HT instruments HT9022 - Manual (Page 56)

HT9022
EN - 54
9.7. CONSEQUENCE OF THE PRESENCE OF HARMONICS
Generally, harmonics of even, 2 nd , 4 th etc. order do not create problems.
Designers must consider the following points when designing a power distribution system
containing harmonic currents:
Installation parts Effects attributed to Harmonics
Fuses
Non-uniform heating of internal fuse element and consequent overheating which can also lead to
an explosion of the fuse casing.
Cables
Increase in “body” effect; this means that, for cables with many wires, the internal wires have
higher impedance than the external wires.
As a consequence, current, which normally distributes along the external surface of the wire,
produces:
– over-heating of the conductor;
– a premature degrading of the cable’s insulation;
– an increase in line voltage drop.
Neutral
conductor
Triple harmonics, odd multiple of three, sum on neutral (instead of nullifying themselves), thus
generating a potentially dangerous overheating of the conductor.
Transformers
Increase in copper loss due to a higher TRMS value of the current that circulates on internal
circuits, and also due to the “body” effect on protected wires.
Increase of iron loss due to hysteresis cycle distortion and due to the generation of leakage
currents on the magnetic core.
Heating of insulation material due to a possible DC component that can generate saturation of the
magnetic core column.
Motors
Increase of loss due to overheating of internal circuits and possible damage of insulation material.
The 5 th and 11 th harmonic components generate some abnormal electromagnetic coupling that
can increase motor speed.
Re-phasing
capacitors
Increase in “parallel resonance” present inside a circuit, due to inductive loads and re-phasing
capacitors, 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-phasing capacitors.
RCD devices
Possible saturation of current sensing toroidal transducers resulting in malfunction, both in terms
of untimely intervention and increase of the intervention threshold.
Energy disk
counters
Increased rotation speed of a disk resulting in measurement errors (especially in case of low
power factor loads).
Power controls
switch
Reduction of electric duration of contact surfaces.
UPS Reduced power generation from UPS.
Electronics
devices
Internal damage of electronic components not protected by suitable devices.