Interharmonic currents cause interharmonic distortion of the voltage depending on magnitudes of the current components and the supply system impedance at that frequency. The greater the range of the current components frequencies,the greater is the risk of the occurrence of unwanted resonant phenomena, which can increase thevolt age distortion and cause overloading or disturbances in the operation of customers' equipment and installations. Among the most common, direct, effects of interharmonics are:
a) Thermal effects
b) Low-frequency oscillations in mechanical systems
c) Disturbances in fluorescent lamps and electronic equipment operation.
d) Interference with control and protection signals in power supply lines. (This is now the main harmful effect of the interharmonics)
e) Overloading passive parallel filters for high order harmonics
f) Telecommunication interference
g) Acoustic disturbance
h) Saturation of current transformers
