Reactive power --- confusing --- pls advise

In some textbooks, reactive power is said to be the power that is transferred back and forth between the source and the load. If the load is inductive, the load is said to be consuming reactive power from the source. If the load is capacitive, the load is said to be supplying reactive power to the source.

I'm confused as follows... Since reactive power is said to be transferred back and forth between the source and the load, why do we say that inductive load consumes reactive power and capactive load supplying reactive power? Pls advise.

this may clarify, have a look
**broken link removed**

ivar4ever said:

this may clarify, have a look
**broken link removed**

Click to expand...

Thanks for the link. However, it didn't explain how to determine the direction of the flow of reactive power. Pls advise.

Reactive power is the component of instantaneous power P(t)=v(t)*i(t) that have average value zero, this means that v(t) and i(t) have harmonics that aren't in phase (due to presence of reactive/storage elements at circuit), may be, pi/3, pi/4, -pi/6, pi,... All out of phase.

In RC circuit excited by a sinusoid source, in resistance v(t) and i(t) are in phase -No reactive power. but in capacitance v(t) and i(t) are out of phase by -pi/2, in time domain this mean that when v(t)=max i(t)=0 (remember V,I phasor with lag pi/2 between them), or that the maximum phase angle that the capacitance stores/devolve energy to line is pi/2. Then if mean value of energy stored in cap is zero, the number of storage times=number devolve (v(t) and i(t) different signals one >0 other <0) =2 in a cycle (excitation sinusoid source).


Don't forget push the helped button.

Thanks teteamigo... but your explanation still didn't cover how to determine the direction of reactive power flow at a point in a network. Pls advise. Thanks.

Added after 2 hours 30 minutes:

Many textbooks claimed that 'reactive power' represents the power that is first transferred from the source to the load, and then returned from the load to the source. Since 'reactive power' continually bounces back and forth between the source and the load, why we still use the terms like 'consumes' or 'supplies' reactive power? And why inductive 'consumes' and not 'supplies'? Pls advise.

Reactive loads such as inductors and capacitors dissipate ZERO power.
but as they drop voltage, and draw current gives the deceptive impression that they actually DO dissipate power.
This pseudo power is called as Reactive Power.
so in practice the power wont TRAVEL from the source to Reactive load.
but it might be explained so in the text books just to make students understand this pseudo concept!!
Reactive power is NOT the power consumed. it is hypothetical. (in this case)

there is another usage for the term "reactive power" , used in the power generation sector:
"Power provided and maintained for the explicit purpose of insuring continuous, steady voltage on transmission networks. Reactive power is energy which must be produced for maintenance of the system and is not produced for end-use consumption. Electric motors, electromagnetic generators and alternators used for creating alternating current are all components of the energy delivery chain which require reactive power. Losses incurred in transmission from heat and electromagnetic emissions are included in total reactive power. This power is supplied for many purposes by condensers, capacitors and similar devices which can react to changes in current flow by releasing energy to normalize the flow, and regulating generators may also have this capability."
Definition Source: **broken link removed**

hope this is clear, see **broken link removed** for a non-technical anology of real-reactive power. this is good to understand.

powersys said:

Thanks teteamigo... but your explanation still didn't cover how to determine the direction of reactive power flow at a point in a network. Pls advise. Thanks.

Added after 2 hours 30 minutes:

Click to expand...

Please...

Storage times-->Source supplies energy to reactance (cap, induct)
Devolve times-->Source receives energy from reactance.


Simple as that...

Storage times (v(t) and i(t) are both >0 or <0)

teteamigo said:

Storage times-->Source supplies energy to reactance (cap, induct)
Devolve times-->Source receives energy from reactance.

Simple as that...

Storage times (v(t) and i(t) are both >0 or <0)

Click to expand...

teteamigo, thanks for your reply. I got your points now:
1) Reactance (cap or ind) receives energy from source when both v(t) and i(t) are >0 or <0.
2) Reactance supplies energy to source when either v(t) or i(t) is <0.

As we discuss above, inductive load will receive energy from source at certain intervals, and supply energy back to source at other intervals. I don't understand why in many textbook, inductive load is said to 'consume' reactive power from source, and capacitive load is said to 'supply' reactive power to source... I thought inductive load or capacitive load consumes and supplies reactive power at different intervals of a cycle right? Pls advise.