# What are harmonics ?

Note: This post is extremely simplified to give some brief information.
Generally a harmonic is a integer multiple of the fundamental frequency (nominal frequency fn). The fundamental frequency is either 50 Hz or 60 Hz.
So, when we have a nominal frequency fn of 50 Hz, the 3rd harmonics is traveling with a frequency of 50 Hz multiplied by 3 = 150 Hz.
We can have harmonics in the voltages and in the currents.
Current harmonics
In a normal AC power system we have a sinusoidally current with the same frequency as the voltage. When a non-linear load is connected, the current waveform will become complex. But the wave can be split in harmonic sine waves with the help of the Fourier analysis. Don’t worry, the calculations are done by the CLOU reference standards and advanced AMI meters.
What can cause current harmonics?

• rectifiers
• computer
• UPS
• fluorescent lighting
• battery chargers
• variable speed drives
• PV- and wind power converters

Voltage harmonics
Voltage harmonics are caused by the current harmonics, so they are typically smaller than the current harmonics.

Beside of a magnitude harmonics also have a phase angle, indicated relative to the fundamental wave.

What is the impact of harmonics?
Harmonics can cause

• overheating of motors, transformers, cables
• malfunction of relays and breakers
• disturbance of PLC communication
• damage of capacitors or capacitor banks for power factor compensation

What are the limits?
Most countries follow the IEEE 519 recommendations.
Voltages up to 1 kV are allowed to have a individual harmonics content of 5 %, the THD (total harmonic distortion) should not exceed 8 %. Odd current harmonics (between order no. 3 and 11) with a current between 50 A and 100 A are allowed to have 7 % for individual currents and a maximum THD of 8 %.
Please note that utility regulations might be different.

With CLOU portable reference standards you can monitor the harmonics behavior on site during a calibration. Our AMI systems can provide long time statistics.

order no.amplitude %phase shift °
fundamental
2nd
3rd
4th
5th
6th

The fundamental wave is blue, the total harmonic distortion is red.

Reference literature:
IEC 61000-4-7
IEC61000-4-30