High frequency disturbances are usually produced by electronic converters used in speed drivers, both in DC and in AC and in the UPS. These high frequency disturbances are called EMI disturbances and are caused by sudden changes in voltage and current caused by transistor switching or IGBT.

EMI are is transmitted in two ways transmission and radiation.
Differential mode disturbances; the coming and going of high-frequency disturbing currents are caused by phase and/or neutral conductors.
Common mode disturbances; Disturbing currents pass in one direction through the phases and neutral and return through the protection conductor. These signals may cause the PLC, computers and control equipment operating with low signal levels to malfunction.