Power factor correction experiment

[Besoeker]

From #244: The reduced efficiency and reduced power factor are for speed control

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4111787

It states that efficiency does not decrease when voltage is reduced in direct proportion to square root of load torque.

It also states "to maintain the required slip during part load operation."
Maintaining the slip is maintaining the speed. I already mentioned that.
Can't you see the disparity between your two posts?

So the motor current by calculation in post #244 will not exceed full load current up to a load of 50% or so.

I believe I have already explained why that calculation is invalid.

 

[T.M.Haja Sahib]

It also states "to maintain the required slip during part load operation."
Maintaining the slip is maintaining the speed. I already mentioned that.
Can't you see the disparity between your two posts?

I am sorry you misunderstood it:Maintaining the required slip means maintaining the required speed.

 

[T.M.Haja Sahib]

''From #244: The reduced efficiency and reduced power factor are for speed control''

Please see that post # 244 again.I said 'The reduced efficiency and reduced power factor are for speed control with thyristor control'',because such control unlike auto-transformer control, introduces harmonics at low speed.

 

[T.M.Haja Sahib]

I'll be right back. I'm taking a print-out of this and a dictionary over to the local community college for some help with sentence diagrams and creating some decomposition charts so I'll know how to respond.

Me too.I can't believe there is a literary genius in iwire!

 

[iwire]

I can't believe there is a literary genius in iwire!

There is not, I am just a good Googler.

 

[mivey]

There is not, I am just a good Googler.

Great Googly Moogly!

 

[Besoeker]

I am sorry you misunderstood it:Maintaining the required slip means maintaining the required speed.

No misunderstanding on my part.
Did you miss this:
Minimum input power and maximum efficiency occur at a characteristic optimum slip value
Now, what do you think optimum slip value is?
Look back at #177.
Do you really think optimum slip is 0.3 pu?

I think the paper is about voltage optimisation, not speed control.
It's a feature that some variable frequency inverters have typically for cube law loads like fans and pumps. The V/f ratio gets reduced for lower speeds but it's for energy savings, not a method of speed control. I'm not sure how effective it is for energy saving. Reducing the voltage reduces stator current in the stable region and that may reduce stator losses some. It also increases the slip a little. That in turn increases rotor current. Which increases rotor losses and the increased current reflects back to the stator side. In short, each case needs to be looked on its merits. I have tried it on some fairly big VSDs with no convincing figures to demonstrate any savings.
That said, I do believe that voltage optimisation for fixed frequency applications can achieve energy savings. Your #151 example demonstrates that. It also clearly demonstrates that a large change in voltage does not equate to a significant speed difference. And, so far, I think that's only actual example you have presented.

 

[Besoeker]

Well anyone who is inordinately infatuated with polysyllabic obfuscation, preferring never to employ a less complicated syntactic arrangement of descriptive words when there exists a single expressive unit that amalgamates the multiplicity of morphemes comprising the simpler phrase. Among the manifold objectives of multisyllabic, holophrastic verbalism are those of: rendering the author's meaning indisputably precise yet simultaneously incomprehensible; demonstrating through superior orthography and lexical awareness that the writer is manifestly more erudite than the reader; disempowering intellectual challenge to the proponent's argument by using logomachinations to divert discussion to the establishment of the opponent's comprehension of the vocabulary as opposed to addressing the factual import of the treatise which, upon analysis, may well prove amphigorous. The obscurantist sesquipedalian is likely to compound the reader's difficulties by indulging in glossosynthesis, thus enabling the author to dismiss all opposing views as ultracrepidarious. In other words, a sesquipedalian is one who would call a spade a manuo-pedal excavationary implement would know the answer.

Brilliant........
Not all in the OED, but brilliant nevertheless.

 

[Little Bill]

Well anyone who is inordinately infatuated with polysyllabic obfuscation, preferring never to employ a less complicated syntactic arrangement of descriptive words when there exists a single expressive unit that amalgamates the multiplicity of morphemes comprising the simpler phrase. Among the manifold objectives of multisyllabic, holophrastic verbalism are those of: rendering the author's meaning indisputably precise yet simultaneously incomprehensible; demonstrating through superior orthography and lexical awareness that the writer is manifestly more erudite than the reader; disempowering intellectual challenge to the proponent's argument by using logomachinations to divert discussion to the establishment of the opponent's comprehension of the vocabulary as opposed to addressing the factual import of the treatise which, upon analysis, may well prove amphigorous. The obscurantist sesquipedalian is likely to compound the reader's difficulties by indulging in glossosynthesis, thus enabling the author to dismiss all opposing views as ultracrepidarious. In other words, a sesquipedalian is one who would call a spade a manuo-pedal excavationary implement would know the answer.

You've taken that "hooked on phonics" thing way too far!:blink:

 

[T.M.Haja Sahib]

No, I see your typical misdirection and evasion, but carry on.

What a rude remark.God only knows when you would stop being rude.

 

[T.M.Haja Sahib]

No misunderstanding on my part.
Did you miss this:
Minimum input power and maximum efficiency occur at a characteristic optimum slip value
Now, what do you think optimum slip value is?
Look back at #177.
Do you really think optimum slip is 0.3 pu?

I think the paper is about voltage optimisation, not speed control.
It's a feature that some variable frequency inverters have typically for cube law loads like fans and pumps. The V/f ratio gets reduced for lower speeds but it's for energy savings, not a method of speed control. I'm not sure how effective it is for energy saving. Reducing the voltage reduces stator current in the stable region and that may reduce stator losses some. It also increases the slip a little. That in turn increases rotor current. Which increases rotor losses and the increased current reflects back to the stator side. In short, each case needs to be looked on its merits. I have tried it on some fairly big VSDs with no convincing figures to demonstrate any savings.
That said, I do believe that voltage optimisation for fixed frequency applications can achieve energy savings. Your #151 example demonstrates that. It also clearly demonstrates that a large change in voltage does not equate to a significant speed difference. And, so far, I think that's only actual example you have presented.

But you did not comment on the IEEE paper stating that the efficiency is independent of output power............

 

[iwire]

What!You can't see my emphatic 'NO' in it ?!

No, I see your typical misdirection and evasion, but carry on.

What a rude remark.God only knows when you would stop being rude.

There was nothing at all rude in that remark, it was just an observation of fact.

And to this point you have still not provided a simple yes or no answer.

 

[T.M.Haja Sahib]

you see that at rated voltage and 0.7pu or 0.3pu slip the current is nearly 7.0pu which, in my experience is in line with expectations. This means that at half voltage you would get about 3 pu current.

Instead of determining within which slip (speed) range the motor current comes down to within full load current,you are stuck with the above statement.Please do not take it as a criticism but an invitation to do some computations.I am going to do anyway,but if you desire the honor of doing it,please do.Will you?

 

[T.M.Haja Sahib]

There was nothing at all rude in that remark, it was just an observation of fact.

What a ''nice'' way of your observing ''facts''.

 

[Besoeker]

But you did not comment on the IEEE paper stating that the efficiency is independent of output power............

And it does nothing to support you assertion made in post #188 and elsewhere:

that speed of the induction can be controlled over a wide range with that control method by reduction of applied voltage

Keeping the slip the same keeps the speed the same.
I should have thought that rather obvious.

 

[Besoeker]

Instead of determining within which slip (speed) range the motor current comes down to within full load current,you are stuck with the above statement.Please do not take it as a criticism but an invitation to do some computations.

You mean like this sort of thing?

I am going to do anyway,but if you desire the honor of doing it,please do.Will you?

I hope you make a better fist of it than you did the last time.

 

[T.M.Haja Sahib]

You mean like this sort of thing?

No.Please do not try to prove by depicting details of just one motor.I am afraid that you again misunderstood.I urged you to derive the slip ( speed) range within which the motor current falls to within full load current in the general case.

I hope you make a better fist of it than you did the last time.

I expected you as an 'expert' to give some useful suggestion.

 

[Besoeker]

No.Please do not try to prove by depicting details of just one motor.I am afraid that you again misunderstood.I urged you to derive the slip ( speed) range within which the motor current falls to within full load current in the general case.

There isn't a general case. The slip at full load current and torque will vary from one design to another. There is no "one size fits all".

I expected you as an 'expert' to give some useful suggestion.

I think I already gave you an explanation of why your previous calculation was wrong. If you don't care to accept that, fine.

 

[T.M.Haja Sahib]

And it does nothing to support you assertion made in post #188 and elsewhere:
''that speed of the induction can be controlled over a wide range with that control method by reduction of applied voltage''

But it does.I already told about 'Input=output+losses' in a motor.

In other words,

Input=output/Efficiency.......................................(1)

Here we know the output at the required slip.It is percentage of mechanical power requirement at rated load.We know the input is also given by Sq.RT(3)*VOLTAGE*CURRENT*POWER FACTOR i.e.,

Input=Sq.RT(3)*VOLTAGE*CURRENT*POWER FACTOR.................(2)

From (1) and (2),we have

CURRENT=Output/ Sq.RT(3)*VOLTAGE*POWER FACTOR*EFFICIENCY.........(3)

In equation (3) above,if power factor and efficiency are known,the motor current can be calculated with known output and voltage.The IEEE paper states that efficiency does not drop.Since the power factor is similar to efficiency curve and few points below it up to a mechanical power of 50% or so,you may agree with me that the motor current will not exceed full load current up to a load of 50% or so.Don't you?

 

[Besoeker]

But it does.I already told about 'Input=output+losses' in a motor.

In other words,

Input=output/Efficiency.......................................(1)

Here we know the output at the required slip.It is percentage of mechanical power requirement at rated load.We know the input is also given by Sq.RT(3)*VOLTAGE*CURRENT*POWER FACTOR i.e.,

Input=Sq.RT(3)*VOLTAGE*CURRENT*POWER FACTOR.................(2)

From (1) and (2),we have

CURRENT=Output/ Sq.RT(3)*VOLTAGE*POWER FACTOR*EFFICIENCY.........(3)

In equation (3) above,if power factor and efficiency are known,the motor current can be calculated with known output and voltage.The IEEE paper states that efficiency does not drop.Since the power factor is similar to efficiency curve and few points below it up to a mechanical power of 50% or so,you may agree with me that the motor current will not exceed full load current up to a load of 50% or so.Don't you?

I think all here are very familiar with the equations for power

This is about voltage optimisation which is an established method of energy saving and I wouldn't argue with that.
But, it in no way supports your assertion that speed of the induction can be controlled over a wide range with that control method by reduction of applied voltage.
At values of slip outside the normal operating range both PF and efficiency are greatly different from those in normal operation.
That's where this from your post #244 went wrong:

using values 264V,2200W and same efficiency and power factor values

I have already explained this in #319 and #321.