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 The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

#1
03-11-2008, 06:03 AM
 fancy102 Junior Member Join Date: Dec 2007 Posts: 26

hi..i am carrying out power factor measurement system and i need to know the power quality.

my problem is how can i know the current is leading the voltage or lagging the voltage?i can know it through ossiloscope only?still got any other way to know current leading or lagging voltage?thanks
#2
03-11-2008, 02:06 PM
 thingmaker3 Super Moderator Join Date: May 2005 Location: Rural, Oregon GMT -8 Posts: 5,072 Blog Entries: 6

"ELI the ICE man." Current lags voltage in an inductive circuit. Current leads voltage in a capacitive circuit.
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#3
03-11-2008, 04:32 PM
 mrmount Member Join Date: Dec 2007 Posts: 59

You can use power factor meter if you want!
#4
03-12-2008, 12:19 AM
 fancy102 Junior Member Join Date: Dec 2007 Posts: 26

I am doing the power factor metre...so i would like to show the lagging or leading to the user...so except ossilocope i cant know leading or lagging through calculation?
#5
03-12-2008, 01:47 AM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

Quote:
 Originally Posted by fancy102 hi..i am carrying out power factor measurement system and i need to know the power quality. my problem is how can i know the current is leading the voltage or lagging the voltage?i can know it through ossiloscope only?still got any other way to know current leading or lagging voltage?thanks
You can connect a very low resistor (lets say 1 ohm or less, take care it can handle the power dissipation ) in series with the load. Then monitor the voltage across the resistor with an amplifier which drives a led. Also monitor the voltage across your load with an amplifier too or if it does not need amplification use a buffer which again will drive a led. Note that both the amplifier and buffer must have high input impedance.

Then with this method you will see which led goes to full illumination first.
If the led from the resistor goes bright first it means that you have a capacitive load and the power factor is leading
if the led from the load goes on first it means you have an inductive load and the power factor is lagging.

Note: make the appropriate connections to the buffer and dont connect it directly to the load if it high voltage.
#6
03-13-2008, 11:51 PM
 fancy102 Junior Member Join Date: Dec 2007 Posts: 26

u mean connect a LED series to the load? then the other one connect to the ouput of the comparator(current)?

why do i need buffer??sorry for the poor knowledge...thanks
#7
03-14-2008, 12:09 AM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

Quote:
 Originally Posted by fancy102 u mean connect a LED series to the load? then the other one connect to the ouput of the comparator(current)? why do i need buffer??sorry for the poor knowledge...thanks
why do you need to know this about the power factor?
#8
03-14-2008, 02:12 AM
 fancy102 Junior Member Join Date: Dec 2007 Posts: 26

because i am carrying out power factor measurement system. i need to know the power factor of the system and current is leading or lagging...
#9
03-15-2008, 11:46 PM
 fancy102 Junior Member Join Date: Dec 2007 Posts: 26

sorry to ask again...the phase angle of the power factor should not more than 90 degrees no matter what is the load?is this correct?

if it is capacitive than should negative phase angle and if inductive than should be positive phase angle?is the concept correct??

thanks a lot!!
#10
01-07-2010, 08:56 AM
 hitmen Senior Member Join Date: Sep 2008 Posts: 156

sorry to ask again...the phase angle of the power factor should not more than 90 degrees no matter what is the load?is this correct? (Not sure never encountered before)

if it is capacitive than should negative phase angle and if inductive than should be positive phase angle?is the concept correct?? (yes)

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