# Confused about the reactive power

• Gavroy
In summary, there was confusion around the calculation of reactive power and apparent power. The formula for reactive power was defined as Q=UI sin(a) and for apparent power as S=UI. However, in solving an exercise on heat loss in a power grid with a power factor of cos(a)=0.85, it was instructed to use Q=I²R sin²(a) and S=I²R instead. The question was then raised on when to use each formula.
Gavroy
hey,
i am a little bit confused about the reactive power.
we defined it as
Q=UI sin(a)
and the apparent power as
S=UI

Now I have to solve this excercise:
Which percentage of heat loss in a power grid is caused by the reactive power, when the powerfactor is cos(a)=0,85?

Now I thought:
Q/S=sin(a) would be the solution

but instead of this it is said that one has to set:
Q= I² R sin²(a)
S= I² R

and therefore Q/S=sin²(a)

now my question is: when can I use Q=U I sin(a) and when do I have to use Q= I² R sin²(a)...can somebody explain this to me?

Put it in the homework section

## 1. What is reactive power and how is it different from active power?

Reactive power is the power that flows back and forth between inductive and capacitive elements in an electrical circuit. It is different from active power, which is the power that is consumed by the resistive elements in the circuit.

## 2. Why is reactive power important in electrical systems?

Reactive power is important in electrical systems because it helps to maintain the voltage levels and overall stability of the system. It also helps to reduce the amount of active power that is required to be generated, thus saving energy costs.

## 3. How is reactive power measured?

Reactive power is measured using a unit called volt-ampere reactive (VAR). This unit takes into account both the magnitude and phase difference between the voltage and current in an AC circuit.

## 4. What are the sources of reactive power in a circuit?

The main sources of reactive power in a circuit are inductive and capacitive elements, such as motors, transformers, and capacitors. These elements absorb and release reactive power as needed to maintain the balance in the system.

## 5. How can reactive power be reduced or compensated for?

Reactive power can be reduced or compensated for by using power factor correction techniques, such as adding capacitors to the circuit. These techniques help to balance out the reactive power and improve the overall efficiency of the system.

Replies
9
Views
1K
Replies
11
Views
1K
Replies
7
Views
470
Replies
9
Views
5K
Replies
7
Views
5K
Replies
76
Views
10K
Replies
7
Views
3K
Replies
4
Views
1K
Replies
3
Views
992
Replies
13
Views
1K