Supplied Power 2

[shaniel21]

Hi. The three types of power (Apparent, Reactive and Active) are not so clear to me. What power do we supply from a low voltage room to running of machines in a plant???

 

[jtkirb]

Think of a right triangle.
The watts (real power) is the horizontal.
The vars (reactive) is the vertical.
The voltamps-VA (apparent) is the hypotinuse (sp)
The cosine of the angle between Watts and VA is the power factor

When a motor runs it uses watts as the power to get work done, but because it's a non-linear load it shifts the phase angle between current and voltage causing vars. This creates the power triangle described above. Motors consume vars, capacitors supply vars, resistive loads are linear and don't do any var shift.

Transformers are rated in VA (or kVA) because they have to supply the apparent power of watts and vars. Putting caps at motors is used to correct the var problem will make the apparent power closer to the real power used by the motor (reduce the var vertical leg- reducing the angle). This will improve electrical losses in wires and transformers.

did that help? You are supplying all those depending on what loads are in your plant. The main goal is often trying to get plant power factor close to 0.95 or at least whatever the limit the utility gives you before starting pf fines on your bill.

 

[14041972]

Well said jtkirb, fine and clear explanation.
Shaniel21, if you are still not happy try

http://www.powerstudies.com/content/resources/Diane Power Factor.pdf

 

[waross]

I concur with jtkirb;
In different words;
Active Power;
This is what you pay for on your power bill. Kilo-Watt Hours
Reactive Power (Lagging). This is caused by the magnetising current of transformers, motors, and other induction loads.
Reactive power
This causes an increase in Current but no increase in work done.
This increased current causes increased heating in wires and transformers.
Reactive power is measured in Kilo-Volt-Amp-Reactive-Hours, or KVARHrs.
The power company will use a formula to compare this to the Kilo-Watt Hours and if the result is too high, they will charge you a penalty.
There is another type of Reactive Power.
Reactive Power (Leading). This is caused by capacitors and will cancel Reactive Power (Lagging)
Look at your power bill and if you are paying a penalty for reactive power, or power factor, have a professional install a capacitor bank to correct it.
The last correction that I did paid for itself in about 40 days. This was much better than usual, but typical pay-back times are almost nearly always less than a year. 8 to 10 months is typical.

 

[CJCPE]

Another way to look at it:

Real power is the flow of energy from the source to the load.

Reactive power results from energy flowing back and forth between the source and an energy storage device such as a capacitor or the magnetic field in a motor. Current is required for the energy to flow back and forth, but there is no net transfer of energy.

Apparent power is the combination of real and reactive power calculated as voltage times current without regard to the net flow of energy.

 

[waross]

note to shaniel21
I assume that you are a professional in another field who is asking for help.
With a non electrical background, you may not understand some of these posts. Don't worry. We are all saying the same things in different ways to help your understanding. If you understand any one post, you got it!