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Electrical generation

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Electrical generation

Old 28th Mar 2014, 11:04
  #21 (permalink)  
 
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The step change from 60W to hypothetical MW as described by the op is of course very unlikely in the extreme across the national grid but the control principles are the same.
Of course, but my 'stalling' scenario was the 60w to sudden many MW, not the power station 'no stall' scenario you describe.
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Old 28th Mar 2014, 11:18
  #22 (permalink)  
 
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The reason the lights flickered when an electrocution was carried out had nothing to do with increased load stressing the system.
The utility companies of yore were much like today's drug companies and had serious reservations about their product being used to do in convicts. Therefore, the prison would turn on the standby generator to do the deed.

Last edited by 421dog; 28th Mar 2014 at 12:24.
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Old 28th Mar 2014, 13:30
  #23 (permalink)  

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was it really 1972?
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Old 28th Mar 2014, 14:03
  #24 (permalink)  
 
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The "new" electrical supply model does not use distant spinning things driven by megatons of electrical bulk and rotating physical mass.

The modern alternative to 19th-century turbine and motor-generators, wires, and hierarchies of transformers is a distributed sea of electronic "charge-switches", operating at microsecond speeds and driven from incoming near and far "charge pools", that collectively can and do shuffle bits of energy around in packets like grains of sand, a milliwatt here, megawatt there, cleverly arranging for the right-stuff to arrive at the right destination at exactly the right moment.

Such is the method and mechanism that allows nuclear generators and solar panels and various sorts of butterfly wings to all contribute some bit of share
(from each according to their ability) to local and also to far distant loads in an equitable and constructive way. Just coming on, it is... a hundred-year process, at minimum, to displace the Victorian infrastructure now existing in many places.
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Old 28th Mar 2014, 14:24
  #25 (permalink)  
 
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Any producer system coupled to highly variable consumer system will often incorporate a buffer inbetween. Be it computers, hi-fi amplifiers, hydraulic power, water supply or electricity generation.

Interesting point about the "new" electrical supply model, I guess it scales well and can take compliant input from many different forms of electricity generation. It's distribution seems to be modelled on data communications.
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Old 28th Mar 2014, 23:42
  #26 (permalink)  
 
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Looking at the thread title I thought the topic was about today's kids, who unlike us oldsters who could play happily with a stick and a ball, need electricity for their everything- I-pad, I-pod, I-phone, I-gamebox, I-gotta-have-one-because-everyone-else-does. Were it not for rechargable batteries parents would starve from excessive battery purchases for their progeny

The grid system is not as good an idea as it seems- the worst regional blackouts in N. America were all caused by single-point failures which could not be switched out in time to prevent the rest of the regional grid from collapsing. It needs to be able to switch out as fast as it switches in and that capability is not possible with current designs in N. America As the "I-gotta-have" world increases the electrical loads, something is going to have to give and it won't be them, so plan to see more Nukes because that's about all we've got that can keep up with their pace!
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Old 28th Mar 2014, 23:47
  #27 (permalink)  
 
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Here's an interesting site where you can watch the mains frequency varying as the load changes
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Old 29th Mar 2014, 01:30
  #28 (permalink)  
 
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I read or heard somewhere that a decade or so after the war when people started buying fridges washing machines fridges televisions and such the industry extrapolated the power needs ten twenty years in the future and built the power stations accordingly that would be needed,however the invention of the transistor and more efficient kit meant we ended up with a surplus.
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Old 29th Mar 2014, 01:35
  #29 (permalink)  
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With the predicted reduction in the availability of gas, the industry is now worried that the network etc. will not be able to cope!


I must admit to stalling a 250kVA diesel generator on full load one day. That was quite exciting and very smoky!
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Old 29th Mar 2014, 07:13
  #30 (permalink)  
 
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We're experiencing daily blackouts over large parts of SA. No forward planning was done so no new power stations were built, combined with maintenance funds being diverted for more worthwhile projects such as building a new home for the prez and padding the bank accounts of the pilferati. It's going to be even more fun in winter when demand goes up.

Meanwhile, cheap electricity continues to be exported over the border to our neighbours while the SA consumer (who bothers paying for it instead of stealing it) is getting screwed with constant price increases, while coping with those regular blackouts.

Oh, another thing... The Grande Fromage at the electricity supply company is also one of the highest paid people in the country and receives regular bonuses, despite the failures mentioned.
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Old 29th Mar 2014, 10:56
  #31 (permalink)  
 
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I must admit to stalling a 250kVA diesel generator on full load one day. That was quite exciting and very smoky!
Ahh memorys, watched a Cummins on a pontoon have a fight with Flygt pump one day, the Cummins won. Musn't have had under speed protection because it was touch and go for a while. Didn't think the gensets could be pulled that low, and more smoke, than you could believe, but after about 30 seconds, she went back up to high idle with no load on it.

Scratch one pump
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Old 29th Mar 2014, 11:16
  #32 (permalink)  
 
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Worked with a chap once who was a engineer on the Harlepool Power Station when it was under construction, he said as part of the project they were obliged to test one of the generators to destruction before installation.
Well I assume he meant before the remaining ones were installed.
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Old 29th Mar 2014, 12:34
  #33 (permalink)  
 
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A relative had responsibility for witnessing acceptance tests on HV power generation & distribution kit of various sorts. Destruction was optional, it seemed, but the voltages and currents were spec'd in advance, and product survival was TBD. Occasionally I got to tag along.

Can still see the scene, standing in a faraday cage built of welded chain and lined outside and inside 100 percent with very fine gleaming copper mesh some four storeys above a test floor holding a transformer the size of a modest house. Metal balls maybe 2m in diameter and spaced a precise distance apart -- maybe 2 or 3 meters --- just forward outside the cage, quite near under our feet, it seemed to me, with a trigger electrode smaller ball in-between.

For the test, bells rang, horns, lights flashing, all as prep. One half expected a Glockenspiel next, but instead there was a really brilliant flash, a line of incandescing plasma maybe 20 cm diameter in a slightly ziggy line between the spheres -very bright white in the middle , and what seemed minutes later a sharp-edged kerwhack noise of
cannon-blast proportions filtered into the mind through the heavy-duty earmuffs.

Quite a rush that was! The transformer survived, smiles spread all around, and shortly after a really great lunch, ears still ringing.

Last edited by arcniz; 29th Mar 2014 at 12:51.
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Old 29th Mar 2014, 20:31
  #34 (permalink)  
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I must admit to stalling a 250kVA diesel generator on full load one day. That was quite exciting and very smoky!
Testing Motor/Alternator packages with a resistor bank to 2000KVA is one thing VFD has done.
The early design diesels up to Tier 2 EPA requirement did definitely produce massive amounts of smoke when you hit them with a large loads. Most relied on mechanical type fuel controls.
Since Tier 3 and now Tier 4 interim requirements engines use electronic injection techniques and do a pretty good job of with the smoke and particulate matter although there is still visible evidence.


Worked with a chap once who was a engineer on the Harlepool Power Station when it was under construction, he said as part of the project they were obliged to test one of the generators to destruction before installation
Well I have to say I have seen some pretty spectacular failures, although usually on engine side but not always. I have seen some huge engine blocks with large windows put in them from rod failures. However, those issues usually crop up long before rated output if it is an engine problem.


Since electronics have come along way, most voltage regulation will stop exciting at about 57Hz on a 60Hz system and 47Hz on a 50Hz system. So if you drag down the engine the voltage regulator will just turn off the excitation to the alternator and it quits producing electricity to protect the alternator.


The biggest problem I run into is trying to convince the customer that has requested a load bank test is that his 10 year old 1365KVA engine/alternator set is only producing 700KVA is that the problem is the engine not the alternator.


VFD

Last edited by VFD; 29th Mar 2014 at 20:35. Reason: comma
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Old 29th Mar 2014, 20:33
  #35 (permalink)  
 
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We were installing a no break power supply system (battery and inverter) at Pyongyang but the electronics in the controller refused to put the battery charger on line due to low mains frequency. This was finally worked around by setting the battery charger to accept down to 15Hz which apparently is a European railway standard.

According to our instruments the mains frequency there was 41.6Hz and rock steady. It was 50Hz at the hotel. I have an idea why the mains frequency might have been low at the site.
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Old 29th Mar 2014, 22:08
  #36 (permalink)  
 
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Consider also the reverse scenario, all those pumps drawing full load and suddenly being disconnected. All the energy being put into the turbine has to go somewhere, so it starts spinning faster. As it goes faster, bits start flying off until it disintegrates. (This is how my power lecturer described the process at uni.)

In practice you wouldn't design a system with such a load change. If you were going from 300MW to 330MW as a step, that's not too bad, but 0.00006MW to 30.00006MW in one go is a bit drastic.

Of course, if there's a power cut, they have to be prepared for a surge on the grid as stuff is brought back on-line, but even then it's usually done one breaker at a time.
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Old 29th Mar 2014, 22:35
  #37 (permalink)  
 
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A late friend became a Chartered Engineer and was Charge-engineer at several power stations up and down the UK. He finished his carrer in Largs, just up the road from a nuclear power station which was shut down for political reasons.

He said they used to read the paper to find out what events would affect demand...a generator would be bought up to speed and the phase had to be synchronised, before switching it into the grid.....get it wrong and the bang would shake the whole building.....anyway, come the advert break on the telly, several million 2-Kw kettles would suddenly switch on...but they were ready!
n interesting fact, the generators were filled with Hydrogen....the concentration had to be maintained high enough that it could not explode....why?....the rotating mass had a lot less power -absorbing drag in Hydrogen, than air, presumably it was easier to fill with gas than to attempt a vacuum! IIRC, it also had something to do with spark-quenching.

He also told of a large, reinforced -steel switchgear door which blew a few hundred feet, demolishing a wall along the way........ the chamber was, again, gas-filled and a seal somewhat akin to the airlock familiar to home-brewers, was incorporated.....oversight allowed the water-level to drop, air got in, the ratio got critical ....then the switch operated

many fascinating yarns about an industry that has changed massively in the last 30 years.....Alan Binns MICE remembered with affection.
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Old 29th Mar 2014, 22:36
  #38 (permalink)  
 
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Once again, consider the energy stored in the rotating mass of the generator as you add load or the energy necessary to accelerate that mass once the load is removed. In practice the system has many sources and many loads all connected by links of varying impedance. Some generators are kept spinning just for PF correction and these add to the ability of the system to absorb transients most of the time. Sometimes the system becomes unstable and when that happens there is hell to pay as the system has to be broken down into manageable sizes of source and load and then reassembled.

After an excellent landing etc...
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Old 29th Mar 2014, 22:45
  #39 (permalink)  
 
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'the pilferati', 'The Grande Fromage'


Thanks SRT, I'll be using those! Got any more?
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Old 29th Mar 2014, 22:52
  #40 (permalink)  
 
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'Grand Fromage' Is that anything like Big Kahuna?

After etc...
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