Any HV Motor 'Experts' around?

[ban-all-sheds]

Bas's "knowledge" stops somewhere around 80Amps.

Ooh no - it can easily go to 100A. It's got voltage- and phase-limiters on it, not current. It has definitely hit the buffers before it gets to HV motors though.

Apart from the fact that they go round and round - I do know that.

But why the quotes? I've never claimed to be anything other than what I am, or know anything that I don't, but what I do lay claim to, and what I do know, is perfectly genuine.

 

[conny]

Jaymack,
that was the original reason for me going to site. " other lads had worked through the night changing brushes and boxes but the centre boxes were so bad they had to remove the complete arm assemblies and fit 4 new ones. After they had fitted the brushes, (some were old ones because they didn't have enough new ones), they meggered the rotor and it had a 'dead' earth. After removing all the brushes it was still down to earth and time for them to go home. They had been on shift since 8.00am the previous day. I went down expecting to find something obvious that they had missed due to the long hours they had put in under such difficult conditons but discovered what did appear to be a dead earth. It even showed up on the resistance scale of a 'Fluke' meter! To cut a long story short when I went back on Monday the tests had come up a bit to around 23Megs, high enough but still on the low side so I was instructed by my boss to reconnect but we were not responsible if they went against our advice of waiting a bit longer to see if it came up anymore before switching on. By the following day we had fitted all new brushes and replaced all the centre arm boxes, (16) and reconnected all the auxillary wiring and main incomers for the stator and rotor. Final tests consisted of 1.000volt megger test, 37Megs, Ducter resistance tests, (balanced), Hi-Pot earth leakage test,(5,500v on rotor and 11,500v on stator) 54Megs, and infinity respectively,Surge tests, (perfectly balanced, Polarisation Index test. (1.5, our pass mark is 1.2). These tests were performed on both rotor and stator. Sliprings were checked using digital gauge and run out was less than 2thou. Sliprings are original manufacturers with about 12 dust grooves running parallel in each one though the running surfaces are perfectly smooth and equal. There were a mixture of grades across all 3 rings though only the centre ring was affected. Customer said all stator currents were normal and equal, (though don't know what actual readings were). Bearings are insulated roller bearings and there is no breakdown of insulation, also checked they were not dry or over greased.

Sorry for the long reply.

PS couldn't find any info on the liquid start as head honcho wasn't in today, try on Monday.

 

[ban-all-sheds]

(My knowledge) has definitely hit the buffers before it gets to HV motors though.

Apart from the fact that they go round and round - I do know that.

But I'm finding this thread very interesting.

Q to those who know - is an electrician doing work like this also expected to cover off mechanical checks, e.g. bearing run-out, slip ring eccentricity?

 

[ricicle]

(My knowledge) has definitely hit the buffers before it gets to HV motors though.

Apart from the fact that they go round and round - I do know that.

But I'm finding this thread very interesting.

Q to those who know - is an electrician doing work like this also expected to cover off mechanical checks, e.g. bearing run-out, slip ring eccentricity?

If he is being paid for being multi-skilled then yes

 

[conny]

BAS,

I'm actually employed as an electrical engineer having served my apprenticeship as an armature winder/electrical fitter. This is the work I do on a daily basis, either winding or fitting, so yes I am expected to be 'competent' at both disciplines. I also do most of the in-house maintenance though I don't do 'engineering work' involving lathes, milling machines etc but I do have to know their operating modes if you see what I mean. I also have this uncanny knack of volunteering for any courses that crop up.As one boss said of me recently, "he's got so many strings to his bow he should have a harp!" I think I'm a bit like you, I have a thirst for knowledge! not a bad thing in my opinion.

 

[conny]

Ricicle,
do you think I should be on twice as much then?

 

[conny]

Just bumping and hoping for some more suggestions.

 

[jeepmadmike]

liiquid resistances on slip ring motors are very common, 2.5kv aint very high either!

From all my years of playing with them there is one thing which does more damage than any other- lack of maintaince

the rings brush gear etc should be kept clean

brushes have a habbit of sticking in the holders

i would be nice it you had a picture of the fault, was the slip ring damaged? how was it repaired?

also if your not experianced with this type of kit y are u maintaining it?

 

[conny]

Jeep,

first off we were not maintaining the motor, we had been called in to investigate a fault. The company does their own maintenance. The slip rings were not damaged in anyway which was a surprise considering the state of the brush gear. I know 2.5kv isn't very large, we do occassionally work on 6kv and 11kv. As for being familiar with this type of motor then yes I am familiar with the motor but not the control side of things. No pics I'm afraid as it is on site and no cameras/cameraphones are allowed for security reasons. If it had been in the workshop I would have had plenty. Only a numberof boxes on the centre phase were damaged and these were replaced.

PS You don't 'PLAY' with this type of equipment!

 

[jeepmadmike]

it does sound like a real weird one this, i have worked on hundreds of LV slip ring motors but only a few real big HV ones. its very odd that the ring was not damaged what state where the brushes in?

I only use the term play loosely, HV is dangerous stuff with fault levels that house bashers would not be able to comprehend!

 

[conny]

Worked on loads of LV slippys myself so never came into contact with liquid starts, thought I was having my plonker pulled when someone mentioned the leads were in a salt bath!

No there was no damage at all to the slip rings, just a number of brushes 'welded' into their boxes. Have been back twice since the repair and everything is fine, it's really puzzling all of us as to why the centre ring is the only one that keeps having problems. Hopefully we have sorted it though I don't know how.

I hate the phrase, playing with ***, it conjures up images of people fooling around. Yes you are right, fault levels can be extremely high in these situations. Are you a winder by any chance?

 

[jeepmadmike]

im an electrical engineer, part of a family business so i've been with it all since birth just about, also multi skilling is my thing. I love to learn, make things repair things, improve other peoples ideas and come up with new ones.

my work day can involve everything from PLC programming, electrical work on every thing from 11Kv down to millivolts or using a sledge hammer and the gas axe to adjust something

LV rotor liquid resistances in the form of vapourmatics mainly have been about for 25+ years im surprised you've not met with them

 

[conny]

In my late 20's I came out the motor repair game to work in the distibution network, building and wiring switch cabinets, all-in-one power supply units etc. I was out for about 15 years before moving in and out for a number of years during which time I done a variety of things from repairing welding/generator sets to house renovations. Then when I got back into the winding game I was pretty much factory based for quite a few years. It is only over the past 5 years or so that I have started doing site work again so not had a lot of opportunity to come across them.

 

[IJWS15]

Many years ago was involved in building trains.

One contract was supplied with Greenbat 200A 28v alternators (driven from the free end of the diesel engine which drove the train.

They failed regularly. Problem was the brushes you used to get 200A out of them lasted a few days, put a brush in that lasted a bit longer and the alternator rating fell to around 50A.

Turned out Greenbat had designed the thing inside out and were drawing load current through the slip ring instead of exitation current. This problem put Greenbat out of business.

Are the brushes the right material?

 

[conny]

Brushes are correct grade according to OM. This was our first suspicion when it went wrong and we aere called in originally. Another firm had been 'looking' after the motor so we thought they had cut corners but apparently not. When they couldn't figure out what was wrong they decided not to renew their contract as it was costing them too much to keep sending people to investigate.

Discovered yesterday that a 'colleague' had taken some pics on his phone!
Not very helpful but here they are.

Non Drive End.

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• conny
• 6 Dec 2008
• 1

Slip Ring Cable Entry.

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• conny
• 6 Dec 2008
• 1

Nameplate Details.

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• conny
• 6 Dec 2008
• 1