EPQU Magazine - Vol 2 Issue 1

Virendra Ajodhia, Konstantin Petrov, Gian Carlo Scarsi, Bart Franken

Both theory and practice suggest that incentive price regulation, without additional quality measures, eventually leads to quality degradation: the strong cost reduction incentives (driven by the profit incentive) have the perverse effect of inducing sub-standard quality levels. Thus, under economic regulation models using incentive schemes, quality regulation becomes imperative.

This paper describes experience in Italy, the Netherlands and the UK with regulation of network quality. It shows that regulation could influence network quality significantly using different types of regulation. Starting with indirect instruments like the publication of reliability statistics, Regulators proceed with introducing standards and attached penalties, e.g. in case a power interruption takes longer than a predefined threshold, the customer facing the interruption receives a payment. Finally, incentive schemes are introduced. Incentive schemes compare measured network quality and targets. In case the network companies fail to meet their targets they are penalised. In contrary, when they exceed their targets they are rewarded. We show that, especially in Italy, network quality improved significantly, after the incentive schemes were introduced. However, the limited information about relations between costs and quality, and about customer preferences, strongly affects the effectiveness of such quality incentive schemes. Designing a method to properly compare companies and translate this into an integrated price and quality regulation system is a challenge that still lies ahead.

J.F.G. Cobben, J.F.L. van Casteren

Ongoing processes of restructuring and regulation are taking place in the electricity sectors of all European countries. These processes are targeting towards more transparent competition in the generation and retail of electrical energy. The physical transmission and distribution of electricity is thereby considered to be a natural monopoly that is to be unbundled from generation and retail and which needs to be regulated. New performance based regulatory frameworks are discussed, such as price caps or revenue caps. In order to avoid transmission and distribution companies reducing their costs at the expense of power quality, some type of quality regulation has to be put in place. In addition to the economical regulation, which aims at providing strong incentives for cost reduction and efficiency, the quality regulation must at least provide incentives for safeguarding minimum levels of power quality. More ideally, a regulatory framework shall create an environment where it becomes a natural ambition for transmission and distribution companies to provide their customers with an optimized mix of low price and high quality.

As modern societies become more and more sensitive to power quality problems, some kind of PQ-regulation will become inevitable in the near future. Such regulation will not be possible without sound and transparent tools for monitoring and reporting the PQ levels. These levels are used not only for regulatory issues, but also for coordination between the manufacturers of electrical equipment, the customers and the transmission and distribution companies. This article shows methodologies for quantifying PQ-levels for a range of power quality problems.

Roberto Chouhy Leborgne, Gabriel Olguin, Jose M. Carvalho Filho, Math H. J. Bollen

This work addresses the influence of the PQ-monitor connection on the estimation of voltage dip site and system indices. Voltage dip indices are estimated for a set of events obtained from simulation and measurement of voltage dips. The simulated dips are obtained applying the method of fault positions on a large transmission network and the measured dips come from a one-year survey realized on three buses of a sub-transmission and distribution network.

The site and system indices estimated to compare phase-to-phase and phase-to-neutral dips are SARFI-90, SARFI-70, SARFI-ITIC, expected voltage dip amplitude (µ[VDA]), and the cumulative distribution frequency of voltage dip amplitude. These indices are estimated at the bus level and then they are aggregated to estimate the system performance. The comparison of phase-to-phase and phase-to-neutral indices indicates that, at high voltage level, phase-to-neutral dips are more frequent and more severe than phase-to-phase ones. However, these differences are damped at low voltage level, where the monitored bus presented similar indices for phase and line voltages.

These observations must be taken in consideration to compare voltage dip benchmark because the lack of information about the type of the measured voltages may lead to derive inaccurate conclusions about the site and system performance regarding voltage dips.

L. Horton, N.G. van Luijk

During the past 20 years an increasingly competitive power industry has recognised the importance of addressing the issue of power quality. Many companies now take an active roll in addressing the problems associated with power quality. They are investing in the research and development of equipment to overcome power dips, surges and interruptions, and offering the customer a wide and varied choice of solutions and services to their power quality needs. These solutions are usually based on overcoming the limitations of individual equipment, which is being used by the customer, rather than making improvement to the quality of power supplied. This paper aims to bring to light the incipient problems experienced on LV underground networks, the reasons for the problems and their affect on the end customer and a utilities CML statistics. (Customer Minutes Lost CML is a method of measuring the performance of the network in the UK) This paper presents the research work carried out by LEM and EDF Energy to identify how to detect and locate faults using online techniques. The finding of this research is being used to reduce the downtime experienced by customers by decreasing the time involved in resolving these reoccurring problems.

Hossein Mokhtari, Abolfazl Zebardast, Mostafa Parniani

This paper presents the results of a thorough analysis of failure of TSC modules in a steel mill plant. The TSCs are used to reduce the flicker level caused by the arc furnace loads used in the plant. The plant is modeled and Harmonic analysis is carried out. Statistical analysis is performed and the results are compared with IEEE 18 standard limits. The system is analyzed and the resonance modes are extracted. Site measurements are carried out, and the results, which verify those obtained by the simulations are also presented.

Jordi Cusido, Javier Rosero, Emiliano Aldabas, Juan Antonio Ortega, Luis Romeral

Double frequency tests are used for evaluating stator windings analyzing the temperature. Likewise, signal injection on induction machines is a well-known technique on sensorless motor control fields to find out the rotor’s position. Motor Current Signature Analysis (MCSA) is the most widely used method for identifying faults in Induction Motors. MCSA focuses its efforts on the spectral analysis of stator current. Motor faults such as broken rotor bars, bearing damage and eccentricity of the rotor axis can be detected. However, the method presents some problems at low speed and low torque, mainly due to the proximity between the frequencies to be detected and the small amplitude of the resulting harmonics respectively. In both cases, the problem of frequency accuracy is very tricky since the sideband harmonic is close to the fundamental harmonic. This paper proposes injecting an additional voltage into the machine under test at a frequency different from the fundamental one, and then studying the resulting harmonics around the new frequencies appearing due to the composition between injected and main frequencies.

Jaroslaw LUSZCZ, Krzysztof IWAN

Conducted EMI generated by an inverter-fed induction motor drive systems with the pulse with modulation (PWM) are one of the most difficult current technical problem which limits power electronics drive’s evolution. The conducted and radiated emission of PWM drives is essentially related also to the electric behaviour of the frequency converter’s load which is AC motor and motor cable. Detailed analysis of the impedance characteristics of the converters load (motor and cable) is fundamental to interpret the common and differential mode of emission spectra of the converter. Presented identification of the impedance parameters of the evaluated drive system is based on the measurement of impedance characteristics, which allows determining the adequate circuit model for different frequency ranges. Obtained results illustrate the different behaviour of the investigated motors for different frequency ranges and explain the influence of the motor power cable on the investigated phenomena in the high frequency ranges. Presented analysis and measurement results leads to the conclusion that the impedance characteristic of the converters load can be very helpful for analysing high frequency phenomena in the converter-motor link. The over-voltage and conducted EMI problems in many of ASD application with high power motor and long cable can be clarified by load impedance analysis. The impedance analysis allow to determine the high frequency range where for modelling transmission line based model is evidently necessary, instead of much more simple circuit model.

Roger Bergeron

Multi-Cycle symmetrical control (MCSC) for application above 1.2 kW fails compliance tests once IEC 61000-4-7 edition 2 introduced a new assessment method which groups inter-harmonic into the harmonic levels. MCSC-driven apparatus up to 3 kW may succeed the compliance test if IEC 61000-4-7 neglects interharmonic components at frequencies below the second harmonic order. Upon the power level, MCSC-driven apparatus could disturb the ripple-control system needed for communication. Probabilities of disturbance at 116, 183 and 216 Hz with MCSC applications above 1.2 kW exceed the 5% EMC rule particularly for power rating nears to 3 kW.

By Walter Hulshorst, At Keet and Johan Enslin

At its plant in the Dutch town of IJmuiden, steel-producer Corus has its own electricity network. For steel making electrical energy is needed, specially for the mill section, due to older techniques these installations produces more voltage distortion on the Corus network. This can cause equipment outages, and thus halt production. This paper presents an innovative solution to these problems, thereby limiting production losses and system mal operation and without exceeding of harmonic limits at the connection to the grid- operators network.

Published in EPQU Magazine, Vol 2 No 1, pp 57-64

Lucian Asiminoaei, Steffan Hansen, Frede Blaabjerg

This paper describes the measurements and simulations of harmonics from adjustable speed drives in a 1.2 MVA Heat Power Station application. The simulations are done in two ways, one by Pspice circuit simulator and the other by a custom developed harmonic toolbox. It is proven that Pspice is more flexible and offers a better precision in estimation, but in turn the developed toolbox is more practical and relatively accurate for many useful evaluations. Both harmonic simulations are validated by real measurements for the given plant, within an error of 5 % between the measured and the simulated data. Due to a very close match, the simulators are used further to analyze different harmonic mitigation solutions. The best solution found by simulations, for the given plant, is an advanced harmonic filter dedicated for adjustable speed drives, which is currently in the installation stage.

Alex McEachern

Six-pulse rectifiers, five centuries ago