|
Three-Phase posted:
The station I work at has been switching over to vacuum breakers on all of the 13.8 switchgear. The older arc chute style breakers moved the main contacts about 6 inches to break the contact. The new vacuum breakers move the contacts just over an inch and require no pre arcing contact. I maintain the generator excitation system at work so I can answer some questions about that aspect of power generation.
|
#
¿
Sep 4, 2011 02:54
|
|
|
|
| # ¿ Apr 30, 2024 02:35 |
|
|
The DC breakers we use on the exciters are incredibly simple compared to the old arc chute breakers we use. Only a handful of moving parts. A big coil to move it and a few tiny trip coils and a metal plate that presses a row of micro switches for aux contacts. All we really check is that the aux contacts all move at close to the same time and that the pre arcing contact opens after and closes before the main contact. It's a good thing it is simple because the german to english translation of the manual was really really bad. Regrding exciters. I have never worked with brushless exciters but the PSS people seem to hate them because it is hard to verify the computer modeling of them because you cant directly measure the rotor potential. I am quite happy to change generator brushes on a weekly routine but it is a bit freaky knowing each brush holder carries about 120A (2700A/22holders). We run four 900 Mw units and they dont share main output or station service transformers so we are able to run different reactive power on each unit. They get tied together on the 500 kv lines at the switchyard. helno fucked around with this message at 03:20 on Sep 4, 2011 |
|
#
¿
Sep 4, 2011 03:13
|
|
|
Its a GE DC breaker. Most of our other stuff is westinghouse. Tons and tons of really obsolete but reliable protective relays.
|
|
#
¿
Sep 4, 2011 03:22
|
|
|
The agreement with the Ontario power authority requires all generators to be able to take up to 30% of real power as reactive power. This is why wind farms always have those huge capacitor banks. They use inductive generators and cannot use excitation to take or push vars. You can see pretty clearly the reactive power loading every morning as things start to get turned on across the province.
|
|
#
¿
Sep 5, 2011 02:01
|
|
|
50/60hz is a tradeoff between lighting loads that work better with higher frequency and motor loads that perfer lower frequency. As to the GPS discussion I can tell you that the vast majority of the electrical instrastructure doesnt give a poo poo what time it is. Hell most of the hydro plants in ontario still use mechanical governors because they provide better grid stability than newer digital control systems.
|
|
#
¿
Sep 10, 2011 04:19
|
|
|
Aliass posted:AFAIK it takes about 2 weeks to restart a coal turbine. That sounds like bull to me. The coal plants in these parts are used for load foallowing and are up and down on a daily basis. Our nuclear units only take about 2 days from cold shutdown to sync to the grid.
|
|
#
¿
Sep 14, 2011 22:44
|
|
|
Three-Phase posted:Bearings - I've heard several stories about where a power plant experienced a severe power failure and completely shut-down. One thing that was lost in this power failure was lubrication oil to the bearings. So as the massive turbines spun down, they generated tremendous amounts of friction in the bearings, getting so hot they welded in place and had to be jackhammered apart. Not fun when you're talking about a 1000MW turbine. There have been quite a few bearings over the years saved by the EBOP (emergency back up oil pump) The main pumps run directly off the turbine shaft but dont really provide enough lubrication at low rpm. We test our EBOPs every outage, they are large DC motors that are connected directly to class 2 station batteries without any protective relaying. I would be far more concerned with a loss of generator hydrogen seal oil than wiping a few bearings. Loss of lube oil means replacing all of the bearing material but a loss of seal oil means you suddenly have pressurized hydrogen gas spilling out into the turbine hall.
|
|
#
¿
Sep 17, 2011 02:47
|
|
|
squeakygeek posted:Where is this hydrogen coming from? Large generators require lots of cooling. The Stator windings can be cooled directly by pumping highly purified water through channels in the windings. The rotor is much harder to keep cool. The way most are cooled is by high pressure hydrogen gas. Hyrogen is used because it has a really high specific heat capacity but causes very little drag on the rotor. So the rotor just spins in this cloud of gas and large fans on the rotor force the hydrogen through chillers. Here is Ge's blurb on why they use hydrogen. http://www.ge-energy.com/products_and_services/products/generators/hydrogen_cooled_generator.jsp As for total charges Groda I have never really had to deal with that so I cant tell you if it is STP or not. Normally the gas pressure is between 30 and 75 psi.
|
|
#
¿
Sep 18, 2011 14:25
|
|
|
Nerobro posted:And it's conductivity.... Pureified water is a very poor conductor. Most generators have the stator cooled directly by water. By directly I mean they pump it through channels cut into the copper buss bars which are running around 24kv.
|
|
#
¿
Sep 19, 2011 11:21
|
|
|
Nerobro posted:Water inside a motor casing, interacting with commutators, brushes, and windings, isn't going to stay pure long. And "poor" at 3kv is still "holyshitlotsofpower." Yeah we keep those things separate for a reason. The water is continously being demineralized as it is circulated. Slip rings and brushes are in an external enclosure and we check for hydrogen leakage on a weekly basis. The leakage current in the stator water system is down in the mA even at 24kV.
|
|
#
¿
Sep 19, 2011 22:52
|
|
|
^^^^ True. See http://en.wikipedia.org/wiki/BurnupThree-Phase posted:1. The excitation of a synchronous generator must immediately be stopped and the field discharge resistor inserted into the field circuit to prevent a catastrophic buildup of excessive voltage on the stator Static exciters can respond incredibly fast to things like this. The field discharge resistor is just a big piece of folded steel and is connected to the DC bus by a poised SCR. So in a trip the main bridges are immediatly stopped the discharge SCR fires and within milliseconds the DC breaker is open. As to reactors response to load rejections we can dump 60% of reactor power directly to the condenser (this corresponds to the same amount of steam energy that normally makes its way to the condenser during normal operation). In the event of loss of grid events we normally keep the reactors and turbines up and island ourselves (which results in a crapload of steam going out the roof). This is why we didn't poison out in 2003.
|
|
#
¿
Sep 21, 2011 01:19
|
|
|
My experience with exciters is limted to the rather fancy new ones that we have installed. The old ones had crowbar circuits and a DC contactor that had a million ways to brake your hand while maintaining it. Our slip rings are separated by a large nonconductive duct for the ring cooling air.
|
|
#
¿
Sep 21, 2011 02:58
|
|
|
Yeah it never seemed like a great idea. As soon as you have failed fuel your entire system is contaminated with fission products.
|
|
#
¿
Sep 22, 2011 14:18
|
|
|
We have similar failed fuel detection systems. CANDU reactors monitor the individual fuel channels for delayed nuetrons to detect failed fuel. If it is detected we simply fuel that channel till we have removed the failed bundle. Boiler tube inspection and plugging is a massive outage job and I am sure it is similar at all PWR reactors. As to water chemistry we get the added bonus of our PHT and Moderator water containing tritium. We spend alot of time in positive pressure suits to avoid that. Luckily I work mostly on the turbines so I spend very little time "in the bag".
|
|
#
¿
Sep 23, 2011 01:52
|
|
|
It would actually be pretty tricky to do in one of our power reactors. The candu design is mostly a throwback to a time when we couldn't make the pressure vessels needed for a PWR so we designed around it. That then became the trademark of our design. Edit: We also dont have any fuel enrichment facilities due to our lack of a weapons program so running on natural uranium was a plus. Sadly it will probably never be built again now that the reactor division of AECL just got sold to SNC-Lavlin. That sale essentially gave SNC-Lavlin a few million dollars to lay off about 1000 engineers at AECL.
|
|
#
¿
Sep 23, 2011 21:02
|
|
|
grover posted:Typical wet cell: Our station batteries look similar to this just in slightly different racks and in seismicly qualified rooms. Each Reactor has 3 station batteries to back up the uninteruptible station loads (shutdown systems, emergency lighting, back up oil pumps). Two banks are quite large and the third is smaller because it only has to back up shutdown system loads. They only have to last long enough to get class 3 power back online which is supplied by gas turbines and should start up within minutes, but they are sized to last considerably longer than that. For the guy wanting to run a 3 phase motor off of single phase you need to buy a variable frequency drive unit. It will generate the 3 phase you need out of house power and will even give you variable speed.
|
|
#
¿
Sep 30, 2011 21:38
|
|
|
Three-Phase posted:6. Hire someone to check the chemistry on a regular basis, add distilled water to the cells, visually inspect the lead plates, etc. My crew used to be combined with an electrical crew and we did monthly quarterly and annual callups on those battery banks. Monthlys are not to bad but taking specific gravities and voltages of 112 cells takes a long loving time.
|
|
#
¿
Oct 1, 2011 02:53
|
|
|
Ossetepo posted:You work at a CANDU, right? I didn't know you guys had gas turbines as backup power. I imagine that's a lot easier to deal with than the care and feeding of thirty-year old marine diesel engines. Yeah I am a lowly control tech at Bruce B. It is a neat site to work at suposidly the largest nuclear generating station in the world when we have all eight units running. Not only do we have 4 gas turbine SG's but we have 2 gas turbine EPG's that are only for emergency feedwater. Oh and we have four reactors that can be cross connected electrically and we can island ourselves very easily. We were the only nuke plant that stayed up in 2003. So many layers of redundacy.
|
|
#
¿
Oct 1, 2011 18:55
|
|
|
I cant tell you much about the math behind it but I can tell you that tearing apart a neutral bus on a 1 Gw generator is a pain the rear end. Our predictive maintenance guys heard some signs of coronal discharge on a generator bushing. We had to take apart the nuetral bar so that AC hipot testing could be done on the individual phases. The buss bar is two C shaped aluminum bars bolted onto the three bushings. Each half weighs about 100 lbs and is pretty awkward to move since it is made of three peices connected with welded on flexible links. All that is held on with 48 1/16" nuts that will only move with a 3/4 drive impact gun. Turned out the bushing was fine and the corona was from a failign insulator on the IPB. The Y point is grounded using a single 00 cable seems rather small considering how much current flows through that buss bar.
|
|
#
¿
Jan 7, 2012 04:40
|
|
|
24Kv normally puting out about 860 Mw.
|
|
#
¿
Jan 7, 2012 05:38
|
|
|
Our Emergency backup oil pump is unfused. It is also a massively overrated DC motor that gets connected directly across a 250 VDC battery bank. If that pump doesnt start when it is needed you have big trouble.
|
|
#
¿
Jan 11, 2012 00:16
|
|
|
Here are a few things in regards to excitation of syncronous generators. The difference in excitation current required to make rated terminal volts at no load is way less than is required at full load. So if you dump the load the terminal voltage will increase alost instantly. The time constant for rotor current is measured in whole seconds so it takes a really long time to raise or lower things. That field dicharge resistor will drop the rotor field to nothing pretty fast. On the exciters I work on it is not actually a breaker but a pair of SCR's that initiate dexcitation. The resistor is actually just a big folded sheet of steel.
|
|
#
¿
Feb 20, 2012 20:11
|
|
|
Capactitor banks are also used to allow induction generators (windmills) to take the required 30% reactive load. Most windfarms have huge banks that can fail in very spectacular ways.
|
|
#
¿
Apr 19, 2012 19:40
|
|
|
And if you breath it in it has the opposite effect of helium.
|
|
#
¿
Apr 22, 2012 15:13
|
|
|
grover posted:auxilliary set of transformers designed to backfeed the building from the grid We have separate transformers that can supply class 4 power either directly from the generator or from the grid. The unit service transformer is so small that it is completely hidden by the MOT enclosures. We run 3 single phase transformers as main output transformers and the sync breakers are in the switchyard not on the IPB.
|
|
#
¿
Jun 23, 2012 05:00
|
|
|
Three-Phase posted:The brushless exciter bolts directly onto the shaft of the motor, and acts like a little DC generator that makes the field inside the motor. It was explained to me that brushless excitation is accomplished by having a transformer winding and a set of diodes in the rotor itself. The exciter is simply an AC voltage regulator that feeds into the primary of the brushless exciter and it is converted to DC by the diodes.
|
|
#
¿
Jun 27, 2012 21:07
|
|
|
It's quite possible. Most disruptions start as trees hitting lines and hurricanes tend to bend the odd tree.
|
|
#
¿
Oct 28, 2012 22:55
|
|
|
Guy Axlerod posted:Cool stuff. Does my laptop charger care much about these waveform abnormalities? Id really like to see a comparison that shows how this effects the output of the laptop charger. I'm guessing it doesnt.
|
|
#
¿
Nov 7, 2012 01:09
|
|
|
The Cleaner posted:Is such a thing possible? or was it just my imagination? I have to walk under four sets of energized 500kV lines to get to work in the morning never felt a thing. You can never say that the EMF isnt doing something as it is pretty substantial. However the EMF from an MRI machine is probably several million times stronger and people routinely stick there heads in there for extended periods of time with no ill effects.
|
|
#
¿
Nov 12, 2012 23:47
|
|
|
As a pilot who does a bit of low altitude flying I can assure you that power lines are loving invisible. The lines might be lower than the treeline now but don't forget that trees grow and most power infrastructure is rather old.
|
|
#
¿
Dec 14, 2012 22:01
|
|
|
Or were the 1200:5 with two turns through them?
|
|
#
¿
Feb 11, 2013 00:01
|
|
|
We have conventional sliprings and still have a little building on the end, we call it the doghouse. At our sister plant with different turbine that is where the main lube oil pump is located. As for the FDR ours are pretty small rated at maybe a few tens of kW. They only get connected for a moment after the SCR`s stop gating and before the 41 field contactor opens.
|
|
#
¿
Apr 20, 2013 01:46
|
|
|
We have two parallel FDR's (0.1 ohms basically 4 inch wide folded sheets of steel) and two de-excitation SCR's. These quickly discharge the field when the exciter is tripped to prevent overvoltage of the stator windings. One of the FDR's has a second SCR which is in the opposite polarity, this is the crowbar circuit. It come's into play if there is pole slipping and the field potential momentarily switches polarity. These units are about 850 MVA. The deex and crowbar SCR's are 77mm. The main SCRS are 100mm units. helno fucked around with this message at 01:47 on Apr 21, 2013 |
|
#
¿
Apr 21, 2013 01:44
|
|
|
Exciter is all air cooled. Each bridge has a 3 hp fan sucking air through it. The themography guys hate it because the plexiglass air guides stop them from seeing much of anything. The generators are H2 for the rotor with H2 to water exchangers and the stators are direct water cooled.
|
|
#
¿
Apr 26, 2013 03:11
|
|
|
We have hundreds of temperature measurements. Hundreds in the stator. The rotor temperature is measured indirectly with some voodoo magic (pyrolysate collector). It would take a pretty massive post to describe the basic turbine instrumentation. We have multiple backup oil pumps with diverse power supplies and two independent vibration monitoring systems.
|
|
#
¿
Apr 27, 2013 15:08
|
|
|
I honestly wouldn't know were to begin. I have only worked on a handful of the equipment and it is mostly just various instruments that feed up to an analog turbine governor which moves 20 huge valves as required. Alot of what we use is very old, so lots of pressure and temperature switches with only a handful of analog transducers. The turbine control system is a mostly analog GE system from the mid 70's it is pretty reliable but requires a few of my coworkers to do a lot of calibrations during outages.
|
|
#
¿
Apr 27, 2013 21:20
|
|
|
GE EHC mark II for large steam turbines. Hope you really like op-amp's. The reheat/preheat system is pretty cool. Basically it boils down to the fact that nuclear reactors make a shitload of really crappy steam. The steam is not superheated coming out of the boilers and goes into the high pressure turbine pretty wet. The high pressure exhaust is fed into four large pressure vessels that have moisture separators and reheat heat exchangers fed by main steam. With the steam now at a lower pressure with the moisture removed it is actually superheated by this reheat cycle. This goes into the low pressure turbines and then into the condensers. All through this process the steam is bled off between different stages of the turbine to eliminate moisture. This bleed steam is used to preheat the feed water and after all of the stages of preheat the water entering the boilers is already at around 125 C. The preheaters all operate on the principal of reclaiming the latent heat of vaporization so they are tube in shell heat exchangers with the shell fed low quality steam that is condensing on the tubes. It's a bit odd feeling the side of a heat exchanger full of steam that is only at 25 c because it is sub atmospheric. All this preheating/reheating gets us from around 25% thermal efficiency to around 33% with 34% being the theoretical limit based on our boiler output and the condenser input. It seems pretty complicated but most of the preheat system is automatic. There are level controllers on the heat exchangers and as power levels increase the bleed steam demand changes proportionally with feed water flow so level control is all you need.
|
|
#
¿
Apr 27, 2013 22:54
|
|
|
M_Gargantua posted:I'd hate to imagine the impingement damage to the turbine blading. I'd have thought it would have been the other way around with high quality high pressure steam that gets reused as low pressure wet steam. I've only heard wet steam go down our headers once when one of the moisture traps failed and it sounded like the rumble of death. The steam is 4.4 MPa but only around 250 degree celsius because it is being boiled by 305 degree water at 9.8 Mpa. I don't know the math or have the exact numbers but I have heard that it is about 0.1% moisture when it gets to the valve chest. At full power we boil about 1200 kg per second per unit (we have 8 units). The older LP turbines look like a sandblaster have been taken to the last few stages due to impingement damage. We only turn at 1800 rpm so it is not as bad as the plants that run 3600.
|
|
#
¿
May 3, 2013 03:20
|
|
|
We use caution tape with signs describing the hazard in places were you want people to avoid. For places that people must not pass through we use danger tape and it is taken quite seriously if someone was to go through.
|
|
#
¿
Jul 19, 2013 19:52
|
|
|
|
| # ¿ Apr 30, 2024 02:35 |
|
|
I think the idea is that it lights up if you touch a live terminal. I'll stick with a conventional pot tester thank you very much.
|
|
#
¿
Sep 9, 2013 03:30
|
|