Impact Of Harmonics On Power Quality

In the earlier years, harmonics were not prevalent in most of the industries as most of the loads were linear loads such as three-phase induction motors, incandescent lighting, and heating system, etc. These linear loads draw sinusoidal current at the same frequency as that of the voltage. Because of the rapid strides in power electronics, the impact is being felt on the electrical scenarios. Several parameters like accurate speed control, uninterrupted power supply; etc are being achieved with relative ease & all credit goes to electronics.

On the other side, with an increase in non-linear loads, the power system quality issues have also been faced by industries. The harmonics pollute the electrical power network, which is a big problem, and every electrical installation connected to the grid getting affected by the power quality issues. As more and more semiconductor devices based equipment is being used for electrical engineering applications, especially in power applications, the growth of harmonics in the days to come will further increase. It is, therefore, become essential for every electrical and instrumentation engineer to understand the effect of harmonics and take necessary steps to minimize its impact.

As the power electronics is well accepted in industries because of ease of operation and control coupled with power saving, it has become absolutely necessary to understand the effect of harmonics on power quality and how harmonics does affect the other electrical installation. Therefore, before selecting equipment like variable voltage variable frequency drives ( VVFDs ), SCRs based DC drives, soft starters for motor applications, uninterrupted power supplies ( UPS ), Welding generator sets ( SCRs and IGBT based ), it is important to consider the impact of harmonics on power system which are generated by this equipment.

HARMONICS AND ITS IMPACT ON POWER SYSTEM :

Electricity Supply Quality – Technical Aspect

Like any other product, electricity is also considered a product. Consequently, electric energy is subject to have certain quality regulations. If the quality is not sufficient to ensure the security of supply required by the customer, quality measures are to be taken.   In addition to the quality characteristics, the following criteria are of importance:

  1. Security
  2. Reliability
  3. Environment compatibility

The utility company has to ensure a certain quality requirement to energy, on the other hand, the customer must use devices ensuring a certain level of “breakdown security “.

Overview of the voltage quality

Followings parameters must be taken into account for analyzing the quality of the power quality.

  1. Voltage dip
  2. Slow Voltage Changes
  3. Fast Voltage Changes
  4. Short Time Interruption
  5. Long Time Interruption
  6. Flickers
  7. Temporary Over Voltage
  8. Transient Over Voltage

Surges and transients in power system

Surges and transients in power system are undesirable and have the following adverse effects:

  1. Increase maintenance and downtime
  2. Reduced lifetime of the equipment
  3. Cause computers to stop execution of programs
  4. Create false data in computer
  5. Erase data in computer
  6. May damage the hard disk of computer
  7. Cause damage to insulation in transformers and motors
  8. Cause nuisance tripping of adjustable speed drives
  9. Wasted energy

WHAT IS HARMONICS?

Ideally, voltage and the current waveform are sinusoidal. However, because of the increased popularity of electronics and other non-linear loads, the waveform quite often becomes distorted. The distorted waveform can be resolved into fundamental and integral multiples of fundamental frequency according to the Fourier series. Thus, the distorted waveform will contain harmonics.

waveform composed of fundamental, 3rd, and 5th  harmonics

Ac waveform containing harmonics

A pure voltage or current sine wave has no distortion and no harmonics, and a non-sinusoidal wave has distortion and harmonics. Harmonics distortion caused by different non-linear devices contributes harmonics in the network and, as a result, the whole electrical network gets polluted.

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