J.B.M. van Waes

Current distribution in LV networks during 1-phase MV short-circuit

This paper describes the consequences of a fault in a medium voltage network on the grounding systems at the LV-side. To study the current distribution and to verify the models, we deliberately introduced one phase to ground faults in the 10 kV floating MV network. The selected site was the end of a 2 km long buried MV cable feeding a small group of houses; the soil there had a high resistivity. The fault current was 127 A. The current distribution and the relevant voltages were measured at several positions in MV and LV net. We compare the results for a TT and a quasi-TN earthing system in the houses, also taking the telecom cable into account. The distribution of the fault current over the MV cable, measured at another MV station at 2.2 km distance, are in agreement with calculations, based on a model which includes the contact of the lead shield of the MV cable with the ground. Current and voltage data are compared with calculations. Eindhoven University of Technology and the Dutch power distribution company NUON, carry out a joint research project on global earthing. In this project we treat different faults and various interference sources e.g. lightning and switching events together.

Safety Aspects of GSM Systems on High-Voltage Towers: An Experimental Analysis

Low-voltage (LV) applications mounted on high-voltage (HV) towers may pose a safety problem in the low voltage network when a flashover occurs over the high-voltage insulators. To study the effects experimentally, a 150 kV system was made available. On a high voltage tower carrying a cellular phone base station, one phase insulator was shorted to the tower. A current of about 200 A was injected into that phase at a large distance. We measured the current distribution and the relevant voltages in the low voltage net. The experimental current data agree with EMTP calculations. Appropriate measures to guarantee safety for persons and electronic equipment are discussed.

Mitigation of ground loop effects in high-voltage measurements

Ground loops can affect voltage measurement systems, in particular those in high-power test circuits. The net or common-mode current through the signal cable shield induces interference in the signal circuit. A generalized transfer impedance Z/sub t/ describes this undesired coupling. In a low-frequency circuit model, Z/sub t/ decomposes into two terms which vary with the cable length l and with l/sup 2/ respectively. Several divider setups are discussed; all employ the same high-voltage arm. The position and composition of the low-voltage arm vary. A proper design of the signal circuit ensures a low Z/sub t/ at the power frequency. Measurements confirm the model. With the low Z/sub t/, the direct capacitive coupling between the high-voltage arm and neighboring circuits showed up as a comparable interference source.

Safety aspects of GSM systems on high voltage towers

Low voltage applications mounted on high voltage towers may pose a safety problem in the low voltage network when a flashover occurs over the high-voltage insulators. To study the effects experimentally, a 150 kV system was made available. On a high voltage tower carrying a cellular phone base station, one phase insulator was shorted to the tower. A current of about 200 A was injected into that phase at a large distance. The authors measured the current distribution and the relevant voltages in the low voltage network. A experimental data agree with EMTP calculations. Appropriate measures to guarantee safety for persons and electronic equipment are discussed.Low-voltage applications mounted on high-voltage towers may pose a safety problem in the low-voltage network when a flashover occurs over the high-voltage insulators. To study the effects experimentally, a 150 kV system was made available. On a high-voltage tower carrying a cellular phone base station, one phase insulator was shorted to the tower. A current of about 200 A was injected into that phase at a large distance. We measured the current distribution and the relevant voltages in the low-voltage net. The experimental current data agree with EMTP calculations. Appropriate measures to guarantee safety for persons and electronic equipment are discussed.

Evaluation and updating of harmonic voltage limits

Characteristics of the current emission for new developed devices are changing resulting in lower low order harmonics and an increase in high order harmonics. For the low voltage network this results in an increase in high order harmonic voltages, violating more often the limits for the harmonic voltages at the 15th and 21th order harmonic. To improve this situation harmonic current could be reduced, network impedance could be decreased or the harmonic voltage limits could be increased. Since there are no complaints regarding these higher harmonic voltages, this paper presents an alternative approach to update these harmonic voltage limits.

Development of grid security forecasting processes at TenneT TSO B.V.

The Dutch Transmission System Operator TenneT TSO B.V. is responsible for the Dutch electricity grids with voltages of 110 kV to 380 kV. The company is required to guarantee the Security of Supply at all times, and must comply with both national and international legislation and agreements. Economic efficiency and market facilitation are prompting an increase in interconnection capacity between European countries, together with optimization of asset utilization. Forecasting processes by applying offline grid analysis is one of the core business processes by which TenneT meets these requirements. The aim of this paper is to provide an insight into the complexity of implementing and integrating these processes given the requirements, the IT infrastructure and the demands of the various user groups. The emphasis is specific on the processes close to real time. It addresses the most important design and implementation aspects from TenneTs perspective and provides an overview of best practices.