Non-linear components and loads in a power system generate' Harmonics'. These elements are characterized by a voltage drop which is not proportional to the current flow. There are a lot of such non-linear loads exist, in components and devices such as;

 

- Uninterruptible power supplies ( UPS ),

- Motor starters and variable frequency drives,

- Electronic drive systems

- Computer, TV sets

- Fluorescent lighting

- Welding machines,

- Rectifiers

 

Harmonic currents may have an adverse effect on different electrical components. These include transformers, switches, capacitors, fuses and relays. The detrimental effects are increased losses and heating and/or excessive dielectric stresses. Electric utilities very often impose high charges when certain maximum levels of harmonic distortion are exceeded.

 

DISTURBANCES CAUSED BY HARMONIC DETERIORATIONS

 

Quality of electrical power is downgraded that can disturb sensitive loads,

Increasing in rms current that cause overload in distribution networks,

Increasing in voltage value

Vibration and overload on devices and equipments that cause premature ageing,

Power loss and failures in capacitors

Failures in computers and electronic devices

Overheat on cables and devices,

Quality of the signal transmission incommunication networks and on telephone lines is downgraded

Mono phase loads cause cumulative increasing in third-order harmonics and it causes overloads in neutral conductors

 

Harmonic currents must be eliminated by filter systems, consisting of reactors and capacitors. The filtering system must be installed close to the source of harmonics so as to provide a low impedance path for the harmonic currents. This is achieved by series connection of a filter reactor with a capacitor bank, forming a filter circuit tuned to the harmonic frequency which needs to be eliminated.