Power Quality in Electrical System
The amount of harmonics in the power
system is determined by the total
harmonic distortion (THD)
measurement. High harmonic
distortion negatively affects the
electricity distribution network and
leads to overheating and premature
failure of the motors. The resulting
heat also disrupts the insulation
structure of the cables.
-
The reasons for increasing
interest in power quality are
listed below:
Measurement -
Low power quality affects the
system measurement accuracy.
Protection roles - affects the
optimum functioning of the
rollers. Posture - damages
equipment and causes downtimes.
İDEAL VOLTAGE WAVE TYPE
İideal wavelength, magnitude,
frequency, and waveform distortion
is the size of the predetermined
limits. When the ideal waveform is
applied to the load, the load
current will have its frequency and
size depending on the impedance and
characteristic of the load. Load
current characteristic is called as
non-linear. Non ir sininozidial
current also leads to disturbances
in the supply voltage, which is an
indicator of low power quality.
NON-LINEAR LOAD: RECTIFIER
> Devices that convert
alternating current into direct
current are the most common
nonlinear loads in rectifiers
electrical systems. These devices
are available in the interior of
many devices, from 100W personal
computers to 10000kw adjustable
speed controllers.
> Three-phase rectifiers eliminate
the solid harmonics 3 and 3.
5,7,11,13 harmonics are high. In
electrical systems, each current
harmonic is treated separately.
> Harmonic currents and voltages may
cause faulty tripping of the earth
fault circuits. The measurement
instrumentation can be affected by
harmonics and cause the switches to
open prematurely.
> High-frequency switching circuits,
such as switching power supplies,
power factor correction circuits,
and speed drives, include
high-frequency components that do
not multiply the line frequency. For
example, a switched-mode power
supply operating at 75 kHz produces
high-frequency components that are
fully solid at a switching frequency
of 75 kHz. These frequency
components are sometimes called
interharmonics to separate them from
harmonics. >
Other sources of interharmonics are
cycloconverters, arc furnaces. High
frequency components may interfere
with other nearby electronic devices
(EMI). Medical electromagnetic
devices are particularly sensitive
to EMI because they work with
low-level signals. Telephone
communication may also be
interrupted by EMI.
DESCRIPTION OF POWER QUALITY
> > Power quality is the
energization and grounding required
for the operation of the equipment.
It is not easy to define the proper
power quality because the power
quality required for the
refrigerator may not be sufficient
for computers or sensitive
electronic devices.
|