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8.4.
CONSEQUENCES OF THE PRESENCE OF HARMONICS
In general, even harmonics, i.e. the 2
Designers should take into consideration the following points when designing a power
distribution system that will contain harmonic current:
Installation parts
Fuses
Heating of internal fuse elements. This over-heating can cause an explosion of the fuse casing.
Increase in "body" effect. This means, for cables with many wires, the internal wires have higher
impedance than external wires due to their inability to dissipate heat.
The consequence of this is the current, which normally is distribute along the external surface of
wire, produces:
Cables
–
–
–
The triplens harmonics, odd multiples of three, sum on the neutral conductor (instead of erasing
Neutral conductor
themselves) and generate a potential danger over-heating situation of the same conductor.
Increasing of copper loss due to a higher TRMS current value that circulate on internal circuits
and due to "body" effect present on protected wires also.
Increasing of iron loss due to hysteresis cycle distortion and due to generation of leakage
Transformer
currents on magnetic core.
Heating of insulation material due to eventually DC component that can generate saturation of
magnetic core column.
Increase of loss due to over-heating of internal circuits and possible damage of insulation
material. Increase in motor vibration reducing efficiency and causing premature motor wear.
Motors
The 5
can increase motor speed.
Increase in "parallel resonance" present inside a circuit, due to inductive loads and re-phased
Re-phased
capacitance, when at least one of the harmonics has the same frequency as the resonance
capacitance
phenomenon. Effects of this event can be very dangerous. with explosion of used re-phased
capacitances.
RCD devices
Possible saturation of current sensing toroidal transducers resulting in incorrect measurements.
Increased rotation speed of a disk resulting in measurement error (especially in cases of low
Energy disk
counters
power factor loads).
Power controls
Reduce of electrical duration of contact surfaces.
switch
UPS
Reduced power generation from UPS.
Electronics
Internal damage of electronic components.
devices
nd
, 4
an over-heating of the conductor;
a premature degrading of the cable's insulation;
an increase in line voltage drop.
th
th
and 11
harmonic components generate some abnormal electromagnetic coupling that
th
etc., do not cause problems.
Effects attributed to Harmonics
EN - 28
HT4020 - HT4022
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