Retrofitting of VFD

[bob]

Hi,

 

We have two 1000 k W 400 V VFD which have been running for the last eight years( without major problem ) and these VFD are now earmarked to be used on a new project. We wish to retrofit the VFDs and basically I wish to know what should be done.

I presume the caps will need to be tested for deterioration but what else ?

 

Bob

[marke]

Hello Bob

 

I would strongly recommend consulting the manufacturers if you are able.

 

One of the weakpoints will the the main bus electrolytics. Some of the Japanese manufacturers rate these as a five year item! You could find that the capacitance has dropped as the electrolyte dries out.

I would also look sideways at electrolytics on the circuit boards, especially those associated with switchmode supplies etc.

 

Best regards,

[jraef]

Excellent advice, and another otential problem area is the dust and debris build up that will have accumulated in 8 years. The process of disconnecting and moving them will result in disturbing the satus quo of contaminants and may allow tracking or flashovers on re-installation. A very thorough cleaning at the very keast is in order.

[bob]

Hi,

 

I agree with both of you so far as the electrolytics are concerned but what about the small electolytic capacitors located on the control and firing cards. Are they not exposed as well to the operating environment and are subjected also to deterioration.

We are planning to replace the entire electrolytics on the dc bus and have contracted the manufacturer for a general servicing.

Now, the other parts viz the rectifiers, transistors, IGBTs, inductors , current transformers, LCDs and others also have lifetimes. I am asking myself the following question- Is it not better to invest in a new VFD rather than to spend so much to rehabilitate two eight years!!!! equipment.

What do forum members think about it ?

 

Bob

[jraef]

Everything has a lifetime for sure, but most of the devices you listed have lifetimes that exceed our own. The LCD has a sort of "half-life" where the visibility will decrease by 1/2 over time, but still, that's probably a lot longer than 8 years. Small caps on PC boards are usually dry film, and if kept energized for most of those 8 years (i.e. not in storage), they should be fine.

 

The bigger problem may be functionality. Technology in VFDs has come a long way in 8 years, and you may want to consider performance improvements that were not available to you then. On the other hand, if your applications is fairly simple you may not need more useless features. That is something only you can answer.

 

1000kW drives are very very expensive. I would investigate keeping them running. The risk is you investing a bit of money in refurbishing, and then the drive blows anyway. That is still a lot less than buying new drives. If the refurbished drives last even another 2 years, the cost of a new drive will have likely come down enough by then to offset this investment.

[bob]

Thanks jraef for you honest reply. If I have read well, the lifetime of a VDF , particularly the large size, is less than 10 years.

 

Bob

[msdaif]

Dear Bob

 

I would

 

1. clean the drives very thoroughly

2. replace the capacitors but not the CT's

3. if possible, replace the LCD's if display quality is poor

4. keep the power electronic devices

[marke]

Hi Bob

 

All electroytics in the unit should be considered to be potentially failing after this period of time. I highkight the "power" electrolytics as these are usually operated clower to their ratings than the small DC filter type on the pc boards.

I service soft starters and drives in NZ from a company that I used to be associated with. - they do not service or carry spares for them, and many of the control pcbs are still functioning OK after 20 + years. It is the Electros and contamination/corrosion that are the major issues.

I would target the power electros and any switchmode (high frequency) electros first, and then for extra insurance I would target the rest of the electros.

Also look hard at connectors. Check for any green growth on gold connectors, clean and silicon coat any tin connectors.

The other weak point, is the fans. These have possibly been rep[laced already. I find where good fans are used, they can last 10 years plus. (I know of some that have lasted in dirty environments for 20 years). I believe that you should be able to extend the life for another equal period if the functionality is not an issue.

 

Best regards,

[rotormtr]

Hi Bob

 

One very important thing that no one has mentioned is the cooling fans. Most older VSD's such as the vintage you have typically have fans that run whenever the 400V is applied i.e they run all the time. Being electromechanical devices, they tend to wear out. I would rate this is being more important than changing your DC bus caps.

 

Over the years I have undertaken a lot of maintenance on high power drives and one thing I always replace at this age is all the cooling fans. If you lose a fan on this sized drive you can end up with overtemperature tripping problems.

 

I hope this helps.

 

Regards

rotormtr

[Subhashish]

Hi

 

bob ,I agree that old fans can lead to trouble . Bearings of fans meant for cooling power electronic components of large drives generally have sealed bearing which should generally undergo replacement after a fixed period .

However need to take care of balancing of fans after replacement of bearings . Recently I had a big problem with balancing of fans of a 1 MW drive after bearing replacement . If balancing gets disturbed there is tremendous noise in the system and the panel electronics experiences mild jerks .

Processor and control boad cooling fans are small and fan as a whole should probably be replaced during such retrofitting .