In the earlier years, harmonics were not prevalent in most industries as most of the loads were linear loads, such as three-phase induction motors, incandescent lighting, heating systems, 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 in 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 hand, with an increase in non-linear loads, industries have also faced power system quality issues. The harmonics pollute the electrical power network, which is a big problem, and every electrical installation connected to the grid is affected by the power quality issues. As more and more semiconductor device-based equipment is being used for electrical engineering applications, especially in power applications, the growth of harmonics will further increase in the days to come. It is, therefore, essential for every electrical and instrumentation engineer to understand the effect of harmonics and take necessary steps to minimize its impact.
As power electronics are 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 affect other electrical installations. Therefore, before selecting equipment like variable voltage variable frequency drives ( VVFDs ), SCRs-based DC drives, soft starters for motor applications, uninterrupted power supplies ( UPS ), and 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 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:
- Security
- Reliability
- Environment compatibility
The utility company has to ensure a certain power quality requirement; on the other hand, the customer must use devices to ensure a certain level of “breakdown security”.
Overview of the voltage quality
The following parameters must be taken into account for analyzing the quality of the power quality.
- Voltage dip
- Slow Voltage Changes
- Fast Voltage Changes
- Short Time Interruption
- Long Time Interruption
- Flickers
- Temporary Over Voltage
- Transient Over Voltage
Surges and transients in the power system
Surges and transients in the power system are undesirable and have the following adverse effects:
- Increase maintenance and downtime
- Reduced lifetime of the equipment
- Cause computers to stop the execution of programs.
- Create false data in the computer.
- Erase data in the computer.
- It may damage the hard disk of a computer
- Cause damage to insulation in transformers and motors
- Cause nuisance tripping of adjustable speed drives
- 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
A pure voltage or current sine wave has no distortion and no harmonics, and a non-sinusoidal wave has distortion and harmonics. Harmonic distortion caused by different non-linear devices contributes to harmonics in the network, and, as a result, the whole electrical network gets polluted.