Confusing with this text... Pls help - Electronic Circuits Projects Diagrams Free

powersys · 10th January 2006, 06:39 AM

We know that:

Lagging power factor means that current lags voltage, implying an inductive load.
Leading power factor means that current leads voltage, implying a capacitive load.

An inductive load is represented by R + jX
An capacitive load is represented by R - jX

The attached text was copied from a textbook. Do you think there are mistakes in the text and figures?

For example:

... line-5 of paragraph P1
For a load of capacitor VAr is produced and considered negative or lagging as in Figure 3.10.

... line-2 of paragraph P2
A capacitive load on the other hand will be represented by R-jX as shown in Figure 3.12 and hence produces lagging VArs.

Pls check if there are other mistakes.

Please advise. I'm confused now....

Thanks

Russlk · 11th January 2006, 02:58 AM

You need to find a better text book. This one is very confusing and the author's invention of VAr is bullshit, in my opinion. What you need to know is that the current in an inductive circuit lags because the magnetic field of the inductor produces a back emf which reduces the effective applied voltage as the voltage increases. When the voltage decreases, the magnetic field collapses which induces an emf that keeps the current flowing.

With capacitive load, the current flow into or out of the capacitor is proportional to the rate of change of voltage. Since the rate of change (for a sinewave) is maximum at zero volts, the current is maximum and 90 degrees leading.

Power factor is just another way of stating the phase angle.

I hope this helps your understanding.

powersys · 11th January 2006, 03:05 AM

I agree with you that the VAr given in the text book is very confusing. Would u pls help me in the following threads:
http://www.electro-tech-online.com/v...ic.php?t=19820
http://www.electro-tech-online.com/v...ic.php?t=19819

Thanks.

Quote:

Originally Posted by Russlk

You need to find a better text book. This one is very confusing and the author's invention of VAr is bullshit, in my opinion. What you need to know is that the current in an inductive circuit lags because the magnetic field of the inductor produces a back emf which reduces the effective applied voltage as the voltage increases. When the voltage decreases, the magnetic field collapses which induces an emf that keeps the current flowing.

With capacitive load, the current flow into or out of the capacitor is proportional to the rate of change of voltage. Since the rate of change (for a sinewave) is maximum at zero volts, the current is maximum and 90 degrees leading.

Power factor is just another way of stating the phase angle.

I hope this helps your understanding.

tj107us · 11th January 2006, 03:25 AM

You need to find a better text book. This one is very confusing and the author's invention of VAr is bullshit, in my opinion. What you need to know is that the current in an inductive circuit lags because the magnetic field of the inductor produces a back emf which reduces the effective applied voltage as the voltage increases. When the voltage decreases, the magnetic field collapses which induces an emf that keeps the current flowing.

Whats do emf stand for

Russlk · 11th January 2006, 04:25 AM

emf stands for ElectroMotive Force = Voltage. I use emf when it is an induced voltage as apposed to an applied voltage.

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10th January 2006, 06:39 AM	(permalink)
powersys	Confusing with this text... Pls help We know that: Lagging power factor means that current lags voltage, implying an inductive load. Leading power factor means that current leads voltage, implying a capacitive load. An inductive load is represented by R + jX An capacitive load is represented by R - jX The attached text was copied from a textbook. Do you think there are mistakes in the text and figures? For example: ... line-5 of paragraph P1 For a load of capacitor VAr is produced and considered negative or lagging as in Figure 3.10. ... line-2 of paragraph P2 A capacitive load on the other hand will be represented by R-jX as shown in Figure 3.12 and hence produces lagging VArs. Pls check if there are other mistakes. Please advise. I'm confused now.... Thanks

11th January 2006, 02:58 AM	(permalink)
Russlk	You need to find a better text book. This one is very confusing and the author's invention of VAr is bullshit, in my opinion. What you need to know is that the current in an inductive circuit lags because the magnetic field of the inductor produces a back emf which reduces the effective applied voltage as the voltage increases. When the voltage decreases, the magnetic field collapses which induces an emf that keeps the current flowing. With capacitive load, the current flow into or out of the capacitor is proportional to the rate of change of voltage. Since the rate of change (for a sinewave) is maximum at zero volts, the current is maximum and 90 degrees leading. Power factor is just another way of stating the phase angle. I hope this helps your understanding. __________________ see my website: www.geocities.com/russlk

11th January 2006, 03:25 AM	(permalink)
tj107us	You need to find a better text book. This one is very confusing and the author's invention of VAr is bullshit, in my opinion. What you need to know is that the current in an inductive circuit lags because the magnetic field of the inductor produces a back emf which reduces the effective applied voltage as the voltage increases. When the voltage decreases, the magnetic field collapses which induces an emf that keeps the current flowing. Whats do emf stand for

11th January 2006, 04:25 AM	(permalink)
Russlk	emf stands for ElectroMotive Force = Voltage. I use emf when it is an induced voltage as apposed to an applied voltage. __________________ see my website: www.geocities.com/russlk