L&T Electrical & Automation OMEGA, Manual

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45
Matrix
Protection and Control Units
Linear Loads:
The AC loads are called linear loads when the current and voltage resultant waveform is sinusoidal in nature (i.e. not
distorted). Also the current at any instant is proportional to the voltage at that instant.
Thus in linear systems there are no harmonic components in current and the voltage waveforms.
e.g. Heaters, Power factor improvement capacitors, etc.
0 0 0 60 0 120 0 180 0 240 0 300 0 360 0 60
Ir Iy Ib
3 PHASE FUNDAMENTAL WAVE
RESULTANT CURRENT I = Ir+Iy+Ib = 0
CURRENT WAVE FOR LINEAR LOAD
N o n - L i n e a r L o a d s :
The AC loads which cause the current waveform to distort from the normal sinusoidal nature are called as non-linear
loads. Current distortion leads to the distortion of the voltage waveform also. Thus the voltage and current are no
longer proportional.
The distorted current and the voltage waveforms can be decomposed into pure sinusoidal and associated
frequencies of the higher order through Fourier Transformation.
Harmonic spectrum gives a clear analysis of amount and order of the harmonics present in the system, which helps in
the designing the filter for the system.
e.g. SMPS, Rectifiers, PLC, Electronic Ballasts, Laser Printers, Computers, etc.
RESULTANT CURRENT
WITH 3rd HARMONICS
RESULTANT CURRENT I = Ir+Iy+Ib
0
0
0
60
0
120
0
180
0
240
0
300
0
360
0
60
CURRENT WAVEFORM FOR NON-LINEAR LOAD
100
80
60
40
20
0
3 6 9 12 15 18 21 24 27
Component
R-Phase
23:59
%
HARMONIC SPECTRUM