Power factor correction experiment

[Besoeker]

Yes.At 60% speed,the power required by load is proportional to cube of o.6 i.e 0.22 of that at rated speed only.Let us take an example.Let KW of load be 10 kW at rated speed.If its speed reduces to 60%,its power requirement is 2.2kW only.Let it be driven by a 10kwmotor.The current corresponding to 2.2 kW can be calculated taking into account the reduced efficiency and power factor of the motor for this reduced load by using the formula for input power to motor.Can you demonstrate any suitable values for this reduced efficiency and power factor to be used in that formula?

This is how I do it:

It's actually from a workbook with three tabs and that's the results part of one of them.
The Tqerr button (top right) runs a Visual Basic routine to get the slip right to match the load torque.

The data is for a real motor that has now been in service for quite a few years in a water pumping application.
The purpose of the calculations was to provide guaranteed efficiencies at various operating points at the bid stage of the project. Getting them wrong isn't an option.

 

[Besoeker]

For a centrifugal machine, the power required is a function of the square of the speed, not the cube.

Power is speed times torque.

P=Tω in SI. (No conversion factors required - you guys across the pond need to get up to speed on this........groan)

For a centrifugal load, power is proportional to the cube of the speed. Torque is thus proportional to the square of the speed.

 

[mivey]

Power is speed times torque...

It occured to me later what I had posted and I posted a correction.

When performing energy audits, I find a lot of motors with dampers and throttle valves. A VSD conversion is a typical savings option and I make a quick and dirty calculation of energy savings by using 1-(%speed)^2.

(No conversion factors required - you guys across the pond need to get up to speed on this........groan)

Them UK-ians again! At least you married right.

 

[T.M.Haja Sahib]

Yes.At 60% speed,the power required by load is proportional to cube of o.6 i.e 0.22 of that at rated speed only.Let us take an example.Let KW of load be 10 kW at rated speed.If its speed reduces to 60%,its power requirement is 2.2kW only.Let it be driven by a 10kwmotor.The current corresponding to 2.2 kW can be calculated taking into account the reduced efficiency and power factor of the motor for this reduced load by using the formula for input power to motor.Can you demonstrate any suitable values for this reduced efficiency and power factor to be used in that formula?

The reduced efficiency and reduced power factor are for speed control of motor by reduction in supply voltage with solid state thyristor control.But for auto transformer control as discussed in post #193,there is slight increase in both.So,let the full load current for 480v,10kW,0.8 p.f motor with 85% efficiency be 18 A.Even though there is slight increase in efficiency and power factor at reduced voltage for auto transformer control,let them be same at reduced voltage at 0.55 p.u.By applying the equation for input power to the motor and using values 264V,2200Wand same efficiency and power factor values,the current taken by motor is 7A only.

 

[gar]

111130-0914 EST

An interesting site:

http://watthourmeters.com/about.html
http://watthourmeters.com/history.html
http://watthourmeters.com/

.

 

[Besoeker]

The reduced efficiency and reduced power factor are for speed control of motor by reduction in supply voltage with solid state thyristor control..

Won't work.
Goodness knows, I have given you plenty of explanations, real life data, and you even cited examples yourself that confirm this.
Fine, if you want to believe that it's not the case.
Just try it for yourself.

 

[T.M.Haja Sahib]

Won't work.Just try it for yourself.

It is not becoming of an expert to say that way.Also your examples,explanations etc.,etc., did not at all illustrate the behavior of motor at much reduced voltage,Why not try that to convince yourself ?
I already offered you a homely example also:A ceiling fan with a voltage regulator.Why do you still resist?

 

[iwire]

It is not becoming of an expert to say that way.Also your examples,explanations etc.,etc., did not at all illustrate the behavior of motor at much reduced voltage,Why not try that to convince yourself ?
I already offered you a homely example also:A ceiling fan with a voltage regulator.Why do you still resist?

TM,

Besoeker has been extremely patient with you.

You have been told by many that your posts are rude and in fact they have been.

 

[T.M.Haja Sahib]

TM,

Besoeker has been extremely patient with you.

You have been told by many that your posts are rude and in fact they have been.

If you, as a moderator, think my post is rude,you can delete it .Please do not play game on that context.

 

[Besoeker]

Them UK-ians again!

Well, I'm old enough to have been educated in Imperial units too.
Pounds, ounces, feet, yards, chains, furlongs .......the whole nine yards.....groan again.....:roll:
Quarts and pints......actually the pint is one of the few units we have retained that can legally be used as an official measure. Beer is sold by the pint in pubs. Oddly, wine by the glass is in ml and in cl for bottles.
Slightly more seriously and somewhat back on topic, there are, as far as I know, no Imperial equivalents for many common electrical units. Gar's capacitors are in uF, the Farad being an SI unit.

At least you married right.

That I most certainly did. Along with all her other attributes, she is a brilliant cook. She prepared a fabulous spread for nine of us on Saturday past.
It was a family occasion celebrating my age thingy.

 

[gar]

111130-0929 EST

topgone:

From post #212. You indicate you have considerable experience with watt-hour meters from the utility perspective. Can you provide some quantitative data?

My house meter just for reference is a Sangamo
J2SB, Test A 50, 200 CL, 3W, 60 Hz, kH12, handwritten 8-92

What kind of accuracy specifications can you provide on meters of the general type on my house, and of other manufacturers that are similar?

How is accuracy defined?

What is the accuracy variation as power factor is varied from 0 to 1.0 in increments of 0.25 for both leading and lagging? How does this vary with current for 0, 5, 10, 25, 50, 100, and 200 A, and totally unbalanced (all load on one side) vs balanced?

.

 

[mivey]

The reduced efficiency and reduced power factor are for speed control of motor by reduction in supply voltage with solid state thyristor control.

T.M.,

Maybe it would help to back up to the original objective: energy savings on a residence. We are aware that we can save energy by just reducing the amount we use. What we are seeking is a way at keeping the same output but reducing our input by being more efficient. We were talking about a device located at the panel but migrated into a device located at a larger load. We pondered the amount of energy that might be saved by improving the power factor of a motor load (a well pump comes to mind) because we would reduce the heat losses.

Somehow we then got to voltage control of a motor. We all know that some motors can have their speeds controlled by varying the voltage. But what kind of motor are you talking about controlling? I thought we were talking about something like a well pump motor.

Slowing down ceiling fans is not going to reach our original objective, plus in that application you have reduced your output. We are trying to get the same output. At least I thought we were.

 

[Besoeker]

TM,

Besoeker has been extremely patient with you.

You have been told by many that your posts are rude and in fact they have been.

Thanks iwire.
I'm really concerned about the apparently rude comments that have been sent my way. I think TM's language skills are fine but sometimes nuances of our rich language can be lost in translation and something come across as rude when there was no such intent.
C'est la vie.

 

[Besoeker]

It is not becoming of an expert to say that way.

Interesting comment. You call me an expert yet don't believe what I'm telling you?

Also your examples,explanations etc.,etc., did not at all illustrate the behavior of motor at much reduced voltage,

And this that you submitted purports to:

Yet it tells you otherwise.
I straightened it out a wee bit and enhanced the contrast. I hope you don't mind.

Why not try that to convince yourself ?

Of what, I wonder...

I already offered you a homely example also:A ceiling fan with a voltage regulator.Why do you still resist?

As it happens, one of my erstwhile colleagues, who ought to have known better, tried voltage control of induction motors on a test fixture for a client. He used thyristors (called SCRs elsewhere) in an inverse parallel configuration - a W3C arrangement.

It didn't work.
It couldn't.
It doesn't.

 

[gar]

111130-1145 EST

In searching the Internet I re-encountered a document I had found earlier.

This is at
http://www.usbr.gov/power/data/fist/fist3_10/vol3-10.pdf about 73 pages.

On page 22 is accuracy information for a few test conditions. No voltage specified.

At 100% current and PF = 1.0 the error should be less than +/-0.3% of actual kWh
At 010% current and PF = 1.0 the error should be less than +/-0.3% "
At 050% current and PF = 1.0 the error should be less than +/-0.3% "
At 100% current and PF = 0.5 lag error should be less than +/-0.7% "

Yesterday I did not make much progress on obtaining a spinning disk meter. There maybe a problem getting one thru DTE because of a tremendous increase in theft of meters. In my discussions I learned that the new electronic meters will greatly reduce the problem of power theft and meter theft. DTE has 2,100,000 meters to replace. But they are also getting resistance from some customers because of the fear of RF radiation.

.

 

[Besoeker]

Thanks iwire.
I'm really concerned about the apparently rude comments that have been sent my way. I think TM's language skills are fine but sometimes nuances of our rich language can be lost in translation and something come across as rude when there was no such intent.
C'est la vie.

Should have read:
I'm really not concerned about the apparently rude comments that have been sent my way. I think TM's language skills are fine but sometimes nuances of our rich language can be lost in translation and something come across as rude when there was no such intent.

 

[topgone]

T.M.,

Maybe it would help to back up to the original objective: energy savings on a residence. We are aware that we can save energy by just reducing the amount we use. What we are seeking is a way at keeping the same output but reducing our input by being more efficient. We were talking about a device located at the panel but migrated into a device located at a larger load. We pondered the amount of energy that might be saved by improving the power factor of a motor load (a well pump comes to mind) because we would reduce the heat losses.

Somehow we then got to voltage control of a motor. We all know that some motors can have their speeds controlled by varying the voltage. But what kind of motor are you talking about controlling? I thought we were talking about something like a well pump motor.

Slowing down ceiling fans is not going to reach our original objective, plus in that application you have reduced your output. We are trying to get the same output. At least I thought we were.

Very well said, @mivey! I would have wanted to see how most of us feel about doing PFC at the residential level to know if it does give significant savings. By significant, i mean 10% or more.

Also, it could help others in the forum if those who wanted to stretch the discussions into another topic to please create a thread separate from this one. Highjacking this one muddles the discussions, IMHO. Peace!

 

[T.M.Haja Sahib]

Very well said, @mivey! I would have wanted to see how most of us feel about doing PFC at the residential level to know if it does give significant savings. By significant, i mean 10% or more.

Also, it could help others in the forum if those who wanted to stretch the discussions into another topic to please create a thread separate from this one. Highjacking this one muddles the discussions, IMHO. Peace!

My intention was to move the thread in the direction to meet the objectives of the OP.If there occurs significant deviation in the course direction,it would be corrected as the journey proceeds.But if the crews do not enjoy such transient deviations,the plan has obviously backfired.
As for the PFC energy saving,I want to depose that energy saving due to PFC may become significant,if we study not only energy saving due to drop in current in connecting wires,but also how it may improve the performance of motor operated devices.That is why mainly I and Besoeker tried to analyze the performance of induction motor first.

 

[Besoeker]

As for the PFC energy saving,I want to depose that energy saving due to PFC may become significant,if we study not only energy saving due to drop in current in connecting wires,but also how it may improve the performance of motor operated devices.That is why mainly I and Besoeker tried to analyze the performance of induction motor first.

Might I remind you of this from post #5:

Hi Gar
I did a similar investigation about three years ago. I drew similar conclusions - not that I expect to find otherwise.
"The maximum difference observed over 30 minute periods was 0.01 kWh regardless of whether the device was switched in or out."
The last digit.....

I was paid to do this. Those paying me might have preferred a different result. But I prefer to tell it like it is even if it loses me business.
The differences between you and I are simple.
You've talked the talk.
I've walked the walk.

 

[T.M.Haja Sahib]

I was paid to do this. Those paying me might have preferred a different result. But I prefer to tell it like it is even if it loses me business.
The differences between you and I are simple.
You've talked the talk.
I've walked the walk.

But it seems to me that gar's experiment is still inclusive due to meter errors etc.,As you said,'similar experiment........',may be yours also suffered from the same limitations.Is it possible for you to reproduce what you did here?