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Power Quality in Buildings
Published in Moncef Krarti, Energy-Efficient Electrical Systems for Buildings, 2017
Harmonic distortions are common voltage and current variations due to changes in frequencies within the electrical distribution systems. In particular, there are deviations from the typical sinusoidal variations in voltages or currents. Harmonics are mainly caused by nonlinear loads such as those associated with power electronic converters including variable frequency drives (VFDs) installed for fans and pumps serving building air conditioning systems (Vedam and Sarma, 2009). Specifically, these converters draw a nonsinusoidal current/voltage and introduce the nonlinear loads throughout the electrical distribution systems. The problems due to harmonic distortions are nowadays common in buildings since computers and other power electronics are heavily utilized. In particular, harmonic distortions can cause several disturbances and damages, including wire overheating and power loss. More detailed description of harmonic distortions, including causes, assessments, and corrective measures, is provided in Section 11.3. Figure 11.6 shows typical voltage variation due to a harmonic distortion.
Variable-frequency drives and harmonics
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Power quality and energy analyzers are used to quantify levels of harmonics. The analyzers are used to prove compliance of equipment and systems in meeting contractual power-quality requirements and for troubleshooting problematic systems where poor power quality appears to be an issue. In addition to harmonic power analysis, some analyzers have built-in energy-loss calculators that can indicate real and reactive power, power factor, phase imbalances, and even the cost associated with harmonic-energy losses. The Fluke Model 435 is shown in Figure 6.36. This instrument can analyze power quality in real time and can acquire and store data for later analysis and trending.
Electrical Performance
Published in Mukund R. Patel, Omid Beik, Wind and Solar Power Systems, 2021
Majority of the existing VFDs are fed from the 3-phase power grid, use a passive rectifier to converter the AC to DC that is supplied to an inverter. Figure 17.11 shows schematic of a widely used VFD. The passive rectifier in a VFD is a nonlinear device as it draws a non-sinusoidal current from the power grid. The harmonics in a 3-phase rectifier is expressed as: h=6n±1,n=1,2,3,… Without any harmonic elimination method, the harmonics 5th, 7th, 11th, and 13th are generated in the line current on the grid side. The 5th and 7th harmonics are the dominant ones, and there are higher order harmonics present in the waveform. The modern power distribution systems supply many nonlinear loads and VFDs, which introduce heavy and excessive harmonics to the power grid. These harmonics could cause:Failure of power factor capacitors due to overloadingExcessive losses and hence overheating of cables, transformers and other equipment, which leads to reduced life span and failuresUnwanted tripping of circuit breakers and other protection devicesFailures and performance degradation in electronics loads such as computers, etc.
RNN based Control Algorithm for Power Quality Improvement in PV Integrated Distribution System
Published in Electric Power Components and Systems, 2021
Hemant Saxena, Alka Singh, Jitendra Nath Rai
The growing world population needs more energy and resources. Hence, the focus is shifting to green and sustainable sources of energy for a healthy and better human life. Technological advancements have resulted in making alternative sources such as solar, wind, tides commercially and economically viable as compared to conventional resources such as coal, gas, nuclear etc. Solar-PV is a popular and important renewable source due to merits like less maintenance, longer life, lesser carbon footprint, lower installation costs and time and a fall in global prices over the last twenty years [1, 2]. The solar modules can be installed on the rooftop for household requirements or scaled up to produce megawatts of power. Surplus power may even be transferred to the grid. The developments in the last decade in power semiconductor technology have revolutionized the world and the use of power electronic equipment has been increasing in the form of adjustable speed drives, energy-efficient lighting, arc furnaces, computers, refrigerators etc. These non-linear loads inject harmonics into the system and affect the working performance of the other equipment connected at the point of common coupling (PCC). Increased heating and interference in control and possible malfunctioning of equipment are other detrimental effects of harmonics. Power engineers have focused on the mitigation of power quality (PQ) problems to save sensitive equipment and reduce losses in the distribution system.
Effect of Weather Conditions on Harmonic Performance of PV Inverters
Published in Electric Power Components and Systems, 2019
Shadi Hazzem Shehadeh, Hamed Hamed Aly, Mohamed El-Aref El-Hawary
One metric frequently used in the measurement of harmonic levels is total harmonic distortion (THD). This measurement is comprised of the ratio of the voltage or current value of the harmonics present above the fundamental frequency to the value of the fundamental multiplied by 100%. This ratio is given by [37]: where is the fundamental frequency component of the voltage waveform and and are the harmonic components. In this case, the THD is approximately 47%. This is a high level, which can be expected to have negative impacts, as previously discussed. Many techniques are available to reduce the harmonics, including the use of filtering systems, multi-level inverters, and changing the blanking angle of the switches or PWM [38–40].
Assessment of Effect of Load Models on Loss-of-Life Calculation of a Transformer Using a Point Estimation Method
Published in Electric Power Components and Systems, 2018
Kanhaiya Kumar, Balu Ganesh Kumbhar, Saran Satsangi
Proliferation nonlinear loads give rise to increased harmonics distortion in a distribution system. It causes excessive losses in transformer windings and other structural parts, and leads to abnormal temperature rise at higher loading conditions. Therefore, it is essential to consider the effect of harmonics on LOL of the transformer. To include the effect of harmonics, harmonic spectrum of the different classes of loads is measured using power quality analyzer. The current harmonic spectrum of various classes of loads is shown in Figure 3. In the harmonic environment, load, no-load, and stray losses in a transformer get affected differently. According to IEEE std C57.110 [8], total load losses can be divided into three parts, viz. copper loss, winding eddy current loss and other stray losses. Different specifications of test transformer have been listed in Table B.6. As per [13], the percentages of and are 33 and 67%, respectively, in in the case of oil immersed transformer. Once all the losses at rated conditions are known, the losses in harmonic environment are calculated using Eqs. (10)–(12).