Power factor question

[iwire]

And the loads are not always constant. The refrigeration I've seen varies quite a bit and would require dynamic correction except on the base refrigeration load units.

What kind of refrigeration compressor motor has to deal with varying loads? I cannot think of any.

Other than at start up the HP required should remain fairly consistent.

 

[PowerQualityDoctor]

There is patent, but it is more about the technology and not the applications.
You can get more knowledge in my paper at EEMODS conference (EEMODS = Energy Efficiency in Motor Driven Systems). You can download it directly from http://www1.cetim.fr/eemods09/pages/programme/077-Broshi-final.pdf. You may download an older version from Energy Central.

You can see more commercial information here. If the moderator decides that links to products is not allowed, he is welcome to delete the link. You can then Google my nick name, reach my private website and see some interesting links.

 

[iwire]

Don't bother, I have banned myself.

One of the best signatures ever. :grin:

 

[gar]

100215-0920 EST

I have rerun my Slimline intensity variation test and see nearly no change in the GE light meter reading of 25 foot-candles from 100 to 130 V. The meter movement is rather good, zeroes with no hysteresis, and is not a tautband, but simply a jeweled movement. 25 is about 40% of full scale.

As a separate test I used a Clairex cadmium-sulfide cell. This allows higher resolution, but is a less stable material than the GE cell. With the Clairex I see about a 2% increase in light output from 100 to 130 V.

The Slimline does not really have problems until about 65 V.

iwire:

Commercial stores have a large part of their electrical load as lighting and from my experiments here with the magnetic ballast Slimline it would appear that substantial energy savings can be obtained at a reduced supply voltage. So your comments, at least relative to the lighting part of the stores, about reducing voltage appear to be very valid. Are there any undesired side effects?

I agree with you that the refrigeration load is quite constant. Earlier experiments I have run on my freezers shows an initial higher power consumption at the start of a cycle and a gradually reduction reaching a steady value. But the change is not large, 410 W down to 280 W over a 45 minute on cycle.

The data looks like this:

Watts -- Minutes
410 ----- 0
390 ----- 0.56
380 ----- 1.1
370 ----- 1.4
360 ----- 2.1
350 ----- 3.5
340 ----- 4.9

300 ----- 12.8
290 ----- 17
280 ----- 26
280 ----- 45 compressor turns off.

The greatest change is in the first 12 minutes of the 45 minute on period.

iwire you have no need to make any apologies to me for any comments or disagreements. We are just having a discussion back and forth on varying ideas, knowledge, and experiences.

.

 

[PowerQualityDoctor]

This is a change of more than 30%. What is the motor rating?

About lights:
It depends on the type of lamp and its age. Reducing the voltage reduces some of the lumen, but the overall is ok. Note that you have to use controller that can provide starting voltage for 15 minutes or more. See NEMA article for details.

There may be side effects if you use equipment that generates harmonics, usually created by chopping the waveform. Look for those based on transformers which will not inject any harmonics.

Amir

 

[gar]

100215-1057 EST

PQD:

This happened top be an Admiral from a number of years ago. I do not know its age. $50 at the recycle station and works great, even well below 32 ambient. High probability it is a Tecumseh sealed compressor. No idea about the motor it is sealed with the compressor. The change in power consumption I would attribute to the characteristics of the refrigeration system. Similar pattern on an Amana which is about 40 years old. Just a different on-off cycle time.

It might be a thermal time constant relative to the condensing coil and associated area.

.

 

[PowerQualityDoctor]

More or less the load on the motor in percents, plus 10%, equals the power factor.

For example, a motor of 20kW will consume 10kW at 60% (0.60) power factor. So when your motor PF goes below 60%, you can reduce its voltage to improve its efficiency.

 

[robbietan]

Following specific requests from ohmhead and mivey

Motors
For induction motors - when the motor is loaded by more than 60% (by means of power, not current), reducing 25% of the voltage will reduce its consumption. The amount of reduction depends on the loading, motor size, motor efficiency and more parameters. The highest value I measured was 36.6% for 18kW (25HP) motor and much more for laborotary small motors. This idea is known since 1979. The problem that usually it creates harmonics which create other source of losses and it is not recommended. My company developed a unique technology that can do it without any harmonics at all.

If the motor is loaded by more than 80%, usually you can save if you increase the supplied voltage, but the saving is minimal of few percents only.

I thought when a 100kW motor has a load of 80 kW, the power consumption of that motor will be 80 kW plus some motor losses. according to NEMA, you could damage the motor if you lowered the voltage below 10% of operating voltage.

 

[iwire]

I thought when a 100kW motor has a load of 80 kW, the power consumption of that motor will be 80 kW plus some motor losses. according to NEMA, you could damage the motor if you lowered the voltage below 10% of operating voltage.

If you are trying to get full HP from it you could damage it.

 

[PowerQualityDoctor]

Lowering the voltage to fully loaded motor is not possible (the motor will slip, its currents will rise and probably the protection will be activated).
Lowering the voltage to partially loaded motor is not only possible, it is highly recommended. This reduces the motor losses, increases its power factor and saves energy. Of course, only if the voltage is reduces without creating harmonics, otherwise you add also bad issues to the formula.

 

[Cold Fusion]

There is patent, but it is more about the technology and not the applications.
You can get more knowledge in my paper at EEMODS conference (EEMODS = Energy Efficiency in Motor Driven Systems). You can download it directly from http://www1.cetim.fr/eemods09/pages/programme/077-Broshi-final.pdf. You may download an older version from Energy Central.

You can see more commercial information here. ...

I read your paper - the one from the second link. It is long on claims - short on any technical data on how it works.

However, interestingly enough, I suspect your black box device does what you say it does.

Unfortunately, the conditions where this device might possibly save enough to pay off the device (including all life cycle costs), rarely exist. I only saw one in your paper - the escalator example. Most all of the other examples are only cost effective if the underlying installation is unbeliveably poorly engineered.

I won't say that what you are selling is "snake oil". I will say that your ability to sell your device highly depends on scaring accountants to death as opposed to showing the engineers there are true savings available.

Your paper is excellent sales literature - but poor engineering data.

One item that particualrly concerns me is your alluding to the idea that aluminum wound transformers are less efficient than copper transformers. If you are in fact saying that, then my response is, "Horse Pucky". And, if true, I will conclude that the validity of everything else you have to say is suspect.

cf

 

[mivey]

What kind of refrigeration compressor motor has to deal with varying loads? I cannot think of any.

Other than at start up the HP required should remain fairly consistent.

In a cold storage facility where various banks of units cycle in and out as the different products are brought in and the temperature changes during the day. Some of the product adds even more load when it has to be flash frozen.

 

[mivey]

...I agree with you that the refrigeration load is quite constant...

Maybe for some specific apps, but the loading on some chiller plants can change quite a bit.

 

[gar]

100216-1920 EST

mivey:

My home freezers have a rather consistent power vs time curve. In my post of 0920 on 2-15-10 is a sample of one cycle of pretty consistent curve that occurs from cycle to cycle. I believe the only control factor for temperature is the on-off (bang-bang) servo (thermostat).

I believe the on-off cycle and the rate of cool down are the major differences resulting from loading, and not the power vs time curve.

But I have not run an explicit experiment on this aspect.

I have no idea what control algorithm may be used in a large refrigeration unit.

.

 

[iwire]

In a cold storage facility where various banks of units cycle in and out as the different products are brought in and the temperature changes during the day. Some of the product adds even more load when it has to be flash frozen.

In my experience the power used by the compressors would remain relatively consistent unless you are using a VFD type control.

Without VFD generally the compressors pump into a common manifold equipped with a pressure transducer and the goal is to maintain a certain pressure in the header regardless of the number of evaporator coils calling for refrigeration. If more flow is needed to maintain the pressure additional compressors are brought on line. To the compressors the change in load is negligible.

But I have definitely not seen it all.

 

[mivey]

In my experience the power used by the compressors would remain relatively consistent unless you are using a VFD type control.

Without VFD generally the compressors pump into a common manifold equipped with a pressure transducer and the goal is to maintain a certain pressure in the header regardless of the number of evaporator coils calling for refrigeration. If more flow is needed to maintain the pressure additional compressors are brought on line. To the compressors the change in load is negligible.

But I have definitely not seen it all.

For the on/off units, as the different compressors are brought on line, you would also have to bring additional var compensation on line (depending on if the compensation is per unit or for a bank of motors). I have seen banks of 50 & 75 hp motors in the same plant with 200-500 hp units.

For some cooling plants (to the best of my recollection), the motor loading was changed by opening and closing a valve as the cooling load changed. Loading and unloading in this manner caused the currents to go up and down.

 

[weressl]

Improving the power factor reduces losses. The saving depends on the losses and the available improvement. If you have single cable to single load with 2% of voltage drop over it, the losses are 2% divided by the PF. You can see the explanation of this formula on page 3 in my paper presented during EEMODS conference, discussing the efficiency of system.

The question is how long your cables are and how low your power factor is. For losses in transformers - the question is what is their quality (copper, aluminum) and how much they are loaded (the lower the load, the higher the losses).

However the reduction of losses in a feeder almost NEVER justifies the pf correction in your average system.

 

[LarryFine]

However the reduction of losses in a feeder almost NEVER justifies the pf correction in your average system.

Even if it's designed in from scratch, and permits smaller conductors?

 

[ohmhead]

There is patent, but it is more about the technology and not the applications.
You can get more knowledge in my paper at EEMODS conference (EEMODS = Energy Efficiency in Motor Driven Systems). You can download it directly from http://www1.cetim.fr/eemods09/pages/programme/077-Broshi-final.pdf. You may download an older version from Energy Central.

You can see more commercial information here. If the moderator decides that links to products is not allowed, he is welcome to delete the link. You can then Google my nick name, reach my private website and see some interesting links.

Well what is the patent number ?

 

[mivey]

Even if it's designed in from scratch, and permits smaller conductors?

He probably meant the addition of power factor correction and in that case, Lord help me, I would agree with him.