VFD on a lathe drive

[joel89]

Hi all just looking at upgrading one of our lathe control panels, it is a poreba engine lathe the main motor is a 2 speed 3 phase induction motor, 1480rpm- 45kw. 780rpm-29kw the forward and reverse chuck rotation is energised via electromechanical drive clutches, whilst looking at what to do thinking of a VFD anyone ever done this? I have always standardised with Schneider/ Telemecanique so I have looked at the altivar 61 it has sensorless vector control so creates torque at low speeds, but with gear selections and speeds and feeds etc, is it viable?

this is a pic of the same model of lathe we have

cheers Joel

 

[Darkwood]

It depends what you are trying to achieve here by fitting a VFD, what is you goal here by fitting one - Soft start, extended speed control or speed trimming on existing gear select etc etc, also you have to remember you have a 2 speed motor here so how are you planning to achieve the low and high speed settings (before I make any suggestions).

 

[joel89]

Hi darkwood, biggest reason for VFD is to save on energy costs (the management are driving it threw), my plan was to wire into the high speed winding ( set at 50hz) and then put low speed at (25hz) but on looking at the drawings it is currently on 3 contactors 1 main, 1 star(3phases sorted at input of contactor) and 1 one delta, i think although i haven't come across before this is a dahlander or pole changing motor?

 

[Darkwood]

From what I remember about these lathes and the 2 speed motors is its not your usually star/delta set up as it looks from first impressions you need to assess the motor and see what winding arrangements are needed for each speed, secondly, I wouldn't be locking to 1 speed only and running drive at 50% to achieve the second slow speed range, as in doing so you also half the voltage to the motor which reduces your available torque from 100% to below 50%....

If you are planning on fitting a drive I would consider using a dual program drive and leave the contactor solution to change speed in line, this way you can take a signal from your speed selection to choose either of the 2 programs entered into the drive this it will act as different drives (one for each speed). I would have a discussion with technical on your drive of choice here to see if available in their range.. your biggest gain from a drive is losing all the inching options through massive contactors rated at the DOL inrush that you tend to find.

I take it without me having to preach regulations here that you are fully knowledgeble in the EU - LV Directive and relevent BS codes of practice including meeting the latest standards of safety here with a risk assessment to boot?

 

[Besoeker]

Hi darkwood, biggest reason for VFD is to save on energy costs (the management are driving it threw), my plan was to wire into the high speed winding ( set at 50hz) and then put low speed at (25hz) but on looking at the drawings it is currently on 3 contactors 1 main, 1 star(3phases sorted at input of contactor) and 1 one delta, i think although i haven't come across before this is a dahlander or pole changing motor?

I see a couple of issues here. If you use the high speed (1480 rpm) connection you won't get 29kW at 780rpm from a 45kW motor.

If the motor is shaft fan cooled, and many are, cooling may well be inadequate at the lower speed.

But the most important point is related to energy saving. If the motor is to run only at two fixed speeds, as it does now, you are unlikely to achieve energy savings. In fact, a VFD of that sort of rating will have around 3% losses. Losses you don't incur without the VFD.

 

[joel89]

yes the machine, has been fully guarded just last month and puwer assesments carried out by an external company interlocks fitted etc e-stop circuit fitted etc. But the panel is the original so its 1972, never heard or come across drives where the speed can be altered via the contactors but still use a VFD?

 

[joel89]

I see a couple of issues here. If you use the high speed (1480 rpm) connection you won't get 29kW at 780rpm from a 45kW motor.

If the motor is shaft fan cooled, and many are, cooling may well be inadequate at the lower speed.

But the most important point is related to energy saving. If the motor is to run only at two fixed speeds, as it does now, you are unlikely to achieve energy savings. In fact, a VFD of that sort of rating will have around 3% losses. Losses you don't incur without the VFD.

im thinking of going contactors now, it is getting a bit too complicated as well, i am trying to simplify not over complicate

 

[Darkwood]

I can't quite remember the control and operational set-up of the Poreba's but as far as I remember, you start your motor out of gear in your selected speed and it runs constantly there on until you have finished - using clutch system to engage spindle inch and run etc as well as direction.

I have fitted a few drives to lathes before but for very different operational set-ups and for very different reasons, one was for a more a specialised job for a product they were producing and a drive simplified matters and gave more accurate control.

Like Besoker says .... I cannot see massive gains but may see some where your energy company puts the inrush of such a large motor into the calculations of mean average per half hour... if the duty of this motor is high and you find you are regularly starting and stopping it then it could see savings been made but of course the one thing to figure into this is the VFD for a 45KW motor isn't cheap and especially the one you would require IMHO to intergrate this into the existing gearing / control system.

 

[joel89]

I can't quite remember the control and operational set-up of the Poreba's but as far as I remember, you start your motor out of gear in your selected speed and it runs constantly there on until you have finished - using clutch system to engage spindle inch and run etc as well as direction.

I have fitted a few drives to lathes before but for very different operational set-ups and for very different reasons, one was for a more a specialised job for a product they were producing and a drive simplified matters and gave more accurate control.

Like Besoker says .... I cannot see massive gains but may see some where your energy company puts the inrush of such a large motor into the calculations of mean average per half hour... if the duty of this motor is high and you find you are regularly starting and stopping it then it could see savings been made but of course the one thing to figure into this is the VFD for a 45KW motor isn't cheap and especially the one you would require IMHO to intergrate this into the existing gearing / control system.

yes you do start the motor leave it running all the time, then you use clutches to engage forward and reverse of the chuck (so no inching of the main motor) and thanks darkwood for the advice will go back to the management and let them know!

 

[joel89]

just another quick question, the Rapid traverse on the saddle is currently on contactors I have had issues with it it in the past (shearing the shaft) as the operator drags the steady with it, shouldnt do I know but unless I am there 24/7 I am wanting to VFD that for definate 1.5kw motor standard, one to protect the motor and two to give it a steady ramp start and also DC injection braking

 

[Darkwood]

yes you do start the motor leave it running all the time, then you use clutches to engage forward and reverse of the chuck (so no inching of the main motor) and thanks darkwood for the advice will go back to the management and let them know!

AH yes .. no inching as they are pretty easy to turn by hand when in Neutral... problem I have is I look after about 30 different lathes in different companies amongst many other machines and after a while you forget how each works until you are call out to them.

 

[joel89]

AH yes .. no inching as they are pretty easy to turn by hand when in Neutral... problem I have is I look after about 30 different lathes in different companies amongst many other machines and after a while you forget how each works until you are call out to them.

we have 3 of them, they are all I have ever worked on porebas I have only done 5 year in the maintenance game (house basher before that...) but I know I made the right decision love the industrial control work

 

[Darkwood]

Truely a right decision, there is a 20 000 shortage in our industry of Electrical Engineers and Maintenance Engineer is a first step to getting such a demanded position, that and a 20 000 surplus in the housing market... you don't need to be Einstein to work out who has a more secure job and better wages.

 

[Marvo]

The cooling issue is fairly easily addressed with a constant flow fan retrofit to the motor but I also think you energy savings with a VFD will be marginal if any. I wouldn't see energy saving as sufficient motivation alone to go through pain of such a project, especially if the motor is a Dahlander arrangement, or even as being sufficient reason to alter the machine away from its original spec. I've been involved in a similar retrofit of a Tos lathe which was also in the region of 40-50Kw and it wasn't without unforeseen issues that drove the project way over time and way over budget.

 

[Besoeker]

The cooling issue is fairly easily addressed with a constant flow fan retrofit to the motor

Two points again.
There would have to be room to fit it.
And there would be additional controls and wiring.
Not insurmountable issues. But.........

but I also think you energy savings with a VFD will be marginal if any.

And that cuts to the chase. If energy savings is the objective it is, in my opinion, the wrong application for a VSD.