# Guess how many Amps this 220 VAC HVAC motor draws at 110 VAC?

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-------- That's right. ----------------- >

-------- Why? What would be gained? As I see it, all that would happen is that both the core and the conductors would be longer -not an advantage. Mechanically it would be a real pain in the ass to build. Simply put, a magnetic core is used to direct the flux to where you want it by providing a good magnetic path compared to air, etc. The shape of the core is of minor concern (smooth corners rather than square ones are nice, but... ) except that it should preferrably be as short as possible.

------ I suggest that you think about the cross section of the strip (rather than its sides)- where the current would flow. You will not get two turns from one. Another problem is that the current and the field are mutually perpendicular so the same wire cannot deal with that no matter how it is twisted.
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Don Kelly snipped-for-privacy@shawcross.ca
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Hi Don,
So, a question for you. All the large generators I've worked with have a 'saturation curve' listed in the documentation. Open circuit voltage (P.U.) versus field current. Nice and linear, up to about AFNL (Amps, Field, No-Load), then from there the line curves off as the field iron saturates.
(they also have a line for short-circuit operation (short-circuit current P.U. versus field current) and AFFL (Amps, Field Full-Load) that is always quite a straight line. Between these, I can get a pretty good idea of the syncronous impedance of the machine. )
But like you say, the iron doesn't saturate during operation. I've been modeling steady-state generator operation as an ideal voltage source, and an inductance (equal to the synchronous impedance) in series. But I've had some 'discussions' with others trying to model these machines about what to use for the 'ideal voltage source'. I've been using a linear calculation of the field current times the slope of the linear portion of the 'saturation line'. Another bloke as been trying to argue that his results are 'better' because he uses a curve fit of the saturation line that 'flattens' as field current rises.
I maintain that the MMF of the field current is being countered by the MMF of the armature current and the iron doesn't saturate. What you've said here seems to support that idea.
daestrom
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Yes, this was my thinking. Reactive load currents (lagging) create an mmf that is exactly along the direct axis, but displaced 180. There is a 90 shift between the field winding and the maximum induced voltage in the stator, and another 90 shift between the voltage in the stator and the lagging pf load current. This puts the mmf associated with lagging load current in direct opposition to the field mmf, resulting in poor voltage regulation.
The text I've been using ("Standard Handbook for Electrical Engineers", Knowlton) gives the vector diagram for regulation and field excitation, taken from an old ASA Standard. That, along with a 'Blondel diagram' ('two-reaction diagram')have been my primary tools/sources of data. Doesn't mention 'Park' by name though...
As I said, I've been using the linear, no-saturation model to calculate the steady-state excitation requirements at various load levels, and they seem to agree with the actual operating unit data. But some of it is supposition on my part. I felt that the air-gap flux *must* be the net result of these two mmf's (field and armature), and therefore saturation couldn't be occurring under normal operation. Another clue is the much larger field currents that are normally seen when operating near rated conditions.
Interestingly, I found one of our units operating with the field current showing *below* the AFNL value, yet it was carrying enough MVAR to be running about 0.95 lagging. So I concluded that the field current transducer input to the logging computer must be defective. The computer tech swore that his computer was right, and the I&C tech swore that it really was reading the number of milliamps that corresponded to the field current shown. But when we checked the field-current to mA transducer, lo and behold it was way off, reading low. I told them that my 'calculations' predict the field current should be 'X', and the 'as-found' testing of the transducer showed I was within 3%. They were suitably impressed :-)
I haven't tried to tackle transient or sub-transient features in my model yet though. Still working on the steady-state. I am working on the transient rise in voltage with a load-reject sceanrio. It *seems* like I could just drop the load current to zero while maintaining rated field current. But that gives some pretty incredible voltages (as in three times rated). So
Yes, I've found that the synchronous reactance is really the major player in voltage regulation of the unit. In my calculations of generator, main transformer and 'infinite bus', I've found that from the 'ideal voltage' source viewpoint, it carries quite a large 'reactive load', most of it right inside the machine in the 'synchronous reactance' component. And yes, when I compare the synchronous reactance with the winding inductance, there is a large difference.
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Haven't had to model one, but was thinking I could use the exact same components, just swap the torque angle to the opposite side. Sort of just what happens in the machine. This reverses the real component of the current. And what was a 'lagging' reactive current is now 'leading' (the reactive current vector doesn't change, just its relationship to the real current vector that is now 180 from where it was in a generator). But as I say, haven't tried it yet, so.....

Not sure what you mean about "the bulk of synchronous reactance lives" on the rotor.
Your previous statements also help explain why a constant V/Hz is desirable in variable speed applications. As frequency is reduced, the voltage must be reduced concurrently to avoid saturation. I've also seen some small isolation transformers used for attaching instruments to AC servo-motor machinery. Along with other ratings, the label listed frequency as "> V/1.5". As long as you connected to a system with a frequency higher than that, no problem. When it was inadvertently hooked up to a servo-motor incorrectly, the output was nasty 'spikes' every half-cycle as the iron within went from saturated in one direction, to saturated in the opposite (fortunately, the thing wasn't damaged, must have had enough impedance to limit the primary current)..
daestrom P.S. Not to worry, these models aren't being used for design/analysis, I'm not a PE. Just what you might call, 'professional curiosity'. If I can calculate/predict behavior, then I figure I've got a better understanding. (getting too old to actually crawl inside the things, besides carbon dust is hard to wash off :-) P.P.S. Although we have some salient pole units, MG-sets (~5000 hp) and diesel generators (nice EMD 4500kW units), I'm still just working through round-rotor machines (tubine driven).
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-snipped a bunch-

Not just on the rotor, but in the magnetic circuit rolling with the rotor in the air gap.
-snipped more-

I have forgotten how much fun that is! DC machines are much more fun on that regard, but I have seen a mess in AC machines.

What's that big of a MG set being use on?
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Are these the MG sets for a BWR recirculation pumps?
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Why, yes they are. 7000 hp drive motor, 5000 hp pump motor.
Been having some discussions about the losses in the fluid coupling. The losses are related to the torque/speed curve of the pump being driven and can peak out about 800 kW. So modern reactor changes that allow operating with lower core flow end up using almost as much power as rated flow. Just being wasted in the coupling instead of the pump power.
I did a lot of DC machinery repair at sub-base. The DC equipment can be rather 'fun'. Take your average civilian electrician and show him the starter/controller for a 50 hp DC motor and they're amazed at the size of stuff needed, versus a simple MCC 'cubicle' controller.
daestrom
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Having worked at a PWR not a BWR, I didn't realize the MG sets were variable speed. I had thought it was a "multi" speed setup with set frequencies out, with fine adjustments using throttle valves. Do you know if other BRW plants run like that?
Are the MG sets part of 1E systems? If not, has someone evaluated converting them to VFD for energy savings?
Matthew
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All GE BWR's use variable recirculation flow through the reactor as part of the power control. BWR 3/4/5 all use variable speed pumps (the pump motors are ~5000 kW). BWR-6 designs have used flow control valves and two speed pumps.

Surprisingly, no they are not 1E. The only safety-related function is an upper limit on speed (limits power excursions). Unlike a PWR, a complete loss of recirculating pumps is not an 'accident', several plants have experienced this without SCRAM.
I had heard rumor of at least one BWR that went to VFD, but can't find out who it was or any OE about it. The biggest concerns are *reliability*. As you know, unplanned shutdowns (or even downpower to 25%) to recover a lost pump is a 'hit' on generation as well as WANO. For our 'unregulated' generators, being able to boast significant reliability allows us to command a much better price than most 'unit-contingent' without the liability of 'replacement-power' contracts. Not to mention the improved 'quality of life' not getting call outs to deal with equipment failures.
So the system has to reliably operate for 2+ years with zero downtime. And of course it cannot put excessive EMI/RFI in the building or on the supply. Combined with a desired life of +30 years, it's a bit of a challenge.
daestrom
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news:7S9%g.65876

That's probably what I head about. I had a co-worker who previosly worked at Perry, and that may be where this tidbit came from.

That's what I suspected since forced circulation is just needed to crank up the power.

I'm not sure you would use 'accident' in a PWR either. Yes it's a trip for most plants (I think there are some units with TS allowance with 3 of 4 pumps). It most likely would also be a Unusual Event classification since the bulk of the time it would occur on loss of offsite power.

Try posting on nukeworker.com. If that identified the right plant the chances of finding a EE to talk to go way up.

I'm sure it is. Harmonics of course would be a big concern. Add to that, frying the motor is REAL expensive. I just wonder how much savings are? You're in the unusual position where power costs you what, 2 cents / kWHr?
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Yes, but it's even 'less' of an issue with BWR. Unless you're not licensed for single-loop ops (most are), you just stabilize at around 50% power, fix the MG, start it back up and recover. No 'cold water' interlock or other loop-recovery problems.

No, that's the wrong way to look at it. It's not what it cost to produce that energy, it's what I could have sold it for if I hadn't wasted it. Say it 'costs' me 200 kW. That's 1752 MWHr each year. I could have sold that 1752 MWHr for something like \$45 / MWhr (unit contingent, long-term power purchasing contract). So that's a lost opportunity of \$78840 / year.
But you're right about the pump motor. No way we want to risk damaging that!!!
daestrom
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I was just taking deference to the term 'accident' The more I learn about BWR, the more they seem the way to go. No question in my mind that availability and safety are better. I also note that there has yet to be a big BWR shut down - they all have been PWR plants.

That's the "cost" I was figuring in, lost sales. \$45/MWHr is good, at least from the perspective of a resident of the northwest where there is lots of hydro.

A VFD risks the motor in medium voltage applications due to partial discharge induced by the rapid rise and fall times. Output filtering is becoming the norm on medium voltage drives to reduce the rate of failure. I'm assuming the pumps are 4160 or 6900.
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Well, 'transient' that is anticipated to occur several times in the life of the unit. The recent issues with PWR's seem to be the RPV head issues. BWR's are dealing with RPV internal inspections (core shroud cracking, jet pump/ ram's head cracking). BWR's are easier to start up and operate (no worry about 'flux tilt', just manipulate the rod pattern a bit; start up cold and use reactor heat for heating up the plant;). But issues with off-gas treatment, and personnel exposure during maintenance (just about *everything* is contaminated to some degree). I look forward to GE's ESBWR design, if it ever gets built.

That's also a good price for long-term PPA's here in the northeast. But that's 4.5 cents/kWh, not 2. We could get better if we could 'get' the power to NYC, but the transmission systems are pretty well maxed. A new line was proposed to run north-south down towards NYC, but all the NIMBY's have been protesting it. So I say, "Fine, pay your congestion fees to the NYISO and watch your rates climb."

Well, actually they're *rated* for 56.5 Hz @ 3920V. But that works out to 4160V/60Hz, same V/Hz ratio. Yeah, I'd heard that about some VFD systems, even some motor vendors de-rating their motors based on VFD drive. I've also been hearing about VFD that go straight from AC to AC without the conventional DC-Bus. But I don't know much details about them, the only type I've worked with are the AC-DC-AC type.
I used to see something similar with DC motors. If run on 'pure' DC (such as a station battery), they may be X hp. But if run on full-wave, unfiltered AC, then they had to be derated to some fraction of X.
daestrom
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I was refering to the fact that the big units shut down - San Onofre 1, Rancho Seco, Trojan, Zion 1&2, TMI 2, Yanke Rowe, Conneticut Yankee - they are all PWR units. I'm not aware of a big BWR shut down, just the BWR 1 & 2 units.
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Well, Big Rock, which wasn't really a 1 or 2. NMP1 and Oyster Creek are the only BWR 2's I know of, and they're still running.
You're right, I can't think of a BWR that's been shutdown, only PWR (and the HTGR at Fort St. Vrain). But IIRC, many of the PWR's that were shutdown it was the high cost of steam generator replacements. Something I thought was supposed to last the life of the unit (40 years), but haven't (nasty sorts of corrosion on tube/tube-sheet and tube/supports). Lately, the RPV heads with their numerous nozzles (of materials that are susceptable to certain corrosion-cracking) have also been 'door closing' challenges.
BWR's are facing some of their own challenges though. In-vessel inspections of shrouds and jet-pump assemblies are raising concerns. Various in-vessel repairs of shroud cracking have been acceptable so far, but if one needed to *replace* the shroud, well that could be a 'door-closing event'. BWR lower heads have large number of nozzles, much like PWR's upper head. But there is no feasible replacement process (entire RPV). So we'll see I guess.
Of course, any *new* plant would have the benefit of the advances in metallurgy and better understanding of many of the corrosion processes.
daestrom
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I thought BRP, Pathfinder and Humboldt bay were the true BWR1 units. I also thought Lacrosse and Elk River were the 'not BWR 1' early plants.
Weren't Shoreham and Millstone 1 also BWR 2?

And the other oddballs of Saxton, Shippingport, Piqua, Fermi 1, Bonus and ???

I would argue that was a pretext. Until ~ '92, utilities shut the plants down rather than face the cost of replacing the SG. After that, SG replacement became a 45 to 60 day turn around project. I doubt we will see any further early shutdowns from SG corrosion.

Actually, the predicted life up front was less than the unit life - it is stated in more than one FSAR. What happened in many cases is that they didn't even hit the expected 25 year life.

The NRC has a good page on the SG issues. http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/steam-gen.html

Is the shroud removable, or is it welded in? The core internals on a PWR are replaceable, but I'm not sure how often it has been needed.
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Millstone was a -3 (I think). BRP, Pathfinder and Humboldt Bay are too early to really be considered 'turn-key' designs. They were all one-of-a-kind, proof-of-something type plants. The -2/3/4/5/6 were/are from the 'turn key' power plant generation ('69 + ) where a utility would buy a nuclear plant 'turn key' from the NSSS vendor and AE. Many didn't really appreciate what they were getting in to and did it more for the prestige of having an "Atomic Power" plant in their portfolio.
But those early units didn't really fall into a BWR-XX category, they were one-of-a-kind designs.

Well, yes, you're right about there being a wide variety of early designs that have long been shutdown. Fermi 1 was liquid metal, Shippingport was a 'quick' adaptation of Naval design for political motives, and a host of others.

I think it's a combination of better turn around and higher capacity factors. Back in the '80's, if it took 200 days to do a SG job, and you only had a capacity factor in the 60-70 % range, the 'bean counters' would sharpen their pencils and say, "We'll never pay it back." But now, with a much higher capacity factor (most in the 90+ range), and shorter turn around, you're right, it is more economic to do the work and keep operating.

Well, for a \$\$PRICE\$\$, anything can be done :-) They are welded in. A sort of flat 'ring' around the bottom head / belt-line hold the circular arrangement of jet-pumps and the shroud. But depending where you want to try and cut it off, you'd have to either a) reach in a very tight place on the outside between the shroud and jet-pumps (or remove jet pumps??) or b) remove the lower core plate that directs the flow into the fuel bundles. And of course even with the fuel off-loaded, it's pretty 'hot' around all that steel that has been irradiated for many years.
Problem is, nobody's done it yet and the uncertainty/cost is a big 'unknown'.
Mark I BWR containments (those that look like an inverted light-bulb sitting in a doughnut) are now reviewing some issues with the torus steel developing fatigue cracks. A manageable issue, but just one more part of the plant that needs another inspection program. "Like my daddy always used to say to me, 'Little Rosanna Danna, If its not one thing its another' "
daestrom
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Matthew Beasley wrote:

What are PWRs? (I assume BWR is boiling water reactor.)

What is partial discharge?
bud--
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Pressurized Water Reactors. The reactor is cooled by water (called primary loop water) maintained at high enough pressure not to boil at the operating temperature. The primary loop water flows to a heat exchanger where water at a lower pressure is boiled to steam to run a trubine.
2/3 of the US reactors and most of the French reacotrs are PWR About 1/3 of the US reactors are BWR. Japan appears to favor the BWR on new units.

On higher voltage AC systems, the local electric field can exceed the breakdown potential of the insulation, but the gap is large enough to prevent a arc from forming. The circuit is completed through the stray capacitance of the air or other insulation. In air, it forms a blue glow, and is often called corona. The crackling sound heard on high voltage power lines is from this phenomenon. In solid insulations it is usually destructive to the insulation and will eventually lead to a full arc.
Because the current flow though a capacitor is proportional to frequency, partial discharge can worsen as the frequency rises.
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The synchronous reactance includes the relatively small leakage reactance of the stator winding as well as the larger effect of armature reaction-(the mmf produced by the armature). a) You have correctly recognised the effect of armature reaction as essentially demagnetising and simply assume no saturation. This is considerably closer to the truth than your colleagues approach which overestimates drastically the effect of saturation. b) There is no way that one can realistically get any more than an estimate of saturation under load. You can do it by putting on a load at a given open circuit voltage and measuring the terminal voltage, current and phase and calculating the effect -which would be true for that one load condition but not true for any other condition- just not practical.
I have just been checking a couple of references and trying to adapt the process for estimation of saturation. A correction curve could be made. This would involve what you have intuitively recognised - subtract the armature reaction mmf from the field mmf- essentially look for the voltage behind leakage reactance and base saturation effects on that - this is not quite true but is better than what your colleagues are doing. Then a corrective factor can be determined and, guess what- it requires an interative approach to get a solution. An older approach to the estimation is through use of what is called a Potier triangle- still a guestimate.
As for a synchronous motor- note that a motor is simply a generator producing negative power. Simply stick a minus sign on the "generator" current and all is well. As to vars, they will work out as well. Under excited motor sucks vars -lagging pf as motor or leading as generator.
Have to go now, time is out for now.
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Don Kelly snipped-for-privacy@shawcross.ca