Apparent Power

Thread Starter

biferi

Joined Apr 14, 2017
203
In A.C. I know this.

Volts X Amps = Watts.
Watts is Real Power and can do work.
Real Power is when Current and Voltage are in Phase and get to the same place at the same Time.

V.A.R is Volt Amp Reactance.
V.A.R is a Wattless Watt and can do no work.
V.A.R is when Current and Voltage are Out of Phase and get to the same place but not at the same Time.

Please Tell me if I have all of that Right?

Now I have a Formula for Apparent Power.
Apparent Power is Real Power Plus V.A.R Squared = V/A.

If V/A is V.A.R then how is this Apparent Power?
Or is Apparent Power the Measure of a Wattles Watt in a Reactive Circuit?
 

drc_567

Joined Dec 29, 2008
1,156
... The way to make sense of this is to place the relevant quantities in a right triangle.
... Something like this:
1626719413801.png
The real power is the vector on the horizontal axis, and is the actual watts.
The apparent power, VI, is the hypotenuse, and may be understood as that quantity which is applied to a device or appliance consisting of either real or reactive components. ... For example a power cord going to any kind of motor or electrical heater. The vertical leg on the right side is a vector representing the reactive power, in units of VAR ... volts-amps reactive.
 

crutschow

Joined Mar 14, 2008
28,226
Another way to look at it is that the real power at any instant in time is the volts at that instance times the current at that instance.
The integrated average of those over a complete cycle is the average power.
 

Dodgydave

Joined Jun 22, 2012
10,095
Here is a simple drawing explaining how it effects your electricity bill..the nearer to 1 20210719_220231.jpg( smallest angle) for a Power Factor the better, .

Cosine of the angle is the power factor.
 

Thread Starter

biferi

Joined Apr 14, 2017
203
Ok I think I should Tell you what I know then you can Tell me what I do not Understand.

There is 3. Types of Power
Real Power
Reactive Power
Apparent Power.

Now Real Power is if Current and Voltage are in an all Resistive Circuit like a Hair Dryer.
And Real Power can do work and is Watts.

Reactive Power is if Current and Voltage are in an all Reactive Circuit like something that has a Capacitor and an Inductor Coil.
The Capacitor will get the Current then the Voltage and the Inductor Coil will get the Voltage then the Current.
So this Circuit has all Reactive Power and can do no work and is called V.A.R and this is Volt Amp Reactance.

Just Tell me if I have this Right do not Tell me anything more thanks?
 

Dodgydave

Joined Jun 22, 2012
10,095
Sort of, the Current and Voltage are in phase in a resistive circuit, thus no wastage, but in a Capacitor or Inductor circuit the voltage and current are out of phase with each other by a few degrees depending on the total reactance , and this is the Reactive power which doesn't give any useful energy. "The more Reactive power the more wasted energy and lower power factor.." this Reactive power can be Leading or Lagging depending if the loads are Inductive or Capacitive.

This is ok in domestic situations, but in commercial industry you are penalised for having a low power factor.

You forgot that the hairdryer has a motor inside, thus this is an Inductor and will have slight reactance.

There is a Mnemonic to remember which leads or lags voltage or current,

CIVIL
Capacitor Current leads Voltage,
Inductor Voltage leads Current.
 
Last edited:

crutschow

Joined Mar 14, 2008
28,226
The more Reactive power the more wasted energy
I think "wasted energy" is not a good term for reactive power as it would seem to imply it is somehow real power being wasted in the reactive circuit, and that is not the case.
The only loss is due to power line resistance loses from the reactive current flowing in the wires from the generator to the circuit, which is only indirectly related to the reactive power.
 
You can make a reactive power supply to power a LED if you wanted too.

Reactive power is bad for the utility. Solar farms that use inverters can to local power factor correction.
 

MrChips

Joined Oct 2, 2009
24,650
This is how I understand it. Please correct me if I am wrong.

The electric utility measures real power in kWh and bills you for it.
For residential users that is what you pay.

For commercial and industrial users the power factor often falls below 100%.
For these users the utility has to apply a surcharge in order to compensate for the extra demand.
In other words, consuming power at P.F. lower than 100% is putting extra demand on the supply.
 

Thread Starter

biferi

Joined Apr 14, 2017
203
Ok thanks now I understand Real Power and Reactive Power.

So is Apparent Power when Real Power and Reactive Power are in a Circuit?
And they have to put the Current and Voltage back in Phase?
 

nsaspook

Joined Aug 27, 2009
8,911
Ok thanks now I understand Real Power and Reactive Power.

So is Apparent Power when Real Power and Reactive Power are in a Circuit?
And they have to put the Current and Voltage back in Phase?
Let's repeat what's already been said in this thread.

https://whatis.techtarget.com/definition/apparent-power
In an AC circuit, the product of the rms voltage and the rms current is called apparent power. When the impedance is a pure resistance, the apparent power is the same as the true power. But when reactance exists, the apparent power is greater than the true power. The vector difference between the apparent and true power is called reactive power.
A typical industrial facility will have lots of electrical motors for fans, pumps, etc ... Reactive power is required for the magnetization of an electric motor but does not perform any work. These inductive loads increases the amount of apparent power normally expressed as a Power Factor for ease of calculation.
power_factor.png
A industrial plant draws 200 A at 400 V and the supply transformer and backup UPS is rated 400 V x 200 A = 80 kVA.

If the power factor - PF - of the loads is 0.7 - only

80 kVA × 0.7
= 56 kW
of real power is consumed by the system. If the power factor is close to 1 (a purely resistive circuit) the supply system with transformers, cables, switch-gear and UPS could be made considerably smaller.

  • Any power factor less than 1 means that the circuit's wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load.
https://www.engineeringtoolbox.com/power-factor-electrical-motor-d_654.html
Benefits of Power Factor Corrections
  • reduced power bills - avoiding low power factor penalty from the utility power company
  • increased system capacity - additional loads can be added without overloading the system
  • improved system operating characteristics by reduced line loss - due to less current
  • improved system operating characteristics by gaining voltage - excessive voltage drops are avoided
 

Ian0

Joined Aug 7, 2020
3,784
You can make a reactive power supply to power a LED if you wanted too.

Reactive power is bad for the utility. Solar farms that use inverters can to local power factor correction.
Reactive power supplies for LEDs are generally capacitive with leading power factor.
Reactive power in industry is generally inductive (usually motors) with lagging power factor.
One cancels the other out, so the power companies should thank people for installing "capacitive dropper" LED circuits.
 

Thread Starter

biferi

Joined Apr 14, 2017
203
I am in the USA so my House Voltage is 120 Volts.
So when I take my VoltMeter to my Wall Outlet and it Reads 120 Volts this is the RMS Voltage.

Now if I Plug a Fan in this is an Inductor and will have some Loss of Energy.

This Loss is Reactive and is V/A witch is a Wattless Watt.

Do I have this Right?
 

Thread Starter

biferi

Joined Apr 14, 2017
203
A Toaster Oven would be a Resistive Circuit and this will be Real Power.
Real Power can do work and is in Watts.

Right?
 

Thread Starter

biferi

Joined Apr 14, 2017
203
I found this on Google Real Power Plus Reactive Power is call Apparent Power.

And Apparent Power is Volt Amps or V/A.
But Reactive Power is V/A.

What am I not Understanding?









Image result for is apparent power when reactive and real power are together
https://www.google.com/search?q=is+apparent+power+when+reactive+and+real+power+are+together&tbm=isch&source=iu&ictx=1&fir=s1sngcygSTcQTM%2C8r6hROgQjww15M%2C_&vet=1&usg=AI4_-kSWTumTJgjrqgb3AyUVe2ukp83IQw&sa=X&ved=2ahUKEwjV2u_BgrLyAhWFTN8KHdLzBIAQ_h16BAgUEAE#imgrc=s1sngcygSTcQTM
Image result for is apparent power when reactive and real power are together
Image result for is apparent power when reactive and real power are together
View all



The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current, without reference to phase angle. Apparent power is measured in the unit of Volt-Amps (VA)
 

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BillB3857

Joined Feb 28, 2009
2,549
Sort of, the Current and Voltage are in phase in a resistive circuit, thus no wastage, but in a Capacitor or Inductor circuit the voltage and current are out of phase with each other by a few degrees depending on the total reactance , and this is the Reactive power which doesn't give any useful energy. "The more Reactive power the more wasted energy and lower power factor.." this Reactive power can be Leading or Lagging depending if the loads are Inductive or Capacitive.

This is ok in domestic situations, but in commercial industry you are penalised for having a low power factor.

You forgot that the hairdryer has a motor inside, thus this is an Inductor and will have slight reactance.

There is a Mnemonic to remember which leads or lags voltage or current,

CIVIL
Capacitor Current leads Voltage,
Inductor Voltage leads Current.


I'm old, but I learned ELI the ICE man as a way to remember which came first.
 

dcbingaman

Joined Jun 30, 2021
498
Another way to look at it is that the real power at any instant in time is the volts at that instance times the current at that instance.
The integrated average of those over a complete cycle is the average power.
Absolutely and the 'instantaneous' power can be positive when the source is supplying it to the circuit or negative when the circuit is returning it to the source and your statement is applicable to all circuits not just AC ones.
 
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