The term power quality (PQ) is generally applied to a wide variety of electromagnetic phenomena occurring within a power system network. The ability of the power systems to deliver undistorted voltage, current and frequency signals is termed as quality of power supply. Unexpected variation of the voltage or current from normal characteristics can damage or shut down the critical electrical equipment designed for specific purpose. Such variations happen in electrical networks with a great frequency due to a competitive environment and continuous change of power supply. In a highly evolved electrical system PQ sensitive demands can be classified as
- Digital economy (such as banking, share market and railways),
- Continuous process manufacturing industries, and
- Fabrication and essential services.
Cost incurred to operate all the above types of loads vary from 3 to120 per kVA per event. This is huge and greatly affects economic operation of power industries. To mitigate PQ issues; customers are also equipped with some back-up instruments apart from grid supply. According to IEEE standard 1159-1995, the PQ disturbances include a wide range of PQ phenomena namely transient (impulsive and oscillatory), short duration variations (interruption, sag and swell), frequency variations, long duration variations (sustained under voltages and sustained over voltages) and steady state variations (harmonics, notch and flicker) with a time scale which ranges from tens of nanoseconds to steady state.