Previous in Forum: Mech to Elec & Vice Versa   Next in Forum: 2-Phase 415V Load Using 3-Phase Transformer (Dyn11)
Close
Close
Close
21 comments
Rate Comments: Nested
Anonymous Poster #1

Imaginary Current

07/10/2013 6:21 PM

Is it possible to measure an imaginary current in an inductive circuit containing for example a 3 Phase induction Motor, and how?

Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Guru

Join Date: Oct 2008
Posts: 42355
Good Answers: 1693
#1

Re: Imaginary Current

07/10/2013 6:25 PM

I imagine there is.

Maybe an imaginary current meter?

Reply
Guru

Join Date: Jul 2006
Location: CA (Central Arkansas, USA)
Posts: 599
Good Answers: 10
#16
In reply to #1

Re: Imaginary Current

07/12/2013 4:56 PM

Use digital meter. Remove battery. Imagine any reading you like! -- JHF

__________________
If it's too good to be true, it probably isn't
Reply
Anonymous Poster #2
#18
In reply to #1

Re: Imaginary Current

07/19/2013 2:44 PM

An imaginary "imaginary current meter".

Reply
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#19
In reply to #18

Re: Imaginary Current

07/19/2013 2:58 PM

I think you are only imagining that such a thing exists in you imagination.

__________________
Think big. Drive small.
Reply
Anonymous Poster #2
#20
In reply to #19

Re: Imaginary Current

07/19/2013 3:05 PM

I have an image in my mind where I imagine the existence of imagining an imaginary current meter in my imagination

Reply
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#21
In reply to #20

Re: Imaginary Current

07/20/2013 3:34 PM

Incredible coincidence! I was just imagining you with that image in your mind! Imagine that!

__________________
Think big. Drive small.
Reply Off Topic (Score 5)
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#3

Re: Imaginary Current

07/10/2013 8:08 PM

Without definite facts it's hard to imagine the answer.

__________________
The reports of my death are greatly exaggerated.
Reply Score 1 for Good Answer
Guru

Join Date: Feb 2011
Posts: 7025
Good Answers: 207
#4

Re: Imaginary Current

07/10/2013 8:40 PM

Take another hit, anything is possible

Reply
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#5

Re: Imaginary Current

07/10/2013 8:50 PM

I suppose, indirectly. Measure the resistance. Measure the wattage consumed. From that calculate the reactance. Then reactance x V = imaginary current.

Z= R+jX

V= IZ

therefore V= I (R+jX)

__________________
Think big. Drive small.
Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33392
Good Answers: 1817
#6

Re: Imaginary Current

07/11/2013 12:54 AM

"in an AC waveform in which the voltage and current are in phase then you are referring to a resistive load and all the energy is being converted to heat. whereas most of the loads are inductive in nature and hence the voltage will lead the current and the cos of the angle between them is called the power factor. the load now has a resistive and an inductive component. the resistive component creates heat which treated as the real part and the inductor pushes back the energy that was stored in the inductor and hence did not contribute to the heat generation. this is the imaginary part."

I = x + yi

http://en.wikipedia.org/wiki/Complex_number

http://answers.yahoo.com/question/index?qid=20100519004314AA1Xe4r

__________________
All living things seek to control their own destiny....this is the purpose of life
Reply Score 1 for Good Answer
Commentator

Join Date: Apr 2011
Posts: 57
#7
In reply to #6

Re: Imaginary Current

07/11/2013 6:17 AM

Good answers indeed, but would ampere meter readings (digital or analogue) include the imiginary component of the current?

Reply
5
Power-User
Engineering Fields - Instrumentation Engineering - New Member Engineering Fields - Control Engineering - New Member Technical Fields - Technical Writing - New Member Technical Fields - Education - New Member Fans of Old Computers - Apple II -

Join Date: Sep 2011
Location: Bellingham, WA
Posts: 191
Good Answers: 46
#8
In reply to #7

Re: Imaginary Current

07/11/2013 8:15 AM

A current measurement given by an analog or digital ammeter will show the "apparent" current in the circuit. Multiplying this value by the cosine of the phase shift angle (between voltage and current waveforms) will give you the "real" or "true" circuit current, while multiplying the apparent current by the sine of the phase shift angle will give you the "reactive" or "imaginary" circuit current.

In other words, you will need to use an oscilloscope to measure the voltage/current phase shift angle, then do some trigonometric calculations to convert the ammeter's current value into your desired imaginary current value.

__________________
They call me "lightning" when wielding a hammer, because I never strike twice in the same place
Reply Good Answer (Score 5)
3
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#9
In reply to #7

Re: Imaginary Current

07/11/2013 11:51 AM

In practice, this is easy. A Kill-a-Watt meter will show either VA or watts, power factor, etc, so getting the imaginary part is a simple matter of subtraction.

__________________
Think big. Drive small.
Reply Good Answer (Score 3)
Guru

Join Date: Oct 2008
Posts: 42355
Good Answers: 1693
#10
In reply to #9

Re: Imaginary Current

07/11/2013 1:08 PM

Kill-a-Watt meters are great toys tools.

Seriously, I use mine a lot. (My wife thinks I'm crazy)

Reply
Guru

Join Date: Dec 2010
Location: North West England
Posts: 1170
Good Answers: 153
#11
In reply to #10

Re: Imaginary Current

07/12/2013 2:50 AM

Yes but does she think you're crazy because you use a Kilowatt hour meter or are there other factors that you are not willing to share?

Reply
Power-User

Join Date: Jan 2009
Posts: 250
Good Answers: 7
#12

Re: Imaginary Current

07/12/2013 7:51 AM

It's not an imaginary current, it's an inductive one. The AC current thru an inductive load is a real current (it will heat feeding conductors and can be measured) associated with a complex number (a real + an imaginary number) by means of a model.

Reply
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9910
Good Answers: 1141
#13

Re: Imaginary Current

07/12/2013 7:57 AM

It's not really imaginary, it's the component of current that is 90 degrees out of phase with the voltage. An ammeter will measure the total current regardless of phase. It's called imaginary because electrical engineers use complex numbers (real + imaginary) to do calculations.

Reply Score 1 for Good Answer
Power-User

Join Date: Dec 2008
Location: Anthem, AZ
Posts: 392
Good Answers: 8
#14

Re: Imaginary Current

07/12/2013 10:41 AM

Use a current probe to feed a signal to any Dynamic Signal Analyzer, compute the average FFT. The Imaginary function is the reactive component. Be sure to calibrate the magnitude (across a resistor) to be sure, because some FFT magnitudes do not compensate for the magnitude of the negative frequencies.

Reply
Power-User

Join Date: May 2013
Posts: 351
Good Answers: 22
#15
In reply to #14

Re: Imaginary Current

07/12/2013 11:25 AM

It is not only possible but relatively easy to measure the reactive VAR (imaginary) current or power. Meters are made for that, but the easiest way is to measure the watts (real power), current, and voltage. It is to get the total VA (but don't forget the square root of 3) Figure out the cosine to get the watts and the sine to get the VAR.

As a sidenote: It is possible on a good AC drive to regulate the VAR input and the WATT input separately so that the speed, horsepower, and torque can be separately regulated as is done with DC drive. What is interesting is to observe a motor that can put out more starting torque than the same motor started across the line while never exceeding rated amps.

Reply
Power-User

Join Date: Jan 2010
Location: Dayton Ohio
Posts: 265
Good Answers: 10
#17

Re: Imaginary Current

07/17/2013 3:00 PM

Yes it is measured directly with a Gnome meter

__________________
MikeMack747
Reply
Reply to Forum Thread 21 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

4wsilver (1); Anonymous Poster (2); Candlez (1); Circuit Breaker (1); Fredski (1); jhhassociates (1); K_Fry (4); lyn (3); MikeMack747 (1); Rixter (1); Snel (1); SolarEagle (1); tonykuphaldt (1); TonyS (1); WoodwardDL (1)

Previous in Forum: Mech to Elec & Vice Versa   Next in Forum: 2-Phase 415V Load Using 3-Phase Transformer (Dyn11)

Advertisement