Active, Reactive and Apparent Power

Active Power

Definition: The power which is actually consumed or utilised in an AC Circuit is called True power or Active power or Real power. It is measured in kilowatt (kW) or MW. It is the actual outcomes of the electrical system which runs the electric circuits or load.

Reactive Power

Definition: The power which flows back and forth that means it moves in both the directions in the circuit or reacts upon itself, is called Reactive Power. The reactive power is measured in kilo volt-ampere reactive (kVAR) or MVAR.

Apparent Power

Definition: The product of root mean square (RMS) value of voltage and current is known as Apparent Power. This power is measured in kVA or MVA.

It has been seen that power is consumed only in resistance. A pure inductor and a pure capacitor do not consume any power since in a half cycle whatever power is received from the source by these components, the same power is returned to the source. This power which returns and flows in both the direction in the circuit, is called Reactive power. This reactive power does not perform any useful work in the circuit.

In a purely resistive circuit, the current is in phase with the applied voltage, whereas in a purely inductive and capacitive circuit the current is 90 degrees out of phase, i.e., if the inductive load is connected in the circuit the current lags voltage by 90 degrees and if the capacitive load is connected the current leads the voltage by 90 degrees.

Hence, from all the above discussion, it is concluded that the current in phase with the voltage produces true or active power, whereas, the current 90 degrees out of phase with the voltage contributes to reactive power in the circuit.

Therefore,

True power = voltage x current in phase with the voltage

Reactive power = voltage x current out of phase with the voltage

Active component of the current

The current component, which is in phase with the circuit voltage and contributes to the active or true power of the circuit, is called an active component or watt-full component or in-phase component of the current.

Reactive component of the current

The current component, which is in quadrature or 90 degrees out of phase to the circuit voltage and contributes to the reactive power of the circuit, is called a reactive component of the current.

VOLTMETER

Definition: The instrument which measures the voltage or potential difference in volts is known as the voltmeter. It works on the principle that the torque is generated by the current which induces because of measurand voltage and this torque deflects the pointer of the instrument. The deflection of the pointer is directly proportional to the potential difference between the points. The voltmeter is always connected in parallel with the circuit.

Symbolic Representation of voltmeter

The voltmeter is represented by the alphabet V inside the circle along with the two terminals.

Why is Voltmeter connected in Parallel?

The voltmeter constructs in such a manner that their internal resistance always remains high. If it connects in series with the circuit, it minimises the current which flows because of the measurand voltage. Thus, disturb the reading of the voltmeter.

AMMETERS

Definition: The Ammeter is a measuring instrument used to find the strength of current flowing around an electrical circuit when connected in series with the part of the circuit being measured.

The ideal ammeter has zero internal resistance. But practically the ammeter has small internal resistance. The measuring range of the ammeter depends on the value of resistance.

Symbolic Representation

The capital alphabet A represents the ammeter in the circuit.

 

 

 Three Phase Wyes and Deltas

Three phase voltages can be generated and transformed as either a Wye or a Delta. Wye and Delta refer to the connections between the single phase windings which connect to create three phase voltages. Notice the polarity of each winding at the connection points. In a Wye all the ends or 2's are connected together while the beginnings or l's are connected to the three phase power source, Ll, L2, and L3. In a Delta the end (2) of one winding is connected to the beginning (1) of .another winding. Three phase power is connected to each of these 1, 2 junction points.

 Star or Wye (Y) Connection

In this method of interconnection, the similar ends say, ‘star’ ends of three coils (it could be ‘finishing’ ends also) are joined together at point N. 

Delta (Δ) or Mesh Connection

In this form, of interconnection the dissimilar ends of the three phase winding are joined together i.e. the ‘starting’ end of one phase is joined to the ‘finishing’ end of the other phase and so on. In other words, the three windings are joined in series to form a closed mesh.

3-PHASE POWER

   

Most power is distributed in the form of 3-phase AC. Basically, instead of just one coil turning in agenerator, there are three coils, spaced 120 degrees apart.

As the coils turn through the magnetic field, power is sent out on three lines. Three current and voltage sine waves are generated, 120 degrees out of phase with each other. Each sine wave represents the current or voltage on one of the phases.

Three-phase electricity powers large industrial loads more efficiently than single phase electricity. When single-phase electricity is needed, it is available between any two phases, or, in some systems, between one of the phases and ground.