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Diesel Engine Driven Generator Operation without Cooling Fan
2

Diesel Engine Driven Generator Operation without Cooling Fan

Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
Dear All Members,
We have been operating a Diesel Engine Driven Generator of following specs:
Generator:
Make: UNELEC France.
Rating:1900 KVA, 1520 KW, 174 Amps, 6.3KV
Diesel Engine:
Type / Model:240-V16-GS-PE-1977
MFG'R: SACM

Recently during startup of Generator after oil change, its cooling fan got damaged. I have following queries:

1. The weight of fan is about 170 kg. Is this fan used for cooling of Generator only or is it used as fly wheel as well.
2. We are going to get this fan casted from local market. In the mean while, is it safe to run the generator in case of emergency requirement by application of external air with an arrangement of hose pipes and external industrial grade fans. Insulation class of Generator stator and rotor windings is B.
3. How can we re-design the fan to make it light weight and less prone to damage, while providing the same cooling air to Generator.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

How was it damaged exactly?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Engine Driven Generator Operation without Cooling Fan

A photo would be helpful.
At hat weight it may be used as a flywheel or dampener of sorts.
Running with jury rigged cooling could burn up the generator.
And an improper replacement fan could burn it up as well.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Running the engine at any load, without a rad-fan, will likely cause significant damage to the engine. I dare say you could run for a couple of minutes, without a rad fan, but I would not recommend this as a viable option for any longer duration. Plus, any warranty on the machine will be toast as well, but I suspect you are well past that now.

I would suspect that installing some temporary fans could be made to work under the following conditions;
1) all cooling streams are consdidered (ie jacket-water, lube-oil, intercooler, etc), and
2) the return temperatures are monitored to ensure that they stay within spec, and
3) if the existing rad-fan provides air-flow around the engine for cooling of the engine/alternator, means will be needed to provide this air-flow as well.

You did not mention the engine rpm, but a 170kg fan won't provide any significant inertia, compared to that provided by the engine and alternator.
Are you seriously considering having a local shop cast you a fan impeller? Are there not local radiator/ fan companies who could provide a more standard product?

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Please clarify - are you taking about the engine-mounted fan or the alternator-mounted fan?

I'm intrigued how you managed to damage it and why you think damage is going to happen frequently enough that you should re-design the fan. Diesel generating sets are in use all over the world and you appear to have either an unusually awkward machine to overhaul or unusually poor maintenance techniques. Photos would definitely help us understand what the problem is, and especially if you describe how the damage occurs.

You must be desperate and/or crazy to use a locally-cast fan unless you have balancing and NDT capability and can adequately specify the material and have a first-rate foundry to produce flawless castings. Do you really want to risk a 170kg fan breaking up at 1500 rpm? Buy an OEM part and stay safe.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
I am talking about alternator mounted fan and not engine radiator fan. This alternator fan got damaged during synchronization with a 10,000 KVA steam turbine generator. We are still in process of finding out exact cause of this damage. This is an old 1977 UNELEC generator and OEM parts are not available. Therefore we have to locally cast the fan. Engine RPM is 1000.

In case of emergency we may have to use this generator for smaller durations (without cooling fan) and for that I wants inputs that can we use it by applying external air sparger & industrial fans & continuously monitoring winding & bearing temperatures?? is it safe? Arrangement for air sparging is attached in pics.



RE: Diesel Engine Driven Generator Operation without Cooling Fan

Do your pictures show what you plan to do?

Was the original fan mounted essentially where you're planning to mount this new unit?

Is your temporary air system going to move the air in the same direction through the generator?

If you move the same amount of air in the same direction you can certainly use whatever means you want to move the air. The original method was just the most expedient way.

A separate source could actually be an improvement allowing extended cool down or even increased cooling.

Hopefully you have knowledge of how much air and with what velocity or at least what force it presented, to give you a feel for the effectiveness of your new system. You should be able to test this new system without even running the generator.

Indeed, do monitor the temperature and watch it closely until you have proven its capability in removing the heat and definitely at full generator loading.

One negative of a separate fan is if it is not directly driven by the rotor shaft then that means it could conceivably not run at all while the generator is running. Perhaps a tripped overload, bad contactor, idiot and the switch, a dead motor, frozen bearing, etc, etc. This means you need to include an over-temperature limit alarm unit that disconnects the generator from the load in the event of an approaching over temperature event. The alternative is a destroyed generator at the least and major fire at the worst.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Engine Driven Generator Operation without Cooling Fan

That picture helps immensely - it isn't what I had envisaged your problem to be. My opinion would be to fabricate the fan from sheet / plate rather than attempt to cast a fan of this size - you will have far better control of the key performance characteristics and the resulting fan should, if correctly manufactured, be both stronger and more efficient than the cast fan.

I agree with Keith - if the proposed temporary solution moves an equivalent volume of cooling air through the fins then it will work. The key will be ensuring that the airflow passes through the fins, which may require some form of ductwork or cowling. Make sure you make use of the stator RTD's to monitor , and ideally trip, the machine in the event of serious overheating.

Check if this is a thermal Class B or Class F winding. It is common for machines to be built using Class F materials but operated within the Class B limits to ensure a long operating life for the insulation system: you may have a lot more operating margin than you think provided that you are prepared to sacrifice some long-term operational life by running near the Class F limit.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
This is the damaged fan which was connected on driven end of generator. Can anyone comment is it only cooling fan or flywheel as well??



RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
This is the location of fan originally installed on alternator near coupling.


RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
This picture shows air hose pipe connected to air sparger system. Please give your suggestion on this, after that we will try this on load.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
This pic shows complete engine & alternator.


RE: Diesel Engine Driven Generator Operation without Cooling Fan

This machine is coming up to the 40 year old mark. Unless it has been rewound lately I would treat it gently.
I would be contacting fan manufacturers to see if an off the shelf fan is available with similar performance specs. It may be easier to modify the drive hub than to fabricate a fan from scratch.
You may want to add some shrouding to direct the air between the fins.
Possibly the original fan had a shroud that may still be used.
Simply direct the air supply to the opening where the air was originally drawn into the fan.
It may be safer and cheaper to forget the fan and use the external air supply permanently.
As long as there is enough air flow in the proper place to keep the generator cool, the generator will not care where the air comes from.

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I don't think the sparge pipe arrangement is going to move air in the volume you require. If you want to use compressed air as the air source then you might get better results using multiple venturi-type air movers which use high pressure, low volume air to move high volumes of low pressure air, or possibly it would be easier to just use electrically-driven blowers. Either way you need some sort of cowling or shroud to form a plenum to direct air where you want it - through the fins.

It must have been a scary moment when that fan broke up, I hope no one was hurt. It's a odd-looking fan design. I wonder if it 'sucks' air through the fins?

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I hadn't seen the latest pictures when I was composing my last post.
Hi Scotty. I would go with a blower and cowling as you suggest.

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

If the fan damage was due to (faulty) synchronizing, as you say, then you must be careful with the integrity of the remainder of the generating set components. Generating sets are designed to withstand the torques resulting from short circuits, not "faulty" or out of phase synchronizing, where the torques are much higher than those from short circuits.

You should look for damage to couplings, stator and rotor windings of the generator and even the crankshaft etc of the engine.

Replacing the generator fan may not fully repair the damage.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I don't see using that compressed air system as working at all. You need lots of mass moving between every single fin or you will get very uneven cooling with extremely hot spots between less hot spots and all the uneven damaging thermal expansion that goes with that.

That original 'fan' is really nasty looking. I see why you have concerns that it might also be a flywheel. That outer rim that looks completely counter to air flow and adds greatly to that structure's moment of inertia. It's still probably not a needed flywheel.

I think any of several different fan setups could actually be better. I'd consider finding a very large air handler preferably used or discarded and set it up next to the generator with a simple, big, U shaped duct that would tightly seal it to end face of the generator. The duct work could even be well built (ply)wood if expedience is required.

Alternatively a large axial fan that is completely shrouded would also do the job.

If you absolutely must use compressed air you need to refine that design considerably. As Scotty was saying you need to us a venturi outside the U of each and every fin pair that entrains air caused by the nozzles, thereby quadrupling the actual air (mass) being propelled down each channel. That will likely require far more air than you're going to get in thru that one measly inlet. I'd guess 100PSI air through 1" airlines in no less than about 4 inlets with venturies would maybe be enough. That's about 140 venturies! That's why they used a blower instead.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Engine Driven Generator Operation without Cooling Fan

The more I look at the wrecked fan the more I think we can only see the rear face of the fan disc complete with stiffening ribs. The side hidden from view must have been provided with radial blades like those fitted to pretty much all TEFC machines. Presumably these have been smashed off during the event? If the fan is aluminium then I doubt it was intended as a flywheel.

Hoxton makes a very good point about residual damage to the machine caused by the crash synchronisation. At least is a relatively small machine so the forces are relatively low. Similar events on large sets have caused spectacular problems. You should certainly consider an inspection of the areas mentioned by Hoxton. I would add con-rods (still straight?) and foundation anchor bolts as things to check for damage.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

It was an axial, not radial fan. The blades were bolted to the outside circumference of the fan disc. You can see a pitched blade with base plate resting on top of the broken disc. There is a base plate still bolted to the OD at the bottom of the picture with the pitched blade sheared off.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I agree with the comments by Hoxton and Scotty. I also have been wondering about other damage from the event.

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

That looks so much like someone took a welded fan and used it as a pattern for a cast fan, practically straight from the Lincoln Arc welding book on replacing castings - the ribs aren't what I would expect from typical casting techniques; sharp edges and small fillet radii, and all those small gussets.

With that in mind, perhaps return to having a new one fabbed as a weldment with decent materials. It could be all one piece that is sawn in half after the main fab is done.

As to the failure, it looks more like either a fatigue crack started at the hub and this failure has been waiting to happen, so nothing else should be directly affected, or someone pushed something like a fork-truck into the fan and exposed everything there to a huge side load.

It doesn't look like a torsional failure, but I haven't seen all possible failures.

In either case, identifying the exact failure mode should be a high priority in order to understand the requirements for a replacement.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Sorry, the 'air sparger' just looks silly.
No way can compressed air at any pressure suitable for the couplings and pipe in the photo, induce enough airflow to carry off the waste heat from a huge alternator like that.

Mike Halloran
Pembroke Pines, FL, USA

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
An old crack has been found in the fan, which has dust ingress. This shows fan was damaged due to starting jerk which old crack couldn't bear. Fortunately no one was hurt in this incident.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I suggest a shroud and about a 10 HP blower. Or what you have to hand.
Check the running temperature (at part load if possible) and if it is running too hot increase the blower size and air flow.

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
Thanks all of you for your valuable suggestions & comments.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Re my above comment. If you faulty synchronize two dissimilar sets, then it is the smaller set which suffers the worst damage.

As an example, I one saw a 2 MVA set and a 1 MVA set after being synchronized out of phase. The 2 MVA set seemed to have no damage, the 1 MVA set had its stator core pack spinning inside the frame, snapping off the retaining dowels and the phase connections to the terminal box.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Compositepro,

It is certainly not an axial flow fan, it is a centrifugal (radial) type. An axial fan passes air through the blades along the axis of the shaft, something which is clearly impossible when the fan comprises a solid disc.

I think we are looking at the reverse face of something similar to this. Coincidentally, this is also a cast fan which has broken in half.

Hoxton - wow! Was that a machine from a reputable manufacturer in good repair which suffered the damage? I haven't come across that as a failure mode before at any size or rating. surprise

RE: Diesel Engine Driven Generator Operation without Cooling Fan

ScottyUK - a closer look at the disk will show a pad on the rim that looks a lot like an airfoil. Then notice there are a number of smaller bits that also look like airfoils. The really big, disk shaped chunks are the central disk to hold the fan blades that were broken off when the disk ruptured.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
This is the arrangement prepared to cool the alternator in absence of cooling fan. The air pressure is 4~5kg/cm2 and air flow is 7~8 m/sec measured on driven end side of alternator. Please comment on this air pressure & air flow, will this be sufficient to cool the genset on load?? Ambient is around 25 deg celcius max. 2 industrial blowers have also been installed (as shown in pic). The correct insulation class of winding as mentioned on name plate is F (wrongly mentioned above as B which was from data sheet)

We plan to start the genset without excitation initially and measuring all parameters like bearing & winding temp, vibrations etc. The shaft is being fitted with half key balanced.

If everything goes well, then we will load it upto 0.5MW and measure all values. Meanwhile the fan is under casting.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

That looks good, however a lot of the air will probably be deflected out sideways. A shroud to direct the air through the cooling slots will give a dramatic improvement economically.

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Scotty, brush generator, Ruston engine.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Quote:

air flow is 7~8 m/sec measured on driven end side of alternator.

Is this measured close up at the vanes where the measured velocity is from air actually coming out of the vanes? If so then that should do it. Proceed with lots of monitoring and care. The F insulation is good to hear too.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Quote (CompositePro)

It was an axial, not radial fan. The blades were bolted to the outside circumference of the fan disc. You can see a pitched blade with base plate resting on top of the broken disc. There is a base plate still bolted to the OD at the bottom of the picture with the pitched blade sheared off.
Good observation... I couldn't figure out how this fan was supposed to work until I read your comments.

=====================================
(2B)+(2B)' ?

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I suspect that the majority of the air is not going down the slots where you want it.
Compare the air flow at the fan discharge with the air flow out of the slots.
Shrouding?

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

3Ddave,

You may well be right - apologies Compositepro.


FARHANRAZA,

The air from that fan will hit the stator end and be deflected - you need to form a pressurised plenum between the fan discharge side and the stator casing.


Hoxton - that's really surprised me. surprise

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Yes, you definitely need ductwork between those fans and the alternator vents to force the air through the alternator.

I would bet money the old fan was an axial fan. The disk in the picture is the center hub and the blades were around the outside so the blade length was the same as the width of that cooling vent opening ring. If you look at the picture posted with the PM in the foreground, the disk would be approximately the size of the part of the end bell inside the vent openings with the blades reaching the rest of the way to the outside of the frame.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

ScottyUK, It took a couple of looks for me to get it. It's a puzzle with a lot of pieces gone. It must have been exciting with all that metal zipping about; lots of chance to injure or kill someone.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Lionel,

Have a look at the photo again: 3Ddave is right (as is Compositepro) - there's the remains of a bolted-on axial fan blade (highlighted) and to the right of it are the marks where others have been smashed off. It's a peculiar fan for an odd-looking generator. Axial fans are typically used inside the machine, forcing cooling air from the stator ends into the airgap and venting air outward through the stator core slots, but radial designs are more common for the external fans where a cowling is used. Not in this case though!

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Yes, that's what I posted??? An axial fan with a big hub and little stubby blades. I would be quite wary of another cast replacement fan unless the casting company has the proper experience and engineering to ensure the new casting will survive without failing like that fan did.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Clearly, the axial fan's 'buckets' were cast individually, and bolted to a large central rimmed disk, which appears to have been fabricated from plate and bar, joined by welding, and split for radial assembly.

On the disk, I don't see the draft, fillets and radii that I would expect to see in a single large casting, or two large cast halves of a fan cast with integral buckets.

I can't find an indication of a drive key on the shaft, but the photos do not provide complete coverage. Where the fracture surface intersects the central bore, the near side detail looks a bit like the remains of a keyway.

... which is where it should fracture in a bad sync event.
... and not in a startup, ever.

... but a bad sync event that was bad enough to fracture that fan wheel just against its own inertia, could cause a lot of other damage.

HAVE YOU INSPECTED THE ENGINE CRANK AND INTERNALS?

Mike Halloran
Pembroke Pines, FL, USA

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Quote (OP)


FARHANRAZA (Electrical)
(OP)
21 Dec 16 03:35
An old crack has been found in the fan, which has dust ingress. This shows fan was damaged due to starting jerk which old crack couldn't bear. Fortunately no one was hurt in this incident.

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

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
Today we have successfully test run the generator without cooling fan and with above arrangements:

Max Power: 1.46 MW
Max winding temp: 70 deg celcius
Max Driven end bearing temp: 56 deg celcius
Max Non Driven end bearing temp: 45 deg celcius
Max vibration on generator bearing = 5 mm/sec

RE: Diesel Engine Driven Generator Operation without Cooling Fan

That's nearly full load!

That was with the two fans and no ducting?

Did you confirm the temperatures actually stabilized and reached steady-state?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Engine Driven Generator Operation without Cooling Fan

(OP)
Yes, the test was performed without fans ducting. Actually as rightly pointed out by everyone fans without ducting were of no use. I switched off the fan after sometime, and it made nearly no impact on the temperatures.

Test was performed for about 2 hrs, and yes temperatures were stabilized. Air spargers helped alot and fans like this were of no use.

Thanks all for your continued support. We hope to get fan casted & balanced in 2 weeks time and after that it will be installed back.

RE: Diesel Engine Driven Generator Operation without Cooling Fan

I am very surprised FARHANRAZA by the results you report.

Thank you for keeping us informed. Thanks for the informative pictures too. We all learn that way. Good luck with the new cast fan! We'd like to see it when it shows up.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Well, I'll be dipped in ... er, used food.

Mike Halloran
Pembroke Pines, FL, USA

RE: Diesel Engine Driven Generator Operation without Cooling Fan

Don't feel bad MikeH
I missed that post myself the first couple of times through.
Can I buy you one in the Pub?

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

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