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

The flux doesn't follow a wire round and round as implied by the looping. Take a cross section of the wire core - it appears as a number of parallel flux paths. Ideally it would be nice to have the ends of the wired joined as when they aren't the flux coming to an end has to cross over to adjacent wires so for a short distance the flux distribution is not uniform. In practice this is negligable with many turns of wire. Note that with laminated cores, the laminations are not continuous but the layers overlap so flux has to cross over from one layer to the next through the varnish gap between layers.

The main problem with a wire core is that good magnetic material is also relatively brittle. A thin flat strip is easier to roll than a wire of the same cross-section in that case and (I haven't worked this out) will have lower eddy current losses (longer eddy current path and higher resistance for a given cross-section and voltage induced in the path.) Use of wire wouldn't reduce hysteresis loss per se but it would reduce eddy current losses compared to a solid core but possibly not as much as with a rolled strip or conventional laminations. These are likely the historical reasons why wire cores are not seen nowadays.

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.

| The flux doesn't follow a wire round and round as implied by the looping. | Take a cross section of the wire core - it appears as a number of parallel | flux paths. Ideally it would be nice to have the ends of the wired joined as | when they aren't the flux coming to an end has to cross over to adjacent | wires so for a short distance the flux distribution is not uniform. In | practice this is negligable with many turns of wire. Note that with | laminated cores, the laminations are not continuous but the layers overlap | so flux has to cross over from one layer to the next through the varnish gap | between layers.

So with a bunch of wires, which would be more distinctly separate parts of the core, the flux is always going to cross over anyway? So it really won't matter if this is 1000 tiny steel wire loops, or one long wire that loops around 1000 times.

| The main problem with a wire core is that good magnetic material is also | relatively brittle. A thin flat strip is easier to roll than a wire of the | same cross-section in that case and (I haven't worked this out) will have | lower eddy current losses (longer eddy current path and higher resistance | for a given cross-section and voltage induced in the path.) Use of wire | wouldn't reduce hysteresis loss per se but it would reduce eddy current | losses compared to a solid core but possibly not as much as with a rolled | strip or conventional laminations. These are likely the historical reasons | why wire cores are not seen nowadays.

My ultimate experimental idea is to have a topology where the core itself spirals around the windings, which also spiral with it. It would be kind of like those double-pretzel sticks where 2 pretzels wrap around each other. Or like how certain snakes make love. This would then be wrapped around to connect on the ends. Topologically, the windings do wrap around the core wires, so there should be an induced magnetic field. Then the field itself would be a spiral.

Then the next trick would be to use insulated steel wire and make it wrap around itself in a double-Mobius fashion. So if you follow a bundle of wires around, you go around twice to get back to the same spot. This whole circle would be all a bunch of spirals. The steel wires would be both the electrical winding and the core at the same time. I have no idea if that could possibly work. But mentally picturing the topology tells me it should. Of course steel is not as good a conductor as copper so this is not likely to be of any practical value on a large scale.

Possibly answering my own question:

Are these the MG sets for a BWR recirculation pumps?

-------- 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.

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

I've run across 'Potier' reactance and such several places, but not found a satisfactory explanation for what it really is. I assume it's named after someone? (always capitalized, like a proper noun). I've noticed most of the older texts did a fair number of solutions by converting to P.U. and then graphical analysis (one definitely had to know their plane geometry to follow along).

Yes, in the Navy we had MG sets where they often ran as AC synch motor and DC generator. Operating as AC synch. motor, we learned quite well the affects of field excitation. Since they were connected to 'ships service turbine-generators' for power, we could shift the reactive load from the SSTG's to the MG and back, just by adjusting MG AC-Voltage adjustment. But we normally left it split 'evenly', so the voltage of the MG AC unit would be correct should the SSTG and MG set get split apart (then the MG reversed power flow to supply the vital AC loads from the DC supply).

Thanks again. So hard to find anyone to talk this sort of 'shop' with. Most electricians are more about NEC compliance, where AFCI are required and such. Not that that is a bad thing, just not many folks interested in large machinery theory/practice.

daestrom

---------------- Potier reactance basically comes down to leakage reactance. Roughly the voltage behind leakage reactance is used to determine the effect of saturation. This voltage is considerably less than the voltage behind Xs. Older texts seem to mention it more than newer ones. Fitzgerald, Kingley & Umans may cover it.

Thanks again. Back to some textbooks :-)

daestrom

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

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

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?

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

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.

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

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

What is partial discharge?

bud--

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.

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.

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