GE Auto-TransformerSoft Start Problems

[LRB]

Good Evening:
A week ago our client smoked the Auto-transformer (actually caught fire) in their 100HP Soft Starter. The cause of the fire was mechanical interlock malfunctioned and 1S contactor only partially opened and auxiliary contacts did not switch positions, therefore the motor ran in the closed transition stage until the transformer self destructed. This is a GE CR 331 NEMA size 4 Auto transformer soft starter. Customer air freighted new transformer. New transformer had no labels or manufacturer name plate nothing.

Customer also has a 50 HP GE auto transformer soft starter which has a Hevy-Duty transformer with connection points labeled H1, H2, H3, 01,02,03, and each phase coil has Tap connections for 50, 65, and 80. New transformer has 3 connection point for each phase coil, 2 at top and 1 at bottom. Applying 120 volts across the various combinations I was able to determine that the 2 at the top were the H and 0 connections and the bottom was 65 % tap. One of the top connections had 4 copper ribbons, and the other connections each had 2 copper ribbons. I labeled the 4 ribbon connector H and the other top top 2 ribbon connector 0, and of course the bottom 2 ribbon connector I labeled 65.

After hook up I opened motor disconnect and monitored voltages through a dry start cycle. I was reading 177 leg to leg, which is 37 % 480. We tried the motor and it does start, however if there is any product left in (hay pellets) the motor will stall. The owners want to run as is until next Wed. and I will be able to make corrections to hook up. I would like the Auto-Transformer pros on this forum to confirm that if I swap the connections that I have labeled H and 0 on each phase I should have ~65 % 480 voltage leg to leg.
I have attached 2 schematic diagrams. The first schematic is from GE website, and the second one was supplied with the Starter. I have done a complete as-built on the cubicle and confirmed that the starter is wired per the schematic supplied by the supplier, however, the write up supplied by the vender does not completely match either schematic, however it does give you an over all sequence of events.

 

[Jraef]

So the new transformer doesn't appear to have taps? Sounds almost as if someone sent you a 65% motor starting reactor, not an autotransformer. That takes a different starting scheme so the strange voltage may be the result of you connecting that reactor as if it were an autotransformer and it is not functioning as it should.

If it were me, the price of a solid state soft starter would have likely been less than the time and materials you have already invested in this and there would have been no controversy. That may still be the cace now if you are planning on removing and re-installing the correct transformer and rebuilding those contactors. This is the reason why most mfrs no longer sell small RVAT starters any more, so what happens is that inside sales people don't know what to sell you to fix them.

 

[LRB]

Jraef:

Thank you for the fast response. I hoped you would give your thoughts. You may be correct that this is a reactor instead of auto-transformer.

I presume that you looked at the schematics I included. The contactors are in near new condition. New coil and contacts < 1000 hrs. The owners have been in pelleted feed production with diesel powered prime mover for 25 yr. They wanted to up grade with new electric powered mill. Only single phase power available so they bought 205 KW Cat gen set (per Cat nameplate,256 KVA @ .8 PF, 205 KW). We priced VFD and solid state soft start. I consulted P E's I had worked under for 20 years on the Trans Alaska Pipeline (TAPS). They run mostly AB VFD's and Soft Starts. from 25 HP through 6500 HP (6000 V). First they advised me to stay away from Solid State applications with our size Gen and load. One P E contacted AB engineering for me and AB said they would not warranty their solid state starters used with Generator power.

All this being said if I roll the leads I labeled H and 0 do you think I will see 65% start voltage and the increased start torque? The transformer coils are energized about 15 seconds when the the systems works normally.

Thanks again for the input.

 

[Jraef]

Jraef:

Thank you for the fast response. I hoped you would give your thoughts. You may be correct that this is a reactor instead of auto-transformer.

I presume that you looked at the schematics I included. The contactors are in near new condition. New coil and contacts < 1000 hrs. The owners have been in pelleted feed production with diesel powered prime mover for 25 yr. They wanted to up grade with new electric powered mill. Only single phase power available so they bought 205 KW Cat gen set (per Cat nameplate,256 KVA @ .8 PF, 205 KW). We priced VFD and solid state soft start. I consulted P E's I had worked under for 20 years on the Trans Alaska Pipeline (TAPS). They run mostly AB VFD's and Soft Starts. from 25 HP through 6500 HP (6000 V). First they advised me to stay away from Solid State applications with our size Gen and load. One P E contacted AB engineering for me and AB said they would not warranty their solid state starters used with Generator power.

All this being said if I roll the leads I labeled H and 0 do you think I will see 65% start voltage and the increased start torque? The transformer coils are energized about 15 seconds when the the systems works normally.

Thanks again for the input.

I doubt that info came from anyone at A-B who knew what they were talking about. A Solid State Soft Starter is the PREFERRED method of starting behind a generator. 25 years ago some generators had issues with their AVRs (Automatic Voltage Regulators) being corrupted by the noise created by ramping the soft starters. So there were people, especially in Alaska where generators are the norm, who got "gun shy" of electronic soft starters. But that issue was fixed by the generator mfrs decades ago now by simply using a better filter on the sensing circuit. I haven't seen any issues with soft starters on gensets in over 20 years now. You want the generator kW to be about 2x the motor HP, so yours is fine. I wouldn't have hesitated in the least, and there is no policy at Rockwell for not warrantying a soft starter run from a generator.

Without something that shows what you actually have, I can't comment on how to connect it. But if it is actually a 65% primary reactor and not an autotransformer, this is what the circuit would look like. In this diagram they show primary resistors, not a reactor, but the concept is identical. There are a couple of connector lines missing from this diagram between the resistors and the OL relays on phases 1 and 3, but you can fill in the blanks here. There are only 2 contactors. The power goes through the reactor first on Contactor A, then shunts around it via contactor B a few seconds later.

 

[Ingenieur]

http://apps.geindustrial.com/publib...iagram|55-682982|PDF&filename=55-682982s1.pdf

pretty sure you have te right device
there are 3 connections
in
out
tap 65
perhaps you have it in backwards?

http://www.geindustrial.com/publibr...l-reduced-voltage-starters/connection-diagram

 

[Ingenieur]

I think the 4 ribbons are the tap labelled 2(ph) on the dwg I attached
2 go to the R contactor and 2 to the OL

The other 2 are:
F(ph) goes to the S contactor
O(ph) goes to the Y contactor

which is which??? Determines whether you get 35 or 65 out
measure with a good ohm meter on lowest range
from 2(ph) to F then O
the higher reading should be O
if you still get 35% reverse F and O

 

[Tony S]

I’ve got to agree with JR, a solid state soft starter is the way to go.

Korndorfer (closed transition auto transformer) starters are temperamental at the best of times, poorly maintained they can be lethal.

I can only assume you didn’t buy the transformer from the OEM but bought something similar (cheaper). How much did that cost in comparison to a soft starter?

JR mentioned a choke, during Korndorfer transition the 100% to 50% section of the transformer winding act as a choke.

 

[Ingenieur]

I've seen starters of this type still chugging along in water/sewer plants built in the 70's
yes contactors or relays may fail every decade or so but they are fairly robust and reliable devices

 

[Tony S]

I’ve worked on gear from the 30’s that was still chugging along that doesn’t mean I trusted it.

 

[Ingenieur]

I’ve worked on gear from the 30’s that was still chugging along that doesn’t mean I trusted it.

I would say it earned it lol
still working
killed no one

I work in an industry where across the line is preferred and solid state is avoided
a mechanical clutch is preferred over ss despite all the complication
more reliable in the given environment
and a mechanic or electrician can work on it vs a technician

 

[Jraef]

I would say it earned it lol
still working
killed no one

I work in an industry where across the line is preferred and solid state is avoided
a mechanical clutch is preferred over ss despite all the complication
more reliable in the given environment
and a mechanic or electrician can work on it vs a technician

Any electrician can work on a soft starter, just get past the fear of the unknown.

What can go wrong with an Across the Line starter? The contacts are bad or the coil is bad, right? If the starter is bad, do you disect the coil or contacts to see what went wrong? No, you swap out the bad parts and get on with life. In a soft starter, you either have a bad SCR or a bad board. If the board is good, most will tell you if you have a bad SCR (a contactor coil will not tell you that a contact is welded). So if you have a bad SCR, swap it out. If the SCRs are good, swap out the board. It's basically the same thing as any starter. When you have an Autotransformer starter, you have 3 contactors that can go bad, plus the transformer, plus the mechanical interlocks and electrical interlocks, plus the overload relay. So technically an RVAT starter is actually HARDER to work on than a soft starter. It's just the fear that makes people shy away from them.

And, I might point out, the OP has ALREADY experienced not only a complete failure of this supposedly simple device, but is struggling to rebuild it in the field and get the right parts to do it. Could not proven point any better.

Related side issue: my dad taught me, at a young age, how to fix a Ford flathead V8 engine. By the time I could drive, I could have rebuilt one in the dark with a crescent wrench, a screwdriver and a hammer, assuming I didn't want to use the crescent wrench as a hammer. They were extremely simple and reliable engines. By the time I turned 16, that was a nearly useless skill, NOBODY was hot rodding flathead V8s any more. Simple and reliable got beat out by performance, hands down. By the time I rebuilt my first 289 V8, which was a LOT more complicated, I never looked back. Sure, it was harder at first, but not really THAT much harder once I broke it down to being 8 cylinders, a crankshaft, heads, valves, a cam and a few appurtenances. Life moves on.

 

[Ingenieur]

Any electrician can work on a soft starter, just get past the fear of the unknown.

What can go wrong with an Across the Line starter? The contacts are bad or the coil is bad, right? If the starter is bad, do you disect the coil or contacts to see what went wrong? No, you swap out the bad parts and get on with life. In a soft starter, you either have a bad SCR or a bad board. If the board is good, most will tell you if you have a bad SCR (a contactor coil will not tell you that a contact is welded). So if you have a bad SCR, swap it out. If the SCRs are good, swap out the board. It's basically the same thing as any starter. When you have an Autotransformer starter, you have 3 contactors that can go bad, plus the transformer, plus the mechanical interlocks and electrical interlocks, plus the overload relay. So technically an RVAT starter is actually HARDER to work on than a soft starter. It's just the fear that makes people shy away from them.

And, I might point out, the OP has ALREADY experienced not only a complete failure of this supposedly simple device, but is struggling to rebuild it in the field and get the right parts to do it. Could not proven point any better.

Related side issue: my dad taught me, at a young age, how to fix a Ford flathead V8 engine. By the time I could drive, I could have rebuilt one in the dark with a crescent wrench, a screwdriver and a hammer, assuming I didn't want to use the crescent wrench as a hammer. They were extremely simple and reliable engines. By the time I turned 16, that was a nearly useless skill, NOBODY was hot rodding flathead V8s any more. Simple and reliable got beat out by performance, hands down. By the time I rebuilt my first 289 V8, which was a LOT more complicated, I never looked back. Sure, it was harder at first, but not really THAT much harder once I broke it down to being 8 cylinders, a crankshaft, heads, valves, a cam and a few appurtenances. Life moves on.

Not any electrician can work on a ss device

'tips', coils and OL's are often replaced rather than the entire contactor
misc lamps and push buttoms
much less parts inventory

much less susceptable to (or causing power quality issues)
less trouble from vibration, dirt, moisture, etc.

speed control vs starting is another matter

how long did it operate between failures?
to first failure?
initial cost?
and what is the status now? Kind of curious to know

let's not forget the small block Chevy is going strong lol

it all depends on application

 

[LRB]

Good evening folks:

I never thought this would become a Ford versus Chev thing. Any way I guess we have a Ford flat head and that's what we are stuck with right now.

Seriously I respect all the opinions and like I said earlier we did consider VFD, SS soft start, and finally the RVAT soft start. We priced ABB Semins,AB Rockwell, Square D, and GE. 100 HP VFD with by pass were 20-25,000, SS Soft start 10-12,000, RVAT soft start 5-8,000. We got this starter mounted in 8000 series MCC cubicle < 5,000 plus freight. The starter has been in service < one year so we have to give that one to Jreaf and Tony S. Problem was caused by mechanical interlock rubbing contactor. Problem corrected. Transformer covered under warranty. Owner paid shipping. Owners are large farmers (10,000 acres) and dirt contractors, loaders, dozers, graders, dirt trucks, ect. They have had some bad experiences with computerized equipment shutting down leaving them in a very dangerous position. They are the ones with the check book and they want to stay away from Solid State control as much as possible.

I have 40 + years experience starter controls and any maintenance suggestions I am open to. I normally vacuum /blow out cubicles every 6 months, visually inspect, listen for contact chatter.

Annually check contacts,megger motors and wiring, megger transformer winding's, do inferred scan of connections. Check mechanical interlock will be added to 6 month PM.

I will do some more tests tomorrow and report findings. Thank you all for your input.

 

[Ingenieur]

Was the starter new when purchased?
what is the duty cycle?
starts and runs for days
or started several times an hour
etc

the mfg covered it under warranty due to faulty assembly?

let us know once you got it sorted out

 

[topgone]

Good evening folks:

I never thought this would become a Ford versus Chev thing. Any way I guess we have a Ford flat head and that's what we are stuck with right now.

Seriously I respect all the opinions and like I said earlier we did consider VFD, SS soft start, and finally the RVAT soft start. We priced ABB Semins,AB Rockwell, Square D, and GE. 100 HP VFD with by pass were 20-25,000, SS Soft start 10-12,000, RVAT soft start 5-8,000. We got this starter mounted in 8000 series MCC cubicle < 5,000 plus freight. The starter has been in service < one year so we have to give that one to Jreaf and Tony S. Problem was caused by mechanical interlock rubbing contactor. Problem corrected. Transformer covered under warranty. Owner paid shipping. Owners are large farmers (10,000 acres) and dirt contractors, loaders, dozers, graders, dirt trucks, ect. They have had some bad experiences with computerized equipment shutting down leaving them in a very dangerous position. They are the ones with the check book and they want to stay away from Solid State control as much as possible.

I have 40 + years experience starter controls and any maintenance suggestions I am open to. I normally vacuum /blow out cubicles every 6 months, visually inspect, listen for contact chatter.

Annually check contacts,megger motors and wiring, megger transformer winding's, do inferred scan of connections. Check mechanical interlock will be added to 6 month PM.

I will do some more tests tomorrow and report findings. Thank you all for your input.

Good for you! Your clients are not pushing for quick resolution of problems. Problems like that will probably mean to us like replacing the starter bucket with a new one right away. Better still, it could mean the whole gear (RVAT and starter) goes to the yard, a new one in its place. Time is luxury we don't have here.:happysad: