Spare motors for the 40 year old equipment

[krisys]

We have forty (40) year old Frame-5 gas turbine generator (GTG) units in our site and still operating. As the units are old, failure rates are slowly creeping up. At this stage the original spares are exhausted in our stores. However, sourcing these spares have become very difficult. Either the models are not being manufactured any more or the sub-suppliers are not existing.

We have to procure the following motors:
a) Two (2) DC 125 V motors (one 5 HP, Frame NEZ D 160 and the other is 0.75 HP, Frame size 74)
b) Two (2) AC motors 415V, 3 phase 50 Hz (one 30HP, 2900 rpm, E200LD Frame and the other is 5HP, 1450 rpm, 184T Frame).

I have a challenge in procuring these motors.
a) I feel the AC motors, appear to be having the standard Frame size and hence should be able to procure them from the open market (any manufacturer). Is my assumption correct?
b) How to source these DC motors? Any suggestion or experience to share with?

 

[sreid]

Check with Baldor (Recently bought by ABB).

https://www.baldor.com/brands/baldor-reliance/products/motors/dc-motors

 

[krisys]

Is there anyone who can supply the custom built DC motors?

 

[edison123]

Try

https://www.int-elec.com/

Of course, since it is custom built, you need to provide all the mechanical details along with your electrical specs.

Muthu

http://www.edison.co.in

 

[jraef]

Most decent electric motor shops can supply, modify or even create a DC motor for you with enough specs and a big enough check (cheque). Without knowing where you are in the world, it’s difficult to advise you on sources though. Given that you are looking for 400V 50Hz AC motors we can deduce that you are not in North America, and given your use of HP instead of kW we can guess you are not in continental Europe, but that’s about it.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[ScottyUK]

I'm interested in this thread because we have some similar motors on GE turbines of similar vintage and finding an ATEX-certified DC machine on a North American frame is quite difficult. Not many people left in the DC motors business, and even fewer in the hazardous area game. GE will sell us one, but not properly certified which means we can't use it. AC motors are a bit easier to find replacements for.

 

[Skogsgurra]

Is it possible to make a virtue out of necessity?

I mean, put a certified AC motor there. And a VFD.
You need to change a few mechanical things, but I know it can be done. Have done it myself.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[krisys]

The location is in the MENA (Middle East and North Africa) region.
I will check the standard of the design. But my gut instinct tells that it was designed as per IEC standards.

I have seen in some of the older European motors, you see HP instead of kW. There are some name plates which give both kW and HP ratings (like "Rating: 5.5kW/7.5HP")

 

[ScottyUK]

Hi skogs,

With only a pre-existing and very expensive 125V NiCad battery available my VFD choices are limited. This motor is the last line of protection for the GT and gas compressor bearings in the event of a total power loss, and these emergency systems are normally built to be brutally simple with bombproof reliability. A radical departure from that will be a tough sell to the insurers / underwriters.

 

[Skogsgurra]

Scotty,

Not so limited. A VFD can easily be fed from a battery. I have done tests with VFD:s with DC supply for DC distribution with great success and also done consulting for a huge gas turbine manufacturer where the problem was just the GT bearing oil supply. There is an NDA that stops me from sharing the results. But it can be done. That is for sure. One of the toughest problem in that case was that the VFD did shut itself down when there was an overvaoltage on the DC link. The overvoltage protection had a 2 ms delay, which everyone thought was fast enough until we found out that the internal hardware reacted in 70 microseconds and stopped the oil pumps long Before the overvoltage protection knew that there was an overvoltage.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[krisys]

My end user will not permit for such changes. As ScottyUK rightly said


I an not allowed to do such changes. It is like an in-situ replacement.

 

[edison123]

Agree with Scotty that emergency lube oil pumps are always driven by good ole simple & reliable DC motor system but bomb proof?

I have also seen giant loft oil tanks mounted near the power station roof in case the DC system fails with controlled gravity flow as additional back up. White metal bearings are so finicky.

Muthu

http://www.edison.co.in

 

[Skogsgurra]

Agree. Just wanted to mention that there are VFD:s for lube pumps in modern systems. A DC motor has lots of life problems that an ASIM does not have. And VFD:s with MTBF from 50 000 to 200 000 h (see ABB etcetera), a VFD system is more reliable than a DC motor system can ever be.
The complexity and inner workings of a VFD may indicate otherwise but it has been proven over and over again that VFD+ASIM is a lot more reliable.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Is it possible to view the problem not as a motor replacement but as a bearing protection issue and replace the backup lube system with an complete, approved backup lube pump system designed for a newer turbine and still available?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Muthu -

More the starter gear than the motor. I've never had problems with the motors themselves (yet) because they rack up such low hours.

The starter gear is typically a two or three-step resistor starter, and the better designs use normally-closed shorting contactors so the only normally-open contacts are the main starting contacts: less chance of a failure leaving a starting resistor in circuit - always exciting! - and if the starting resistances do burn out then the motor starts across-the-bars. The worst design I've seen was an emergency oil pump which tripped itself on overload and cut off the lube oil to a 300MW generator, leaving it to coast down without oil. The insurers weren't exactly happy about that design.

 

[edison123]

Scotty - In 80's, fresh out of college, my dad involved me in developing an emergency lube oil DC motor control system with NO and NC contactors, resistors and timers, the whole works, for a 210 MW turbo as as automation project. I believe it is still working.

I don't think power plant engineers will ever replace the solidly reliable and simple direct DC motor lube oil system with other alternatives.

Muthu

http://www.edison.co.in

 

[davidbeach]

Done well, that DC lube oil pump is extremely robust. Unfortunately there's something like a gillion ways of implementing it and something like a gillion minus 10 ways of doing it wrong. If I had to do one from scratch, I think I'd just have a pressure switch that would turn off the DC pump if there was sufficient pressure from other sources; otherwise run the DC system continuously if the shaft is above 75% of turning gear speed. I'm glad Muthu's NO and NC contactors as well as resistors and timers worked out, but that seems like too many parts. By the time you need the DC lube oil pump you've already needed a clean change of underwear or two, no need to gather additional heartburn on the lube system.

 

[ScottyUK]

David,

Your control strategy is about right - a number of pressure switches hold off the pump, and if any one sees a drop in pressure while the shaft is moving then the pump starts.

The resistor / contactor arrangement is typical for virtually all of the emergency oil pump starters I've seen. The shunt-wound motors are too big for an across-the-bars start, and typically cause a deep sag on the turbine battery if they are started this way. I imagine that doing it more than a couple of times will damage the commutator too because the armature currents can be a couple of kA without the series resistors to calm things down a bit. The starters are pretty basic to be honest, the timers are pneumatic and there's not a lot of bells and whistles on the design.

 

[itsmoked]

How many HP are these lube motors anyway?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

David - The primary lube oil system for TG's is AC motor driven. The backup DC motor comes into play when AC fails. No way you can start a DC motor DOL on batteries. We did multiple experiments with actual system to get the starting resistors and timers just right. The contactors were DC duty rated and oversized to prevent failures. DC system racks up low running hours and so the reliability and maintenance of the system is not a big issue.

Muthu

http://www.edison.co.in