Download network 3

Power System Harmonics
Power systems are designed to operate at frequencies
of 50 or 60Hz.  Pure Sine Wave
However, certain types of loads produce currents and
voltages with frequencies that are integer multiples of
the 50 or 60 Hz fundamental frequency.
These higher frequencies are a form of electrical
pollution known as power system harmonics.
Harmonic Sources
Systems  HVDC SVC Transformer etc.
Loads  Nonlinear Loads
Examples
• Adjustable speed drives
• TVs
• Computers
• Gas discharge lamps
• Switching mode power supplies (SMPS)
• Arc furnaces
• etc.
Three Phase
3rd harmonic
the 3rd harmonic and its multiples have their own
special name: triplen harmonics
Y-Y 4 wires system
Harmonic currents add in neutral conductor
Y-Y 3 wires system
Delta-Y system
Delta-Delta system
Harmonic phase sequence
THD = 30%
Single Phase
Typical waveforms
voltage
current
Transformer magnetizing current
THD = 76%
Refrigerator current
THD = 6%
Air conditioner current
THD = 10%
Fluorescent lamp current
THD = 18%
Light Dimmer Circuit
220
Nonlinear components are those that draw a nonsinusoidal current waveform when energized by a
sinusoidal voltage.
Since any distortion of an originally pure sine-wave
constitutes harmonic frequencies, we can say that
nonlinear components generate harmonic currents.
Fourier series
Periodic functions and signals may be expanded into a
series of sine and cosine functions
• Analysis
• Synthesis