N. Schofield

Bio: N. Schofield is an academic researcher from University of Delaware. The author has contributed to research in topics: AC power & Harmonics. The author has an hindex of 1, co-authored 1 publications receiving 5 citations.

Shunt active power filtering for smart appliances

Abstract: Due to the increasing trend towards energy saving white goods appliances and the commercial viability of power electronic components, there has been an expansion in the use of solid state electronics and variable frequency drive motors in these applications. However, a major drawback of using such energy efficient loads is the introduction of current harmonics onto the local distribution grid. Furthermore, the proliferation of such devices elevates the supply harmonic content and can potentially impact residential distribution networks. This paper investigates the harmonic content generated by some household appliances and suggests a solution to minimize harmonics by means of active filtering. An active filter circuit was simulated to compare filter performance when used as an active front versus a feeder input compensator.

Evaluation of harmonics impact on digital relays

Abstract: Digital relay is an important part of the power system and actually is based on fundamental frequency (50–60 Hz). Digital filter is applied for further processing and performs mathematical operations on sampled values. The digital signal processing (DSP) becomes more applied and used in proactive relays. Obviously, DSP is used in wide range of application (controls, radio, communications and other devices). In this paper the comparison between the conventional digital relay and developed relay using Matlab/Simulink is performed. As known the conventional relay is using mathematics algorithm to calculate the current input signal and to evaluate the fault current, total harmonic distortion (THD) and harmonic components. Likewise, the developed relay is using the current signal and evaluates it and converts the input signal to digital signal. Since the digital signal is more flexible and easier to progress it and work on it. Importantly, the test is used to evaluate the functions and mathematics for both relays.

Development of Shunt Active Power Filter for Harmonic Reduction using Synchronous Reference Frame with Space Vector Pulse Width Modulation

Abstract: The work aims at development of Shunt Active Power Filter (SAPF) for harmonic reduction. The current harmonics are being caused by nonlinear characteristic of power electronics based equipments which increase power losses and in turn reduce power quality. Synchronous Reference Frame (SRF) was used as a control strategy and for reference harmonic current generation and Space Vector Pulse Width Modulation (SVPWM) was adopted as switching signal generation. With RL load under balanced input voltage condition, the developed SAPF-SVPWM achieved a reduction of THD of 0.91% as compared to 25.60 before compensation. In addition, the developed SAPF- SVPWM model was compared with SAPF without compensation using RL load under unbalanced voltage and the result shows that the developed SVPWM achieved reduction in THD of 1.74 % as compared to 26.68% after and before compensation. The developed SVPWM model was also compared with SPWM balanced and unbalanced voltage condition. The results show that SVPWM performed better than SPWM. All the results obtained are within IEEE 519 harmonics standard (i.e. THD less than 5%) with nonlinear load under balanced and unbalanced voltage. Keywords: Shunt active filter, input voltage, harmonics, space vector pulse width modulation, nonlinear load.

The effects of harmonics on overcurrent relays

Abstract: This paper analyses the influence of current harmonics on protections devices connected to the power system which can cause serious problems. This paper outlines work that has been conducted to test of overcurrent relay and to identify the impacts of harmonics on distribution utility protection and control systems. The overcurrent relay REJ 525 is based on a microprocessor environment. A self-supervision system continuously monitors the operation of the relay.

Evaluation of Active Filter Design and Harmonics Analysis Using MATLAB

Abstract: Nowadays, electricity becomes one of the most important necessities in the world. Designing the filter is one way to improve power quality in delivering electrical power to the consumer. In recent times, the usage of non-linear loads has been expanded throughout the world. These loads carry harmonic non-sinusoidal voltages and currents with the utility in the cohesion point and disperse them through it. The generation of these voltages and currents into the grid affects the client’s equipment and the power systems. This paper presents the evaluation of filter design and harmonic analysis of the system network. For filter design and analysis, MATLAB/Simulink is used. Shunt Active Power Filter (SAPF) has been proposed as an effective tool to compensate reactive power and improve power quality. DC link voltage is used to boost the SAPF’s efficiency in an un-balanced and distorted voltage system. Simulation result shows that SAPF will lessen the Total Harmonic Distortion of line current from 30.73% to 8.21%, which satisfies the standard of IEEE-519.

In-Situ Domestic Load Harmonic Detection and Reduction Based on GLRM Algorithm for Optimum Filter Excerpt

Abstract: Power Quality measures the reliable operation between the system and to the connected loads of same system. A poor power quality causes physical damage to the equipment and also results in lower productivity with increase in energy costs. Power disturbances range from micro seconds to hours and the prolonged disturbances in hours would damage the equipments. The power quality decreases due to growth of nonlinear loads in domestic appliances, such as home Uninterrupted Power Supplies (UPS), Induction stove, Television etc. Nowadays Domestic loads are controlled or powered with power electronic devices. The power electronic devices with Direct Current (DC) components generate high frequency signal for DC-Alternating Current (AC) conversion. The conversion introduces multiple frequencies in the AC power supply. The multiple frequencies in AC power supply are called as harmonics. The harmonics in AC supply affects the lifetime of home appliances, consumes more electric current, affects the power factor, transformer efficiency, and other electricity supply systems. Till now, to avoid harmonics, the filters are erected only in industrial loads or in the substations. In this paper a novel method to detect and control harmonics in domestic appliances is proposed. Harmonic control with various filters in the filter bank, based on detection of harmonic voltage let out from the domestic appliances for power saving. To select the appropriate filter to improve power quality, we apply a novel Genetic Algorithm based Linear Regression Method (GLRM) algorithm for optimum Filter Selection. From the results we were able to reduce the total harmonic distortion level to 3.68%.The current consumption of each household appliance is reduced considerably and finally the electricity bill is reduced to 15% and overall system efficiency improves to 85%.