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What are they and what are they used for ?
Often one speaks of Reactance, Impedance and
Inductance, but in the end they are all the same subject.
When we speak or write, we usually refer to a coil with
or without a magnetic nucleus, which effects the electric
line in AC.
A coil, usually wound on an isolated support, features an
Inductance which represents the value of it's inherent
This coil, with a preset Inductance value, when followed
by an AC currency, features a braking effect to the
electric current circulation and this occurs thanks to the Reactance,
which is only causing resistance against the AC.
The effect it produces in a circuit, is to limit the
moving AC and to change it respectively to the voltage of
abt. 90° .
To speak generally of a Reactance is incorrect, as it is
more precise to speak of an Inductive Reactance against a
Inductance in Henry
Xr = 2 * p * f * L
Xr = Reactance in Ohm
Z = R + jXr
Z = Impedance in Ohm
Often we speak of a Filtered Impedance, but an
Impedance is only a total Inductance, a coil with
or without a nucleus, and has both a Reactance value and a
ohm Resistance value. The two values put together
determine the Impedance value at the moment of the
presence of current
The Reactance value is proportional to the used frequency
(see the formula) and brakes the higher
frequencies, when not wanted, which is the same effect
given by a filter.
In magnetic start-up motor systems, the AC resistances
used cause a voltage drop and feature a lower voltage than
the actual nominal one, thus needing resistance groups
with high dissipating powers.
If a circuit features high waveform deformations, there
are surely multiple frequency harmonics, which can be
blocked at the input with a series of Inductances.
Frequently, one can find rebuilt waveforms, as in
inverters for three-phase motors, there are both a base AC
component and many kHz frequencies, generated from the
actual system. In these cases is better to use an
iron nucleus free Inductance and substitute it with one
that has a magnetic circuit that is completely air bound.
Magnetic nucleus used for the frequency feature losses,
which continue to increase when working. The result
will be, for the frequency at the kHz level, the inductive
value of the coil is almost null and the magnetic nucleus
increases it's losses and overheats in an uncontrollable
We could discuss further about Inductance or Reactance or
Impedance, but it is better to see them directly in their
forms and most interesting uses.