Power Station Grid Synchronization



----------- 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. ------------

--------- 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:)
--

Don Kelly snipped-for-privacy@shawcross.ca
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cable
stupidity
such
of
time
of
be
decellerate
standing
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

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On Wed, 21 Feb 2007 21:43:06 +0200, Tzortzakakis Dimitrios wrote:
<snip>

Synchronous inverters.
Bill Ward
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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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writes:

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 www.areva.com for more info).

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
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writes:> Since the synchronization will never be perfect, there must still be a

If have been beside a 1250 MVAR unit when synchronized to the grid. No discernable sound when it synchronized. The shafting was painted with black and white stripes at one point, and under the discharge lighting in the turbine bay, the difference speed prior to synchronization could easily be observed. The shaft was rolling very slow above synchronous speed, and when the breaker closed, the difference in speed stopped. As load is added, I could easily see the phase angle shift a little.
What does make noise is when the phase angle shifts due to grid disturbances. Being a fairly big machine there is some flex in the shaft and it made funny noises, in combination with the sound GIANT steam valves closing and re-opening trying to damp the oscillations.
A trip under load did bang, but that was the steam valves snapping shut plus the breakers. The breakers were opened and closed using 450 PSI air. When opening the breakers did make a pretty big retort, even though there was a muffler. The cylinder was about 6" by about 3', so that's a LOT of air to vent when charged to 450 PSI.

The breakers would have PM after a certain number of cycles or years went by. I believe that usually it was the time limit that expired. I don't think the contacts were ever replaced, but that wasn't the area I worked in. The responsibility for the HV breakers were under the substation maintenance department of the company, far removed from plant operations.

Figure 50 to 200 MW for gas turbine combined cycle plants. Figure 300 to 750 MW for coal fired plants Figure 600 to 1400 MW for nuke plants. Hydro anywhere from the kW range to 600 MW Wind turbine from the sub MW to 10MW, but most new in the 2-5 MW range.

I don't think they used grading resistors to cut the lines in and out at first so it may have well banged because of the current inrush when the line closed in. I have only once heard a 500kV line energize (the highest we have on the west coast, at least for AC), and it had grading resistors to energize the line. Lots of buzzing as the arms went by each resistor, but I didn't hear any "bang" from the line.
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On Feb 14, 2:58 pm, snipped-for-privacy@yahoo.com wrote:

There are too many misleading texbooks on the subject to even bother listing. Since if you noticed the blackouts in the northeast US over the last 60 years, the "grid" is a complete fiction, invented by your state power regulators, not a national organization of anything. So the only way to synchrinize any two pieces of wire is basically what amounts a high power phase-locked loop.

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----------------------------
wrote:

--------- Unfortunately, in phase locking a generator to a system which consists of a "grid" (which is not a fiction) the result is that the output of the generator will be 0.
Do not try to apply electronic ideas to a power grid which involves both mechanical and electrical . They very often , at best, don't work. Also considering the number of independent variables and non-linearities involved, electronic systems, including computers, are relatively trivial and uncomplicated.
Phase locking is the ideal in smoothly synchronising a generator to the grid BUT once the machine is "on line" it is neither beneficial nor wanted. Shifting the phase of a generator with regard to the other generators on the system is necessary for production of power from that generator. Of course the dynamics of the electrical system and the mechanical systems involved are factors.
Another case is maximum power transfer: Maximum power transfer is not a desirable operating strategy from an efficiency viewpoint or from a stability viewpoint. Not only will it not be efficient, it would not be a possible operating regime.
--

Don Kelly snipped-for-privacy@shawcross.ca
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On Feb 14, 7:56 pm, snipped-for-privacy@netscape.net wrote: >

So...when *you* plug your toaster into the wall socket, you are drawing power from what exactly????
David
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On Feb 15, 7:57 am, snipped-for-privacy@comcast.net wrote:

From Corning.
Since GE is too stupid to make toasters that work in anything other than moron Boeing 10g fields, And Black&Decker is too pathetic to make anything other than 7-11 pinups for Ford morons.

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wrote:

------------------ There are many good technical and economic reasons for a "grid" interconnection. You mention blackouts but consider this- the overall reliability of the grid is well above that of any electronic system in existence and the interconnections aid this. That doesn't mean that MBA's in charge of some utilities know any more than you do about this and practice short term, short sighted policies. Their ignorance is just as great as yours. That is the problem.
--

Don Kelly snipped-for-privacy@shawcross.ca
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wrote:

-------------- This is blatently false and based on personal bias which is not backed by facts.
--

Don Kelly snipped-for-privacy@shawcross.ca
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wrote:

----------------------------- Ah, yes, don't try to find out the facts- they might not fit your favourite misconceptions.
--

Don Kelly snipped-for-privacy@shawcross.ca
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wrote:

So sayeth someone that has probably never brought a generator on-line.
The 'grid' is what it is. A major network of interconnected generation and load stations. There are actually several 'sections' that are *not* synchronized, such as the west to east and Texas has it's own 'grid'. Nevertheless, there are interconnecting points with DC links to allow power to flow between sections.
A major part of the reason for the blackout in 2003 was 'grid' disturbances in Ohio, lower Michigan, and Ontario affected power flow over a much wider area, up through New York and into New England.
As for your ideas about 'phase-locked loop', well, let's just say you haven't taken any power transmission courses or operated any transmission lines, have you?
daestrom
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wrote:

100% correct. "There is no grid"!! A huh. What is it I parallel my gas turbines to everyday? My hot-tub?
David
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On Wed, 14 Feb 2007 22:20:11 -0500, "daestrom"

What is the location (terminal points) of the various DC lines that provide inter-regional connections?
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wrote: ...

Check out this link: http://eceserv0.ece.wisc.edu/~dobson/PAPERS/industrialphysicistNov03.pdf
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