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Topic Title: Diesel Generator and wind direction
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Created On: 25 January 2012 04:49 PM
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 25 January 2012 04:49 PM
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Peddler

Posts: 36
Joined: 28 May 2008

Hi Gents,

We have two new diesel generator package snapping fan belts.
(125 kW) weight 6 tonne.
There are a number of mechanical avenues currently being explored.

Anyway one of the HVAC Engineers has suggested the prevailing wind could be a problem. I find this a little obscure as we have very light winds here in the first place and also the fact at the commissioning stage there was no adverse weather conditions and little wind.
The belts snapped within 3 hours.

I would like anyone's take on this from an experienced point of view. I.E someone who regularly installs diesel generators.
Is the wind ever a factor when positioning the sets?.

Please don´t confuse this with exhaust direction, I am talking about air intake and out. The ambient temp is the same both directions as there is no external heat source or fumes etc in the vicinity

The suggestion is that there could be abnormal heat build-up inside the set even though during tests they were all well within the parameters.

The cooling system is very strong as we need the water temp to be as low as possible as its cools the exhaust system keeping the exhaust temperature down to around 85 deg , this is in order for it to operate in a class 1 div 2 hazardous area. So the main cooling fan is very large and the force of the air leaving the package is very high. The HVAC Engineer suggests the wind direction could stop this air coming out. He suggests we turn the sets round 180 degrees but I cannot possibly entertain this. Even if it was a factor what would happen if the wind changed.

In my case I think it's pretty clear wind has no affect with this particular problem but I would like to know what you think

Thanks in advance

P

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You can Learn from an Apprentice
 26 January 2012 12:28 PM
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broadgage

Posts: 1244
Joined: 07 August 2007

If the cooling fan is larger than normally fitted, as is implied, have the belts been uprated ? or are they as supplied for a much smaller fan ?
It could be as simple as the belts being unsuited for the duty.

Are the belts of reputable make and obtained directly from a reputable stockist ? Not fakes of much reduced strength compared to the real thing.
Fake MCBs and cable is certainly a problem, so why not drive belts ?

Can the pulleys be changed for multi grooved ones, so as to divide the load over perhaps 3 belts ?

I doubt the wind makes much difference, in an adverese wind the fan will be "fighting" the wind and thus more heavily loaded, but that should be allowed for. Turning the set round would still result in the wind being in the wrong direction at times even if less often.
 26 January 2012 04:50 PM
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Peddler

Posts: 36
Joined: 28 May 2008

Hi Broadgage,

thanks for the reply and input.

I went back to the manufacturer and they have been liaising with the designer of the pulley system. They re-designed the pulley system.
I am electrical discipline so mechacnical side is not my strong point but the pulleys were made wider to accomodate a wider belt and of better quality. Everything was put in place but there is still a problem witht the belts slipping.
I found some data on wind and mainly points to exhast direction. However it did state that in a hurricaine that there may be an effect.
The soluton to the wind problem is to angle the louvers , My sets have angled louvers so by the look of it I can eliminate the wind issue.

P

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 27 January 2012 01:45 PM
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chrisjtaylor

Posts: 34
Joined: 10 August 2005

Peddler
Can you give a little more info, what engines? exactly how big are the fans, is your load stable or dose it have sudden impacts. I'm thinking there may be inerita of the fan at work here. Do the belts scream on load change?
You say the sets are 125KW but is that the standard rating before the oversized rads were added, the engines should be oversized for this.
It does sound like they are undersized, an oversized pully on the engine would not be the most stright forward thing to provied unless it was dirven directly from the crank, this would limit what could be done.

Personaly I always go for electric fans in cases like this. TÜV TA-Luft complience damands very low intercooler return temperatures so this sort of setup is not unique.

I don't think wind is your problem

Chris

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Is the search for the Higgs Boson mass hysteria?
 30 January 2012 01:49 PM
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Peddler

Posts: 36
Joined: 28 May 2008

Hi Chris,

The fan and pulleys are coming off the main crank.
The belts are squealing on Load change but the load change is vey rare ( if air receiver on platform is nearly empty) so belts are slipping and wearing down on constant load.

The sets are Volvo Engines modified to operate in a hazardous area.
Essentially the cooling system is upgraded which cools the exhaust gasses low enough for safe operation. This negates the use of flame traps.

There were two machines installed on two different unmanned platforms
When we first run B machine we noticed that the fan belt started to slip, within a hour or so the belts and snapped off.
At that point we could only surmise what the problem was so we proceeded to the other platform to check the belts on A machine.
We noticed the belts were worn into the pulley on this machine which indicated to us that the belts were wearing down.
We request new belts from the manufacturer in the UK.
The new improved belts arrived and we fitted them. We started a 72 run test on both sets; both units failed the 72 hour run test; they lasted approx. 60 hours each set.

We contacted the supplier and had them look at their loading calculations for belt load on these engines and the calculations showed that each XPA 1357 AS belt is capable of handling 9.6kW of power. These units are fitted with two of these belts
giving a load capacity of 19.3kW. The fan requires 12.1kW to drive it so they did not envisage any issues with this belt drive.
They have manufactured several Volvo D7 engine packs with this belt arrangement and
have had no reported issues in the field.

The manufacturer of the sets discussed the issues with their belt suppliers and they ran their own calculations and concluded that each belt could handle 11.6kW giving a total load capacity of 23.2kW, which is higher than their own figures showed.
They suggested that it could be due to a heat issue and recommended using the Gates Quad power belts as these have a different material specification capable of taking higher temperatures. These were fitted to the engines, and whilst increasing the time to failure, have not resolved the issue.

We took temperature readings of the belts after a long run session and reported to the manufacturer to be 122oF. We also checked the pulley alignment was and found to be good. The issue has occurred on both units so cannot be attributed to a specific engine. The manufacturer conclude that for some reason, that is not yet ascertained, the belt
load if far higher than expected. At first they deduced that a new drive system was required and they had planned to use a 40mm wide toothed belt. This would have required new pulleys to be designed and manufactured.
They then recommended moving to s x B section belts in place of the A section currently
used. These would provide a 50% increase in load capability over the A section belts. They felt these were a better solution than a toothed belt.
This proposed solution was implemented but unfortunately this has not solved the problem. The new wider pulleys and belts are still slipping and again the belts squeal on the large load changes and wearing down on constant staedy load.

So we are basically back at square one and now the manufacturer wants to try another solution but I must admit I'm running out of patience.

The new proposed solution is difficult to describe without a drawing but the pulley system is like a triangle with the tensioner pulling away from the main pulleys to get the required tension. The suggested modifications are to tension onto the back of the belt. More like a car arrangement I suppose. The effect of this modification would be to increase the belt wrap on both the drive and the driven pulleys thereby increasing the contact area between the belt and the pulleys and making the system more resistant to belt slip.

To do this they have to convert the tensioner pulley to a smooth roller.
The tensioner mechanism, which consists of a long threaded rod, would need to be reversed so that it either pushes or pulls the tensioner towards the centreline of the engine, rather than away from it. They will also need to measure the required belt length to suit the new arrangement and source new belts.

It is essential to eliminate the belt slip and if it is not currently possible to get enough tension on the belt to avoid this, then they recommend making these modifications to increase the belt wrap.

They did explore the option of using a poly-vee belt to replace the two "A" section belts, but the pulley manufacturer recommended the two "B" section belts instead. Their opinion was that these would be more robust than Poly-vee belts.

At this stage no one knows if this fix will work and now we basically have a prototype on our installations that require sorting out.

Even though the fix is the responsibility of the manufacturer as project manager I welcome any feedback on this.

I'll keep you informed

P

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 30 January 2012 02:43 PM
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giason

Posts: 18
Joined: 19 March 2004

Another electrician so excuse me if this is a bit mad. You say the outlets are louvered. has the manufacturer retained the outlet area and clean air flow allowing for the louvres. It could be the louvres are restiricting the air flow causing the fan to try stagnate / cavitate against it's own air flow. Could you try running the unit without the louvres in place and see if this improves the problem. It could just be that the louvres have restricted the airflow to a point where the fan is pulling excessive load to move the air due to the restricted inlet / outlet louvres.

The reason I say is we had an HPU where they tried tro fit a massive cooling fan until I pointed out they were creating a negative pressure in the HPU and with the fan running you wouldn't open the door and the fan would also be trying to compete with a restricted louvred inlet causing it to pull a higher than normal load (in this case was electric fan) and reduced airflow from the calculated rate. This was also 'calculated' by professionals in their respective fields but they forgot to allow for the other modifications and were just looking at the direct problem.
 30 January 2012 05:04 PM
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williamjohn

Posts: 178
Joined: 22 November 2010

Giason
Restricting the suction or increasing the back prssure on a fan usually reduces the load. The lower flow usually has a bigger effect on the load than the higher pressure ratio.
If the belt tensioning system is common to both belts, then one belt may be carrying most of the load. Toothed or polyvee belts would avoid risk of one belt slipping due to uneven tensioning.
Best wishes
John
 30 January 2012 05:09 PM
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chrisjtaylor

Posts: 34
Joined: 10 August 2005

Peddler.

Not so good then, basically the fan is creating more load calculated. The manufactures are not daft, and have done this before. What makes your installation different? What can contribute to fan loading?

The load is created by pushing/pulling air. If it's stalling or creating a vacuum then generally its not working as hard as it could, to see what I mean, put your hand over the end of a vacuumed cleaner pipe and you will hear the motor speed increase.

Check the pitch of the fan blades match the design spec, check the number of blades, a lot of bosses will allow up to 12 blades so it's not unusual to have some missing. Is the fan speed correct?
One other thing that comes to mind is the engine breathers, it's unlikely but could it be possible for the engine breathers to be lubricating the belts, causing slippage and wear?

If they have had other sets with the same original configuration working well then beefing up the belts seems to be a way to overcome a problem by force rather than solving it, its worth remembering that very KW used to drive the cooling is lost from the output.

I look forward to hearing the outcome.

Chris

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Is the search for the Higgs Boson mass hysteria?
 31 January 2012 10:44 AM
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Peddler

Posts: 36
Joined: 28 May 2008

Gents,

I'll report back in more details in a coupe of days, but after extensive investigation by the supplier into the pulley and cooling fan suggests we may be at our full capacity for the belts to operate without problems.

They need to go down the route of making sure they re design a new pulley system , once which has the strongest arrangment that can possibly fit into the package , we cant have it just be on the limit because if the coalecer has any restriction in air flow due to contaminent then we would be faced with problems all the time.

I have suggested that their propsal of an increase in belt rap "fix" will not be sufficient alone

P

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 31 January 2012 06:25 PM
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Jaymack

Posts: 4479
Joined: 07 April 2004

It appears to be a belt/pulley design problem. Have someone else submit a quote for the application, having given all the relevant ambient, mechanical, physical, duty cycle and electrical information.

Regards
 24 May 2012 10:19 PM
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simonjulie

Posts: 3
Joined: 24 May 2012

Any news on how this has gone ?

Increased load on the fan, I agree that changing the blade angle can have this effect but how could this happen between testing and installation. ?

The air breather could be an issue, the lubricating of the pully system being time based and thus not showing up at testing.

Constant Load ? What value is this ?
And what is the load useage characteristic ?

Could the belt be constantly being put on a jirking action, with the governor constantly adjusting ?
 06 June 2012 03:55 PM
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simonjulie

Posts: 3
Joined: 24 May 2012

Another question.......

Outlet louvres, are they bouncing open and closed ?
 08 June 2012 09:06 AM
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energy90

Posts: 3
Joined: 30 May 2012

Diesel generation is the combination of diesel engine with an electrical machine to generate electrical energy. A Series of diesel generator are fully used in many important fields such as telecommunications, highways, skyscrapers, hospitals, airports, armies and factories.Thanks.
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