Power factor correction experiment

[jumper]

Yes. The fault current.

I cannot remember, but the UK is 400Y/230?

Do electricians there have to contact the power company for typical house services for the available fault current for each install?

 

[Besoeker]

I cannot remember, but the UK is 400Y/230?

Yes, that's the normal arrangement for the LV supplies here. And it's 50 Hz.

Do electricians there have to contact the power company for typical house services for the available fault current for each install?

The wording in BS7671 ("The Regs") is:
The prospective fault current, under both short-circuit and earth fault conditions, at every relevant point of the complete installation shall be determined. This shall be done by calculation, ascertained by enquiry or by measurement.

 

[T.M.Haja Sahib]

That is what I call grasping at straws.

If you had placed your objections with calculations showing that voltage improvement effected by a capacitor connected across the terminals of a pump motor in a residence does not have any economical value,it would be very beneficial.

 

[T.M.Haja Sahib]

See post#22.
And I directed you to that in post#29.

The difficulty I had was you first depicted voltage wave to look like almost sine wave in your post #22 and later showed it to be distorted in post #25.What about the incoming voltage wave prior to connection of capacitor?

Ummm....

I wonder how many residential users actually know their fault level?

The waveforms I recorded are in numerical format. I can and did download that into a spreadsheet to display. Nice.
More importantly, I can use the numbers to perform calculations of instantaneous power, mean power, I_rms current, harmonics etc.
For the purposes of the study, I wasn't required to do so. No harmonic analysis was required despite your assertion to the contrary in post #28.

Back to resonance.
Any LC circuit will have a resonant frequency.
ωL = 1/(ωC) determines that frequency.
In order to close out your point on this, I did some further calculations.
I don't actually know the rating of our local 11kV/400V transformer but, having seen it physically (over the fence in a locked compound) I can make a reasonable guess. I can then assume an impedance of around 5% and calculate Z. That I can resolve into typical R and X_L components and calculate the inductance. I worked on the basis of 1500 kVA.
The resonant frequency with the capacitor worked out to be about 6.7 kHz - 19uH, 30uF.

Now, look at one cycle of the current:

The major components are power frequency related.
There are also higher frequency components. Take the period between 4ms and 6ms.
You can count maybe 13 or 14 cycles over that 2ms period.
So somewhere between 6.5 kHz and 7.0 kHz.
On that basis, the calculated 6.7 kHz seems a reasonable shot at it.
But why bother with the calculations when you have real time data?

It would have been far better if you had applied the formula discussed earlier,because your method is very crude as it did not take into account the system impedance upstream to the transformer.Anyway, to confirm whether resonance is actually taking place or not this question is also to be answered:
Does this harmonic current of frequency between 6.5 kHz and 7.0 kHz also present on the load side of the residence without the capacitor?

 

[kwired]

This what I was trying to say. This pretty typical for the US.

180.3 On initial services and reconnection after alterations to existing services, the Company will limit
the available fault current on single family detached homes (including mobile homes not in mobile home
parks) to 10,000 symmetrical amperes. This is provided the service size does not exceed 200 amperes.
For all other Customers, both on initial connection and reconnection of an existing service after
alterations, the Company will only notify the Customer of the available fault current.

http://www.dom.com/dominion-virginia-power/customer-service/for-businesses/pdf/bluebook.pdf

I don't know that is a common standard, but maybe just a practice of the company that made that statement. Other companies may have similar self imposed standard.

I think the size of transformer needed for typical 200 amp single phase service is small enough that available fault current is limited to start with. Sure you may have a larger transformer supplying several homes, but you also have the length of drops or laterals that decrease the available fault current by the time it hits the building. Unless you have a padmount transformer immediately adjacent to the structure served there is usually enough conductor to reduce the available fault current to less than 10000. Having the transformer right next to the building just does not happen that often on a single family dwelling.

 

[Besoeker]

The difficulty I had was you first depicted voltage wave to look like almost sine wave in your post #22 and later showed it to be distorted in post #25.

Same voltage, same data - just a different time scale.
From #25:
"First I look one cycle out of the five previously displayed"
I'm so sorry that you find it difficult.

What about the incoming voltage wave prior to connection of capacitor?

I did. And presented it.
Post #22:
"I took voltage and current without the magic device connected."

It would have been far better if you had applied the formula discussed earlier,because your method is very crude as it did not take into account the system impedance upstream to the transformer.

Yet, my crude method accords very well with the observations of what was actually happening.

Anyway, to confirm whether resonance is actually taking place

Ummm......
Post #55 clearly shows a resonance. I don't know why you question that. It's as plain as the nose on my face and twice as ugly.
But, for your benefit, I have extracted a portion of the waveform:

Seems like the 6.7kHz calculation for resonant frequency that you deemed crude is vindicated don't you think?

or not this question is also to be answered:
Does this harmonic current of frequency between 6.5 kHz and 7.0 kHz also present on the load side of the residence without the capacitor?

And, from my post, #29:
"Please don't confuse harmonics with resonance."

 

[USMC1302]

Once again, I'd like to thank Besoeker, Mivey, Gar, and indeed most all members who contribute, in the detailed explanation of these topics. I appreciate the patience and thoroughness in the manner in which you present your data. Thanks.

 

[jumper]

Once again, I'd like to thank Besoeker, Mivey, Gar, and indeed most all members who contribute, in the detailed explanation of these topics. I appreciate the patience and thoroughness in the manner in which you present your data. Thanks.

I agree. They are are pretty smart fellas.:thumbsup:

Although Besoeker spells some words funny. (jk Mr.B)

 

[T.M.Haja Sahib]

QUOTE=Besoeker;1349110]Same voltage, same data - just a different time scale.
From #25:
"First I look one cycle out of the five previously displayed"
I'm so sorry that you find it difficult.


I did. And presented it.
Post #22:
"I took voltage and current without the magic device connected."[/QUOTE]

Please represent the above incoming voltage wave to the same time scale you represented the voltage wave in post #25.I want to see how much distortion is introduced into the voltage wave due to connection of the capacitor.

Yet, my crude method accords very well with the observations of what was actually happening.


Ummm......
Post #55 clearly shows a resonance. I don't know why you question that. It's as plain as the nose on my face and twice as ugly.
But, for your benefit, I have extracted a portion of the waveform:

Seems like the 6.7kHz calculation for resonant frequency that you deemed crude is vindicated don't you think?

My reasoning is simple.If there were resonance between power supply and capacitor,the current component for which there is least impedance offered by capacitor would be magnified.The magnitude of current remains unaltered till circuit conditions change.But here current becomes minimum (in absolute value)at around 4.10kHz i.e parallel resonance is taking place and at around 6kHz,it is maximum (in absolute value) i.e series resonance is taking place.This could not take place unless circuit conditions change.More explanation of the phenomenon is required.

And, from my post, #29:
"Please don't confuse harmonics with resonance."

It is an established fact that a harmonic component of the load current can cause resonance between the shunt capacitor and power supply.

 

[T.M.Haja Sahib]

If you had placed your objections with calculations showing that voltage improvement effected by a capacitor connected across the terminals of a pump motor in a residence does not have any economical value,it would be very beneficial.

If h.p,power factor,and efficiency of the pump motor are known,it is possible to calculate the increased current X at reduced voltage without the capacitor and the reduced current Y at increased voltage with the capacitor across the terminals of the motor.Once the values X and Y are known,further calculations can be made to ascertain the saving that could be achieved.

 

[Besoeker]

Please represent the above incoming voltage wave to the same time scale you represented the voltage wave in post #25.

It is the SAME voltage.
"First I look one cycle out of the five previously displayed"
"Same voltage, same data - just a different time scale."
I don't how that can be made any plainer.

i.e parallel resonance is taking place and at around 6kHz,it is maximum (in absolute value) i.e series resonance is taking place.This could not take place unless circuit conditions change. More explanation of the phenomenon is required.

Resonant frequency is when:
ωL = 1/(ωC)
This is straightforward high school physics. What else is there to explain?

It is an established fact that a harmonic component of the load current can cause resonance between the shunt capacitor and power supply.

Harmonics and resonance are two different phenomena.

You seem to have lost sight of the facts that I do this sort of thing as part of my day job. I have provided a lot of real world data, information of the type I usually get paid to produce. You've got it for free.
So, how about you reciprocate a little by explaining what you have done/do that is related to the topic being discussed and maybe you could accompany that with some calculations and diagrams?
Reasonable request, don't you think?

 

[GeorgeB]

It is an established fact that a harmonic component of the load current can cause resonance between the shunt capacitor and power supply.

As rude as your responses are, I'm tempted to just ignore you, but this statement is just plain wrong. Resonance is a characteristic of an LC circuit. If an LC circuit is given a signal at its resonant frequency, certain (voltage or current peaks, magnitude and bandwidth of those mostly determined by something called "Q") observations can be made.

If I drive (mathematically easy although I've forgotten my circuit analysis from 40 years ago, physically more difficult) with a "unit function", limit of t>0, limit of e or i >infinity, product==1, the resonant frequencies of the circuit may be observed.

Even when you are right, you are not politely asking to learn, you are beating people down. I assume that English (Queen's for Besoeker, whatever you want to call it for we who escaped England and don't know how to talk<g> for most of us) is not your first language, and some of that lack of tact is understood, but you REALLY should have another person help you with understanding being polite in a public forum.

Besoeker HAS DONE these things; he has used theory to explain real-world observations. Learn from him. Ask questions when you don't understand. I don't believe you will find anyone here who is not willing to help another; we wouldn't be here otherwise. It is not good form to tell someone that something they report is wrong without furnishing the correct information. That is what you continue doing.

 

[Besoeker]

As rude as your responses are, I'm tempted to just ignore you, but this statement is just plain wrong. Resonance is a characteristic of an LC circuit. If an LC circuit is given a signal at its resonant frequency, certain (voltage or current peaks, magnitude and bandwidth of those mostly determined by something called "Q") observations can be made.

If I drive (mathematically easy although I've forgotten my circuit analysis from 40 years ago, physically more difficult) with a "unit function", limit of t>0, limit of e or i >infinity, product==1, the resonant frequencies of the circuit may be observed.

Even when you are right, you are not politely asking to learn, you are beating people down. I assume that English (Queen's for Besoeker, whatever you want to call it for we who escaped England and don't know how to talk<g> for most of us) is not your first language, and some of that lack of tact is understood, but you REALLY should have another person help you with understanding being polite in a public forum.

Besoeker HAS DONE these things; he has used theory to explain real-world observations. Learn from him. Ask questions when you don't understand. I don't believe you will find anyone here who is not willing to help another; we wouldn't be here otherwise. It is not good form to tell someone that something they report is wrong without furnishing the correct information. That is what you continue doing.

George
Thank you for that.

 

[T.M.Haja Sahib]

As rude as your responses are, I'm tempted to just ignore you, but this statement is just plain wrong. Resonance is a characteristic of an LC circuit. If an LC circuit is given a signal at its resonant frequency, certain (voltage or current peaks, magnitude and bandwidth of those mostly determined by something called "Q") observations can be made.

If I drive (mathematically easy although I've forgotten my circuit analysis from 40 years ago, physically more difficult) with a "unit function", limit of t>0, limit of e or i >infinity, product==1, the resonant frequencies of the circuit may be observed.

Even when you are right, you are not politely asking to learn, you are beating people down. I assume that English (Queen's for Besoeker, whatever you want to call it for we who escaped England and don't know how to talk<g> for most of us) is not your first language, and some of that lack of tact is understood, but you REALLY should have another person help you with understanding being polite in a public forum.

Besoeker HAS DONE these things; he has used theory to explain real-world observations. Learn from him. Ask questions when you don't understand. I don't believe you will find anyone here who is not willing to help another; we wouldn't be here otherwise. It is not good form to tell someone that something they report is wrong without furnishing the correct information. That is what you continue doing.

I am trying to get a consistent picture. Please refer to the first reply at post #71.The implication is that there is no voltage distortion caused by capacitor,although it takes distorted current.But once in resonance,it is bound to cause voltage distortion.But Besoeker is telling it is the SAME voltage.What kind of consistent picture can one get under this circumstance?
I rarely let my emotions take over my reason when posting replies to purely engineering subjects and hope others will do the same.

 

[T.M.Haja Sahib]

but this statement is just plain wrong. Resonance is a characteristic of an LC circuit. If an LC circuit is given a signal at its resonant frequency, certain (voltage or current peaks, magnitude and bandwidth of those mostly determined by something called "Q") observations can be made.

I want to submit that the fallacy of your assertion stems from your mistaken assumption that an LC parallel or series circuit can have only one resonant frequency.Wrong,my friend,quiet wrong.You would be correct if that circuit is excited by purely sinusoidal voltage.But if the same is excited by a voltage consisting of harmonics,resonance can occur at a different frequency.

 

[T.M.Haja Sahib]

It is the SAME voltage.
"First I look one cycle out of the five previously displayed"
"Same voltage, same data - just a different time scale."
I don't how that can be made any plainer.

Please refer to post #74

Harmonics and resonance are two different phenomena.

Please refer to post #75

how about you reciprocate a little by explaining what you have done/do that is related to the topic being discussed and maybe you could accompany that with some calculations and diagrams?
Reasonable request, don't you think?

Only recently power quality issues are gaining momentum in India.I am in charge of Electromechanical services in telephone exchanges for which we are planning to conduct power quality study.Once it is completed,I shall submit the results.

 

[iwire]

I want to submit that the fallacy of your assertion stems from your mistaken assumption that an LC parallel or series circuit can have only one resonant frequency.Wrong,my friend,quiet wrong.You would be correct if that circuit is excited by purely sinusoidal voltage.But if the same is excited by a voltage consisting of harmonics,resonance can occur at a different frequency.

Please refer to post #74





Please refer to post #75

How about this, how about instead of just expecting us to take your word that you are correct that you actually prove you are correct with some independent source?

Members continue to provide you with very detailed info yet you provide nothing.

 

[T.M.Haja Sahib]

How about this, how about instead of just expecting us to take your word that you are correct that you actually prove you are correct with some independent source?

Members continue to provide you with very detailed info yet you provide nothing.

I shall provide independent source but in the mean time tell me why you got the impression I provide nothing?

 

[T.M.Haja Sahib]

Members continue to provide you with very detailed info

I have great fascination for these electrical veterans and I feel invigorated by reading their views in their(my) field.

 

[T.M.Haja Sahib]

How about this, how about instead of just expecting us to take your word that you are correct that you actually prove you are correct with some independent source?

Members continue to provide you with very detailed info yet you provide nothing.

Here is a reliable source:
http://ecmweb.com/powerquality/electric_power_factor_correction_3/
What more is required?