Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


PMG retrofit to Stamford alternator

PMG retrofit to Stamford alternator

PMG retrofit to Stamford alternator

One of many things I'm responsible at work for is a 500kVA diesel genset which I inherited via my predecessor. It isn't a particularly well-specified machine for the job it is doing - standby duty - but I'm toying with retrofitting a PMG in lieu of the bus-fed excitation to improve its fault-clearing capability. The alternator has a cover which, when removed, would allow access to the outboard end of the shaft which I believe is machined to accept an adaptor or coupling to a PMG.

Brief inquiries have drawn a blank in terms of OEM parts for this machine, and because it wasn't originally supplied with a PMG Stamford aren't being overly helpful in converting it. I understand why, it's just a little frustrating too. I can probably obtain a PMG for a similar set and have an adaptor ring manufactured if needed. Has anyone done anything similar in the past?

RE: PMG retrofit to Stamford alternator

When I was at Brush, the original turbogenerators from late 60's on had a Newton Derby PMG, sat on a stand at the end of the main brushless exciter. This was coupled to the exciter by a small flexible coupling. When this failed, customers found that a length of garden hose was a satisfactory engineering solution, secured by a couple of terry hose clips!

The PMG was small, say 6-inch diameter and 6-inch long. This for a 30MVA generator. Later we developed an integral pmg system, I think.

Newton Derby are still there, and part of winder. their website says they can do excitation solutions, so give them a try http://www.winderpower.co.uk/product/rotating-mach...

RE: PMG retrofit to Stamford alternator

What is the model number of the generator?

RE: PMG retrofit to Stamford alternator

Thanks Hoxton,

We already deal with Winder Power on the transformer side of the business, I will inquire whether they can help us.

Genhead - will have to find out, not at work right now.

RE: PMG retrofit to Stamford alternator

I have done it a number of times, in sizes similar to your unit, as asked above, can you provide specific info on the unit you have? For some reason since Stamford got bought by Cummins these type of inquiries seem to not get much attention, at least in the USA.

Here is a link to their customer service, service-engineers@cumminsgeneratortechnologies.com

I think this is still the factory authorized Avk/Stamford house in the UK, r.taylor@baumuller.co.uk or mail@baumuller.co.uk

I've used these guys in the US to get parts for most of the smaller (less than 1MW) units I run across, http://www.dieselgeneratorsmiami.com

If you do retrofit a PMG I would suggest you consider adding set of fuses or a breaker on the PMG output, Stamford does not protect the output of their PMG's and I find in many cases a failed AVR also results in a toasted PMG. I had an interesting discussion with a Stamford engineer on the subject at PowerGen last year. Maybe they just like selling the parts. I do it pretty much anytime I replace an AVR or PMG.

Hope that helps, MikeL

RE: PMG retrofit to Stamford alternator

Let us know what happens Scotty, please.

RE: PMG retrofit to Stamford alternator

As an alternative to the garden hose, you may consider belt driving the PMG.

Quote (Hoxton)

Let us know what happens Scotty, please.
Second that.

"Why not the best?"
Jimmy Carter

RE: PMG retrofit to Stamford alternator

Certainly will gents. It's school holiday week over here, I'm enjoying spending some time with the kids and I'm not back in the office until next week. smile

RE: PMG retrofit to Stamford alternator

So what happened, scotty?

The engineering world awaits!!

RE: PMG retrofit to Stamford alternator

Erm... nothing yet. blush Been busy with about a million other problems!

I promise I will update this thread when I have something to add! smile

RE: PMG retrofit to Stamford alternator


No, I hadn't seen those before. Thanks. smile

I've already converted this machine a sister machine with a steam turbine prime mover from being dependent upon residual magnetism for build-up to one with active field flashing from a battery source, so most of the infrastructure is in place to incorporate one of those devices. A few years ago I'd never heard of Kutai until I fitted one of their AVRs to my little B&S standby set at home, and that choice was largely down to them being cheap. What is the general opinion on quality and reliability? The last thing I need is an emergency set failing on demand!

Edit: see crossed out bit.

RE: PMG retrofit to Stamford alternator

Stamford also produces a series boost type system, called "EBS" that can be applied to some generators as an aftermarket add-on, here is a USA source,
However I think these are only used for their smaller units, up to about 50kVA I think.

I have only a small amount of experience with the Kutai products, all I can say is they are "ok", had to deal with one of their excitation boost modules (different Model) that I was not impressed with, we ended up retrofitting that unit to a PMG. This was several years ago so maybe they have improved, not sure. Need to make sure you have enough output power if you do use it, I think most Stanford tail ends today in that size range are about 4 amps nominal FL excitation current, but some of their older units had excitation systems that had higher field current requirements.

From my own experience with units in this size range, for AVR power overall I find best long term success with a PMG, they are simple, robust and reasonably resistant to problems. Auxiliary winding can also be good, but no real good way to field retrofit them. Over the years have dealt with a number of series boost modules (or Current Boost or Excitation boost if you prefer), mainly Basler and Caterpillar. They work fine but finding someone who understands and can fix them is getting more rare. Personally the idea of a smaller battery powered device wouldn't be my ideal solution, especially one sourced different form the AVR and/or generator manufacturer, but a lot of factors get involved in making that kind of decision.

Field retrofitting a PMG for many years was a Stamford selling point, again, not sure which tail end you have but I'd bet it's likely a pretty good option, just need to find someone willing to do the legwork to get you the right part. But looking back thru some old notes, I can only find a couple of different PMG part numbers, and their excitation system designs in recent years all seem to use the same field voltage and current levels.

Hope that helps, MikeL.

RE: PMG retrofit to Stamford alternator

Well, I promised an update...

The alternator is an HCK544 D 415V 50Hz 4-pole type with a self-excited AVR.

The official answer from Stamford is that the alternator is now 19 years old and the 'old' PMG kit is no longer available, and there's no way the 'new' PMG can be made to fit. They declined to confirm the part number of the old PMG when asked, and there are a fair number of PMG's to choose from. I have an idea that it may be p/n 45-0059A but I can't get this confirmed. there are a lot of other possibles.

Quoting Stamford's customer support, "I've been asked for this part number many time over the years and I'm very sorry but there is no stock anywhere in the world."

RE: PMG retrofit to Stamford alternator

By self powered do you mean that the AVR has common power and sense terminals?
Have you considered using an AVR with separate power and sense terminals powered by a UPS?

"Why not the best?"
Jimmy Carter

RE: PMG retrofit to Stamford alternator

Sorry Bill, self-powered as in it comes up on residual magnetism and feeds off the main terminals.

That's one solution I guess - maybe a little inverter running off the cranking battery and alternator? It's still a kludge though, a proper PMG shouldn't be that hard to obtain. sadeyes

RE: PMG retrofit to Stamford alternator

Here's another kludge.
Rewind the battery charging alternator for 220 VAC. Use a small charger to charge the battery.
Anecdote warning.
I was faced with an under performing solar system out in the jungle.
The diesel set was used for a couple of hours each day to was clothes and fill the water tower.
I used the gen-set alternator to help charge the solar batteries.
A small charger charged the starting battery.
Anecdote off.
Rewiring the charging alternator may make the UPS look good, but it does have the advantage of avoiding issues with UPS battery life expectancy.
Can you have a friendly machine shop adapt an available PMG to your set? I imagine that the only issues are mechanical fitting.

"Why not the best?"
Jimmy Carter

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close