Power Factor of Variable Reactance Transformer

I am not an expert in arc furnace technology. However, from my short experience with this kind of furnaces, in my opinion, in order to assure a stabilized welding you have to control the current precisely. Using capacitors in order to fix the power factor you could reduce the total impedance and so the supply current would be out the controlled limits.

Thanks for answering quickly on a weekend!

These are not arc furnaces; they have either molybdenum sheets or carbon bars (in different furnaces) as the resistance heating elements. They are mostly used for brazing, but also for heat treating and forming.

In any case, yes, the current must be precisely controlled to achieve the correct ramp rates and temperatures, as well as to avoid overly rapid temperature changes in the heating elements and their contacts.

Check with your accounting office. With a large load like that operating a long way from a power factor of 1.0 (called unity) you might be paying a substantial payment to the power company - who would would not tell you because you would get power factor correcting equipment installed = less $$ for them.

For a variable inductive load you should find out the cost for an auto-correcting power factor corrector.

It is possible that you have this installed already, as no-one wastes this sort of money on an ongoing basis

Again, thanks for answering quickly on a weekend!

I've done that, and yes, the electric company is making LOTS of money from us! These furnaces are by far our greatest consumers of energy, and electric is the only form possible. At the moment, it looks like our average power factor is close to 0.5; if I understand correctly, that means we are donating half our energy cost to the electric company.

Lot's of bad things are possible out of ignorance! We acquired a failing company and moved their equipment to our facility, installing it just as it was previously installed. It looks like the lack of of power factor correction may have been a major factor in their failure. I observed the installation, but was not in charge of it. I'm virtually certain that there are no power factor correction devices currently installed. This is obviously out of my region of expertise, which is why I posted the question here. I had ignorantly been assuming that, because the heating elements are simple resistors, the power factor would be unity; the control system didn't even enter my mind...

It is definitely on my mind now!

It could be (and is) done with SCR controls, but that has no effect on the power factor if the transformer must still be there, which is nost likely the case. The VRT is dong two functions; controlling the current, but also increasing the current ratio by transformer action. An SCR controller can only DECREASE current, so you would likely still need a transformer down stream to increase the ratio, which means you are back to square one with power factor.

The PF gets worse because the current needed to maintain flux in the transformer core remains relatively constant, regardless of load and is primarily reactive current. So as the load decreases, the percentage of total current represented by the reactive current increases. But in this case, although the PERCENTAGE is bad, the TOTAL kVAR value remains somewhat more constant. I wouldn't worry about it until you check your bill from PG&E (or SMUD as the case may be). So much manufacturing has moved out of California that the major utilities are not necessarilly penalizing large users for poor PF percentages, only kVAR demand. If your kVAR demand remains relatively steady, you may find there would be no benefit to correcting the power factor, unless you want to grow the facility and need more capacity from your existing infrastructure.

You are absolutely correct on the VRT. It is dropping nominal 480V to nominal 30V, obviously with a commensurate increase in current. So your comments on SCR controls are valid.

Although my home does indeed get its electric energy from PG&E, the plant is in the San Diego area (I frequently go there for a week or so at a time), so the provider is SDGE.

I believe the following contains the pertinent information from a recent bill (I converted all charges to %, to protect privacy):

Some of the furnace runs last as long as 22 hours, so it is impossible to avoid the on-peak charges, although we do consider that when possible.

I suspect that the "Non-coincident Demand" is the charge for power factor. At 41% of the bill, it corresponds pretty closely to an average power factor of 0.5.

You also hit the nail on the head regarding the facility: we do need to obtain more capacity from the existing infrastructure, hoping to avoid having to get a larger main transformer.

You "... suspect that the "Non-coincident Demand" is the charge for power factor..."; however your suspicions are unfounded, you really should contact someone familiar with utility tariffs for assistance in understanding your bill. Since your demand is over 20kW and you are billed for the Summer Non-Coincident Demand charge, you are probably on the AL-TOU rate plan, a simplified explanation is contained in this presentation prepared by them.

A few things should jump out at you; one is that the actual definition of Non-Coincident Demand is entirely different than your "understanding", the other is that since you are not specifically billed a Power Factor Penalty you have probably not had a Power Factor Test Failure as defined on Sheet 6. If you had, then you would have had Power Factor Metering installed by the utility (at your expense), and would be billed for a 0.25$/kvar charge. A quick look at the top of the bill will confirm which rate schedule you are being billed under.

Thanks.

You are apparently correct on the rate. Ours is "Rate: ALTOUCP2-Commercial". I have only the vaguest of ideas what that means.

Although there is a list of definitions on the bill, there is no definition of "Non-Coincident Demand charge".

...more after I've had a chance to see/study the linked presentation.

You have seen many suggestions and have responded too.Your intention is to utilize existing infrastructure effectively- so that you could expand in future. APFC will help- but will be expensive. Adding capacitor banks fro such a large variation is also not easy. SCR controls could be considered - not with phase angle controls, but integral cycle controls. You could consider both integral cycle controls + transformer primary side tapping selection to get a wider choice.

OK, I've had a chance to study the presentation. Now I gather that the Non-Coincident Demand charge is a charge for peak demand regardless of time of day.

How could a difference in definitions "jump out at me" when I hadn't seen a definition?

"...Power Factor Test Failure as defined on Sheet 6". Sheet 6 of what? I saw no mention of power factor anywhere in the presentation, and definitely not on slide 6. There are only 4 pages of our SDGE bill, including the definitions.

Although we are not specifically billed for poor power factor, we are billed for total energy use, which includes all those KVARs, so reducing the KVARs will reduce our bill. I do understand how total power is the hypotenuse of the power triangle, so reducing KVARs will not produce a directly proportional reduction in the bill, but the reduction will still be significant, won't it?

try a few of these links

You might find a company to sell/install the right sized automatic PF adjustor.

Also find out how much is $$ is due to PF away from 1.0

Thanks. I had already suggested APFC to one of the significant individuals, but your links added to my arsenal. See my response to JRaef.

ok, you are on the scent now...

Unless you get a cheaper tariff or avoid a penalty from your utility, or generate your own power, PFC will not save you money.

The truth is that what led us to this discussion is our desire to correctly size a solar PV system. We moved into this facility just under two years ago. It had been abandoned for some time, and most of the copper had been stolen, so we are rebuilding.

"...PFC will not save you money." That's not what I'm hearing from most everybody else! Do you have some numbers or personal experience to back your statement?

various places deal with power factor, and call it this and that.

San Diego speaks of distributed loss factor?

I've looked at quite a few links now, including some of those.

One of those said something to the effect that poor power factor should be obvious by looking at your bill. I fail to see that! When you install additional devices, you expect the bill to go up. I suspect that the percentage of accountants who could predict how much the bill should rise for a given piece of equipment is in the low single digits, perhaps even lower...

Obviously the people who sell power factor correction devices will choose bad situations to illustrate their rapid payback, such as Aerovox, which indicates a 9 month payback period for an investment of $16k. We would need a larger system than that, or multiple systems, but even quadruple that payback time would still be a good investment.

I'm disappointed that I apparently haven't gotten a response from anyone who has actually used any VRT-powered devices and knows what their power factor should be when lightly loaded.

Now that I know a bit about it, I'm also surprised that power factor correction isn't an integral part of these furnaces. They are old (≈30 years), so perhaps power factor correction was not considered important at the time they were built.

Before you make any decision on PFC you must be absolutely sure that it bis costing you a lot of money. Are you the only customer on the feed from the utility?. Putting those Noise and spikes back into a shared supply will create havoc in the equipment of the other users. This is mostly the reason why Utility companies put a fine on bad PF control. In your factory you can spread the cost for PFC by doing it per VRT and not on the incoming supply. Work out more expensive but easier to control as with servicing you only lose the equipment on one system and the other systems in the factory can stay in production. Make sure to get PF systems with noise control circuits and easy monitoring with PF adjustable alarm point. You must use a company that survived the economic crash and that offer a spare parts paid service contract with specified 3 monthly inspection services. You win two ways.

1. They will use Capacitors and contactors that can handle the job as cheaply as possible for them.

2. If they go the cheap way the cost become theirs.

Fortunately, at least a few of the power factor correction companies offer free analysis before purchase. I am suggesting to my superiors that they take advantage of such an offer.

"Are you the only customer on the feed from the utility?". I guess that depends on your definition of feed. We have our own transformer to drop from distribution voltage down to 480V. There are a couple of other divisions within the company that also draw from the same transformer, but there are no other customers on the 480V side of that transformer. There are presumably other customers on the distribution side of the transformer, but I have no knowledge of who or how many, other than a second similar transformer powering a different building of our complex.

By the "noise and spikes", are you referring to existing conditions, or to the new noise and spikes that will be introduced by the automatic switching in and out of the correction capacitors? The latter will definitely be less using a separate correction for each VRT. Once we get into this, we may well find that some other large intermittent current devices we use can benefit from PFC as well.

Good points on the kind of equipment and the provider...

I'm talking about other customers using the same high voltage feed as you for your Main transformer.

I'm referring to what you are putting back into that feed through your HV transformer at the moment on the high voltage line.

Any irregularity happening on one side of a transformer will be reflected on the other side of the transformer in both directions.

Running at near 80% the disturbance will be minimum it is the startup that causes the most irregularities into the HV line to other customers.

80% is the maximum value we use for these furnaces, and it always takes at least 15 minutes, usually over an hour, to reach that level. They always start low and gradually work up. There is no startup surge like there is for large motors.

One of the most interesting blogs I have seen recently, thanks to all concerned.

I totally agree with you Andy and the intelligent quick response from the OP made it a fluent conversation. Thank you guys interesting discussion.

Thanks. I'm always amazed when OPs rarely or never come back to refine their problem or confirm/deny solution thereof.

If the furnace heat generation is done using resistive elements, why not use a variable DC power supply, using SCRs as the controlling element? Except for isolation purposes, reactive AC component may not be a big concern?

But then again, ignore the above suggestion if the heat generation is done via induction heating? Just a thought from the past....

Because the heating elements of a single furnace require up to 10,000 Amperes at up to 30 Volts.

If, as I understand it, we are paying thousands of dollars a month for that reactive AC component, that is a pretty big concern!

I may not be noticed in the many comments!

To me "Variable Reactance Transformer" suggests it has a high reactance to limit the current at cold, this would logically have a very low power factor (mostly inductance, with low resistance from cold elements). At full power, the inductance would be small, the resistance much more, giving high power factor.

I would expect the "variable reactance" to be achieved by a saturable reactor.

However, If you start up one furnace (low current, low power factor) while another is running (high current, high power factor) I would expect the overall power factor to be high - not really a bad "site" power factor hitting "reactive power costs".

As others comment, you need to understand the electricity charge rules. Maybe they hit you because you start all furnaces at same time, taking maximum VAr.

You are noticed!

These units are around 30 years old, so current devices presumably use different technology. I have been unable to determine the exact configuration of these specific transformers, but the basic concept is that a DC current in a control winding saturates the magnetic field of a core, preventing it from acting as an inductance for AC currents.

Unfortunately, the data I currently have available does not (at least not directly) show me the kVAR values, so I don't really know how much reactive power we are wasting.

I have been under the impression that a power factor of 0.5 meant that the active and reactive powers were equal. In that condition, the power triangle would be a 45° isosceles triangle, so for 50kW total power (one furnace at the setting having a power factor of 0.5), we would have 35kW of active power and 35kW of reactive power. Thus we are paying for 50kW, but only getting 35kW of useful power. If, for example, we could cut that reactive power in half, then the total power would be roughly √(35²+17²)=39kW, so we save 11kW. At this point, it seems logical that 11kW of power lost/saved makes a significant investment worthwhile!

Anyone who understands this better than I do is welcome to shoot me down!

This may be a duplicate... I thought I submitted a reply, but it did not appear.

Thanks! You are correct (¶2), that I assumed we were paying for the hypotenuse. Since your post #10 cleared up my understanding of noncoincident demand, I think I now understand what I need. I knew about the demand charges, I just didn't know the terminology used in billing.

You can see that our peak demand is indeed lower than our noncoincident demand, showing that we are aware of TOU. We already avoid starting up more than one furnace at any given time, but with some furnace runs lasting well over 20 hours, it is impossible to avoid starting one furnace while another is already running. Where it now appears we can save the most is by analyzing the demands of the various kinds of furnace runs (which we already started doing), and then programming the start times of runs to avoid coincident peaks. Some runs have multiple peaks, so it will take serious analysis and forethought to achieve that.

We do commonly run the furnaces at night, but I don't believe anyone is currently taking into account the real details of when the peaks occur to avoid coincident peaks.

Thanks again for your time!

Thanks! GA! You're the first one to directly answer all three question areas. The details provided by others are also definitely appreciated.

I think it safest to not say more right now, as we are currently experiencing a thunderstorm, with about a cm of graupel on the ground.

There is no relationship between thunderstorms and a variable reactance transformer's power factor, so safety is not an issue.

Actually, the plant is in southern California, while I'm currently in northern CA. I was concerned about the safety of my computers due to possible surges or power outages. The center of this storm did pass directly overhead, and it was sufficiently intense for the NWS to issue a "severe Thunderstorm Warning".

What are you using for a power logging device?

Is it installed at the main or at the feeder for the furnaces, and will it help you monitor your usage and diagnose problems going forward?

Have you checked those measurements with something else?

There are power saver consultants who will do a survey of your power useage pattern. They will come in and assess the situation and do some monitoring runs with each piece of equipment running by itself and in your common production pattern(s). and they will record a typical week of use on a logger.

They will then advise you what to get in the way of PF correction and advice as to scheduling for minimal power use and lowest PF. This may well involve operating some machines at night or on weekends = higher labor cost. Will that be matched by a power saving?

They will charge a large fee for this.

To avoid the fee, develop these skills in-house. You might be able to get a paid by the day consultant?

"To avoid the fee, develop these skills in-house."

That's exactly what I'm trying to do! This thread has helped immensely!

At least one of the Power Factor Correction companies offers a free analysis...

dkwarner,

A relevant point....

You seem to be billed on energy (kWh) which is what a normal domestic meter logs, but you also get a "parking ticket" if you go over a "non-coincident" kW level.

So where is the meter which catches that maximum kW? Is it recording "whole site" (in which case, you could turn off non-furnace loads to avoid peaks) or just furnaces? And how is it designed to respond (instant peak, y kilowatt-minutes over x minutes, etc)?

If you find the meter, send a picture, someone will recognise the type & know how it works & what the settings mean.

Having a model of how the "watchman" responds will enable you to see how different loading schedules will help, perhaps using a spreadsheet (managers & accountants will understand them). If logged load data fed into a computer & processed gave kW that matched the "watchman" meter, it would show you had a good model.

Lastly, I do not think the power factor is critical here, kWh and kW meters record energy and real power, ignoring power factor.

67model

The meter is a whole building meter. There are two other sections of the plant that get their power from this meter, but the energy used by the other sections is very small compared to the furnace section.

Here is a picture of the meter. I have blocked out the serial number and part of the barcode for privacy. The meter is located behind a door only accessible by the power company, so I had to reach around behind the cabinet with my cellphone to get the picture.

It is a 'smart' meter, so it is capable of sending data to the power company. I have no idea how frequently that occurs, but I presume it must be at least several times a day. Otherwise they would not be able to correctly bill us for Time Of Use.

Your last statement confirms RAMConsult.

How convenient, a meter the customer cannot read for himself! Well, you can read kWh I presume, but it does not tell you kW.

Over here, the sales pitch to justify the extra charge on the customer, was these smart meters would help the customers save energy by giving them more information.

Our church hall got a new "smart" meter, but since it only appears to tell us import kWh, but not export & we have a solar power system with generation meter we do not know our total energy consumption. If you push a button on it, indications of KVAh & kVArh can be accessed. It does have a relay & LED lamp output at 1000 pulses per kWh though, so potentially one can count time between flashes to estimate kW.

This is exactly why I opted not to get a smart meter from my utility. The promised benefits and features of the smart grid are many years down the road, but you are expected to give up your privacy and help lay off the meter readers today.

Better to have your own meter of equal or greater accuracy that would tell you what you are buying (quantity and quality) and help you manage your load and diagnose problems. If you own the logged data then you can shop for consultant services from a better negotiating position.

I don't think you have to spend $10K to get there...

We are using a Dent ELITEPro XC, with Rogowski CT's, currently set to record every 30 seconds.

It is connected after the main disconnect for a single furnace, where the 480V enters the VR transformer of that furnace. Yes! It has already helped considerably, as we now know exactly where in a given type of furnace run the power peaks occur.

Yes. we checked the indicated currents with two different clamp-on meters, with good agreement. At first I was bothered by the indicated voltages around 275V, until I realized they were line-to neutral voltages.

Transformer power factor is affected by several things with the most prevalent being that transformer efficiency and PF are maximized when the transformer is fully loaded or slightly overloaded.

There has been some breakthroughs in transformer design that offset this phenomenon and improve transformer efficiency at lower loading.

If you are looking at purchasing a new larger transformer to satisfy plant demand, it would be a good idea to contact at least three major transformer manufacturers to get their input and recommended solution(s).

Once you obtain the information a power study is in order so that evaluation of the power efficiency cost savings verses transformer purchase cost can be determined for identifying recapture of investment dollars.

It most likely will be that you can justify the purchase by demonstrating a payback for investment in a new transformer(s) in less than 5 years.

It does not cost anything to obtain transformer manufacturer input and opinion.

I'll have to double check, but I think the main transformer is property of the Utility, and I know for sure that they install it, so I doubt if we have any say in choosing it, other than specifying the expected load.

"...breakthroughs in transformer design..." Do you have any more info on this?

If a new transformer has a payback of only 5 years, I'd think the utility company would take every opportunity to replace them. The one on the pole outside my home has been there over 50 years; it has a light on it that has been illuminated for at least 40 of those years - someone told me that the light indicates that the transformer has experienced an overload.

I just recalled in the mid 60s the maximum value for the pf I usedh in the design was 0.8 -- for all types of transformers the company manufactured! This pf rating is applied to all transformers whether the intended applications is for welding, electroplating, UPS, saturable core reactors or for battery forming rectifiers... Over the years, I am not sure if the design parameters or approach in transformer designs has significantly changed?

Thanks. I'm now comfortable with the PF of the transformers, although I still haven't done a serious investigation into whether PF correction, either fixed or switched, would be worth the expense.

Now I've got another, only vaguely related, question, which I'll probably ask in a separate thread...

Resistive loads are Unity PF devices, why i s trafo provided?

Can you share the diagram?

best Regards,

Sharad Gaharana

India

As JRaef indicated back in post #4, the transformer serves two functions:

1. It provides a turns and wire size ratio. It drops the nominal 480V down to nominal 30V, and increases the current from a nominal 600A to a nominal 9,600A. In practice, we never exceed 400A input current, so 6,400A Heater current.

2. The variable reactance allows a small DC voltage in a third winding for each core to control the output voltage and current. These heaters must NOT experience sudden full voltage; they would break, and the temperature in the furnace must always be increased gradually, to avoid rapid thermal expansion of the parts being heated.

I wish I had the actual circuit diagram, but I don't. In fact, I suspect that there are at least two different diagrams in our various furnaces.

In semiconductor industry tubular furnaces are used to maintain temperature at say 1250D+/- 0.5 deg C. Transformer could be used to reduce voltage on secondary side probably considering safety issues. Further power = I^2 R. Hence by increasing I, power increases faster than by reducing R.

On input side back to back thyristor controls are used to control temperature with PID controls/feedback. Here again one could think of phase angel controls or integral cycle controls to avoid EMI issues- which I have mentioned in my previous posting. When you have back to back thyristors - they can remain in turned off condition when not in use or when there is no load. Hence question of huge reactive load currents do not arise. So the whole blog seems to be around reactive current of transformer when not loaded fully.

I am working at a facility in Bangalore where a huge transformer has been connected with 220KV input and 440 V output. Power rating is also huge for testing loads - which come once in a blue moon- once or twice a year. But on all other occasions the load is hardly 5% I ma told. Hence the utility charges penalty charges for poor power factor and high reactive current!!!!

Are you referring to some such condition???

Not really...

We currently have 4 furnaces, 2 horizontal and 2 vertical, which vary in size from about 2 cubic meters to about 20 cubic meters in usable inside volume. Each furnace uses one of these VRTs to reduce the voltage, increase the current, and control the power. During the vast majority of the time they are running, they are set at between 5% and 50% of maximum power. There are brief periods where they go as high as 80%, but never higher than that. So these transformers are always lightly loaded, leading, as I now understand, to very low power factors. The bill information was posted earlier; we are not currently penalized for the low power factor, only for maximum demand. We're working on that...

There are of course many other machines in the building, so our overall power factor is significantly higher than the PF of the furnaces. I don't think I have access to the main power cables, so I can't directly determine the PF of the whole plant, even though the logger is capable of doing it.

Hi dkwarner,

I just stumbled upon your post here, I've experienced exactly the same here!.

We are using Hunterdon VRT transformers on our furnaces which, obviously, have the same poor power factor. We also pay a good deal to the electric company.
I have solved it by adding "compensating Capacitors" to raise the power factor.

The cabinet has a lot of capacitors inside which can be switched on an off to adjust to fluctuating load.

I'm trying to upload a photo to show you, can tell if it works however...

Hi RVE

Thanks, and Welcome to CR4! I'm anxious to hear more. When you say you have "solved it", I assume you are referring to solving the power factor issue by adding the capacitors.

To upload the photo, have it saved as a jpeg image in a known location, click on the green camera icon in the tool bar, click on "Browse", navigate to the image and select it, then click on "Submit". If you don't have a tool bar, then try a different browser. I use Firefox.

I'm confused about your last phrase. Did you mean to say "can't tell..."?

The real question is: Did adding the capacitor bank lower your electric bills?

Hi dkwarner,

What I meant to say is that I hope I've solved it...
The system is up and running since 2 weeks, so the proof is in the next bill!

Uploading the photo in the text didn't work so I added it in my profile photo.
I've got the toolbar but it won't upload. (and that's why I said can't tell if it works).

We will have to wait for the next bill to be sure that it works, but I'm sure it will.
I did not find this out all by myself, but recognized the problem and found a company that could help me solve it.
So if you have got any questions, by all means, let me know and I'll try to answer them.

That's an interesting way to submit a photo! I have no idea why it would upload to your profile, but not to the post...

No need to answer this 'till you get the next bill, but is the capacitor array connected to your main power line, or to a machine?

We are watching our electric bills too. A power logger showed us that an air compressor was both oversized and faulty. Replacing that one compressor is saving us between 3 and 4 thousand dollars a month in electric energy! We have another similar one to replace...

Please do come back when you get that next bill! Thanks.

Hi everyone,

received the network bill last week. No more reactive power charges!.

@dkwarner:
still can't post photo's, don't know what's going on with that, but:
Our array is connected to the machine itself, which is parallel to the power connection itself. It is a 300kvar system for the VRT, and two smaller system for each large electric motor.

Regards.

Excellent! Thanks for getting back to CR4. I'll pass that on, even though we currently are not, to my knowledge, being charged for reactive power.

I'm still far from expert on this matter, but I'm learning... If I understand correctly, the reactive power does not contribute to heating of the supply lines. Is that correct?

300 kvar would be about the right size for ours as well. Can you give a ball-park figure for the installed cost?

regarding the posting of pictures, have you tried a different browser? I've been using Firefox successfully essentially all of the nearly 10 years I've been on CR4.

Excellent! Thanks for getting back to CR4. I'll pass that on, even though we currently are not, to my knowledge, being charged for reactive power.

How would the electricity supply company differentiate between reactive and "normal" power usage? Why would they even if they could?

That is between a good and a bad power factor. That is why some companies fit capacitors to improve the power factor (generally too much inductance causes the problem, so caps negate it) and thereby save money by improving the power factor, simply by reducing the angle between current and voltage....Current lags with inductance and leads with capacitance.

I'm still far from expert on this matter, but I'm learning... If I understand correctly, the reactive power does not contribute to heating of the supply lines. Is that correct?

If the wiring is too small, it could contribute, at least I have never heard differently....more power is being used/passed through the wiring, so why would it not?

I hope this clears up some misunderstandings....

Check here:-

http://web.ornl.gov/sci/decc/RP%20Definitions/What%20is%20Reactive%20Power%20_ORNL_.pdf

Thanks Andy.

The second paragraph of your link starts: "The additional current flow associated with reactive power can cause increased losses and voltage sags."

That answers my need (and tells me I was wrong thinking that reactive power did not cause heating). We are running two furnaces on the same set of 9 conductors (3 per phase), that carry the current a distance of around 70m from the main switch to the furnaces. If both furnaces happen to use peak current at the same time, the total exceeds the rating of the fuses (Yes- it's an old installation that does indeed use fuses, rather than breakers.). Currently our limiting factor appears to be heating in those fuses. Thus anything we can do to reduce the current is desirable. We try to start the furnaces at appropriate times to avoid coincident peaks, but various factors can affect the timing, so it is difficult to guarantee different peak times.

You ask: "How would the electricity supply company differentiate between reactive and "normal" power usage? Why would they even if they could?". It seems to me you have already answered that via your link. If reactive power increases losses in the transmission lines, surely they will want to charge accordingly.

As far as I am aware, even if they could differentiate, (its not impossible, just impractical in my opinion!), it uses the same amount of fuel as does the normal power.....

Its certainly something to be avoided.

But what "impedance" are the furnaces? I would be amazed if they had much of an inductive signature (until checked, even if the elements are wound, and good elements are wound first in one direction then the other, to reduce that), so there should be problem with the power factor....

But if elements have been incorrectly installed/connected, by someone who did not check the winding directions, its theoretically possible that the inductance may be higher than it should be.

But I am REALLY clutching at straws in this area.

Assuming the power factor is actually greater than 0.9, then there is little you can do to reduce current usage with say capacitance..........

One could add an ammeter, note the "starting" current from one oven and watch.

Once it gets up to temperature (I am guessing at the amount of difference there is between a cold and a hot element), that will be the point of the lowest current draw.....as most metals increase resistance as they heat up...but by how much in your case, I have no idea...Check.

Then start the 2nd oven.....

That might help.

Also, I would get the fuses replaced with breakers.....simpler to reset.....

It looks like you have forgotten earlier posts in this thread. The impedance of the larger furnace heater set is 3.1mΩ, almost entirely resistive. The heating elements themselves are either carbon or molybdenum bars, wired in series/parallel groups. I have not traced the wiring to determine if they are connected is a way that reduces the small amount of inductance. The Variable Reactance Transformers required to reduce the voltage and control/increase the current to the several thousand Amps used by the heaters are very inductive, especially at low outputs.

These VRTs are extremely robust, and do their job (controlling the heater current) very well, but rarely get above a power factor of 0.5.

There are already current transformers with appropriate meters on each furnace. These indicate the current between the output of the (VRT) transformer and the heaters in kA.

"Also, I would get the fuses replaced with breakers.....simpler to reset....." We would love to do that, and plan to do so when we add additional furnace(s), but it will require replacing the entire 2kA 480V Main Breaker Panel, and cost in $ix figures to do so.

I had read it and forgotten.....sorry.

Inductance is easily measured with a fairly cheap meter.

Also, a power factor meter, especially if secondhand, will probably not be too expensive, and maybe a really good idea........

They start VERY cheap on ebay.....

http://www.ebay.de/itm/Multi-functional-LED-Digital-Rail-Current-Power-Factor-Ammeter-Voltmeter-N4-/281961797309?hash=item41a63b96bd:g:74UAAOSwZQxW4mMo

Or here:-

http://www.ebay.de/itm/Three-Phase-True-RMS-Digital-Power-Clamp-Meter-Power-Factor-Tester-RS232-MS2203-/331796536787?hash=item4d409d5dd3:g:SOIAAOSw54xUXDFQ

Which can display the following:-

Features:1.Single-phase, 3-phase 3-wire, 3-phase 4-wire power measurement2.AC voltage, AC current, apparent power, reactive power, power and power factor, frequency measurement3.True RMS measurements in a non-sinusoidal current, can accurately measure the active current4.9999 display count, two scale bar showing fluctuations in the value of the voltage and current Dual display show two different parameters and can store 28 sets of measurement data5.In the three-phase power measurement, and the total power of each one of the five power parameters can be displayed separately6. RS232 standard interface and PC recording software
Only costs €113
Here is a picture:-

I hope this provides some inspiration!!

We have, and are using, a DENT ElitePro XC with Rogowski current transformers:

We have the WiFi version, about $2k with three Rogowski CTs (not shown). It paid for itself in a single month!

How can a meter with a single CT clamp (per your illustration) measure 3 phase power? There is commonly significant imbalance between the three phases, and this imbalance changes over time, so a single clamp can only approximate.

Hi Guys,Using another browser now, submitting photo's is working!
here's a short overview of the pre and post figures of the savings.to translate; "voor", means before, and "na" means After.

As you can see in line 1 the cos of the VRT was 0,61 before compensating!
Second and third line are electomotors.

regards.

Here are a few photo's of the project;
Here you can see the Cos value, and how many capacitor arrays are switched in (every + means one bank is active). This is adjusting at a rate of a switch everey few seconds. This is for the VRT transformer.This is the inside, the capacitors are behind the red panels.

These are the two fixed value capacitors for the electromotors.

This is how the inside looks.
As for a "ballpark" figure, our contract had a guaranteed payback time of just under 2 years. This was a justification for us to invest around 17k in this project.
I think that for all of us "in the business" it's important to identify and eliminate all energy inefficient processes or "spills". It's good for your wallet and good for the environment.
good luck with your projects.RVE

Beautifully carried out!

Many thanks for sharing.

Just out of interest, what browser were you using before?

Hi Andy, I was using Interne Explorer 11.

that didn't work properly so I used Chrome instead.

I'm using Chrome also, simply because my favourite, Mozilla Firefox in both 32 & 64 bit versions, has problems in the Ubuntu version that apparently cannot/will not be fixed!!

Probably not enough "gain" to do a proper job, so Chrome it is!! Their loss.....

Guaranteed payback of 2 years! Definitely worthwhile!

In our case, that reduction in current should easily allow us to concurrently run 2 furnaces on the same existing cable set, without danger of blowing a fuse. I suspect that may be the factor that convinces the "powers to be". We commonly have 30k worth of parts in each furnace, so a single failure would cost way more than the Capacitor unit.

I had to enlarge it for my eyes to see it, but I can indeed see that Caps #4 & #6 are activated at that point.

I appreciate all the photos!

Thanks again!

Thanks again!

After thinking about it a bit, it appears that there is a contactor in each of the two motor boxes. Since there is a single value of capacitor for each motor, why is a contactor required? Does it disconnect when the motor is at high load? It seems like one could just connect the capacitor permanently across the motor... When it is at high load, there might be a bit of excess capacitance, but if your plant is anything like ours, there are plenty of other inductive loads, so the overall plant power factor would still be net inductive.

Another look at those motor boxes: it looks like one box has a single capacitor, while the other has two. I suspect that What looks like one capacitor is really three. Surely these are three phase motors, requiring one capacitor per phase...

Are these motors both vacuum pumps?

This seems a bit like dropping a joker into the melt but voltage regulation has been mentioned & the diagram below is for full load regulation of a power distribution transfo (from The Performance and Design of Alternating Current Machines by M.G. Say).

You can see that regulation is very good at unity power factor and that low power factor loads cause seriously increased voltage change. In a usefull, practical way the voltage regulation can be seen as due to the reactive power component VAr. Power suppliers have to ensure a steady voltage at the consumer - also the current flow in power lines is determined by the voltages at the ends - VArs are the enemy of voltage and system control, so large users get charged for them.

In your situation, changes of voltage starting one furnace may react on a running one, affecting control, ultimately product quality & maybe life of heater elements.

Good power factor will contribute to steady voltage. It will increase the normal voltage & may make it higher than is good for efficiency (distribution transfos normally have taps which can be changed while de-energised).

67model

Thanks. I only begin to understand that graph. I assume that the zero crossing a bit to the left of center indicates the capacitance required to compensate for the inductance of the transformer itself. I'm curious why they show negative regulation above the center and vice versa.

Fortunately, the furnace heaters are always started at low power and brought up slowly; it's nothing like starting up a large motor, so each furnace has time to react to any changes in line voltage caused by other furnaces. Here is a typical startup:

It takes another hour for the power to reach its peak, near the top of that graph. That graph looks to me suspiciously similar to to a servo with poor PID settings, but that's a whole separate issue.

The increase in voltage will actually be a good thing, because we have about 200 feet of cable between the the main switch panel and the furnaces, and currently have several volts of drop along the way.

Great! Thanks a lot!

That reduction in Amps is truly impressive!

Which browser worked for you?

I have never used one, I had hoped (ebay!!) that there was a grain of truth in there.

All the meters I ever used were built into the RN switchboards.......50 years ago, I doubt if any portable units were available or needed.....

You neglected to mention what you already had, I was just trying to help you!!

Maybe I should just give up helping?

When I started this thread, I hadn't yet convinced the company to get a logger. Shortly thereafter, we rented the unit for a month. Since I'm only at the plant part time, I had just begun to analyze the data when the month rental was nearly gone. At that point, I had been able to show them the worth of the unit, so they bought it.

Since then, it , together with a FLIROne infrared camera attachment for my iPhone, have led to saving several thousand dollars a month in energy bills. I hope to add thousands more!

Don't stop trying! Even less-than-fully-informed comments can lead to viewing things from a slightly different angle, and thereby result in better understanding.