# Reactive power, RL RC circuits

• Bassalisk
In summary, the conversation revolves around understanding the power network and synchronous machines, specifically the concept of reactive power. The person is struggling with the basics and goes back to their old course to review. They discuss the components and behavior of a RL circuit, and question whether an inductor consumes or gives out reactive power. They also consider the role of the voltage source in controlling and cancelling out transient states. The conversation ends with a helpful resource for understanding the differences between consuming and giving out reactive power.

#### Bassalisk

Trying to understand the power network and synchronous machines, led me to the fact that I am not sure about the basics.

The terms the generator is delivering or consuming reacting power made me halt.

So I went back to my old course(which I allegedly passed) where the reactive power is addressed. I couldn't understand that back then(1 year) because I barley handled the phase angle, let alone problems of reactive power and its true meaning.

Consider a RL circuit. Plain. (or real inductor).

Solving the differential equation(which I didn't know how to do back then) gives me this:

for $u(t)=U_m\cdot sin(\omega t+\theta _u)$

I get that the current is changing like:

$i(t)=I_m\cdot sin(\omega t+\theta _u-\phi _L)-I_ m\cdot sin(\theta _u -\phi _L)\cdot e^{-\frac{R}{L}t}$

Lets discuss this:

We have 2 components. First component represents a steady-state current.

Second component represents a transient-state which slowly fades.

My question here is:

Do we say for an inductor, that is consuming reactive power?

If we make the angle of the voltage source u(t) such that it cancels the transient-state, did we in fact, "configured" that voltage source, to give OUT reactive power, and give it out just SO much that it cancels the "needs" of that inductor?

These are the questions for now, tons of other are awaiting, but first I have to make a clear distinction between giving out and consuming reactive power.

I usually forward people to this. I think it describes the differences well.

Do we say for an inductor, that is consuming reactive power?

It's all a agreement how we call that.. consuming means that the current is lagging. There is no power consumption - the reactive power is stored in inductiors magnetic field (stored in one period and moved out in another period).

If we make the angle of the voltage source u(t) such that it cancels the transient-state, did we in fact, "configured" that voltage source, to give OUT reactive power, and give it out just SO much that it cancels the "needs" of that inductor?

First of all.. where from comes the transient state ? Tranient occurs when You start from "u(t=0) not eq amplitude". Why ? When U is at it's peak I is equal to 0 (90deg phase shift, obvious). But what about reactive power ? When "q(t=0) is eq to 0" the circuit starts with no transients. At point (t=0"-") the total energy stored in inductor is zero, and there can't be a discontinous energy change.

es1 said:
I usually forward people to this. I think it describes the differences well.

## 1. What is reactive power?

Reactive power is a type of electrical power that is used to maintain the voltage and current levels in an alternating current (AC) circuit. It is necessary for the operation of inductive and capacitive components, such as motors and transformers.

## 2. How is reactive power different from real power?

Real power is the actual power consumed by a circuit to perform useful work, while reactive power is the power used to maintain the voltage and current levels. Real power is measured in watts (W), while reactive power is measured in volt-amperes reactive (VAR).

## 3. What are RL and RC circuits?

RL and RC circuits are types of circuits that contain inductive (L) and capacitive (C) components, respectively. In an RL circuit, the inductor stores energy in the form of a magnetic field, while in an RC circuit, the capacitor stores energy in the form of an electric field.

## 4. How do RL and RC circuits affect power factor?

RL and RC circuits can affect power factor by introducing reactive power into the circuit. This causes the current to lead or lag the voltage, resulting in a lower power factor. In order to improve power factor, reactive power must be compensated for with the use of capacitors or inductors.

## 5. How can reactive power be minimized in a circuit?

Reactive power can be minimized by using power factor correction techniques, such as adding capacitors or inductors to offset the reactive power. Another way is to use more efficient equipment and reduce the amount of reactive power needed to maintain voltage and current levels.