Utility Power Supply Research Articles

Fault Diagnosis of Power Distribution Feeders with PV System Using Equivalent-Input-Disturbance Approach

This paper describes a fault diagnosis method based on the equivalent-input-disturbance (EID) approach to power distribution feeders connected to a photovoltaic (PV) system. Node faults are treated as a system disturbance and are estimated using an EID estimator. First, a dynamic model that contains both the PV system and a power supply utility for the feeder is built. Second, an EID estimator is constructed to estimate the disturbance to the system on the control input channel. Third, a method for abstracting the amount caused by the PV system in the EID is presented to estimate the effect caused by faults. Simulation results demonstrate the validity and superiority of the method.

Development of a Solar Photovoltaic Power System to Generate Electricity for Office Appliances

In this paper a solar photovoltaic power supply system was developed to power office appliances. The system forms an alternative power source to the government own utility power supply in Nigeria, which is unreliable and epileptic in nature. It consists of photovoltaic array, mounting frame, storage device, inverter, charge controller and wiring system. The solar power system was tested in Akure, Nigeria (Latitude 7.15 o N) and the results obtained showed a good performance of the system. The output of solar power system is a function of solar radiation. The power output was high between 10.00 and 16.00 hours, which corresponds to the period of high solar radiation and coincides with the office hours. An average solar power output of 334 watt was obtained during test, while the total load of office appliances carried by the system was 290 watt.

ENGLISH

Arc fault protection of RF and microwave tubes generally needs short circuiting the high voltage DC plate power supply within few microseconds. A crowbar device is used for the purpose. This conventional method puts enormous stress on the power supply and can cause considerable disturbance in the power lines. Such short circuits of conventional supplies can be avoided by using a suitable solid-state series switch that can open the fault. A trigger circuit for eight IGBTs connected in series is designed, developed and tested for the purpose. Each IGBT floating at different DC voltage imposes strict isolation requirements for individual driver circuits. They must also be suitably isolated from utility power supply. Further, if IGBTs are switched ON at different instants of time (known as jitter), the last IGBT would see a full voltage switch-on and may get damaged. Hence, the jitter among different output signals of different driver circuits should be as low as possible. This paper presents the design requirements of isolation and jitter. The design of optical transmitter, optical receiver and driver circuits would be discussed in detail. Results of four of the channels trigger circuit, assembled and tested to obtain less than100nsec jitter, are highlighted.

Asset management frameworks for outdoor composite insulators

Power supply utilities are continuously working to maintain reliable and efficient electrical networks that meet the growing demand for electricity. This is a complex task in which appropriate maintenance, refurbishment and replacement policies for all the assets are critical. Optimising business processes through these constitutes a key challenge of balancing service quality and stakeholder value. Here we present two frameworks that can be used to effectively condition monitor both ethylene propylene diene monomer (EPDM) and silicone rubber (SiR) composite insulators during their lifetime in service. The frameworks are tools to assist asset management decision making. The first framework is derived from a generalized dielectric ageing framework and a more specific one on composite insulators that points out the elements that govern composite insulator materials? ageing on power transmission and distribution lines. The second framework defines four aged states in relation to the risk to failure that a composite insulator has in service before its replacement. Properties of materials that can be measured in order to identify ageing are reviewed. The techniques available as engineering tools for measuring these properties are introduced. These are distinguished as techniques that can be carried out on-line and off-line, and as destructive and non-destructive tests. These techniques are then reviewed in the context of monitoring and maintaining reliable and efficient operation of power networks.

Development of a universal DC power supply using solar photovoltaic, utility and battery power sources

In this paper, a universal direct current (DC) power supply system was developed and tested in order to provide uninterrupted power for DC appliances. The system employs simple Diode OR logic for the three power sources (mains from utility power supply, the solar photovoltaic and battery). The parallel combination of the three diodes at the output functions like a comparator circuit and compares the outputs voltage of the three sources, so that the highest voltage at a particular time feeds the DC output and supplies the charging current to the battery. The universal DC power supply system was tested under various operating conditions and the results obtained showed a good performance of the system. The system outputs, when all the power sources were available, during utility power failure and when only the stored energy in the back-up battery was available were 13.8, 13.1 and 12.2V, respectively. The system guarantees an uninterrupted power supply, which can be used to power telecommunication equipment, audiovisual materials, computers, DC motor driven devices and other DC appliances. A typical day solar radiation varied from 547 W/m2 to 865 W/m2 while the generated voltage from PV varied from 11.8 V to 13.7 V. The generated voltage from solar power source increases with the increase in solar radiation.

Costes normalizados y completos en la prestación del servicio eléctrico, como herramienta para la toma de decisiones empresariales

The purpose of this paper is to discuss the calculations of costs of power supply utilities for internal management purposes. To this end, we analyze the major phases of the value chain in the electric power sector, i.e. generation, transmission, distribution, and trading. The author suggest ways to overcome the shortcomings and describe practical applications of the proposals. The methodology makes it possible to estimate the cost of each of these variables and then to aggregate them to show the costs per state and activity. Finally, a summary showing the operational performance in terms of revenue and costs per service, sales office, and estimated benefits paid, among others. The paper provides tools for recognizing departmental structures whose performance should be improved.

Design control and implementation of a three-phase utility power supply based on the matrix converter

A matrix converter and a variable-speed diesel generator are integrated to create a three-phase utility power supply. The matrix converter is designed to meet strict harmonic and transient response requirements while allowing variable voltage and frequency input from the generator's permanent magnet alternator. This enables the generator to provide stable power over a range of engine speeds and load conditions. A 10 kW experimental prototype is designed, realised and tested as an offline power supply, and the results are provided to demonstrate the system performance.

Application of Cost Effective Solutions for Improving Voltage Sag Immunity of an Automated Cement Manufacturing Plant

Quality of the power supply becomes a key issue in factory automation. Especially voltage sags appearing on the electricity supply cause voltage sensitive equipment to shutdown and incurr heavy financial losses by interrupting the manufacturing process. However, effects of voltage sags can be minimized considerably if both the utility and the factory are working with good cooperation. This paper presents a Sri Lankan experience of finding out sag minimization or mitigation techniques through a study jointly carried out by the power supply utility and a customer. By analyzing the plant disturbance reordered for a five a year period and measurements taken with a sophisticated power quality disturbance recorder it has been observed that voltage sags appearing on the factory supply are mainly caused by faults and subsequent switching operations taking place on the transmission and distribution network of the power utility. In addition to that switching operations carried out in the factory owned distribution network also result in voltage sags. In this study, investigations were carried out for estimating the severity of voltage sags associated with different types of faults in the utility network and their effect on the equipment installed in the factory. Especially the effects of voltage sags on the equipment vulnerable for production process like large induction motors and vector controlled Variable Speed Drives (VSD) were investigated to find out the possibilities for improving their voltage sag immunity. Simulations are extensively used to describe field observations. Adequate theoretical descriptions are given to justify field observations and simulation results. Even though well proven sophisticated equipment is available for voltage sag mitigation these are not taken into consideration here due to their high cost. Instead, simple solutions such as distribution network rearrangement, reviewing protection settings and activating already embedded control algorithms in sensitive equipment are considered. Most of the solutions discussed here do not incur additional cost. Remarkablygood results have been gained by applying these techniques.

A Utility Power Supply Based on a Four-Output Leg Matrix Converter

A four-output leg matrix converter and a variable-speed diesel generator are integrated to create a three-phase plus neutral utility power supply. The matrix converter is designed to meet tight harmonic specification and the fourth leg provides the facility to supply unbalanced and single-phase loads. This enables the generator to provide stable power over a range of engine speeds and load conditions. Two modulation techniques for four-output leg matrix converters have been considered and compared. Test results for a 10-kW offline power supply are provided to demonstrate system performance.

Control Design of a Three-Phase Matrix-Converter-Based AC–AC Mobile Utility Power Supply

This paper describes the control analysis and design of an ac-to-ac three-phase mobile utility power supply using a matrix converter capable of high-quality 50-, 60-, and 400-Hz output voltage and reduced input harmonic distortion. Instead of the traditional structure employing a diode bridge rectifier, a dc link and a pulsewidth-modulated inverter, a three-phase-to-three-phase direct ac-ac (matrix) converter has been used as the power-conditioning core of the system, working in conjunction with input and output LC low-pass filters. An optimizing control design method using a genetic algorithm approach has been used, which yields designs to minimize a cost function, taking into account transient and steady-state output voltage performance targets, together with robustness to different operative conditions and system parameters drift. Simulation and experimental tests have demonstrated that the system meets the power-quality requirements of the application.

Back to basics: Filtration in the power generation sector

Ken Sutherland looks at the use of filtration and related separation equipment in the generation of electrical power for the power supply utilities and other large users.

Selecting ASD systems

This article covered a large number of issues that are addressed by the NEMA Application Guide for Adjustable Speed Drive Systems that must be considered for successful application of an ASD system. The material covered here should be helpful in bringing issues to light that may be critical for the application engineer to consider while creating an initial specification. It is clear that such a specification must consider the interrelationships between the driven load, the motor, the control, and the utility power supply. The authors believe that all users of ASD systems would be llserved by having a complete copy of the NEMA's freely available application guide for ready reference when planning and installing a new ASD installation.

Ride-through for critical loads. Exploring a low-cost approach to maintaining continuous connections between buildings and/or industrial systems

A low-cost approach to provide ride-through capability for critical loads has been explored. The approach provides continuous power to the load under two operational modes. Normal mode allows the load to be connected directly from the utility power supply, as long as it remains undisturbed. Once a voltage sag appears, the load is transferred to an inverter that provides the ride-through mode. The output of the inverter is synchronized with the utility input and is regulated by keeping the DC-link voltage regulated, too. An external energy source can be incorporated in the DC-link to provide ride-through during short-term power interruptions. Results show that the detection of the disturbance is quick, and the transfer between operational modes is seamless, causing no evident problems to the load. High efficiency is only achieved by applying the ride-through operational mode during the disturbance duration. Reduced size and low cost are additional characteristics of the proposed approach.

Design and operation of burn-in test system for three-phase uninterruptible power supplies

In this paper, a new approach for the burn-in test of three-phase uninterruptible power supplies is proposed. This method can perform the energy recovery for reducing the test cost, while the current supplied from the utility can be steered to be more sinusoidal. When a large number of burn-in test systems are activated such that harmonic problems may become more serious, the proposed method is also suggested based on its immunity to possible harmonies infiltration coming from the tested product to the utility power supplies. This method has been tested through simulation study and hardware experiments. Test results help consolidate the feasibility of the approach for the applications considered.

Study on Predicting Lightning Damage to Utility Power Supply Systems Using Cloud-to-Ground Lightning Information from the Internet

Study on Predicting Lightning Damage to Utility Power Supply Systems Using Cloud-to-Ground Lightning Information from the Internet

New high power, high performance power converter systems

A new, high performance, low cost power converter system architecture is proposed. The system consists of a main converter and a multifunctional load conditioner. The main converter deals with most of the power flow running at a low switching frequency. The load conditioner is designed at a much lower power level running at a high-switching frequency. The load conditioner can (1) act like a current source and inject harmonic currents required by the load; (2) act like an active resistor to provide damping to the main converter; and (3) for three-phase inverters, decouple the coupling sources in the main inverter model in the rotating coordinates to make the control loop design for the main inverter much easier. The concept has been proved by simulation and experimental results on a 150 kW high performance three-phase utility power supply prototype. The proposed system configuration can be used in high power DC-DC converters, inverters, PFC and UPS applications.

A novel induction machine design suitable for inverter-driven variable speed systems

Induction machines designed for inverter-driven variable speed systems are different from those fed directly from a utility power line. In this paper, a novel design approach for inverter driven induction machines is presented and implemented. This is followed by an investigation on sizing equations and rotor slot shape specifically for this purpose. The proposed approach permits the integration of the design of machines with inverters, comprehensive performance analysis, and system optimization, resulting in 20-30% higher power density for the induction machine than those designed for direct utility power supplies by conventional methods. Simulation analysis and experimental results are presented to substantiate the conclusions.

Implementation of discrete-time field-oriented current control

This paper studies performance sensitive issues encountered in the implementation of all-digital discrete-time field oriented current control of an AC motor. In particular, the focus here is on the interface between the vector current control algorithm itself, and the motor/inverter system. The effects of interface components such as antialiasing filters, rotational transformations, and phase-to-line-voltage transformations are analyzed. In addition, a straightforward all-digital pulse width modulator is presented along with a new algorithm to naturally inject triplen harmonics into the motor line voltages, and thereby increase power supply utilization by 15%. Real-time operation of a discrete-time vector current controller verifies the analysis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Delta-modulated buck-type PWM converter

A delta-modulated, current-source, three-phase pulsewidth modulation (PWM) rectifier is described. The rectifier is intended to be used in conjunction with controlled current inverters. An outer proportional feedback loop regulates the unidirectional output current flowing through the DC link. An inner feedback loop maintains near sinusoidal waveform currents at unity or leading power factor from the utility power supply. The inner loop controls the current indirectly by delta modulation of the voltage across the AC terminals of the converter. The converter has been conceived as the circuit dual of the hysteresis current-controlled boost-type rectifier. Experimental results from a laboratory model are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Expansion Planning of Hydrothermal Power Systems, Optimizing the Multiple Uses of the Water from Hydroelectric Power Plant Reservoirs, via Conversational Multi-Objective Algorithms

Often the development of hydroelectricity has an overwhelming role in the utilization planning of regional water resources. For such situation, it is proposed in this paper to approach the power system expansion problem on a two objective basis. The first one is the cost minimization of the power supply, while the second one is the maximization of the overall net benefit accruing from the multi-purpose regional water usage. The nature of the problem is such that conversational multi-objective methods are particularly attractive for its solution. The joint optimization of the two objectives is carried out with the help of two powerfull alternative conversational techniques: the Surrogate Worth Trade-off Method and the Interactive Sequential Goal Programming Method. Applications to the generation system of a Brazilian power supply utility indicate the former method as the best for this class of problems. The expansion plans are provided by a “global” (it performs the expansion and operation steps simultaneously) generation planning model using linear programming.