HT instruments HT4022 - Manual (Page 61)

HT4020 - HT4022
EN - 28
8.4. CONSEQUENCES OF THE PRESENCE OF HARMONICS
In general, even harmonics, i.e. the 2
nd
, 4
th
etc., do not cause problems.
Designers should take into consideration the following points when designing a power
distribution system that will contain harmonic current:
Installation parts Effects attributed to Harmonics
Fuses Heating of internal fuse elements. This over-heating can cause an explosion of the fuse casing.
Cables
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:
– an over-heating of the conductor;
– a premature degrading of the cable’s insulation;
– an increase in line voltage drop.
Neutral conductor
The triplens harmonics, odd multiples of three, sum on the neutral conductor (instead of erasing
themselves) and generate a potential danger over-heating situation of the same conductor.
Transformer
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
currents on magnetic core.
Heating of insulation material due to eventually DC component that can generate saturation of
magnetic core column.
Motors
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.
The 5
th
and 11
th
harmonic components generate some abnormal electromagnetic coupling that
can increase motor speed.
Re-phased
capacitance
Increase in “parallel resonance” present inside a circuit, due to inductive loads and re-phased
capacitance, when at least one of the harmonics has the same frequency as the resonance
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.
Energy disk
counters Increased rotation speed of a disk resulting in measurement error (especially in cases of low
power factor loads).
Power controls
switch
Reduce of electrical duration of contact surfaces.
UPS Reduced power generation from UPS.
Electronics
devices Internal damage of electronic components.