Very Large Power Transformers (VLPT) - Page 1
Forum section: electronics / general

author: GreggD
author_rank: Regular Contributor
timestamp: May 23, 2017, 06:19:21 pm
content: Our power company closed a large coal-fired generation plant a year or two ago.They plan to close two more next year. Just one, J.M. Stuart Station on the Ohio river is 2,318 Mega Watts.To sent power to the grid the voltage is stepped up as it leaves the plant by giant transformers.Question, Is it possible to reuse the transformer somewhere else or just recycle it as scrap?I think these are so special that they can't be reused.Here is a mega-sized report on these transformers I thought you might enjoy. (Just makes my head hurt)https://energy.gov/sites/prod/files/Large%20Power%20Transformer%20Study%20-%20June%202012_0.pdf

author: Vtile
author_rank: Super Contributor
timestamp: May 23, 2017, 06:41:19 pm
content: The step up transformers are used almost in every plant since it is more economical to produce generators with lover voltage specks in few tens of kilovolts, which are often set in as parallel and plugged-in as demand arises and then step up the voltage for the grid voltages.If it is standard voltage (in the past or today) rated transformer one could assume there could be a secondary market for plants with same units in use, but as a junior in the field and not from US my word is pretty much in level "I think" and even the transformers are constantly going through technological upgrade (mostly in remote condition monitoring and efficiency) so it might be just be a big lumb of copper and oil.

author: nctnico
author_rank: Super Contributor
timestamp: May 23, 2017, 06:51:19 pm
content: Depending on the age it may even contain materials which are considered toxic nowadays so disposing of the transformer may be costly.

author: calexanian
author_rank: Super Contributor
timestamp: May 23, 2017, 07:19:42 pm
content: They need to be tested for PCB's and such. There are companies who specialize in large transformers like that. If they are safe they will pay you for them. If they are toxic they will remove them and the scrap value will offset the cost of the removal. Safe Harbors is a company that comes to mind. Check out ones in your area. As far as secondary market it's hit or miss.

author: ElektroQuark
author_rank: Unknown
timestamp: May 24, 2017, 07:25:05 am
content: Check the transformer manufacturing data. In the USA PCBs where banned circa 1977.

author: tronde
author_rank: Frequent Contributor
timestamp: May 24, 2017, 05:26:35 pm
content: Quote from: Richard Crowley on May 23, 2017, 06:26:46 pmIt is no problem to re-use or repair them. They even ship them across the Atlantic for repair if that saves time. My father used to work for one of the manufacturing companies that became ABB in Norway. Repair and re-manufacture makes a lot of sense because of the time and material costs saved. Decommisioned transformers are often kept as reserves. If killed by a lightening storm it can take the most of one year to repair one of the big (hundreds of MVA) transformes, so an old spare makes sense. I understand that regular oil analysis and timely oil changes can save the ovners a lot of trouble because the oil is an important part of the insulation in additioin to cooling.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 24, 2017, 09:25:31 pm
content: On this subject, how do they actually keep turbines synced with the rest of the grid, while also maintaining the correct voltage? If you spin it at a certain speed it will produce a certain voltage, the faster you spin it, the higher the voltage, but the frequency also changes. Of course the voltage also changes based on load. Do they also have very large variacs for this? As you almost would need to control the speed just to keep the voltage constant based on load. Say you're feeding a 500kv line, it needs to actually have 500kv added to it, not more not less, if you add more you will surge the rest of the grid. Or is there actually lot of room for error as the extra voltage translates into extra current, and it just self regulates back down?Or do most turbines actually do DC, then get inverted into correct AC voltage/frequency? I know they also have HVDC lines but I'm talking about AC ones. So basically turbine -> rectifier -> 60hz inverter with fixed voltage output -> step up transformer to bring fixed voltage to proper line level -> grid.

author: calexanian
author_rank: Super Contributor
timestamp: May 24, 2017, 11:16:48 pm
content: Quote from: Red Squirrel on May 24, 2017, 09:25:31 pmGenerally generators are synchronously locked. Power is added to the grid in much the same way a bicycle built for tow is powered. Somebody pedals and then if a second person begin pedaling they effectively can move their feet along with the pedals with no power input. Just moving along. How that second person adds power to the system is to begin attempting to push the pedals faster thereby adding power to the system. This is how an AC rotating generator adds power to a grid. It tries to push it faster. This is called leading. A load such as a big AC motor is attempting to slow down the grid frequency and this is called lagging. Current lead and Lag is sometimes used to describe current in inductors and capacitors and applies here as well but in a more mechanical sense. Generally voltage regulation grid wide is handled by switching transformer taps somewhere in the system and motive power is added to maintain 60 or 50 hz. You can demonstrate this principal with two identical stepper motors wired in parallel. Turn one shaft by hand and the other will move along with it. Here is a example of that.As far as DC or non synchronous generation, it used to be done with Thyratrons or Ignitrons and big wave shaping networks. I am sure that stuff moved onto solid state and I have not kept up on it, but I am sure modern switching circuitry is basically doing the same thing. DC to AC motor to generator sets have not been used in many decades for power distribution.

author: Jr460
author_rank: Regular Contributor
timestamp: May 25, 2017, 12:39:47 am
content: Quote from: Red Squirrel on May 24, 2017, 09:25:31 pmOnce synced, you can't really un-sync it.The generator spins at exactly 3600 RPM, The only time faster or slow is when he main breaker is opened and it being started up or shutdown.Voltage control is handled by the amount of current in the rotor which controls the strength of the rotating magnetic field inside the generator. The part of the unit that makes the rotor current is called the exciter. Older units were different, they might have a MG set to supply the field current. New units have an gener-ex, or an alter-ex. on the end of the generator shaft.If you have unit that is synced to the grid and you take away the steam feed, the unit then becomes a large motor.Most units put out 22KV 3 phase. That then goes to the main power transformer which then takes it up to 365KV and into the system. Just before the main power transformer are two smaller Aux transforms that take the 22KV and provide to busses of 4160V. These run all the pumps, motors, lights for the unit. Cold start, power can come back n from the grid, and give you the aux feeds, or their are buss ties to other units in the plant. All else fails, a backup diesel can power things to get the unit back online.As someone else said, how much power you make depends on how hard "push" not how fast you spin. With AC, the direction of power flow is complicated. A higher voltage at one end doesn't always imply the direction of flow.Think of it this way. You have one unit, and fixed load. Thing is spinning at 3600RPM. Now add just a bit more load and and spinning slows down just a fraction of an RPM, the controls kick in and open the control valves a tad more to push harder and the speed comes back up to 3600RPM.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2017, 12:43:59 am
content: Misuse of terminology -- they aren't generators, they are alternators. Generator is PM, alternator is electromagnet.This provides the degrees of freedom needed to match and regulate output voltage, as well as frequency.Tim

author: Jr460
author_rank: Regular Contributor
timestamp: May 25, 2017, 01:03:27 am
content: Quote from: T3sl4co1l on May 25, 2017, 12:43:59 amI'm not going to argue with you. However, you can go to Schenectady, NY and try to convince GE's Large Steam Turbine division and try to get them to change the the name plates on all the equipment worldwide.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 25, 2017, 02:27:20 am
content: Interesting, so are alternators mostly current sources then, so like when you push harder it just causes more current to be drawn, but the voltage always remains the same? So you bring it up to speed so that the frequency is in sync, throw the switch so it's electrically connected, if you stop water (let's assume a hydro electric turbine) flow it will continue to spin but draw current, if you open the water it will start to push harder, and eventually hit equilibrium, or if you push a bit harder then it will start to feed current, but always at the same voltage and frequency. Is that correct?That stepper motor demo is interesting too, I would have thought that it would take a bit of turns for the other one to start spining but it starts right away and always stays in sync.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 25, 2017, 02:28:40 am
content: Quote from: Jr460 on May 25, 2017, 01:03:27 amI'd guess that alternator is the very specific assembly of coils and magnets, while generator can refer to that + anything else attached to it such as a turbine. Ex: the turbine and alternator together is a generator.

author: yada
author_rank: Frequent Contributor
timestamp: May 25, 2017, 04:23:01 am
content: The picture on the left in that report is from a company that builds those in India. Out sourcing. I heard on the news that if we have a large solar flare the 750kv transformers will blow up and we have no spares in north America and they take months to build, assuming the plant has electricity.

author: filssavi
author_rank: Frequent Contributor
timestamp: May 25, 2017, 05:13:09 am
content: Quote from: Red Squirrel on May 25, 2017, 02:27:20 amI'd say It is simplistic and to a degree wrong to think only in termins of voltage/current source, the behaviour you are seing is not determined from just the generator, which by itself is just a normale voltage source,it is the grid which is highy indicative and modifies this behaviour.Here is how roughly it works:First and foremost it can be shown that for a line with low resistance and high inpedance (such ad power lines) the frequency depends almost only from the real power flowing through the line, whereas the voltage depends mostly in the reactive PowerNow that we established that we know that the power supplyed from a generator suddetto spikes up, than the frequency will drop accordingly (depending also on rotor inertia) now the control loops wil detect this drop and open the stream/fuel valves to restore nominal frequency. You can se we never talked about voltageNow to understand how generatore in parallel work we need to look at how the synchronous machines behaviour. In particular the machine's rotor and stator magnetic field must run in sync, when they are not too much out of sync there will bè a pull in torque on the rotor that tends to bring it in sync, if the rotor is too out of sync it will stop in fact to start these machines you need another motor that brings them up to speedNow when you have 2 generators in parallel their ritira will be locked and they will spin synchronously, if one slows down for whatever reason the connection of the two Will generate a torque that tends to being it back in sync

author: yada
author_rank: Frequent Contributor
timestamp: May 25, 2017, 07:50:43 am
content: Quote from: calexanian on May 24, 2017, 11:16:48 pm

author: Vtile
author_rank: Super Contributor
timestamp: May 25, 2017, 01:25:34 pm
content: Generator is the umbrella term of devices that converts mechanical energy to electrical energy. I don't know how widely used (in different fields and languages) the sub-terms Dynamo and Alternator are these days, but mostly you will hear the term generator in use. Most such devices can act as a both motor and generator depending which way the power in shaft is acting (or in piston etc. if it is linear and not rotating machine), like seen on the stepper motor video clip.You can also use asyncronous induction motor as generator if you provide outside power to it and it does have some remanence in rotoror were it stator which had the remanence,since rotor were often aluminium IIRC.. too much time have gone since I last time did any theory related to these(.or you give a DC spike to stator coils to create the magnetic field) and the network do have enough capacitance.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2017, 01:52:11 pm
content: An alternator generates a voltage proportional to RPM * field strength, and frequency equal to RPM * poles/2.I think generators properly also have commutators (i.e., cranking a regular PMDC motor), which is clearly not consistent with present subject.Tim

author: calexanian
author_rank: Super Contributor
timestamp: May 25, 2017, 03:08:08 pm
content: Quote from: T3sl4co1l on May 25, 2017, 01:52:11 pmThe synchronous generator has remained unchanged in basic design for over 100 years and the term generator has been used since. The term alternator came into use in the 50's. Alternator was popularized by the car companies to denote a better product. In reality AC generators were previously used in vehicles but the required rectifiers were not practical until affordable germanium rectifiers were available. 400 hz "Synchros" were used in aviation and large specialty vehicles from the 30's up until this day.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2017, 06:19:48 pm
content: Quote from: calexanian on May 25, 2017, 03:08:08 pmThe terms "alternator", "generator", "dynamo" and so on have been around since the early history of electrical power generation.Example:https://en.wikipedia.org/wiki/Alternator#/media/File:Ames_Colorado_generator_alternating_current_power_plant_1891_Gold_King_Mine.pnghttps://en.wikipedia.org/wiki/Dynamoetc.It seems "generator" is typically used in the broad sense (it generates electrical power, regardless of method or type), hence anything made for mains generation is a "generator".I was just being specific.Tim

author: calexanian
author_rank: Super Contributor
timestamp: May 25, 2017, 06:56:22 pm
content: Quote from: T3sl4co1l on May 25, 2017, 06:19:48 pmDon't be. Life will be much easier.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 25, 2017, 07:59:32 pm
content: Shockingly terrible advice!My customers would be terribly disappointed if I were unspecific.Perhaps you should be more specific.Tim

author: filssavi
author_rank: Frequent Contributor
timestamp: May 27, 2017, 05:33:26 am
content: Quote from: T3sl4co1l on May 25, 2017, 06:19:48 pmA generatore is no just "typically used in a broader sense"the term generator is not related to a particular architetture, it just defines a function, of the electrical macchineHere is ahow it isELECTRICAL MACHINE: anything that converts mechanical ti electrical powers and vice versaMOTOR: an electrical machine that right now is converting from electrical powers to mechanicalGENERATOR: an electrical machine that right now is converting from mechanical to electrical powerAC GENEATOR(ALTETRNATOR) a generatore that is outputting AC Power, some of the most used AC machines are: squirrel Cage asynchronous, permanent magnet and wound synchronous, switched reluctance and in a sense brushless DCDC GENERATOR(DYNAMO) a generatore that is outputting DC Power here you have only wound rotor brushed DC machines