×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Spare motors for the 40 year old equipment

Spare motors for the 40 year old equipment

Spare motors for the 40 year old equipment

(OP)
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?

RE: Spare motors for the 40 year old equipment

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

RE: Spare motors for the 40 year old equipment

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
www.edison.co.in

RE: Spare motors for the 40 year old equipment

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

RE: Spare motors for the 40 year old equipment

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.

RE: Spare motors for the 40 year old equipment

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

RE: Spare motors for the 40 year old equipment

(OP)
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")

RE: Spare motors for the 40 year old equipment

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.

RE: Spare motors for the 40 year old equipment

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

RE: Spare motors for the 40 year old equipment

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

Quote (these emergency systems are normally built to be brutally simple with bombproof reliability)


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

RE: Spare motors for the 40 year old equipment

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
www.edison.co.in

RE: Spare motors for the 40 year old equipment

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

RE: Spare motors for the 40 year old equipment

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

RE: Spare motors for the 40 year old equipment

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. wink

RE: Spare motors for the 40 year old equipment

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
www.edison.co.in

RE: Spare motors for the 40 year old equipment

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.

RE: Spare motors for the 40 year old equipment

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.

RE: Spare motors for the 40 year old equipment

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
www.edison.co.in

RE: Spare motors for the 40 year old equipment

I see that Scotty beat me to it as usual.

Muthu
www.edison.co.in

RE: Spare motors for the 40 year old equipment

The ones I've worked on range between 20HP and 60HP, depending on machine size. I'm sure there are smaller ones, there are very probably bigger ones too. Typically fed at 110V DC or 220V DC from a substantial battery.

RE: Spare motors for the 40 year old equipment

Keith - The one we did was 220 V, 30 KW DC motor.

Muthu
www.edison.co.in

RE: Spare motors for the 40 year old equipment

I know of failures we have had without knowing all the details. But when the AC lube system fails, I know for absolute sure you don't want to also see a DC lube system failure; I know where to find those in the events records... I wrote up the "and it failed to start" entry, but wasn't involved in the nitty-gritty of the multiple steps that lead to it not starting or not continuing to run.

DC lube system failures generally occur because some system condition is outside the tolerances anticipated by the initial designers. If you need staged starting, so be it, but a DC system that simply sees a lack of pressure, for any reason, will be more robust than a DC system that looks for certain AC system conditions before starting.

RE: Spare motors for the 40 year old equipment

Lack of pressure, oil flow etc. are already monitored in AC lube oil system also. Reason why DC motor is not continuously run is due to maintenance, brush wear etc.

Muthu
www.edison.co.in

RE: Spare motors for the 40 year old equipment

(OP)
The subject Lube oil pump motor in question is 5 HP.
This GTG has shaft driven Lube Oil pump which is normally pumping Lube oil while the machine is normally running.

The auxiliary Lube oil pump motor is 400V, 50Hz, induction motor supplied from emergency DG. This will be running during the start up and normal outage, when the mains power is available through other GTGs. This motor is not a continuous running.

The DC Lube oil pump motor in discussion (5HP, 220V DC) is for the back up pump. This will normally start only when there is a total black out. It will be running until the Emergency DG kicks in and restores power to the emergency MCC. This motor is running only during contingencies and the duration of running is very short.

The starting of AC auxiliary Lube oil pump and the DC Lube oil pump motor are based on the pressure. When the Lube oil pressure falls to the first setting the AC auxiliary Lube oil pump will start. If it fails to start, the pressure would go down. When the pressure falls to the second setting, DC Lube oil pump motor.

Academically, this is a good discussion. However, I have a mandate to maintain the existing philosophies and the system. So my task is to source the 5 HP 220 VDC motor. The physical dimension and the operating characteristics of the motor shall be exactly matching with the old motor.

In fact when the motor in service fails I should be able to replace the faulty motor with the new motor, by removing the cable connection and by removing the four bolts!

Is there any motor vendor (reputed) who can supply such motor

RE: Spare motors for the 40 year old equipment

Quote (OP)

In fact when the motor in service fails I should be able to replace the faulty motor with the new motor
"In fact when the motor in service fails..." you may have a bigger problem than may be solved by "removing the cable connection and by removing the four bolts!"

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

RE: Spare motors for the 40 year old equipment

Is it acceptable to supply a complete pump assembly, with equal or better performance than the original?
Contrast that with the cost of shipping an existing pump to somewhere in the world where it may be rewound?
India comes to mind as a possible option for repair.

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

RE: Spare motors for the 40 year old equipment

For the AC motors I would recommend Reuland Electric.
Really good at one off custom motors.
My contact their gave me the name T-T Electric USA for DC.

RE: Spare motors for the 40 year old equipment

Well, you could ask a surviving support company. If they cannot help you, no one will!

I have no connection to them!

http://www.johnbrown.eu/index.asp

RE: Spare motors for the 40 year old equipment

(OP)
Hexton,
Thanks; as you mentioned we are now trying to contact the surviving support company. In the meantime, we are exploring other option as well.

Quote (waross (Electrical)
Is it acceptable to supply a complete pump assembly, with equal or better performance than the original?)


If I consider the replacement with pump, then the job becomes multi disciplinary involving rotating machineries, piping engineer etc. We want to make the job a stand alone for electrical discipline only.

Thanking all for sharing your views so far.

As the time progresses I will keep posted on how we are proceeding.

RE: Spare motors for the 40 year old equipment

A possible solution may be to upgrade one or two Turbine Generator Units with new pumps during normal scheduled downtime rather than waiting for a failure.
That will give you one or two sets of spares that will cover you well into the future and avoid a lengthy, unplanned shutdown.
Many would consider these Turbine Generator Units to be past the end of life.
Many management philosophies would dictate that these machines be replaced with new units now.
Other philosophies will keep these machines running and avoid the expense of new replacements as long as possible, however that may require some compromises from historical maintenance and repair methods.
These units may serve well into the future if some flexibility in care and repair is allowed.
Yes, I know, it is not our place to challenge management philosophy.
The challenge, which may be a greater challenge than procuring spares, is to somehow drop hints to help management to figure this out themselves without negatively impacting any careers.
Good luck.

Bill
--------------------
"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! Already a Member? Login


Resources

White Paper - Reliability Verification for AI and ML Processors
Artificial intelligence and machine learning are seeing growing adoption in a wide range of applications. ICs used for AI/ML applications are characterized by large parallel processing computation units, high power dissipation, and complex circuitry that can deliver maximum performance within a strict power budget. Download Now

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