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NEWSJOURNAL EIGHTH YEARN ° 8 4 / J U N E 2 0 07
Dossier on electrical Power systems anD metrology
Comparison of impedance meters for LV gridsHelping operators make the best purchase decision
Dutch grid operators, among which Essent, asked Laborelec to make a comparative study of different devices for measuring the impedance and fault voltages on LV grids. Our team assisted in choosing the best out of six meters. It also investigated the achievable accuracy of such measurements as well as the possibility to determine those characteristics by calculation.
CONTENTS
Training course on electrical protections p. 1
Comparison of impedance meters for LV grids p. 1
Power quality assessment for the Dutch grid p. 2
State of PQ on the Sotel distribution grid p. 2
CIRED 2007 - Networking in an open electricity market p. 2
Remote reading of energy consumption p. 3
More detailed audits of electrical protections p. 3
New method for tracing flicker sources p. 4
Detecting insulation defects in power generators p. 4
The technical Competence Centrein energy processes and energy use.From innovation to operational assistance.
Training course on electrical protectionsLast February, Laborelec conducted a training course on electrical protections for about 25 staff from Electrabel Marketing & Sales. The purpose was to enable them to answer technical questions from industrial clients on their protection strategy and on any problem encountered. We tackled the protection of low and medium voltage grids, including protec-tion strategies, existing protection devices, and parameter setting. The course was a great success among participants, who suggested extending it from one day to two days.
In the Dutch distribution grid, the safety of the end-users relies on proper interconnection of the neutral and protection conductors of the grid with those of the users (TN system). Grid operators have to measure the short-circuit currents and fault voltages regularly to ensure safety. These measurements haven to be done in service, without disturbing the users, making them quite difficult. Previous studies have demonstrated that the accuracy of the measurement devices in these circumstances can be poor.
Development of a specific test benchIn this context, Essent asked Laborelec to assist them in choosing the best equipment for replacing their measurement devices. We studied the technical performance of six pre-selected meters and ranked them. We first tested their accuracy in laboratory,
on circuits with known impedances. We then studied measurement reliability under various circumstances such as the presence of harmonics or when subjected to large temperature variations. A specific test bench was developed to enable these experiments. Finally, we tested the meters in the field. This led us to establish a ranking of the meters.
Evaluating analytical methods When the topology and characteristics of the grid are known, short-circuit currents and fault voltages can also be calculated. Our team tested the precision of two computation tools by comparing their results with measurements on site. The results were quite satisfactory considering the limited knowledge of the true characteristics of the LV grid and the intrinsic sensitivity of those measurements and calculations. [email protected]
2 JOURNAL EIGHTH YEAR - N° 84 / JUNE 2007 - Dossier on electrical Power systems anD metrology
Power quality assessment for the Dutch grid
The new Laborelec subsidiary in the Netherlands was recently asked by the Dutch government to participate in the EOS (Energie Onderzoek Subsidie – subsidy for energy research) program. This project studies the future of power quality of the Dutch electricity distribution grid.
In the past years, it has become increasingly difficult for distribution grid operators to maintain a high power quality. The main reason is that more and more power electronic devices and small generation units, such as wind turbines and photovoltaic cells are being connected to the grid. Both of these can produce a large number of disturbances.In this context, the Dutch government began launching research programs in 2006, with the aim of guaranteeing a reliable and sustainable energy supply for tomorrow’s grid. Laborelec Netherlands was asked to participate in the EOS program. Our team is currently monitoring power quality at twenty locations on the grid. All locations are close to the connection point of small generation units and power electronic devices. These measurements include, among other things, harmonic and flicker levels.With these data, the Dutch government will be able to better anticipate any future grid disturbances. This will enable it to define new rules for connecting generation units and customers to the grid.
The main sources of disturbances connected to the Sotel grid are three steel plants, which use large arc furnaces. The furnaces have aged and some have been upgraded since their installation about ten years ago. Consequently, Sotel wanted to re-evaluate their impact on grid PQ.
DWR facilitates large measurement campaignOur team used the Laborelec Digital Wave Recorder (DWR) to simultaneously measure the voltage and current signals at the connection points of the three plants. Thanks to this, signals did not require any further synchronization.The signals were monitored continuously for three weeks to obtain sufficient valid data as required by standards. In total, 700 gigabytes of data were recorded directly in the DWR memory.
Neutral interlocutor with industriesOur team deduced individual contributions to PQ disturbances from the DWR measurements thanks
State of PQ on the Sotel distribution grid
The Luxembourg electricity grid operator Sotel asked Laborelec to evaluate Power Quality (PQ) on its network and quantify the main sources of PQ disturbances. Individual responsibilities in disturbance emissions could be identified thanks to the Laborelec DWR tool and to homemade algorithms.
to proven algorithms developed by Laborelec. We calculated, among other things, steel plants contribution to harmonic voltages and flicker. To guarantee neutrality, Sotel asked us to communicate campaign conclusions to the steel industry. This was done last March. The next step will be to discuss the concrete measures that the plants could implement to reduce disturbances.
[email protected]. [email protected]
CIRED 2007- Networking in an open electricity marketThe CIRED is a major international conference and exhibition for the electricity distribution community that is held every two years. Laborelec actively participated to the 2007 edition, acquiring a good perspective on today’s and tomorrow’s distribution challenges.
The topics dealt with cover network components, power quality and electromagnetic compatibility, network operation, control and protection, distributed generation, management and use of electricity, power distribution system development, regulation, management, and organisation issues. In other words: a real opportunity to get a full picture of the electricity distribution business, at a time where the opening of the electricity market is a reality in most European countries.
Key contributor to event successLaborelec was actively involved in the 2007 edition in Vienna. Together with Elia, we organized and chaired the
technical activities related to power quality and EMC. The program included a one-day plenary session, a round table, a research and innovation forum, and a poster session. Our experts also presented several papers and posters.
A good perspective on future challenges Participating to such an international event gives us a complete overview on the very latest challenges and issues facing electricity distribution today and in the future, for the benefit of our sponsors.
3JOURNAL EIGHTH YEAR - N° 84 / JUNE 2007 - Dossier on electrical Power systems anD metrology
Laborelec can now audit protection strategies at industrial sites more precisely and rapidly. This is thanks to its newly acquired 3EI computer tool. It detects improvement potentials and makes concrete recommendations to optimize protection selectivity and installation safety.
An efficient protection strategy is paramount for industrial sites. In case of an electrical defect, it ensures that the defective installation is isolated from the grid, while the rest of the plant remains connected.The 3EI tool enables the analysis of every detail of the protection strategy. Unlike other tools, it enables the simulation of any type of industrial equipment, from any major OEM. Based on the plant model, it calculates all relevant protection parameters at every relevant point in the installation and compares them with best practices as well as with national and international standards. 3EI then automatically produces a comprehensive report including calculation results, recommendations for improvements, and a list of infractions.The report is handed to the plant operators and results are discussed with our experts, who can give concrete advices on the implementation of any necessary measures.
In an increasing number of European countries, conventional meters that are read manually once a year are considered not to be adapted anymore to today’s market needs. Pioneer countries made massive replacement with Smart Meters. Several others are running rollout projects. The technology is still maturing however. Critical issues are the ease of replacement of the meters, interoperability, data communication, data security, components lifetime, and scalability.
More detailed audits of electrical protection
Remote reading of energy con-sumption
Investigating possibilities for data com-munication
In the future, Smart Meters may well replace the mechanical meters that are presently used for measuring the energy consumption of Belgian households. The new type of meters would enable remote reading as well as many other services. Several critical issues have to be investigated for a seamless and successful deployment. Laborelec studies the communication and interoperability aspects.
Focussing on communication techniquesA Smart Metering network consists of intelligent meters located at residential customers, data concentrators that collect data from groups of meters, and a central server that receives these data. Laborelec studied several physical channels that can be used for transferring data between the different network units.
We made a technical and economic comparison of GSM and GPRS communication, taking advantage of the systems presently used for remote reading of industrial customers’ meters.We are also investigating communication by Power Line Carrier (PLC), through the electricity distribution lines. The quality of the communication requires thorough study as it highly depends on the type of network and on the installations behind user connection points. One question to be answered is whether the different modulation techniques (Frequency-shift Keying, Phase-shift Keying, Spread Spectrum) are equally adequate for reliable communication. We will conduct field tests on different types of network to answer these questions. Co-existence of different techniques on the same grid is also an issue to be cleared in due time.
Interoperability It is important for the grid operators to implement open system technologies, allowing to use components from different manufacturers. There is also a clear need for protocol stacks covering all communication and application layers in metering. That is why we are currently investigating the data exchange and communication standards that are suited for residential meter applications. The functions that the smart meters should fulfil to address today’s market needs are still under discussion in forums and conferences to which our experts are participating.
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Responsible editor: André Even
Rodestraat 125B-1630 LinkebeekBelgiumTel: + 32 (0)2 382 02 11Fax: + 32 (0)2 382 02 41
www.laborelec.com
Detecting insulation defects in power generators
On-line monitoring of partial discharges
Monitoring partial discharges in power generators enables to assess insulation quality and better plan maintenance activities. This helps to avoid insulation failure and severe damage caused by short circuits. Laborelec investigated several partial discharge monitoring systems and selected the best diagnostic tool regarding efficiency and reliability.
JOURNAL EIGHTH YEAR - N° 84 / JUNE 2007 - Dossier on electrical Power systems anD metrology
The insulation of generator’s stator windings is subjected to thermal, electrical, ambient, and mechanical stresses that lead to degradation. It is therefore crucial to assess insulation quality regularly. We studied several systems for monitoring stator windings condition in 2005. On-line monitoring through partial discharge (PD) measurements appeared to be very promising for detecting and locating weak spots. On-line measurements have the advantage that they do not require disconnection of the generator and enable an easy follow-up at any time.
Assessing defect sourcesSince not all insulation defects are equally critical, it is important to assess the type of defect before planning maintenance actions. Our team studied the PD monitoring method to make sure that it enables the identification of the defect type. Our analysis revealed that each defect type has its signature PD pattern, determined by the phase angle and the amplitude of PD pulses, as well as by the amount of PD. PD is therefore a good indicator of defect type.
Reliable interpretation of PD patternsWe tested several PD measurement systems and selected the most reliable tool regarding PD detection. The selected tool has the capability of separating mixed patterns. This enables us to make a reliable interpretation and follow up each PD source in the insulation separately.
Building up experienceWe recently installed the selected tool on three generators at an Electrabel power plant. Each had shown evidence of defects. We measured partial discharges before and after repairs and monitored these measurements remotely at the Laborelec Diagnostic Centre. This data will add to our practical experience with the tool and enable us to provide valuable information to the plant on repair quality.
New method for tracing flicker sources
A Swedish team has proposed a new method for identifying flicker sources on the electricity distribution grid. Laborelec has tested the method’s accuracy and familiarized itself with result interpretation to prepare for future implementation.
It is crucial for grid operators and industrial sites to identify flicker sources. Flicker is a small repetitive voltage variation generated by installations with a fluctuating power demand, such as arc furnaces and welding machines. Flicker affects general power quality on the grid and causes annoying light flickering at nearby sites.The Swedish method consists of measuring the voltage and current signals on the grid simultaneously and processing them with a given algorithm. A new value, flicker power, is obtained, which enables the determination of the flicker propagation direction and the tracing of primary flicker sources.Laborelec tested the method on current and voltage signals from previous measurement campaigns conducted near known flicker sources. The method proved to be efficient in localizing the sources. Accurate interpretation of the results however is quite difficult. Currently, our team is applying the algorithm to more signals from various field configurations in order to improve its interpretation skills. In a few months we should be ready to provide this new service to grid operators and industries.
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