Harmonics

1. HARMONICS
Harmonics in an electrical circuit is the distortion of
Fundamental sinusoidal waveform supplied by any
source.
• Following is the example of fundamental
waveform getting distorted due to harmonics.
Fundamental

2. Cause of Harmonics
Harmonics are caused by loads like
⇒ Controlled Rectifiers
⇒ AC & DC variable speed drives
⇒ Solid state heater controls
⇒ Rectifier Transformers
⇒ Zero switching of transformers
Note : Linear loads can cause harmonics during
starting. Capacitor switching also causes harmonics.
Presence of harmonic in applied voltage aggravates
the effect of harmonics in capacitors.
The root cause of harmonics is non - linear current
drawn by loads even after applying linear voltage
waveform.
HARMONICS

3. Effects of Harmonics
• Waveform distortion resulting in components of
higher order frequencies.
• Loads are designed to use only fundamental
frequency.
• Other components of frequency are lost in form
of heat both in source & load.
• It also causes heat loss in cables, circuit
breakers & power factor improving capacitors.
HARMONICS

4. Effects of Harmonics
The extent of distortion in voltage waveform depends
upon the following
• Total Harmonic Content in load
• Size of the source
Same non - linear load will have different distortion of
voltage wave form if it is running on DG set or infinite
source like grid.
HARMONICS

5. Harmonic study & correction / allowance is
necessary before installing any new source -
To prevent
• Premature failure of power factor improving
capacitors
• Overheating of transformers
• Overheating of source Alternator
• This causes increase in active losses.
These are supplied from prime mover
result in “Higher specific fuel oil
consumption”.
HARMONICS

6. • Presence of switching harmonics also cause
differential relay to operate during switching of
power transformers.
• ABB SPAD 346 C relay has the provision for
filtering the 2nd & 5th order of harmonics.
HARMONICS

7. Fundamental
We can mathematically split the non - sinusoidal
waveform in sinusoidal waveform of multiples of
fundamental frequencies.
3rd Order
5th Order
9th Order
13th Order
HARMONICS

8. • Harmonics do not exist separately in a system.
• Harmonic analysers are used to detect the
magnitude & order of harmonic.
The effect of harmonics can be reduced by
• Oversizing of source (Alternator / Transformer).
• Use of suitable harmonic filter.
• Use of phase shifting techniques to cancel the
harmonics (Only in few specific cases).
HARMONICS

9. Harmonic Filter
It is the inductor / capacitor (L-C) circuit.
This L-C circuit is tuned for absorbing the specific
order of harmonics. It offers low impedance path to
bypass / earth specific order of harmonics & also
offer high impedance path for that order to pass to
the load.
HARMONICS

10. → Harmonics are the part of todays modern
electronic loads.
→ We can not avoid them as they are related to
total plant efficiency.
→ We need to measure them & take corrective
actions to avoid power loss & premature
failure of components.
HARMONICS