Holger Pd Dr.-Ing. habil. Schau

Identification of the dominant harmonic source in the LV network on the base of anomalous power flows considerations

The localization of the dominant harmonic distortion source in the electrical network is one of the practical tasks in the consideration of the power quality in electric power systems. The conventional methods of the estimating of the impacts of the utility and the customer to the harmonic distortion at the network node are the harmonic power flow analysis as well as the correlation analysis of the harmonic voltage and current phasors. The practical use of both methods is discussed below by means of the example of the identification of the dominant harmonic source in the LV supply feeder of an industrial consumer. Based on the analysis carried out it is shown that the direction of harmonic active power flows is a more common and reliable criterion in comparison with the correlation analysis for the identification of dominant harmonic sources in electric power systems.

Analysis and prediction of power and energy losses in distribution networks

A new approach for a correct estimation of power and energy losses in urban distribution networks is described in the paper. The method is based on a row of national directives for power and energy loss analysis as well as on authorpsilas investigation. The method allows the calculation of load-dependent (current-dependent) and load-independent (voltage-dependent) power and energy losses in an urban network and their separation between power nets of different voltage levels. On the base of the elaborated method it is possible to analyse and to predict the power loss profiles over time (for instance annual profiles) depending on the power delivered to the urban distribution network under study.

Reproducibility of the box test according to EN 61482-1-2 and influences on the test energy parameters

The box test according to IEC/EN 61482-1-2 is one of the internationally harmonized test methods for textile material and protective clothing for arc flash protection. The standard is now under maintenance in an IEC TC 78 Project Team. In the frame of this work, among others, a round-robin-test was made for analyzing the reproducibility and repeatability of the test method. In the paper the results of this work are presented. Furthermore, the paper reports on laboratory measurements aimed to consider the influences of variations of the box test parameters on the electric and thermal arc energy. Main focus is the time and current dependency of the electric arc energy as well as the direct exposure incident energy. On this base the relationship between electric arc energy and incident energy is derived, allowing conclusions on PPE test energy levels in case of deviations from the standard conditions (class 1 and 2) as well as conclusions on arc exposures at real work places for risk assessment and PPE selection.

Impact of distributed generation facilities on an urban network

Many of modern distributed generation plants are based on photovoltaic cells using power electronic units for energy transmission into the electrical network. This increases the emission of high-frequency currents into the network and affects the operation of power line communication devices and energy meters. A real LV network in Germany was investigated by the authors with the purpose to estimate the actual situation in the network with respect to high-frequency distortion and to characterize the possible impact of the presented distributed generation facilities on the network operation.

Risk parameters of DC fault arcs — Research work on DC arcs in LV systems

Today there is an increasing number of DC applications where powerful DC fault arcs are likely to occur. These arcs are of potential risk for persons while working at the DC power equipment. DC arc conditions have not yet been analysed very well. There is a lack of information and detailed strategies on how to protect workers against short-circuits with fault arcs in DC power systems. Laboratory measurements of DC systems were started with electric parameters which are comparable to those of the Box Test of Personal Protective Equipment (PPE) according to IEC/EN 61482-1-2 (LV, short-circuit currents of some kA) for sampling knowledge in the field of DC fault arcs and personal protection by PPE. First measurements took place in test circuits supplied by a Li-Ion car battery. A High-Volt battery with a varied number of modules was used. Furthermore measurements were carried out in a similar test circuit supplied by a DC induction generator. The no-load voltage was varied between 100 and 750 V, the prospective short-circuit current between 1 and 6 kA. Electrode arrangements of opposing electrodes of different materials with and without box (similar to the Box Test) were used in these DC arc tests. The electric arc parameters and the arc thermal incident energy were measured. Aim was to sample knowledge on the DC arc and risk parameters, and obtain information on arc power and energy levels to be expected in DC systems. The paper summarizes the first analysis results. Similarities and discrepancies of AC and DC arc hazards are considered. Principle correlations and tendencies are derived. The results have to be verified and extended by further research work.

Guidelines for selecting PPE against arc thermal hazards — The new edition of DGUV-I 203-077: Revision status and experience to date

Huge energies being released in electric power equipment, there is a high risk for human injury due to electric fault arcs. Persons working at electric power equipment will have to be protected efficiently, particularly, if direct arc exposure is likely. Additionally to technical and organizational control measures, Personal Protective Equipment (PPE) may essentially contribute to prevent injuries. The selection of PPE and the assessment of their efficiency require a risk assessment. The information document and guideline “Thermal hazards from electric fault arc — guide to the selection of personal protective equipment for electrical work” (published in German under DGUV-I 203-077 as well as in English under DGUV-I 203-078) was prepared for giving support to the users when selecting PPE against the thermal hazards of electric fault arcs. An algorithm was developed for selecting PPE for the particular work place and working activities. This user guideline contains detailed explanation and practical examples on how to proceed in risk analysis and determining the arc hazards to be ma n-aged, and how to select PPE tested in the box test according to IEC/EN 61482-1-2. According to the developments and experiences from applying the guide during the last years, a revised edition of the document was elaborated by an expert group. The new guideline is presented, considering mainly the risk assessment and PPE selection. In the paper, the algorithm is described for analyzing the thermal arc risk in case of direct exposure, e.g. during live working or working near to live parts. Since the arc thermal hazards depend on the electric arc energy and the exposure distance, the risk assessment is based on the energy parameters. The PPE has a certain energetic protection level which is related to the test energy level. When having tested according to IEC 61482-1-2 the test level is known from the test arc energy for the arc protection classes: class 1 or class 2. PPE protection levels result from the actual working distance and transmission conditions of the power equipment. The electric arc energy to be expected in the certain work situation in the electric power system and equipment under study when there is an arcing fault has to be determined from the actual system parameters. The clearing time of the protective devises is an essential influence on the arc energy. There is a necessity to co-ordinate the selection of PPE and electric protective devises.

Coordination of PPE and fuse links for personal protection against arc thermal hazards in LV systems

Cutting-off of 2-phase and 3-phase arcing faults in 400 V systems by means of LV fuse links has been analyzed in laboratory arc test series, with measuring the remaining arc energy and thermal incident energy converted in the fault arcs and limited by the fuse operation. The conditions were determined under which personal protection may be submitted by using of PPE class 1 and class 2 according to IEC 61482-1-2. LV fuses are efficient means to achieve personal safety. The results were also summarized in form of user guidelines supplementing risk assessment and allowing reasoned coordination of fuse and PPE application. These simplified but safe rules need only to know the bolted short-circuit current and the operational current of the fuse of the feeder of the working place equipment, and relieve selection of the proper PPE and /or fuse. The use of an ultrafast working-protection fuse as technical personal protection measure is put on a reliable base. Personal protection is achievable in a very large number of working places in LV systems.

The new ISSA guideline for the selection of Personal Protective Equipment when exposed to the thermal effects of an electric fault arc

Huge energies being released in electric power equipment, there is a high risk for human injury due to electric fault arcs. Persons working at electric power equipment will have to be protected effectively, particularly, if a direct arc exposure is likely. Additionally to technical and organizational control measures, Personal Protective Equipment (PPE) may essentially contribute to prevent injuries. According to the developments during the last decade, a totally revised edition of the ISSA guideline for the selection of PPE was elaborated by an international expert group. The guideline is presented, considering mainly the arc hazards, the current state of PPE standardization, PPE test methods as well as risk assessment and PPE selection.