Hello there, friends. I'd like to begin with an overview of electric power before delving into Active power, Reactive power, and Apparent power.
Electrical power
The power (P) in an electrical circuit is indeed the product of current and voltage. It represents the rate which work is being done in the circuit. Work is accomplished when electrical energy is transformed to other form of energy.
Example : Electrical energy is transforming to lighting energy.
Power Equation: P=V x I
SI Unit for power is the watt.
- The SI unit of mechanical power is Newton- meter /sec.
- The SI unit of electrical power is Joules/ sec or watts. We can also measure the electrical power in kilowatts (kW) Megawatt (MW), Gega-watt (GW), and horsepower (HP).
- Newton x meter = Joules
The unit of electrical power is Watt. For instance, the power required for the single-phase flood light fixture is 110 W
Electrical power can be broadly classified into active power, reactive power, and apparent power occur only on alternating current.
Active power: The unit of active power is the KW.
Reactive power: The unit of reactive power is the KVar
Apparent power: unit of apparent power is KVA
Real-life example for Active, reactive, and apparent power
Here is a Real-life example to understand active power, Reactive power, and Apparent power.
If I ask you to memorize this paragraph in a short period of time. Imagine you took 20 seconds to understand this content and 40 seconds to memorize it. You have taken a total of 60 seconds.
- But, I need only the minimum time taken by you to memorize this content, so it took only 40 seconds. It is like active power or actual power.
- I don't care about the 20 seconds it took you to understand. That is similar to reactive power.
- Your total time taken is 60 seconds, which is equivalent to apparent power.
Active power (KW)
Active power can also be called actual power or real power. The SI Unit of active power is W (watts).
Active power performs useful tasks such as heating iron boxes, running motors, lighting a light bulb, and so on. Active power is the actual power consumed by the load for operation.
We use a wattmeter to measure this active power in watts. The active power is the electricity used by the resistive load and dissipated as heat. Simply put, active power flows from source to load and is dissipated as heat.
P= ✓3VI Cos (Θ)
Waveform steadily extends to 90°. (cos (ө) =power factor)
In your home, you can find purely resistive loads such as an electric cooker, an incandescent bulb, an iron box, and an electric heater.
The phase angle waveform of active power
- In the active power, both the waveform of current and voltage starts at 0°.
- During the positive half-cycle, the waveform of voltage and current on the positive side, so the power is also positive.
- During the negative half-cycle, the waveform of voltage and current on the negative side, but the two negative times (- x - = +) equal to positive so the power is positive.
From the above explanation, the waveform of current and voltage are in phase and always in positive in active power.
Why current and voltage are always in phase at resistive load?
The resistive load does not produce any reactions such as mutual inductance or capacitance. Both current and voltage waveform extends steadily at 90° and accurately without delay.
Reactive power (KVAR)
Although reactive power did not operate any loads, it is required for capacitive and inductive loads. The SI unit of reactive power is VAR (reactive power). The reactive power has the capacity to form a magnetic field. Electric motors require a magnetic field and a high current to start. Reactive power is the power that satisfies this requirement.
In simple Reactive power is the negative power required to create a magnetic field in the load. Load does not consume any energy and reactive power also does not do any actual work in the load. The letter denotes the reactive power as 'Q'.
The formula for reactive power is
∓ Q= √3V I Sin (𝚹)
sin (𝚹) = Power factor.
Do we pay for reactive power?
Yes, we need to pay for reactive power because the power station generates reactive power for magnetization loads such as a transformer, electromagnetic relay, and motors.
Reactance load consumes reactive power. Reactance load is nothing but inductive load and capacitive load. We measure reactive power in a Var meter.
- A Purely inductive load consumes reactive power for mutual inductance. In the inductive load, the current waveform is lagging voltage.
- A purely capacitive load delivers reactive power because of its charging and discharging activities. In this, the waveform of current leads after voltage.
The reactive power moves front and back towards the source and reaches the device where it is available to produce a magnetic field such as an electromagnetic relay, transformers, motors, transmission line.
Why the waveform of reactive power is out of phase?
- In the inductive load, the waveform of the current leads or lags the voltage because of its mutual or self-inductance. Mutual inductance takes some time to the magnetic field, this time delay makes the current lead or lag the voltage waveform.
- If the current increases because of magnetization, then losses transmission lines also increase.
- Active power and reactive power flow take place in the same transmission line but in the opposite direction.
Apparent power (KVA)
Apparent power is the combination of real and reactive power or vector sum of real and reactive power. SI unit of apparent power is VA (volt amp).
S= P + j Q
We express apparent power in volt-ampere (VA). So apparent power S = V (t)* I (t). This power does not have a power factor.
While designing the power generating and distributing electrical equipment, they consider only apparent power so the rated voltage of generators and transformers is KVA or MVA. We can also consider apparent power as the total power that is in VA.