Diesel Engine Driven Generator Operation without Cooling Fan 2

[FARHANRAZA]

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.

 

[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.

 

[waross]

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

 

[3DDave]

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.

 

[MikeHalloran]

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

 

[FARHANRAZA]

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.

 

[waross]

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

 

[FARHANRAZA]

Thanks all of you for your valuable suggestions & comments.

 

[Hoxton]

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.

 

[ScottyUK]

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.

 

[3DDave]

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.

 

[FARHANRAZA]

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.

 

[waross]

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

 

[Hoxton]

Scotty, brush generator, Ruston engine.

 

[itsmoked]

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

 

[electricpete]

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)' ?

 

[waross]

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

 

[ScottyUK]

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.

 

[LionelHutz]

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.

 

[3DDave]

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.

 

[ScottyUK]

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!