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#128632 - 08/08/03 12:34 AM Reactive power/Energy?  
PowerMonitor  Offline
Junior Member
Joined: Aug 2003
Posts: 2
Gandhinagar,Gujarat,India
What meaning of reactive power in electrical system?and how it creating and where it goes?
please explain me inductive load and capacitive load properties which creates reactive energy.
Thanks.


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#128633 - 08/09/03 01:27 AM Re: Reactive power/Energy?  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
To answer PowerMonitor's post: (or at least try to...)

Quote
What's the meaning of reactive power in electrical system?


Reactive Power is the "Other" power flowing within the complete Apparent Power figure.

True Power (Wattage) + Reactive Power (Volt-Amps Reactive, or VARs) = Apparent Power (Volt-Amps, or VA).

The AC Power can be figured by applying the Pythagorean Theorem, created by the Triangle dude, Pythagoras [Linked Image]

This is a simple formula, which is:

A²+ B² = C²

If you have values for any 2 of the 3 sides, this calc will give value for the unknown side.

Looking at the AC power triangle per function, here's the breakdown:

SIN: True Power (Wattage),
COS: Reactive Power (VARs or KVARs if 1000 or more),
TAN: Apparent Power (VA or KVA if 1000 or more).

The Power Factor is the relationship between the True Power and the Apparent Power.

For a simple example, let's say the power figures are:

True Power (SIN) = 4 Watts,
Reactive Power (COS) = 3 VARs,

This would result in an Apparent Power of 5 VA, which equals out to be an 80% Power Factor.

Here's how it was done:

C² (TAN) = A² (SIN) + B² (COS)

4² = 16 (A),
3² = 9 (B)
16 + 9 = 25 (C)

Square Root of 25 = 5, so C (TAN) = 5

Power Factor was figured by getting the percentage between True Power and Apparent Power.

4 (watts) is 0.8 - or 80% of 5 (VA), so the Power Factor in this example is 80%

Quote
and how it creating and where it goes?


This may sound funny, but VARs are created by the Reactive Elements themselves, when an AC is applied to them.
VARs shuttle between the Reactive Elements of an AC Circuit - and are stored within them.

A simple example using a single core, single layer Inductor (coil) and a step down Transformer would show the Reactive Power stored in the Inductor, with Reactive Currents "Shuttling" between the Transformer and the Inductor.

Quote
please explain to me inductive load and capacitive load properties which creates reactive energy.


This is a little beyond simple examples and descriptions - especially using only text! Here, you're best options are to read a few Tech Manuals in order to get the basic ideas of all the principles and such.

In a nutshell, one has an effect on the AC wave, which causes the Current to LAG behind the Voltage, at a certain degree.
This one would be - of course - Inductive Reactance (XL).
The other Reactance effects the AC wave so the Current LEADS the Voltage, at a certain degree.
This one would be - of course - Capacitive Reactance (XC).

The thing about Reactances is they cancel each other out (generally speaking), so to combat an excessive LAGGING (XL) problem, XC is added to the circuit. The same goes for the opposite.

When figuring a Circuit's Impedance (Z), the total Reactance (X) will be a result of subtracting the lower Reactance from the Higher Reactance.
Example:

XL = 10 Ohms, XC = 8 Ohms.
Total X = 2 Ohms (Inductive)
Z = total Reactance, so Z = 2 Ohms

When applying a fixed pure Resistance (R) into the total Z figure, use the Pythagorean Theorem once again. In this case, figure the total Reactance before running the calc.
Example:

R = 4 Ohms,
XL = 9 Ohms,
XC = 6 Ohms.

<OL TYPE=1>

[*]Find total X: 9 - 6 = 3 Ohms.

[*]R² = 16, X² = 9.

[*]R² + X² = 25

[*]Square Root of 25 = 5
</OL>

Circuit's Impedance (Z) = 5 Ohms.

p.s. see any kind of a relationship here??? [Linked Image]

Applying Inductive and Resistive elements in a series circuit across different types of power supplies will result in different readings.

Example:

3 Ohm Inductor + 4 Ohm Resistor in series;

Connected to DC power supply: Total = 7 Ohms.
Connected to AC power supply: Total = 5 Ohms.

Quote
Thanks.


No problem!
Just hope this stuff answers your questions!

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128634 - 08/09/03 09:19 AM Re: Reactive power/Energy?  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
That’s a good, concise overview, Scott. Supporting text may be something like www.ibiblio.org/obp/electricCircuits/AC/AC_11.html, but it’s written from a college-freshman-lecture-with-300-other-students perspective. {Be very careful about relying solely on slasher-grade capsulized web-based technical material.}

Bench testing various meter forms will reinforce these concepts and better tie them to real-world equipment and measurements that energy and demand metering make.

[Fair warning, though—when nonsinusoidal waveforms are introduced, it a while new ball game with a more complex set of definitions.] The EEI handbook is a root reference.




[This message has been edited by Bjarney (edited 08-09-2003).]


#128635 - 08/11/03 04:18 AM Re: Reactive power/Energy?  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Bjarney,

Thanks for the reply.

Hope the info I presented in this thread is useable! The topic(s) are kind of advanced, and my responses are kind of ... basic!

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!


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