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Load shedding

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Tweefo
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« on: November 30, 2014, 17:19:13 PM »

We are back to this again, (Hello darkness, my old friend) but how does this work? I read in a news flash that "with the load shedding over the weekend Eskom will build up enough capacity for the coming week". How is that possible, they cannot store the electricity or do they store the energy in the form of unreleased steam? Meanwhile, it pays to live close to the action, so to speak. The rumor here in Middelburg is that the Arnot power station (close by) has run out of coal.
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Rigil Kent
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« Reply #1 on: November 30, 2014, 17:31:37 PM »

Load shedding causes a lot of unreleased steam, no doubt.
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Mefiante
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« Reply #2 on: November 30, 2014, 18:50:26 PM »

Most of SA’s electricity is produced by coal-fired power stations.  Reducing the weekend load allows the coal reserves in the main feed silos to be built up so that the required power capacity is available during the week.  The feed coal needs to be sized correctly and also washed in some cases.  You can’t just shovel any old coal into a power station.

(One such feed silo collapsed at the Majuba power station a few weeks ago, reducing Eskom’s total power capacity.)

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Tweefo
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« Reply #3 on: November 30, 2014, 19:25:33 PM »

So it's more a case of building up coal reserves. Guess you can't win. We complain about all the coal trucks here in Mpumananga, but why is this just now a problem?
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Mefiante
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« Reply #4 on: November 30, 2014, 19:42:39 PM »

Typically, coal-fired power stations are fed by conveyor belts, not trucks, which are inefficient for this sort of application where a more-or-less constant feed rate is required.  But there are still feed silos that give some surge capacity and also smooth out interruptions when a problem occurs with the conveyor belts.

It’s a question of building up available feed coal at the power station’s doorstep (as it were) so that the power station can produce power at or slightly above its nominal capacity during the week.  It’s become a problem because power demand has gradually increased over the years to the point where it’s now above nominal supply capacity.  Interruptions such as the Majuba silo collapse reduce total supply capacity.  This shortfall must be made up by other power stations, and hence the need for rolling blackouts to curb the average power demand over a whole week.

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Tweefo
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« Reply #5 on: November 30, 2014, 20:10:42 PM »

Typically, coal-fired power stations are fed by conveyor belts, not trucks, which are inefficient for this sort of application where a more-or-less constant feed rate is required.  But there are still feed silos that give some surge capacity and also smooth out interruptions when a problem occurs with the conveyor belts.

It’s a question of building up available feed coal at the power station’s doorstep (as it were) so that the power station can produce power at or slightly above its nominal capacity during the week.  It’s become a problem because power demand has gradually increased over the years to the point where it’s now above nominal supply capacity.  Interruptions such as the Majuba silo collapse reduce total supply capacity.  This shortfall must be made up by other power stations, and hence the need for rolling blackouts to curb the average power demand over a whole week.

'Luthon64
Conveyor belts in the olden days. The power station had a coal mine nearby that fed it via a conveyor belt, but most of those mines are worked out, so now they use trucks to transport it from other mines. If you drive around in the area you'll see most are broken, rusting pieces of scrap. They build a new one for Arnot though, so maybe that rumor is just that, a rumor.
I understand the problem of more demand over the years, but three weeks ago there was no problem.
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brianvds
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« Reply #6 on: December 01, 2014, 03:54:54 AM »

Thus far the load shedding has not affected me too negatively: the past two Saturday afternoons, I was without power for an hour or three. I don't mind the load shedding as such all that much, but I wish they would inform one when exactly they are going to cut the power, so that one can plan for it.
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Rigil Kent
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« Reply #7 on: December 01, 2014, 06:48:41 AM »

Load shedding schedules is published in our local paper. Have you checked in yours? Otherwise you could try here. http://loadshedding.eskom.co.za/


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brianvds
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« Reply #8 on: December 01, 2014, 07:00:23 AM »

Load shedding schedules is published in our local paper. Have you checked in yours? Otherwise you could try here. http://loadshedding.eskom.co.za/


Rigil


Indeed, but what they tell you they are going to do isn't necessarily what they end up doing. :-)

Either way, as long as the outages stay within reason, I don't mind too much. I have had far more disaster with unscheduled "load shedding" due to cable theft some months ago, when the power was out for several days and everything in my freezer defrosted. May the fingers of the cable thieves turn into fish hooks, and they start to itch in their nether regions.
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cr1t
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« Reply #9 on: December 01, 2014, 09:14:57 AM »

I must say here in CT they seem to have it down to a fine art.
There schedule says our area is effected between 10 to 12, and that is what it does nothing more nothing less.

I also think we hit the jackpot is as far as time frames go.
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Tweefo
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« Reply #10 on: December 01, 2014, 09:19:44 AM »

Ok, let's recap:
The load shedding problem seems to be that not enough coal is stockpiled, rather than generating capacity. (Three weeks ago and last winter there was no load shedding.) Generating capacity can be the problem if some of the units are shut down for maintenance, but with the 2008 sheddings it was known to be a stockpile problem. Workers got bonuses if their stockpiles were not too big. A sort of "Just in time delivery" method was preferred, but they got it all wrong. Of course, this was not officially admitted, but like I said, it pays sometimes to be close to the action, you hear the gossip. I also noticed, and remarked on it to my wife three weeks ago, that there is far less coal truck traffic on the N11 between Middelburg and Ermelo and the R35 between M/burg and Bethal.
So, what is the problem? Inept stockpile managers or routine maintenance? A combination of both? As far as their schedules are concerned: Very much like weather forecasts. Cannot be relied upon.
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Mefiante
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« Reply #11 on: December 01, 2014, 09:33:16 AM »

As hinted at twice before, repairs and maintenance at Majuba power station are a large part of the current problem (pun intended).

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Tweefo
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« Reply #12 on: December 01, 2014, 09:47:52 AM »

As hinted at twice before, repairs and maintenance at Majuba power station are a large part of the current problem (pun intended).

'Luthon64
Not so. That problem (the cracked silo) is sorted. They are bypassing that.
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Mefiante
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« Reply #13 on: December 01, 2014, 10:09:09 AM »

Maybe that’s what they say, but Majuba isn’t running at or above its rated output like it used to before the silo collapsed.  Eskom also said that there wouldn’t be any load shedding effect when the Majuba silo collapsed, yet here we are.

Have you even looked closely at the layout of Majuba?  The collapsed silo cannot help but be an obstacle to feeding two of the power station’s six generator sets, even after all the rubble is cleared away.

The diminished capacity problem is aggravated by supply commitments Eskom has with some of our neighbours to the north.

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Tweefo
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« Reply #14 on: December 01, 2014, 10:18:47 AM »

I'm pointing my finger at inept workers and I am sticking to my story.  Grin
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BoogieMonster
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« Reply #15 on: December 01, 2014, 10:20:43 AM »

I have to admit (since I don't believe in 'tempting fate') we've been stunningly lucky with the whole load shedding thing. Only lost power once in the last 2 weeks. This w/e we had 100% power while everyone around us suffered greatly. I'm pretty sure my house is on some circuit that nobody ever notices, on a border line between 2 suburbs that both get cuts when we're still up. Let's hear it for happy coincidences.
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Mefiante
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« Reply #16 on: December 01, 2014, 10:46:36 AM »

The silo collapse at Majuba is directly attributable to poor or non-existent maintenance schedules.  Associated with the coal from the Majuba mine are appreciable quantities of iron pyrites, an iron sulphide more commonly known as fool’s gold.  When left in brackish water (that has some dissolved carbon dioxide in it), the iron sulphides produce sulphurous and sulphuric acid.  These acids leach calcium carbonate from concrete, and thereby weaken it.  Maybe the contractor also skimped on the concrete mix, using less and/or lower UCS cement than the design called for.  Regular turnover schedules (i.e., completely emptying, washing out and refilling the silos) minimises this problem, and acoustic soundness tests will proactively identify the development of weak spots that can be repaired before disaster strikes.  Clearly, none of this was done with any degree of regularity or discipline at Majuba, and therefore all fingers should be pointing at the power station’s general manager and its chief engineer.

More broadly, Eskom as a whole is to blame for not pushing the issue of capacity development much more energetically a dozen or more years ago when they first realised that such development would be crucial.  Instead, they kowtowed to the ANC government’s insistence that it had more pressing issues to attend to, such as handing out social grants.

'Luthon64
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Tweefo
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« Reply #17 on: December 08, 2014, 17:55:03 PM »

I am convinced that there is a spike in motor accidents because of load shedding. Last night, while driving on Zambezi Pretoria (whatever it's called now) parts of it was dark, and I came across three accidents at different traffic lights. All fender benders, nothing serious, but it would be interesting to get hold of some insurance figures.
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brianvds
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« Reply #18 on: December 09, 2014, 04:40:09 AM »

My power was off in the afternoon last Friday, and Sunday. And again yesterday afternoon. And then there was a heavy storm that knocked it out the whole evening as well. This is getting most annoying...
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cr1t
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« Reply #19 on: December 09, 2014, 11:46:55 AM »

My power was off in the afternoon last Friday, and Sunday. And again yesterday afternoon. And then there was a heavy storm that knocked it out the whole evening as well. This is getting most annoying...


http://www.makro.co.za/diy/generators-IEC
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brianvds
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« Reply #20 on: December 09, 2014, 14:41:49 PM »

My power was off in the afternoon last Friday, and Sunday. And again yesterday afternoon. And then there was a heavy storm that knocked it out the whole evening as well. This is getting most annoying...


http://www.makro.co.za/diy/generators-IEC


Can't afford such toys. And I rent the place, so presumably I can't go play around with their electrical system.

Don't know what the problem is anyway. As I understand it, a power station works by burning coal, to heat water to make steam, which turns the turbines for the generators. Now why don't we just replace the coal with our numerous politicians? They spew enough hot air...
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Mefiante
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« Reply #21 on: December 09, 2014, 15:04:10 PM »

Don't know what the problem is anyway. As I understand it, a power station works by burning coal, to heat water to make steam, which turns the turbines for the generators. Now why don't we just replace the coal with our numerous politicians? They spew enough hot air...
Goodness knows, there’s more than enough of them.  Sadly however, your suggestion won’t work because our politicians are so adept at dodging the law that even the laws of thermodynamics are no longer safe…

Slightly less seriously ( Tongue ), Eskom also has a few pumped storage plants.  During the blackouts, they use some of the power to pump water back up into the reservoir in order to increase generation capacity during peak hours.  (Tangentially, it may be worth noting that this is the thermodynamic equivalent of changing from coal to R200 notes.)

'Luthon64
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BoogieMonster
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« Reply #22 on: December 09, 2014, 15:20:19 PM »

... the thermodynamic equivalent of changing from coal to R200 notes.

I'm pretty sure this is what the generators run on at Nkandla.
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Rigil Kent
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« Reply #23 on: December 09, 2014, 19:16:37 PM »



I see there are petrol, diesel and digital generators available. I assume the digital one runs on toes and fingers.

Rigil
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brianvds
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« Reply #24 on: December 10, 2014, 03:50:36 AM »



I see there are petrol, diesel and digital generators available. I assume the digital one runs on toes and fingers.

Rigil


Or perhaps they work on electricity... :-)
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Tweefo
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« Reply #25 on: February 14, 2015, 20:32:00 PM »

I did a bit of sidewalk astronomy again last night, and one guy said that he just came back from the Eastern Cape and that most of the wind turbines were not working. That Eskom does not want to pay. Is this true Rigel? What's the inside information down there?
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brianvds
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« Reply #26 on: February 15, 2015, 04:40:12 AM »

I did a bit of sidewalk astronomy again last night, and one guy said that he just came back from the Eastern Cape and that most of the wind turbines were not working. That Eskom does not want to pay. Is this true Rigel? What's the inside information down there?

And in the meantime, my power is now switched off two to three times every week. Some of my colleagues and friends tell me theirs is NEVER switched off. Another tells me his power is off from 8 to 10 every evening. They can't even do the load shedding right.
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Rigil Kent
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« Reply #27 on: February 15, 2015, 10:12:26 AM »

Is this true Rigel? What's the inside information down there?

Don't know, but wouldn't be surprised, especially now that our esteemed president has announced to some obsequious parliamentary ovation that even more of your tax money will be funneled into the paralysedstatal's coffers.

On the other hand, in high winds the Siemens SWT 2.3 MW turbines are capable of parking themselves in a safe position, so there may well be a non-fiscal reason why most of them appear inactive at certain times. Of course, no wind is also a rare but obvious explanation for a stationary wind farm. Naturally, this cannot be blamed on  government, but is a clear and direct consequence of over consumption on the part of the Dromedaris, Reijger and Goede Hoop.

Rigil
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