Discouraged!

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Harold_V
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Re: Discouraged!

Post by Harold_V »

As you alluded, the meter hooks up to other devices. The amperage side receives signal from a "donut" on one of the output leads from the generator. It also feeds the kw meter and then the amp meter, returning to the opposite end of the donut through a full wave rectifier if that makes any sense. The voltage terminals receive signal from a current transformer which feeds the volt meter, kw meter and the kilovar meter. The current transformer primary is tied across the two generator leads. The kw and kilovar meters each have four connections, while the amp and volt meters have but two.

I scanned that portion of the schematic, but it didn't turn out very clear. I attempted to scan at a greater resolution but the scanner/copier thinks it needs a new color cartridge and will no longer operate. I've ordered new cartridges to get it going again. Mean time, if you think a blurry copy of the scan would satisfy your curiosity, I could either post it or send it to you. It's not easy to read, but then neither is the copy from which it was scanned, although it is somewhat better. Reproductions obviously made from Microfiche or some such storage method. Remember--this is old gear. The power supply was built in 1962.

It's not clear to me why it (the meter) isn't much of a problem. Care to share your thoughts? Just tonight I read where such meters must be calibrated at the appropriate frequency, otherwise they are not accurate. Maybe that isn't a problem for the folks who make them, who likely use a signal generator that permits the required frequency? Dunno!
H
Wise people talk because they have something to say. Fools talk because they have to say something.
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tornitore45
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Re: Discouraged!

Post by tornitore45 »

I am an electrical engineer, but the field is so vast I have no more that general knowledge outside my field of specialization.
Is interesting that for some reason Lagging phase is to be avoided as destructive to the generator.
If the current Lags the Voltage the load is seen as Inductive, meaning more capacitance needs to be switched IN.
I can see the necessity of keeping the VAR near zero since that energy is doing no other work than heating the wires, particularly the generator windings.
What I do not understand is why a small Leading PF is acceptable put Lagging is not.
AFAIK there are power station with generators dedicated to supply any type of power factor from 100% leading to 100$ lagging and everywhere in between. The generator is limited by the current regardless the phase with the voltage. The prime motor turning the generator does not see VARS as a mechanical load since VARS are going back and forth and absorbed by any rotating inertia.
Just thinking aloud.
Mauro Gaetano
in Austin TX
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tornitore45
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Re: Discouraged!

Post by tornitore45 »

Harold a few comments on the nomenclator. What you call a doughnut (the one skewered by the big thick wire) is a Current Transformer.
Is just a special transformer designed to have an output proportional to the current passing into the single wire. Is a safer method to provide a Shunt since it also provides isolation.
The one you call Current Transformer is actually a Votage Transformer. Its function is to supply, scale and isolate the Generator voltage to a suitable level for the instruments.

The Amp Meter and the Volt Meter only need 2 wires because they are not interested in the phase relation with the other measure.
The KWATT and KVAR meter need to "see" both the Voltage and the Current so they need four wires.
Just shedding some light, not trying to be pedantic.
Mauro Gaetano
in Austin TX
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SteveR
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Re: Discouraged!

Post by SteveR »

Harold - Why not just drill a hole in the ruby for the shaft end to sit in?

https://www.youtube.com/watch?v=O-NmjZ4HZEA

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Measure twice, cut once, wait - it was supposed to be brass! :)
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Bill Shields
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Re: Discouraged!

Post by Bill Shields »

Or purchase one from a clock / watch supplier (easier) :mrgreen:
Too many things going on to bother listing them.
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Harold_V
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Re: Discouraged!

Post by Harold_V »

tornitore45 wrote: Wed Feb 08, 2023 7:12 am I am an electrical engineer, but the field is so vast I have no more that general knowledge outside my field of specialization.
That I understand. It's not a lot different from the field of machining. As an example, I was a tool builder, but did only a couple simple dies in my many years in the shop. As a general machinist, I have almost no experience (nor understanding) of gears and gear cutting.
What I do not understand is why a small Leading PF is acceptable put Lagging is not.
That I may be able to address. When the supply is activated it is done so slowly, bringing up voltage and amperage by exciting the generator (a variac is used). The kilovar meter starts to display whether the unit is in unity or not. It is red-lined because the only thing that can happen at this point is for the condition to change towards lagging. Nothing the operator can do would result in a move towards leading aside from adding capacitors, as you alluded. So then, as the charge begins to heat, change is towards lagging. The change becomes more rapid once the charge begins to melt and continues to change until the entire charge is molten and the furnace is full. Only by discharging some or all of the charge does the change move towards leading. One can safely conclude that by allowing leading, the change is towards a better condition and buys time for the operator to perform other duties. Sort of a "fail safe" situation. Running this melting unit demands constant attention.
The generator is limited by the current regardless the phase with the voltage. The prime motor turning the generator does not see VARS as a mechanical load since VARS are going back and forth and absorbed by any rotating inertia.
Just thinking aloud.
The four meters support your comment, as they reflect the output of the generator, not the motor, each of which are wound on a common shaft. Interestingly, the motor/generator is mounted vertically (I've mentioned this before) instead of horizontally. I suspect that was to make a smaller footprint for the entire unit, which is not small.

Thanks for your thoughts.

H
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Harold_V
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Re: Discouraged!

Post by Harold_V »

tornitore45 wrote: Wed Feb 08, 2023 7:24 am Just shedding some light, not trying to be pedantic.
Exactly what I hope to read. I am not well versed in electronics and welcome any and all information that will help me better understand what I'm dealing with. Keep the thoughts coming so long as you feel they can help. I'll not complain.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
rrnut-2
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Re: Discouraged!

Post by rrnut-2 »

I have a Kw meter on the shelf, but not a Kvar meter. Our Brown Bovari motor generator sets were gone by 1980 and replaced with
Inductotherms. Being solid state, they didn't need the Kvar meter, just furnace voltage, frequency, and Kw. Still had to switch in
capacitors once in while, but not often. I never got the chance to dive into the circuitry for the meter circuits on the Brown Bovari's or
the one Ajax mg set.

On the Inductotherms, Kw and furnace voltage was fed back to the control board through transformers call potential transformers.
Frequency was generated by the control board and if I remember correctly, there was a current transformer on one of the buss
bars in the tank circuit and this was also fed back to the control board. The control board would control the lead/lag using the furnace voltage and the tank/furnace current.

Jim B
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Harold_V
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Re: Discouraged!

Post by Harold_V »

The wonders of modern equipment, eh, Jim? Good to hear from you!
I was reading on kilovar meters last night and discovered that they are sensitive to frequency. Not just any old meter will do, assuming one hopes for accurate readings.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Atkinson_Railroad
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Re: Discouraged!

Post by Atkinson_Railroad »

Have been on the fence reading this thread. In a zest to contribute though, I have become discouraged too.
Not by the loss of a power factor meter, but it seems the ICS Reference Library that was on-line… is gone again.
Or at least I’ve lost where it went.

I mention this because at that site, one would have been able to bring up a little “blue book” titled, Electrical Measuring Instruments.
In that book, one can learn what Reactive Power, and Vars mean in connection with reactive power meters, etc.
Because I am not able to find that site, I’ll push you toward one that could be just as helpful if you want to continue attempting to repair the meter you have.

https://babel.hathitrust.org/cgi/pt?id= ... =1up&seq=9

The pessimistic repairman in me does say this:
Hickok made their own items implemented into their products.
That is going to make it even more difficult to adapt something different in the event a working Hickok meter cannot be located.

I’m rooting for you Harold. You’re going to run that machine again using your repaired meter, or by retrofitting a different meter arrangement.

John
davedfsme
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Re: Discouraged!

Post by davedfsme »

http://www.cromptonusa.com/Watt_Var_VA.pdf

Here's an explanation of why the genny overloads when lagging.
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