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Power Quality at Glance

Power quality is related tothe quality of power being supplied or consumed. It ismaintained when:

(1) The State Electricity Board (EB) or Utility provides sinusoidal voltage at rated magnitude and rated frequency to its consumers

(2) Consumers draw sinusoidal current that is in-phase with the input supply voltage. 

EB can assure power quality from their side only when its consumers do meet certain power quality standards (such as, IEEE 519-1992 and/or IEEE 519-2014). Recently, several EBs across the globe have started imposing strict regulations on quality of current, acustomer can draw from the supply linesto maintain a healthy power distribution system.

Harmonic and Reactive Currents, and their Effects:

The power electronic devices (such as, variable frequency drives-VFDs, phase controlled rectifiers, choppers, battery chargers etc.) and other major electrical loads in the industries draw current that has three main components:
(i) Active current at rated frequency,
(ii) Reactive current at rated frequency, and
(iii) Harmonic currents at higher frequencies (commonly at multiples of rated fundamental frequency).

   

Among these three parts, the active current is responsible for the actual work done in factory/plant, while the remaining two parts are just circulating between EB & load, and do not contribute to any useful work. These two non-active currents, however, have significant impact on the other connected loads and distribution system. 

  • Reactive current is responsible for the poor plant power factors and attracts penalty from the EB.
  • Harmonic currents cause adverse effects on other loads in a plant and EB voltage quality.

Key effects of higher level of harmonic currents could be: 

  • Increased heating of transformers, motors and cables
  • Reduced plant efficiency
  • Protective devices malfunctioning leading to increased down time
  • Reduced life span of costly and sensitive plant equipment due to increased stresses
  • Possible malfunction of other nearby sensitive equipment
  • Poor efficiency, overheating, frequent failures, and reduced lifetime of the upstream utility equipment (such as, transmission lines, transformers, and substations)

 
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