Showing papers by "Matti Lehtonen published in 2011"

Calibration of on-line partial discharge measuring system using Rogowski coil in covered-conductor overhead distribution networks

Abstract: Partial discharge (PD) detection has been regarded as one of the most effective on-line predictive maintenance test and diagnostic tool for the condition monitoring of high voltage (HV) equipment. In this study, a methodology for detecting on-line PDs produced because of falling trees on the covered-conductor (CC) overhead distribution lines is introduced and calibration of PD measuring system is carried-out. The Rogowski coil is used as a PD sensor which is non-intrusive and superior to the conventional PD detectors. The experimental set-up was arranged in the HV laboratory for real-time analysis and a pulse calibrator was used to calibrate the PD measuring system. Few real-life PD measurements have been taken and it is revealed that PD magnitudes and signals bandwidth may vary under various circumstances. The calibrated on-line PD measuring system can be used to detect and measure the amount of PDs produced because of falling trees on CC lines, thus improving the reliability and safety of the distribution networks as well as reducing visual inspection work after storms.

Energy efficiency analysis of residential electric end uses: based on statistical survey and hourly metered data

Abstract: By the end of 2013 at the latest almost all electric consumption will be measured hourly in Finland. Beyond billing facilitation and troubleshooting, AMR provided great deal of opportunity for energy efficiency analysis. This study evaluates efficiencies and saving potential factors of household electricity end-use consumption by analyzing data from AMR meters and questionnaire collected statistical data. The interdependency of household appliances in factoring the gross household CO2 emission will be given much attention to achieve holistic approach. The study analyzes the extent of utilization of AMR in improving efficiencies of household consumptions.

Determining wave propagation characteristics of MV XLPE power cable using time domain reflectometry technique

Abstract: In this paper, the wave propagation characteristics of single-phase medium voltage (MV) cross-linked polyethylene (XLPE) power cable are determined using time domain reflectometry (TDR) measurement technique. TDR delivers the complex propagation constant (attenuation and phase constant) of lossy cable transmission line as a function of frequency. The frequency-dependent propagation velocity is also determined from the TDR measurements through the parameters extraction procedure. The calibration of the measuring system (MS) is carried-out to avoid the effect of multiple reflections on the accuracy of measurements. The results obtained from the measurements can be used to localize the discontinuities as well as the design of communication through distribution power cables.

Investigation of lightning arc between conductor and nearby tree under artificial rainfall

Abstract: In the Nordic countries, most distribution networks are installed in forest areas. Direct strokes to a tree can cause severe damage to nearby power lines by initiating an arc channel through air to bare conductors. In this paper, this phenomenon is examined experimentally using a full-scale laboratory setup considering dry-air and wet-air conditions, and the experimental results were reproduced by computer simulations. In a number of the experimental runs performed, it was found that the conducting arc path allows the establishment of a large long-duration lightning current from the lightning-struck tree to the bare conductor under the wet-air condition. Consequently, a higher induced voltage is measured on the conductor. The lightning-triggered arc phenomenon was monitored closely. It was confirm that lightning strokes to a nearby tree can be more intense in the wet-air than in dry-air conditions, and cause a flashover on power lines. The ATP/EMTP computer simulation using the arc model shows that the experimental results, one of which has been photographed and reported in the paper, are reproducible by means of system modeling. Both the experimental and simulation results provide strong evidence confirming the phenomenon of the arc conduction and the induced voltages due to lightning strokes to nearby trees within the vicinity of power conductors. Using a Rusck model, the study is extended to evaluate the induced voltage from the tree to the power conductor for larger clearances.

Near real time energy monitoring for end users: Requirements and sample applications

Abstract: Recent work in the Smart Grid field has concentrated on the utilities' requirements, whereas user research on energy awareness and conservation has only been done at a relatively small scale. We attempt to bridge this gap by analyzing the requirements for a grid-wide real time energy monitoring system and combine them with requirements derived from state of the art user feedback applications, both based on the results of joint projects on the subject. We also present example applications that enable a real time system to better advise end users on their habits and administrative users to monitor the state of whole system.

Impacts of automatic loop restoration schemes on service reliability

Abstract: Automatic loop restoration schemes are employed in electric power distribution systems to perform fault detection, isolation, and service restoration activities sequentially and automatically, so as to significantly reduce customer interruption time This paper aims to quantitatively assess the impacts of employing an automatic loop restoration scheme, with and without a communication link, on the major attributes of the service reliability In addition, the effect of the operational failure of communication facilities is taken into account A typical Finnish urban distribution network is utilized in this paper for the quantitative reliability assessment studies A powerful software package referred to as "Smart Grid Simulator" is used for directing the reliability studies (6 pages)

The impact of the distribution network type and configuration on the transient behavior of the fault and neutral points during earth faults

Abstract: -The main goal of this paper is to investigate the impact of the network type and configuration on the transient behavior of the fault and neutral points during an earth fault. Studying both neutral and fault points enables us to understand clearly the network behavior. The investigations cover the effect of the network type including, feeder types: overhead line and mixed overhead and cable networks with different neutral earthing conditions: unearthed (isolated) or compensated neutral networks. The investigations focused on the transient behavior of the fault point (fault current and voltage) and neutral point voltage. A mathematical simulation model based on a realistic network is implemented using the transient simulation program ATP/EMTP. The effect of the capacitive response of cables in mixed networks has been investigated and presented. On the other hand, the interaction with a compensation coil has been highlighted as well.

Effect of climate change on MV underground network operations in the future smart grid environment

Abstract: In this paper, the steady state current rating calculations for 3-phase XLPE distribution power cables are performed using an analytical set of thermal equations. The analysis is made for different installation configurations (direct burial and tube installations) under various possible extreme Finnish environmental conditions. This study will enable electric power utilities to revise allowable current ratings to avoid damage to their power cables as well ensure safe and reliable distribution of power to the customers in the future smart grid environment. Ill. 6, bibl. 9, tabl. 5 (in English; abstracts in English and Lithuanian). http://dx.doi.org/10.5755/j01.eee.115.9.743

Optimising MV Network Development and Enhancement Using a Routing Algorithm and Cable Re-Rating

Abstract: This paper outlines and illustrates the latest developments in ‘VOH’, an automatic network routing algorithm. The treatment of existing MV network is shown, which should prove invaluable in aiding the development of least cost investment plans. Following a brief discussion on the difference between component ratings when planning and ratings when considering the upgrade of existing components, the significant economic benefit of deferring upgrade by re-rating according to a cyclic load profile rather than a steady-state rating is shown. Forced backup to secondary substations that are supplying important loads while the rest of the network is only backed up where it is cost effective, and the ability of the user to force the algorithm to optimise around a stipulated trunk feeder are also demonstrated.

Modelling and analysis of switching overvoltages caused by short circuits in MV cables connected with overhead lines

Abstract: In this paper, overvoltage transients are investigated and mitigated when a three-phase short-circuit occurs in cable lateral connected with medium voltage (MV) overhead line and fuse is operated. The transients are studied using EMTP-ATP simulation environment and the need of metal oxide varistors (MOVs) is investigated. The cable laterals consist of sub-laterals and their effect on reducing transients is also investigated. The surge arresters are installed at the junction of overhead line and cable and at far end of the cable near short-circuit point. The different mitigation methods are tested and optimal protection scheme to reduce overvoltages is proposed on the basis of surge arresters locations and sub-lateral connections.

Modeling and on-site experiments of shunt capacitor compensation method for deicing of 66kv power line

Abstract: An EMTP-ATP model and a MATLAB model of 66kV double line network are built and simulated. By applying shunt capacitor compensation method for de-icing 66kV overhead transmission line within the models, the simulation results show an increase of the rms line current to 650A for the de-icing line which leads the cable temperature to increase. A COMSOL model for LGJ-120/20 cable is also built to simulate the temperature distribution of current-carrying ice covered cable. The simulation results show that the cable coated with 3cm thickness ice sleeve can be de-iced, which the surface temperature of the cable can be increased to above 310k after 40 minutes. Through the on-site experiment in Mishan primary substation 66kV transmission line, the real-time data were matched by both EMTP-ATP and MATLAB simulation results, which verified the effectivity and feasibility of the shunt capacitor compensation de-icing method.