Power quality of power systems affects all connected electrical and electronic equipment. Power quality is a measure of deviations in voltage and frequency of the particular supply system. In recent ...years, there has been a considerable increase in nonlinear loads; in particular distributed loads, such as computers, TV monitors and lighting. These draw harmonic currents which, when distorted, have detrimental effects including interference, loss of reliability, increased operating costs, equipment overheating, motor failures, capacitor failure and inaccurate power metering. This subject is pertinent to engineers involved with electric power systems, electronic equipment, computers and manufacturing equipment. This book shows readers to understand the causes and effects of power quality problems such as non-sinusoidal wave shapes, voltage outages, losses due to poor power quality, and origins of single-time events such as voltage dips, voltage reductions and outages, along with techniques to mitigate these problems.
Since the beginning of railway electrification, power quality has been a main problem in railway networks because of their special characteristics. Many ways of power quality improvement have been ...investigated and applied to ac and dc traction systems through railway electrification history. This paper presents a perspective on power quality issues through railway electrification development and investigates the necessity of power quality and system requirements for appropriate power quality. Compensation strategies are classified and compared. This aims to provide a comprehensive perspective of the power quality issue in railway power/distribution networks for researchers and engineers working on railway electrification. Less than 100 research articles are referenced for researchers to obtain good background information.
This paper presents a new genetic algorithm (GA)-based approach for the simultaneous power quality improvement and optimal placement and sizing of fixed capacitor banks in radial distribution ...networks in the presence of voltage and current harmonics. The objective function includes the cost of power losses, energy losses and that of the capacitor banks. Constraints include voltage limits, number/size and locations of installed capacitors (at each bus and the entire feeder) and the power quality limits of standard IEEE-519. Candidate buses for capacitor placement are selected based on an initial generation of chromosomes. Using a proposed fitness function, a suitable combination of objective and constraints is defined as a criterion to select (among the candidates) the most suitable buses for capacitor placement. A genetic algorithm computes improved generations of chromosomes and candidate buses until the solution is obtained. Simulation results for two IEEE distorted networks are presented and solutions of the genetic algorithm are compared with those of the maximum-sensitivities-selection (MSS), the maximum sensitivities selection-local variations (MSS-LV), and the fuzzy set algorithms. The main contribution of this paper is the computation of the near global solution, with weak dependency on initial conditions.
The measurement of real and apparent power derating of three-phase transformers is important for transformers feeding nonlinear loads. This paper presents a new digital data-acquisition method for ...measuring derating and reactive power demand of three-phase transformers under full or partial load conditions. The accuracy requirements of the instruments employed (potential, current transformers, shunts, voltage dividers, optocouplers volt- and current meters) are addressed. Application examples demonstrate the usefulness of this new digital data-acquisition method.
The online monitoring of iron-core and copper losses of single- and three-phase transformers is important, particularly for transformers feeding nonlinear loads. This paper devises a new digital data ...acquisition method for the separate online measurement of iron-core and copper losses of three-phase transformers under any full or partial-load conditions. The accuracy requirements of the instruments (voltage and current sensors, voltmeters, and ammeters) employed are addressed. The measurement uncertainties are acceptably low if voltage and current sensors with 0.1%-0.5% accuracy are used.
Experimental and analytical studies of the effects of voltage and current harmonics on induction machines, transformers, appliances, and relays show that the present versions of IEEE and IEC are too ...restrictive for low-frequency voltage and current (integer) harmonics, as they apply to residential power systems. It is recommended that not rigid but flexible guidelines are established so that different harmonic spectra are permitted which result in the same additional temperature rise in transformers and induction machines. Very restrictive amplitude limits for inter-harmonics and subharmonics should be included in the revision of the above standards due to their detrimental effects on under-frequency relays (malfunctioning), lighting equipment (flicker) and rotating machines (harmonic torques).
The eddy-current loss coefficient of a transformer can be determined by using the harmonic amplitudes of input current and the corresponding harmonic copper losses when the transformer supplies ...nonlinear loads. Measured data show that eddy-current loss is a linear function of frequency with a power of 2. Apparent power (kVA) derating of single-phase transformers operating with nonsinusoidal currents and voltages is measured by adjusting the total losses to the rated losses at rated temperature, whereby hot-spot considerations are ignored. Computed results of derating using the harmonic loss factor (F/sub HL/), eddy-current loss coefficient P/sub EC-Rnonlinear/ and iron-core losses match well with measured data. However, the real power derating of transformer is much greater than apparent power derating for a given THD/sub i/ value, and it is independent of the frequency spectra of the harmonics. Experiments show that the other stray losses (P/sub OSL/) in nearby conductive solid components are proportional to the power of 0.8 at low frequencies and are inversely proportional to the power of 0.9 at high frequencies.
A simple, fast and reliable technique for charging batteries by solar arrays is proposed. The operating point of a battery is carefully forced near the maximum power point of solar cells under all ...environmental (e.g., insolation, temperature, degradation) conditions. Optimal operation of solar arrays is achieved using the Voltage-Based Maximum Power Point Tracking (VMPPT) technique and the charger operating point is continuously adjusted by changing the charging current. An optimal solar battery charger is designed, simulated and constructed. Experimental and theoretical results are presented and analyzed. The main advantages of the proposed solar battery charger as compared with conventional ones are shorter charge time and lower cost.
Commonly used speed-control concepts permit speed ranges up to two-three times the base speed via voltage to frequency (V/f), that is, field-weakening control. This paper teaches the extension of the ...speed-control range up to nine times the base speed through online reconfiguration of the motor windings via electronic switches. The switchover of the windings, either from a winding with p 1 poles to p 2 poles, or from series to parallel connection of the number of turns per phase-so-called (V/Nldrf) control-lasts less than a 60-Hz cycle. Such fast switchover causes small transients only, and therefore, this concept is applicable to most variable-speed drives.
