Not clear on power factor

------- Essentially so- indirectly there will be some other losses as well.

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--------- Yes

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----- There is such a generalisation

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---------- It can and that is why utilities do set allowable harmonic limits for industrial loads.

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

Yes, it shows at the generator. Although the I^2R in the wiring/transformers/etc must be supplied by the generator (as extra torque on the constant speed shaft as you say), there is another concern.

Generator armature windings are limited in the total kVA /MVA they can carry. Capability curves for generators have three distinct regions, and one of them is strict kVA/MVA loading. If a poor power factor is allowed, then the generator can not be operated to full *real* power capabilities because you reach the apparent power limit of the windings.

A second region of generator capability curves is maximum *field* current. Running with a severe *lagging* power factor will require more field current to maintain terminal voltage than would be required with unity power factor and the same kVA/MVA load. To avoid burning up the field windings, allowable kVA/MVA loading with a lagging power factor is lower than the armature winding limit.

So you want as close to unity on the generator as you can get to avoid having to reduce the *real* power component to stay inside the capabilities curve. Thus you get the most kW/MW from your unit and create the most revenue (assuming your prime-mover is well matched).

The strict definition of 'power factor' is W/VA. In the 'olden' days, this was affected most by phase shift between voltage and current by inductive loads (motors transformers and the like). Nowadays, with more non-linear loads, the harmonics can cause poor power factor as much as inductive loads.

Yes, if allowed in large magnitude. Large industrial customers with non-linear loads must purchase harmonic-filtering equipment and/or pay an additional fee to the utility for such problems. IIRC, DC arc furnaces are one such culprit.

HVDC transmission lines use SCRs for the AC-DC converter/inverter section. These can create a lot of harmonics, so the installations also have some

*serious* harmonic filtering.

daestrom

capabilities

Thank you for the detailed response.

I did not realize poor power was such a problem at the generator! John

Back in thoe old days, when ac/dc tube radios were the norm, I would ocassionly let my mind wander to worry about dc flowing in a transformer. If all the radios pere plugged in correctly, the half-wave rectifier used would draw a dc current component. This would tend to saturate the transformer.

IIRC a typical radio of this kind consumed no more than 30 W. 18 of these would be to run the heaters. Must used simple capacitor input folowed by an RC stage. This meant that rectifier current was a series of fairly narrow spikes at 60 (not 120) Hz.

While I doubt that these small radiow posed a problem for the power companies, larger power draws using half-wave rectifiers, especially with capacitor input filters could present a problem.

Can anyone enlighten me on how much power companies worried about such things?

Bill

The plug on these were not polarized or grounded in nearly every case. I would think that in all the homes with the radio on the chances that the power for rectifier would be drawn off the positive half of the cycle or the negative half would average out to 50/50. I scoped the current wave form from a transformerless tube radio and, yes the wave for is asymmetrical, but the spikes are rather smooth looking tops to a regular sine wave. The current limiting characteristics of the rectifier tube kept the crest factor low relative to the solid state rectifier that lets "anything go".

Several years back, halogen flood lights had a diode in the base because it was easier to design a 82 volt halogen bulb than a 120 volt one of the needed characteristics. Apparently these weren't an issue either. John

In the old days- not at all. Non-linear loads were such a small part of the total load that the effects were lost in the background "fuzz". For larger loads where it would make a difference, half wave rectifiers weren't used. The number of such large non-linear loads has increased rapidly in the last

25 years, to the point where harmonic content and interaction between harmonic sources is a real problem.

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

in article HMEnb.18980$ snipped-for-privacy@bgtnsc05-news.ops.worldnet.att.net, jriegle at snipped-for-privacy@att.net wrote on 10/28/03 5:32 PM:

There usually were instructions to revrse the plug if you got hum. That is, one position would give better performance than the other.

Some of the sets were death traps. One side of the line may have been connected directly to the chassis. Correct polarization was a safety factor. In some cases, even if plugged in optimally, the chassis could be hot via the string of heaters if the set were not turned on.

Bill

My brother (an old radio fan) tells me that one side of the plug was tied to the chassis inside the wooden case. So if it was the side that went to 'neutral' you effectively grounded the chassis through the service panel. If the other side, then you had the chassis 'floating' at 120V above ground and picking up all the noise in the neighborhood.

As far as all the radios in the neighborhood giving a DC component, I think they would all have to be plugged in 'right' and all on the same 'hot' phase in every home. This would be quite a fluke to happen ;-)

daestrom