-------------- This is blatently false and based on personal bias which is not backed by facts.
-------------- This is blatently false and based on personal bias which is not backed by facts.
Well it has to true, since the only other bullshit facts morons like Washington could possibly throw into the power grid requation at this point in space-time is that Jane Fonda runs the electric power grid.
Since the synchronization will never be perfect, there must still be a substantial surge/mechanical force/BANG at the point the relays close, particularly for the largest generators. Does this cause wear and tear such that components have to be repaired after a certain number of times of bringing the generator online? How large are the largest individual generators, anyway. I know the largest power plants don't put all their power through a single generator.
Speaking of BANG, I heard a description of the first time the St Lawrence Seaway hydropower system (a few thousand MW total) was first brought online, some time around 1960. Supposedly the HV transmission lines themselves went BANG, because the individual wire strands in the cable were attracted to each other when they first carried current. Do HV transmission lines do that (bang) when first placed into service?
With even manual synchronisation, the process can be very smooth. Automatic synchronisers may dither around awhile but also provide reliable and smooth synchronisation. Substantial surges can be easily avoided unless stupidity is at play. As for generator sizes- hydro units in the 500MVA range and thermal units up to 1000-1200MVA are in use. Generally there are multiple units in a plant- economics and the need to not put all one's eggs in one basket determine this. As for the lines going bang- very questionable. The forces between phases won't do it. However, with bundled conductors (multiple conductors in parallel-spaced about a foot apart) , forces between conductors in the same bundle will be attractive and can pull the conductors together. This has happened under fault conditions but it is doubtful under load. Spacers are used to maintain the separation and many are spring loaded so that they give a bit under high forces and then recover the spacing (this is easier on the conductors).
Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer
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----------------------------- Ah, yes, don't try to find out the facts- they might not fit your favourite misconceptions.
OK. I just imagined that if you had a generator spinning at a rate such that it would generate 60.01 Hz being synched to a 60.00 grid, even if you switched exactly in phase, the grid would demand the thing spin at exactly the right rate and even with a small difference, that's a lot of decelleration or acceleration in a very short time, and with something very massive.
Yes I figured the eggs-in-one-basket would be a major factor.
I wasn't thinking of between phases or bundled conductors, I was thinking of individual wires in a single cable (the big 'wire'). Often such cables have 7 or 19 individual strands, and I believe the ones for transmission lines are aluminum except the center one is steel for strength. Substantial current in parallel conductors (the individual strands) in the same direction attracts the strands magnetically, and supposedly the cables magnetically constricted with a bang as the strands were attracted to each other. I suppose at the voltages involved the strands may be repelled from each other by the charge.
FWIW, the towers in the immediate area are the metal lattice towers with
6 single conductors, none seem to be bundled conductors with spacers. It's a forest of those towers there.
No, they do (at least in EU).The new EURATOM reactor nuclear plant has as much as 2000 MVA "on one shaft".It's some very advanced nuclear technology, very safe and robust.What must really be redundant, is the cooling system exchanger for the reactor, from which there are 4, and the backup cooling system.(See under
No, but here in Crete we had one incident where an 150 kV insulator was shorted, and the result was a brownout.I know that for sure the fuses of MV (>= 15 kV) grids must handle 250 MVA of impulse short circuit apparent power, so on 150 kV HV transmission that must be even larger.
-- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist dimtzort AT otenet DOT gr
------------ Your thinking is right and in the scenario the incoming machine would be decelerated and during this time, it would pick up load. At the same time the system would speed up somewhat. If the "droop" or speed regulation of the governor was a typical 5% the load picked up in the above case would be about 0.02% of the machine's rating. How long it would take to decellerate would depend on the intertia of the machine. I doublt whether one, standing by the machine would notice the "bump" Now at 61Hz- you would definitely notice.
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------- First of all, the ACSR cables have individual wires in contact with each other. A typical (smallish)conductor may have 26 aluminum conductors over 7 steel conductors and larger conductors will have more layers of each (7 strand is the smallest and not used for HV transmission). Yes there will be some constriction but this will not cause a "bang" as they are already in close contact- some squeeze- true- but the worst squeeze would be under fault conditions. There will be no repulsion due to charges as all these conductors are at the same voltage.
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------- These would be 2 -3 phase circuits on the same tower and some would be older lines. Many lines at 240KV or lower are not bundled. At higher voltages, bundling is used for its advantages of lower weight of conductor, lower electric fields in the vicinity of the conductors, lower line inductance and easier installation -hence economic and electrical/mechanical advantages. It is a way to effectively approximate a large diameter single conductor (e.g.
2-0.25 inch radius conductors, spaced 12 inches apart will have an equivalent electrical radius of about 1.7 inches but a fraction(4%) of the weight or cost of an equivalent (solid)single conductor.
Actually, synchronization is usually performed with the generator frequency (speed) slightly higher than the grid frequency, just to make sure that it comes on line with positive, not negative loading. The load is then immediately raised (generally to about 5%, if I remember correctly). The grid frequency, and consequently the speed of the turbine generator, randomly fluctuates by the sort of magnitude that you are talking about (0.01 Hz) or more (a good deal more in small grids, such as on an island like Taiwan, for example). This is because of the constant step changes in system demand from large loads being switched on and off. The turbine generators are quite capable of changing speed by that much in very short times (fractions of a second); they do it all the time. Standard speeds, by the way, for steam turbine generators at
60 Hz are 3600 rpm for fossil units and 1800 rpm for nuclear units.Bill Ghrist
What is the location (terminal points) of the various DC lines that provide inter-regional connections?
...
Check out this link:
This is an excellent link. It does point out one of the problems of the "bottom line, now" philosophy(sic) behind deregulation that is a favourite bitch of mine. There is one questionable statement but, in context, it is trivial and doesn't detract from the thrust of the article.
Thank you,
Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer
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In the REAL World, syncronization is simply not a problem, nor has it ever been one. "Wires getting attracted to each other" is ridiculous, this could only occur if one had opposite graveling voltage, which it doesn't.
Big nuclear plants only have to parallel once every fuel cycle (like every 18months to 2 years) and other plants paralleling the unit's is a piece of cake. this shouldn't even be a discussion as it is not a discussion among power plant operators or grid operators.
Wit the grid, when a large loss of gerneration occurs...like when PG&E was testing a dual-full load trip/paralleling breaker opening with the instant loss of 2400 MWs...that is when you feel it. I was on the day they tested this and it seem that our 210 MW generator almost jumped off it's pedestal! Every generator in the system had to instantly make up for loss of 2400 megawatts which meant the steam governor valves (which respond to "speed of the system" immediately opened up to allow for more power. Fun times...
David
What about the wind-turbines (or generators)?How they are paralleled?How it is assured that they have positive loading?There is *no* way to increase the wind speed at will, like you do with steam or water.How do they pick up loads?Is it a bit of snake oil, aka Enron?
-- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist dimtzort AT otenet DOT gr
Synchronous inverters.
Bill Ward
| Wit the grid, when a large loss of gerneration occurs...like when PG&E | was testing a dual-full load trip/paralleling breaker opening with the | instant loss of 2400 MWs...that is when you feel it. I was on the day | they tested this and it seem that our 210 MW generator almost jumped | off it's pedestal! Every generator in the system had to instantly make | up for loss of 2400 megawatts which meant the steam governor valves | (which respond to "speed of the system" immediately opened up to allow | for more power. Fun times...
I wonder how their generator(s) reacted to that (sudden loss of load).
I don't know. I suspect because they are DC, at least they were back then, they were able to absorb the lost of generation. BTW...Load is the demand, Generation is they supply. We lost generation, not load, thus voltage was dragged down in the entire system.
David
----------- Excuse me. Forces between conductors depend on the currents, not the voltage. These forces exist- and will be attractive or repulsive depending on whether the currents are in the same or opposite directions. In the REAL world there are many situations in machines, high current bus bars, transformers, and between parallel conductors in a bundle -hence the needs for spacers and or physical bracing of windings to withstand forces due to fault currents.
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--------- You are right -it is not a problem as either operators are taught how to do it, or, in the present day, it is done automatically. If it is not done properly, it can be a big problem -hence the automatic controls. Aren't you lucky:)
--------- DC??? Since when since Edison's time has any utility system had DC generators? Particularly ones in the multimegawatt range. DC transmission lines- true but that doesn't change the problem with generators which has a lot to do with the mechanical behaviour of the prime movers.
"Tzortzakakis Dimitrios" wrote in message news:eri7g0$mrt$ snipped-for-privacy@mouse.otenet.gr...
Wind turbines do not start unless the wind speed is sufficient to produce net generation.
As Bill Ward notes in the first reply to you, many wind turbines use an inverter to tie to the grid. Where the wind speed is fairly constant, induction generators may be used instead. The inverter units allow the rotor speed to change to match wind speed, resulting in higher efficiency above and below the design wind speed. But the inverter adds loss to the system, so an inverter unit has lower efficiency at the design wind speed. The induction generator wind turbines are more efficient at design wind speed but are less efficient when the wind speed is off the design point. The induction units are also less expensive.
An inverter wind turbine starts real nice. When the rotor is stopped, no torque is generated because the airfoil is in a stall. When the wind speed is high enough, the controller commands the inverter to start motoring the rotor around until the rotor speed becomes high enough that the power flow can be reversed and power is sent to the grid. Everything can be nice and smooth - the generator is sending power to the grid shortly after the blades come out of stall, so the approach to operating speed occurs slow.
Induction generator wind turbines do not start as elegantly. The units I have seen use a SCR based low voltage starter. When the wind speed is high enough to start, a low voltage(maybe 20% of nominal) is applied to the induction generator. This will start the rotor spinning. Once the turbine comes out of stall, the reduced voltage starter will be blanked off, cutting the motoring torque. This is to help reduce the backlash banging as the gearbox goes from motoring to generating torque - by having the turbine do the final acceleration of the induction machine rotor, all of the backlash will be taken up on the generating direction. As the induction machine rotor goes through synchronous frequency the soft start is ramped up to full voltage and then the SCRs are bypassed by a contactor. The rate limit on the second application of voltage is usually based on limiting the maximum kVAR load to the grid. The timing is very critical. If the line voltage is applied early (before synchronous speed is reached), the induction machine will motor then quickly swing to generation. When the torque reverses, a terrible jolt hits because of the backlash of gearbox plus flex in the tower, blades, and nacelle. If line voltage is applied late, the induction machine will have accelerated beyond synchronous speed, and the jolt of decelerating all of the rotating mass can be bad too. All of this is much worse on an induction machine because they start at a much higher wind speed than a variable speed unit would.
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