Watch Free Classes

Reactance (X) is defined as the opposition present in alternating current by either inductance or capacitance in electrical circuits. The phrase ‘reactance’ was coined by a French architect named M. Hospitalier in the year 1893. Sometimes, reactance and resistance are confused with one another but they are not the same. The difference between reactance and resistance is that energy is stored in reactance momentarily in reactance, whereas resistance loses energy continuously. Although the similarity between resistance and reactance is that both are measured in terms of  (Ohms). If the Ohm values are positive, it indicates inductance. If Ohm values are negative, it indicates capacitance. Perfect inductors and capacitors must have null resistance. The letter X addresses the reactance. An important application of reactance is that it is utilised in electrical circuits to figure stage and adequacy changes.

How Reactance Works (Causes)

  • A steady current passing in and across an electrical component (conductor), experiences an opposite force in the coil called electrical resistance.
  •  If the conductor carries an alternating current, then reactance comes into action in addition to resistance.
  • Reactance also comes into play for a short interval of time when a change in direct current is observed when a steady current is departing.

Types Of Reactance and How Their Working

Inductive Reactance

The reactance that is generated due to an inductive component (inductor) is called inductive reactance. It is symbolised by XL. The function of these inductive components is to store electrical energy temporarily in a magnetic field form.

How Reactance Works (Inductive)

  • When an alternating current is passed across an electric circuit with an inductor, a magnetic field is established. The created magnetic field varies when the current varies.
  • Any alteration in the magnetic field causes an alteration in the current as well. The direction of the current is determined with the help of Lenz’s law. The direction of the magnetic field is in the opposite direction of the current.
  • Due to this type of reactance, there is a delay in the current flow and hence, this will establish a phase difference between waveforms of current and voltage. 
  • Therefore, for an electrical circuit that embodies an inductor alone (ideal or perfect inductance), the current lags behind the voltage by 90 degrees. 
  • The reason behind for the lag is – the applied voltage and the current cannot remain in phase because of the opposing force of the counter emf

The Formula For Inductive Reactance

 XL = 2  f L

Where f represents frequency of the voltage that is applied and L represents the inductance (measured in Henry) of the inductor. 

The unit of measurement for inductive reactance is  (Ohm) 

Capacitive Reactance

This type of reactance is created when the reactance is generated by a capacitive component (capacitor). It is represented by the symbol XC. The capacitive components are used for electrical energy temporarily in an electric field form. 

How Reactance Works (Capacitive)

  • When an alternating current is passed through an electric circuit with a capacitor, a magnetic field is established. 
  • Since capacitive elements store electrical energy, capacitive reactance causes a phase difference between the current and voltage waveforms.
  • The lag occurs because of the charging and discharging phase of the capacitive components.
  • In an electrical circuit that embodies only a capacitor (ideal capacitance), then the voltage lags behind the current. 

The Formula For Capacitive Reactance

xc

Where frequency is represented by f and the capacitance (measured in Farads) of the capacitor is represented by C. 

Reactance Properties

  • Reactance is elucidated as a restriction to the movement of alternating current in an inductor or capacitor due to inductance or capacitance respectively. 
  • There are two predominant types of reactance – inductive and capacitive. The type depends on whether the electrical circuit contains an inductor component or a capacitor component.
  • Just like resistance, the unit Ohm () is used for measuring reactance. A positive value of Ohm states that the reactance is inductance and the negative value of Ohm states it is a capacitive reactance. 
  • Capacitive reactance depends majorly on the frequency of the voltage applied and the capacitor value. Inductive reactance also relies on the frequency of the applied voltage. 

Examples of Reactance

This section will include some examples of reactance: 

  • The first example of reactance is the reactance effect as a result of electronic components. The inductors and capacitors will oppose electric currents because of their inductive and capacitive resistances. 
  • The second example of reactance is inductance and capacitance which are observed in transmission lines and magnetic coils, respectively. 

Uses Of Reactance

  • Inductive reactance is used in alternating current circuits to protect against voltage surges.
  • In telecommunication devices, both inductive reactance and capacitive reactance are used.
  • A circuit containing both the inductive reactance and capacitive reactance is used to analyse amplitude, power factor, and phase changes that occur in the circuit. 
  • The utilisation of capacitive reactance is to impede direct current. However, it gives low reactance to an alternating current.
  • Reactance is utilised in electrical circuits to figure stage and adequacy changes.

Conclusion

Reactance is known as the opposition that is present against the movement of alternating current in an inductor or capacitor due to inductance or capacitance respectively. The unit Ohm () is used for measuring reactance. There are predominantly two types of reactances – inductive and capacitive reactance.  Positive values state that the reactance is inductance and negative values state that it is a capacitive reactance. In inductive reactance, the current lags behind the voltage by 90 degrees.  In capacitive reactance, the voltage lags behind the current. Some of the uses of reactance are – it is used in telecommunication devices, it is used to regulate voltage surges, and it is used to figure stage and adequacy changes.