulation - but that is nearly a "so what" for a hoist. It needs some regulation, but not much. That would be the bottom of my list to worry about.

For existing hoist applications with space constraints, DC is hard to beat. If ABB or Siemens don't have the motor you want - buy one from else. Just pick one that requires minimum mounting base modifications. As Gunnar said, new power supplies and controls are available. And it is okay to mix and match. Last one I worked with was a 250hp Reliance with Rockwell (AB) power supplies and speed controls - kind of a mongrel, but it worked great. As for not having expertise, well, at the end of this project, that would be you.

Oh, did I mention - Check the required starting torque.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[Feg]

Thanks for all the replies. It is still a job that we are looking into, we are finding it very difficult to get information from the motor manufacturer.

If the job goes ahead I will let you know but I am thinking of

250kw Siemens Ac Variable Speed Drive built in IP54 mild steel enclosure
Braking Resistor
Braking Module
Encoder Module (CU250S-2 DP)

and a 200Kw 4pl Motor with HTL or TTL encoder

I think the original is on the large size as I have used the official torque ratings of the gearbox and couplings to work out the max rated torque and they are under what this motor can develop I think. Now I know you will say this is the wrong way as there will be peaks and troughs but it gives me a starting point until we get the old motor re-wound and we can then monitor the power demand.

Thanks again for the input.

 

[waross]

Can you monitor the current of the spare motor?

Bill
--------------------
"Why not the best?"
Jimmy Carter