Christian Raunig

Grounding measurements in urban areas - comparison of low and high voltage measurements in common grounding systems

Common grounding systems (global earthing systems) are not very clearly defined in standards. One definition of a common grounding system is that no dangerous touch voltages caused by ground fault currents occur. This means that a common grounding system does not depend only on the grounding system itself but also on the type and operation of the electrical grid and the protection schemes. In a resonant grounded network only low ground fault currents appear because of the compensation, therefore it is difficult to detect and clear single ground faults if desired or necessary. To provide a reliable localization of a ground fault a higher current can be injected intentionally but it must be proved that no dangerous touch and step voltages occur. To prove this in a typical urban grid, different measurements were carried out. Measurements at low and high current levels and an additional simulation are compared and discussed.

An earth fault distance location algorithm in compensated networks with additional estimation of the fault impedance and fault current

Earth fault distance protection with distance protection relays is common practice in solidly grounded networks. However, in compensated networks earth faults can cause big problems, because they do not extinguish themselves. To find the fault point is from high interest also in combination with network expansion [9]. In previous investigations the authors found that the classic algorithm of these distance protection relays principally can be used also for compensated networks, - however the accuracy of the distance calculation strongly depends on the network conditions [1],[2]. In this paper a new improved algorithm is developed. For this purpose an exact 3-phase mathematical simulation model of the investigated network is used to check the results of the improved algorithm. The simulations show, that this improved distance calculation provides very good accuracy up to earth fault transitions impedances of 1 kohm. Furtheron it is shown in the paper that the same algorithm can be used in 2-phase networks as well. With the implemented improvements the algorithm again allows earth fault transitions impedances of up to 1 kOhm. Finally, the simulation results are validated by real test data to verify the usability of this improved algorithm.

Earth fault localization with the help of the fast-pulse-detection-method using the new high-power-current-injection (HPCI)

With todays increased demands on grid operation management new methods for earth fault localization and detection are required. The earth fault localization should be performed as quick as possible and under the condition, that the fault current at the fault location will not be significantly increased. The pulse detection method is widespread because only a current measurement is needed and the implementation is simple. With the installation of more than one relays along a line an in-depth localization of the earth fault is possible. Boundary conditions, which will be described in detail in the paper, will not always lead to an increased resolution into depth with an increased number of relays. In this paper a new and fast method based on a thyristor-controlled high-power-current-injection (HPCI) will be presented. Compared with traditional pulse detection, this method has a lot of advantages, which will be described in the paper.

A new approach for the estimation of interference phenomena between coupled transmission lines

The low frequent electromagnetic mutual coupling of electric high voltage lines leads to a variety of effects in the planning and the operation of such an electrical circuit and their impact onto other line circuits (e.g. telecommunication and signal lines). The authors present a new method for calculating the interference phenomena between inductively coupled circuits. These calculations are performed with the help of the combination between the node potential method and a chain-ladder model under consideration of inductive coupled conductor arrangements. So its possible to calculate the inductive influence, asymmetric currents (zero and negative sequence currents) of extended transmission line circuits under normal and faulty operation conditions. Calculations and results of the optimization of transposition schemes and phase configurations of a transmission line section in Austria will be presented. This method allows an optimization of the phase configuration (twisting) concerning inductive and ohmic interferences under consideration of economic and practical aspects.

Modellierung und Berechnung der mutuellen niederfrequenten induktiven Kopplung

ZusammenfassungDie Bestimmung von induktiven Beeinflussungen sowie die Erarbeitung von Maßnahmen zur Reduktion dieser Beeinflussungswirkungen benötigen Ansätze und Modelle, um induktive Beeinflussungserscheinungen unter praxisnahen Bedingungen zu berechnen. Durch den vermehrten Netzausbau und die daraus resultierenden räumlichen Annäherungen von Hochspannungsfreileitungssystemen und -kabelsystemen in sogenannten Energiekorridoren, höhere elektrische Transport- und Kurzschlussleistungen, aber auch komplexere Übertragungssysteme reichen die vereinfachten Berechnungsmodelle sowie klassische Beeinflussungsberechnungsmethoden nicht mehr aus, um befriedigende Lösungen zu erzielen.Dieser Beitrag befasst sich mit der Modellierung und Berechnung der mutuellen niederfrequenten induktiven Kopplung, wobei ein neuer Ansatz entwickelt wurde, um die induktive Beeinflussung unter realitätsnahen Bedingungen zu bestimmen. Mit Hilfe des Ansatzes auf Basis des Knotenpotentialverfahrens und dem Kettenleitermodell wird neben der Bestimmung der induktiven Beeinflussungswirkungen auch die Möglichkeit geboten, Unsymmetrieerscheinungen und ohmsche Beeinflussungen mit Hilfe eines vollständig gekoppelten Leitungsmodells zu bestimmen.AbstractThe determination of inductive influences, as well as the development of measures to reduce these inductive coupling effects, needs approaches and models to calculate inductive interference phenomena under realistic conditions. Due to the increased grid expansion and the resulting growing number of in close vicinity parallel routed power lines in so-called energy corridors, higher electrical transport loads and short-circuit power as well as more complex transmission systems, the classical influence calculation methods are no longer sufficient to achieve satisfactory solutions.This article deals with the modelling and calculation of the low frequent mutual inductive interference. A new approach is developed to determine the mutual inductive interference under realistic conditions. Using this approach in addition to determining the inductive interference effects the opportunity to determine unbalance currents and ohmic disturbances with the help of a complete inductively coupled model is given.

Comparison of restriking cable-earthfaults in isolated and compensated networks

The results of field tests have shown, that the behaviour of the restriking earthfault in a cable is complete different in isolated and compensated networks. This paper will present these differences in detail and point out the influence to the corresponding earthfault detection methods and the corresponding neutral point treatment. Due to the different behaviour, there are new possibilities to reduce the current via the fault location. One of these new concepts will also be presented in this paper.

Lightnings excite isolated high voltage networks to oscillate

Isolated networks are common practice for operating small high voltage networks. The reason for choosing this type of network are the saving of the arc suppressing coils by coexistence of a self-healing grind in case of an earth fault During the starting up of an isolated network several unexpected voltage oscillation phenomena were detected and measured. Investigations have shown that lightning strokes in the area around the high voltage line are the sources of the voltage oscillation. Comparison between the measurement of the voltages and currents of the high voltage line and the lightning detection protocol of the Austrian Lightning and Detection System (ALDIS) show that the lightning causes the voltage oscillation. This paper describes the phenomena based on measurements, the correlation with lightning strokes and will confirm the measurements with simulation examples.