Electricity with a bad quality is dangerous and uneconomical at both utility and consumer end. There is a big need to focus on the quality of power being supplied to the loads. Read more as we cover causes of poor power quality, different measuring parameters, power quality standards and various techniques to improve the power quality.
Power quality is the ability of a power grid to supply power to the consumers efficiently and it also expresses the ability of an equipment to consume the power being supplied to it. In technical terms, power quality is the measure, study and enhancement of sinusoidal waveform at the rated voltage and frequency.
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Causes of Poor Power Quality
There is need to identify the factors which lead to poor power quality in a power system. These possible causes are uncertain events, utility, consumer and manufacturer.
- Uncertain Events
Click here to read more about the Causes of Poor Power Quality in a Power System.
Common Power Quality Issues and Parameters
Transients are the pulses occurring in a sinusoidal waveform for a short duration but of high intensity. Transients can come from either internal or external sources i.e. either from outside or inside the facility. External sources may include lightning, wind, transformer switching etc. While faults in the system, load switching or arcing are considered as internal sources. These distortions in the waveform are undesirable as equipment can be harmed by several means like dielectric breakdown, fracture, insulation flashover, overload etc. In this way, the transients result in poor quality.
We recently wrote an article on Electrical Transients in Power Systems, click here to read if you want to know more about electrical transients.
Voltage of a system may vary from its nominal value, and the phenomenon is termed as voltage variation. One of the factors causing voltage variation is interruption which may occur due to equipment failure, control malfunction, or fuse/circuit breaker operation. Sag or voltage dip i.e. reduction in RMS voltage is another factor which is caused by starting of large motors, single line to ground fault, load shifting or energizing heavy loads. Also, the under or over voltages lead to voltage variations. Under voltages are caused when system is overloaded and over voltages occur when system is equipped with lesser loads as compared to the utility’s voltage level.
Unbalanced voltages mean that voltages of a 3 phase system are different in either magnitude or phase difference between each of two phases is not same i.e. other than 120 degrees. Blown fuse in any of the 3 phases, unequal distribution of loads in a 3 phase system and no transposition in overhead transmission lines are the major causes of voltage imbalance in the power systems. Such unbalanced voltages may harm or damage the electrical equipment, thus causing poor power quality.
Continuous variations in voltage of the supplied power causes rapid fluctuations in the load currents leading to instability of visual sensation. There is rapid and visible change in brightness of a lamp which puts harmful effect on a human eye. Sudden load changes, motor drives, arc furnaces, welding machines etc. are the common causes of flickering effect. So, the flickers put a question mark on the power quality.
Deviation of a waveform from the steady state sinusoidal waveform is known as distortion in the waveform. These distortions can be of different types like DC offset, harmonics and electric noise. Presence of a DC current or voltage component in an AC system is known as DC offset which is mainly caused by switching devices, leakage inductance of inductor loads etc. DC offsets can harm the power system as it may lead to overheating of an equipment thereby reducing its lifetime. Sinusoidal waveforms having frequencies as integral multiple of the fundamental frequency are known as harmonics. Non-linear loads, switching devices etc. are the main causes of harmonics in the power system which lead to malfunction of controlling devices, losses in an equipment, additional noise etc. Another type of waveform distortion is electric noise which is defined as undesirable electric signals overlaid on power system voltage or current waveform. Common causes of electric noise are improper connections in power system, electronic devices, corona effect etc. All of these distortions have bad impact on the power quality so they must be mitigated.
Total Harmonic Distortion (THD) is defined as the measurement of the harmonic distortion present in a waveform. Power quality of a power system is inversely proportional to THD. More harmonic distortion in the system, lower will be the power quality and vice versa. THD is equal to the ratio of the RMS harmonic content to the fundamental:
Where Vₙ₋ᵣₘₛ is the RMS voltage of nth harmonic in the signal and Vfund-rms is the RMS voltage of the fundamental frequency.
Power factor is directly linked with power quality. Power factor’s value closer to 1 indicates high power quality. As much the value of power factor is less than one, the more poor will be the power quality and higher will be the costs.
There is an article on Power Factor written by us. Click here to read more as we cover significance, calculations and improving techniques of power factor.
Fluctuations in the magnitude of frequency from its nominal value (50 or 60 Hz) are defined as frequency variations. Frequency of power system deviates from the fundamental value if there is an imbalance between generation and demand. Faults in the transmission system are also one of the causes of frequency variations. These fluctuations result in poor power quality as all of the electrical devices are designed according to the rated frequency and any variations in this value may put harmful impact on them.
Effects of Poor Power Quality on Power System
There are harmful impacts of poor power quality on both the utility and consumer end. Some of the main effects of poor power quality in the power system are as following:
- Harmonics add up to the waveform and equipment may receive high peak of waveforms thereby damaging the equipment. High voltages may also cause the equipment to operate in saturation region producing additional disturbances.
- Due to overheating, noise etc. lifetime of an equipment is reduced.
- System’s efficiency or performance is highly decreased due to poor power quality.
- Due to power failure or interruption, important data can be lost or corrupted which may lead to a great loss.
- Costs of a power system are highly increased if there is poor power quality.
- When there is a power failure, consumers can face many problems due to unavailability of power and it affects the utility costs as well.
- Consumer loads are badly affected or even get damaged due to power quality issues.
- Sometimes there is need to oversize the power system due to additional stress imposed by poor power quality. This expansion results in high installation costs.
Power Quality Improvement Techniques
There are many techniques proposed and implemented to mitigate the effect of poor power quality on the power system. Many devices have been introduced to reduce or suppress the bad impact of low power quality. Other than that, deep analysis and monitoring of the power quality is carried out to enhance or maintain the power quality as per requirements.
- Power System Studies
- Power Conditioning Devices
- Power Quality Monitoring
Click here to read the detail of each technique to Improve Power Quality in a Power System.
Does your facility really needs a high level Power Quality Study?
At AllumiaX Engineering, we aim to provide high quality power system study in compliance with the set international standards of IEEE, NEC and NFPA. We ensure that power systems are safe, reliable, operable, maintained, protected and well designed. Contact us for a Power Quality Study of your facility.
About The Author
Abdur Rehman is a professional electrical engineer with more than eight years of experience working with equipment from 208V to 115kV in both the Utility and Industrial & Commercial space. He has a particular focus on Power Systems Protection & Engineering Studies.
Abdur Rehman is the CEO and co-founder of allumiax.com and creator of GeneralPAC by AllumiaX. He has been actively involved in various roles in the IEEE Seattle Section, IEEE PES Seattle, IEEE Region 6, and IEEE MGA.