Parallel drives

[bob]

Hi,

 

We are looking for one 1500 amps variable speed drives @400 V for a particular application. We have two options in hand-one with two 700 amps variable speed drive in a parallel combination that is two single unit drives sharing a common dc bus. The other option is standard drive with a main rectifier, one dc bus and one inverter module rated at 1500 amps.

I have no basic experience with parallel drives and would welcome inputs from members.

 

Bob

[marke]

Hello Bob

 

How about looking at connecting your motor in star and using a 690 volt drive. This will drop the current considerably and increase your options.

The only problem may be uping the supply voltage to the drive, but 690 volts is not a major issue.

 

Just a thought, it is a common solution.

Best regards,

[bob]

Hi Marke,

 

Thanks for your prompt reply. If we go for a 690 V drive, this will be a non-standard drive for us. Basically, it would be the first 690 V in the country. I trust we would need a step up transformer on the input side.

At the end, I honestly think it would be quite expensive.

As far as I am concerned, I prefer standard stuffs that work and whcih have proved themselves sound.

Kind regards.

Bob

[marke]

Hi Bob

 

I would be surprised if this would be the first in the country, but there again I do not know what country you are in. This has certainly been done many times in NZ and Australia and is a relatively common approach in Europe as well.

I would expect that the cost of the drive will be cheaper, the size smaller, the efficiency higher. The motor is not usually a problem as most 400V 50 Hz motors are delta connected for 400V and can be star connected for 690V. The only issue is the 690 volt supply. If this is a new installation, you would probably have to add a tranformer to supply the unit anyway, so a 690V secondary would not be a problem. If it is an existing application, then there is a transformer change required.

 

A number of manufacturers do larger drives by parallel connecting output modules rather than complete drives. - there is only one control module.

 

If you are concerned about standard units, then you need to talk to your usual supplier, but a drive system of this size is not going to be an off the shelf standard, so I would strongly recommend the 690 volt options be considered. It is worth considering the costs both ways.

 

What brand do you normally use??

 

Best regards,

[Guest]

Hello Marke,

 

We have a pretty good stock of Ansaldo and a few PDL as well. The ultradrive of PDL is performing very well and I like its configuration approach which is very simple compared with others. But I am a little worried about the its parallel combination.

 

Bob

[marke]

Hello Bob

 

I do not believe that 690 volt is a problem for either of those brands.

 

One comment before you look too hard. PDL is now owned by Schneider and here in New Zealand (where they are made), there is an expectation that the PDL drives are being phased out. I believe that some customers have been notified of this. It would be worth asking the question on that one, otherwise PDL have been successfuly involved in parallel connection for many years. I would not expec any issues.

 

Best regards,

[jraef]

Yes, the Ultra Drive from PDL is going to be phased out in about 1 year in favor of the Schneider Altivar 71, which at this point does not go that high in amperage.

 

I agree with Marke, parallel inverter modules is really the best way to go, there are several drive manufacturers out there who do this as standard above 600 amps or so. If you post what country you are in I'll make some recommendations.

[bob]

Hi Marke an jraef,

 

Many thanks for this important news. The local supplier has kept us in the dark. Nevertheless, we greatly appreciate the PDL ultradrive series.However, the Altivar series of drives were the most used vsd in the country some couple of years ago and I can say that we had very bad experience with them.Since then, they have almost dissapeared on the local market.

I`m from Mauritius, a small island of 1 million inhabitants loaced in the indian ocean.

 

Bob

[marke]

Hi Bob

 

Two brands worth looking at are Elettronica Santerno (Italy) and Emotron (Sweden). I do not know if these have local representation, but both make rugged drives. Jeff may add some more recommendations, but it does depend largely on the local representation.

 

We are a little bigger in New Zealand, we have a population of around 4 million, although in the South Isalnd where I live, there are around 900,000 so similar number.

 

Best regards,

[jraef]

Elletronica Santerno has a good reprsentative / partner in India for sure, don't know if they cover your country.

[Guest]

Hi jraef,

 

In our market the PDL brand of drives also have a very strong presence at the high power end.

 

We have several customers who questioned the future of PDL since it was purchased by Schneider. From your comments you seem certain that the Ultradrive Elite will be replaced in the very near future. Is this just the talk in the market or do you know this for sure. My customers will be very worried to hear this news? although not surprised.

 

Is there any way you could confirm this for us.

[bob]

Hi all,

 

Many thanks again to Marke and jraef for the information about the phasing out of the ultradrive series.

We queried PDL and they confirmed the rumours.

Hereunder official reply from PDL representative.

PDL was purchased by Schneider Electric approximately 4 years ago and we

have been part of the STI drives group for most of that time. PDL R&D has

been part of the team developing the ATV71 and this drive will eventually

replace the Elite range. It will be mid next year before the full range is

available to completely replace the Elite range and the Elite will be in

production until the end of 2006 at least. We are and have been for a long

time part of Schneider Electric and the replacement of the Elite range with

a new generation of drive is simply natural progression. We are committed

to support the Elite range with spares and service after production ends as

we would any drive range.

I hope this will help.

 

Bob

[Subhashish]

Hi Bob

 

I believe ABB ACS series( ACS 800-04) drive is available with the kind of rating (1500 Amps at 400 volts ) you are looking for .

You can check with ABB .

 

I think using one single unit is always better than parallel operation .

 

Regards

[jraef]

If you tear that drive open, you will find parallel inverter stacks. I don't think that anyone is making single transistors that big. In fact, the manual for the ACS800 shows that they use 3 inverter modules in parallel to attain that rating.

[marke]

One of the things to consider, is if you use a drive that is made up of modules in parallel, it may be posible to remove one module and continue to operate the drive at reduced output. The Control Techniques units certainly allow this. It becomes a bit like an insurance policy. Additionally, if they are stand alone modules, you can have one or two modules as spares rather than complete drives. If you use a number of different sizes all amde up of modules, there can be quite an improvment in security and reduction in spares required.

 

Best regards,

[bob]

Hi all,

 

My concern about parallel inverters was that I had a very bad experience with the Cegelec GD2000 , this drive I believe now has been discontinued as there were many bugs in the soft.

 

Bob

[jraef]

Well, if you had completely separate drives attempting to run in parallel on a single motor, you had reason to be concerned. What we have been speaking of here is separate inverter sections controlled by a single controller, so coordination is transparent as far as the end user is concerned. As I said, most if not all large drives are built this way now, the technology is comparatively commonplace.

 

If your experience with Cegelec was bad, you can't necessarily condemn the entire concept. In general my opinion of Cegelec is somewhat low anyway. They had all the tools in place to dominate the market at one point and failed to do so. That says to me there were endemic problems they could not overcome. Here in the US they have all but disappeared even after several sputtering attempts at brand labeling to other manufacturers such as Saftronics and Cutler Hammer. In both cases, the product had major problems for their partners and ultimately failed.

[Subhashish]

Yes I agree to the fact that parallel operation of inverter stacks is a commonly used technique by many manufacturers for large drives and so does Cegelec but I have seen more failure in Cegelec drives than others and therefore experience with cegelec does not really indicate any problem with the parallel inverter technique .

I have seen some failures in Cegelec drives GD3000E

( in fact the inverter stacks made of Semikron IGBTs ) . I am not sure if this was due to software bugs or some problem with the IGBT's .

 

Running many seperate drives to run a single motor is probably not as comfortable a method as multiple inverter stacks becuse multiinverter technique is perhaps more standardised as far a control is concerned and is generally controlled from one single controller card .

 

I feel its always better to have one control for the system and increse capacity by adding inverter stacks .

 

Regards

[bob]

It`s interesting to note that the GD3000 also had problem. I believed that the problem was solved with the GD3000 version. I am now more concerned as there is till one GD3000 in operation at my place. We have already scrapped six GD2000 in the group.Subhashish, you are right the IGBTs in GD2000 are not standard ones, made by Semikron solely for Cegelec drives, and replacement cost is very high compared to standard IGBTs.

Bob

[Guest]

Hi Bob, Marke and Jraef,

 

Earlier in this forum you mentioned that you had recieved official confirmation from PDL that the Ultradrive Elite was to be phased out and replaced by the ATV71.

 

What does this mean for the future of the PDL manufacturing facility in Napier, New Zealand? At present I do not believe that they manufacture any of the ATV products there. Has anyone heard what Schneider intend to do with this facility?

[jraef]

From what I was told, PDL may still be involved in manufacturing some of the largest units when the product line is expanded because that is considered one of their areas of experise, but not the frame sizes involved in the initial roll-out. These are all being built in France for the time being. Schneider owns part of a joint venture with Toshiba called STI (Schneider Toshiba Industries) outside of Houston Texas where the bulk of the ATV71 will eventually be manufactured for the North American market, but they are not in production yet and I'm not aware of how that afects other facilities around the world.

[bob]

Hi jraef,

 

Honestly if you are to choose between an ultradrive and another make, you would go for which make, bearing in mind the possibilty that the ultradrive will most probably be phased out in the very near future.They used to call it STRATEGIC MANAGEMENT.

 

Kind regards.

 

Bob