AC Inductive and Inductive Reactance

Opposing the current flow through an AC Inductor is called Inductive Reactance and is linearly linked to the feeding frequency.

Inductors and coils are basically coils or wire rings wrapped around a hollow tube builder (air core) or wrapped around some ferromomanetic materials (iron core) to increase their inductive value, called inductenses.

Inductors store their energies in the form of a magnetic field created when a voltage is applied to the terminals of an inductor.The growth of the current flowing from the inductor is not instantaneous, but is determined by the self-induced or back emf value of the inductors.Then for an inductor coil, this back-empress voltage V L is proportional to the rate of change of the current flowing through it.

This current will continue to rise until this self-induced back-to-back emk drops to zero, reaching the maximum stable state condition, which has about five time constants.At this point, a constant state current flows from the coil, no more back emf is induced to counteract the current flow, and therefore the coil acts as a short circuit that allows the maximum current to pass through it.

However, in an alternating current circuit that includes an AC Inductive, the flow of the current passing through an inductor behaves very differently from the stable state DC voltage.Now in an AC circuit, resistance to the current flowing from the coil windings depends not only on the inducing of the coil, but also on the frequency of the voltage waveform applied, as it varies from positive to negative values.

The actual opposition to the current flowing from a coil in an AC circuit is determined by the AC Resistance of the coil, and this AC resistance is represented by a complex number. However, the term Reactance is used to distinguish a DC resistance value from an AC resistance value, also known as Impedance.

Like resistance, the colorance is measured in Ohm, but the symbol "X" is given to distinguish it from a fully resistant "R", and since the component in question is an inductor, the coloring of an inductor is called Inductive Recess (XL) and measured in Ohm. The value can be found in the formula.

Inductive reactance

  • Here:
  • Inductive Reactance in X L = Ohm, (Ω)
  • π (pi) = 3,142 numeric constants
  • ε = Frequency in Hertz, (Hz)
  • L = Induct in Henry, (H)

You can also define Omega, radian, inductive reactance ω equals 2ππ.


Therefore, when a sinusoidal voltage is applied to an inductive coil, the back emf resists the rise and fall of the current flowing from the coil, and in a completely inductive coil with zero resistance or losses, this impedance (which can be a complex number) is equal to the inductive recess.In addition, the recess is represented by a vector, since it has both size and direction (angle).Consider the circuit below.

Sinusoidal Feeding AC Induced


This simple circuit above consists of a pure inductee of L Henries(H), which binds along a sinusoidal voltage given by the expression V (t) = Vmax sin wt. When the switch is turned off, this sinusoidal voltage causes a current to flow and rise from zero to its maximum value. This rise or change in the current will cause a magnetic field inside the coil, which will oppose or restrict this change in the current.

But before the current has time to reach its maximum value, as in a DC circuit, the voltage changes the polarity and causes the current to change direction. This change in the other direction is once again delayed by the self-induced back emf in the coil, and the current is delayed by 90 o in a circuitthat contains only a pure inductant.

The applied voltage reaches the maximum positive value of a quarter (1/4ε) of a cycle before the current reaches its maximum positive value, that is, a voltage applied to a fully inductive circuit "directs" the current by a quarter of a cycle, or 90o as shown below.

Sinusoidal WaveForms for AC Inducing


This effect can also be demonstrated by a phaser diagram, voltage in a completely inductive circuit, which makes the current "LEADING" with 90 os. But using voltage as our reference, we can also say that the voltage of the current is about a quarter of a cycle, or 90 o "LAGGING", as shown in the vector diagram below.

Phaser Diagram for AC Inductee


Therefore, for a pure loss less inductor, we can say that VL "directs" the lyre by 90o "or ıl outperforms vl by 90o".

There are many different ways to remember the phase relationship between voltage and current flowing through a pure inductor circuit, but a very simple and easy way to remember is to use the phrase "HAND". ELİ means electromotor force before an AC induction, L before current. In other words, the voltage before the current in an inductor is equal to E, L, I "HAND", and no matter what phase angle the voltage starts at, this expression always applies to a pure inductor circuit.

Effect of Frequency on Inductive Reactance

When a feed of 50 Hz is connected through a suitable AC Inducte, as previously described, the current will be delayed by 90 o and at the end of each half cycle the voltage will achieve a peak value of I amps before reversing the polarity, that is, before the current rises.

Now if we apply a feed of 100Hz of the same peak voltage to the coil, the current will still be 90o late, but its maximum value will be lower than 50Hz, since the time required to reach its maximum value has decreased.

Then, from the equation above for inductive reactance, it can be seen that if the Frequency or Inductive is increased, the overall inductive reassurance value of the coil will also increase.As the frequency increases and approaches forever, the coloring of the inductors and therefore their impedance will increase forever, acting as an open circuit.

Similarly, as the frequency approaches zero or DC, the coloract of the inductors will decrease to zero, acting as a short circuit.This means that inductive reactance is "directly proportional to frequency" and has a small value at low frequencies and a high value at high frequencies, as shown.

Inductive Reactance Against Frequency


The inductive reassurance of an inductor increases as the frequency opposite it increases, so the inductive reacquance is proportional to the frequency (X L α ε) because the back impetus produced in the inductor is equal to the inductive multiplied by the rate of change of the current in the inductor.

In addition, as the frequency increases, the value of the current passing through the inductor decreases.

We can present the effect of very low and very high frequencies on the reassurance of a pure AC Induct as follows:


In an AC circuit that contains pure inducing, the following formula applies:


So how did we get to this equation?The self-induced emk in the inductor is determined by the Faraday Act, which produces the effect of "self-induction".When a current passes through the inductive coil, the rate of change of the AC current induces an emk that blocks the changing current in the same coil.The effect of its own magnetic field generated by the current passing through it on the coil against any current changes is called "self-inductace".

The maximum voltage value of this self-induced impurity will correspond to the maximum current change rate with this voltage value given along the coil:


Where: d/dt represents the rate at which the current changes over time.

The sinusoidal current flowing through the inductive coil (L), which forms magnetic flux around it, is given as follows:


Then the above equation can be rewritten as follows:


The differentiation of sinusoidal current gives:


The trigonometric identification of cos (ωt + 0 o) = sin (ωt + 0 o + 90 o) as a cosine waveform is actually a sine waveform that is shifted to +90 o.Next, we can rewrite the equation above in the form of a sinus wave to describe the voltage along an AC inductance as follows:


Where: V MAX = ωLI MAX = √ 2 V RMS is the maximum voltage amplitude and ε = + 90 is the phase difference or phase angle between the voltage and current waveforms.So the current outperforms the voltage by 90 o through a pure inductor.

In Phaser Domain

In the phaser area, the voltage on the coil is given as follows:


and in polar form it is written as follows: X L ∠90 o


AC via Series R + L Circuit

Above, we saw that the current flowing from a completely inductive coil outpaced the voltage by 90 o, and when we say fully inductive coil, we mean a coil that has no omic resistance and therefore no loss of I 2 R.But in the real world it is impossible to have only fully AC Inductive.

All electrical coils, relays, solenoids and transformers will have a certain amount of resistance, no matter how small the coil rotations of the wire used.This is due to the fact that the copper wire has resistance.Then we can think of our inductive coil as a coil with resistance, R is serial with an induced, L loosely produces what can be called "impe pure inductive".

If the coil has an "internal" resistance, we need to represent the total impedance of the coil in series with an induced induced and as a resistance in an AC circuit that includes both induced, L and resistance, R voltage, throughout the V combination. The two components will be the sum of the voltage of the phaser, V R and V L .

This means that the current flowing from the coil will still lag behind the voltage, but will be less than 90 o,depending on the phaser total values V R and V L.The new angle between voltage and current waveforms gives us their phase difference, which, as we know, is the phase angle of the circuit given to the Greek symbol phi, Φ.

Consider that the following circuit is a pure non-inductive resistance, R is serially connected with a pure induced L.

Serial Resistance-Inducing Circuit


In the RL series circuit above, we can see that the current is common for both resistance and inducing, while the voltage consists of two component voltages, V R and V L.The resulting voltage of these two components can be found either mathematically or by drawing a vector diagram.In order to create a vector diagram, a reference or common component must be present and is the reference source because the same current passes through the current, resistance and inductanc in a series of AC circuits.Separate vector diagrams for pure resistance and pure inducta are given as follows:

Vector Diagrams for Two Pure Components


From above and from our previous tutorial on AC Resistance, we can see that the voltage and current in a resistant circuit are both in phase and the V R vector is drawn on top of each other to scale on the current vector.It is also known from above that the current is further behind the voltage in an AC induced (pure) circuit, so the V L vector is drawn 90 o in front of the current and on the same scale as V R as shown.

Vector Diagram of The Resulting Voltage


From the vector diagram above, we can see that the OB line is a horizontal current reference and that the OA line is the voltage on the resistant component, which is in the same phase as the current.The OC line indicates the inductive voltage 90 o in front of the current, so it can still be seen that the current is 90 o far behindthe inductive voltage.Line OD gives us the resulting supply voltage.After:

  • V is equal to the rms value of the applied voltage.
  • Equals rms of the I series current.
  • V R equals IR, which gives voltage drop against resistance with intra-phase current.
  • V L is equal to IX L voltage drop along the inducing induct that directs the current to 90 o.

Since the current outstripping the voltage in a pure inducta in exactly 90 o, the resulting phaser diagram V R and V L, drawn from individual voltage drops, represent a right-angle voltage triangle shown above as OAD.We can then use pythagorean theorem to mathematically find the value of this voltage obtained during the resistance/inductor (RL) circuit.


Impedance of AC Inductee

Impedance, Z is the "TOTAL" contrast of the current flowing in an AC circuit containing both Resistance (real part) and Reacktans (imaginary part).Impedance also has Ohm, Ω units.

Impedance can also be represented by a complex number, Z = R + jX L, but this is not a phaser, it is the result of the combination of two or more phasers.If we divide the edges of the voltage triangle above by I, another triangle is obtained, the edges of which represent the resistance, reactance and impedance of the circuit, as shown below.

RL Empedans Triangle


Where: ( Impedance ) 2 = ( Resistance ) 2 + ( j Reactance ) 2 where j 90 represents that phase shift.

This means that the positive phase angle is given as ε between voltage and current.

Phase Angle


While our example above represents a simple non-pure AC inductive, if two or more inductive coils are connected to each other in series, or if a single coil is serially connected with many non-inductive resistance, the total resistance of the resistance elements will be equal. for: R 1 + R 2 + R 3 etc., gives the total resistance value for the circuit.

Similarly, the total reacquance for inductive elements will equal: X 1 + X 2 + X 3, etc., which gives the total reacquance value for the circuit.In this way, a circuit containing many coils, coils and resistance can be easily reduced to an impedance value; Z consists of a single resistance in series with a single reassurance, Z 2 = R 2 + X 2 .

AC Induced Question Example 1

The feed voltage in the following circuit is defined as follows: V (t) = 325 sin( 314t – 30 o ) and L = 2.2H .Determine the value of the rms current passing through the coil and draw the resulting phaser diagram.


The rms voltage on the coil will be the same as the feed voltage.If the peak voltage of the power supplies is 325V, the equivalent rms value will be 230V.Converting this time zone value to a polar form gives us this: V L = 230 ∠-30 o (volts).Inductive coloring of the coil: X L = ωL = 314 x 2.2 = 690Ω .Then the current flowing from the coil can be found using the Ohm law as follows:


There will be a phaser diagram with the current 90 o behind the voltage.


AC Inducing Question Sample 2

The resistance of a coil is 30Ω and the induct is 0.5H.If the current passing through the coil is 4 amps.If the frequency is 50Hz, what is the rms value of the supply voltage?


The impedance of the circuit will be as follows:


Then the voltage drops in each component are calculated as follows:


The phase angle between current and supply voltage is calculated as follows:


The phaser diagram will be as follows:


In the next lesson on AC Capacitance, we will look at the voltage-current relationship of a capacitor when a fixed-state sinusoidal AC waveform is applied, together with phaser diagram representation for both pure and non-pure capacitors.