The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Single Phase Earth Faults in High Impedance Grounded Networks: Characteristics, Indication and Location

Seppo Hänninen

Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and debate in Auditorium S5 at Helsinki University of Technology (Espoo, Finland) on the 17th of December, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-38-5961-4)   [448 KB]
VTT Publications 453, ISSN 1455-0849

Dissertation is also available in print (ISBN 951-38-5960-6)
Copyright © 2001 VTT Technical Research Centre of Finland
VTT Publications 453, ISSN 1235-0621
VTT-PUBS-453
TKK-DISS-1587

Abstract

The subject of this thesis is the single phase earth fault in medium voltage distribution networks that are high impedance grounded. Networks are normally radially operated but partially meshed. First, the basic properties of high impedance grounded networks are discussed. Following this, the characteristics of earth faults in distribution networks are determined based on real case recordings. Exploiting these characteristics, new applications for earth fault indication and location are then developed.

The characteristics discussed are the clearing of earth faults, arc extinction, arcing faults, fault resistances and transients. Arcing faults made up at least half of all the disturbances, and they were especially predominant in the unearthed network. In the case of arcing faults, typical fault durations are outlined, and the overvoltages measured in different systems are analysed. In the unearthed systems, the maximum currents that allowed for autoextinction were small. Transients appeared in nearly all fault occurrences that caused the action of the circuit breaker. Fault resistances fell into two major categories, one where the fault resistances were below a few hundred ohms and the other where they were of the order of thousands of ohms.

Some faults can evolve gradually, for example faults caused by broken pin insulators, snow burden, downed conductor or tree contact. Using a novel application based on the neutral voltage and residual current analysis with the probabilistic method, it is possible to detect and locate resistive earth faults up to a resistance of 220 kΩ.

The main results were also to develop new applications of the transient based differential equation, wavelet and neural network methods for fault distance estimation. The performance of the artificial neural network methods was comparable to that of the conventional algorithms. It was also shown that the neural network, trained by the harmonic components of the neutral voltage transients, is applicable for earth fault distance computation. The benefit of this method is that only one measurement per primary transformer is needed. Regarding only the earth faults with very low fault resistance, the mean error in absolute terms was about 1.0 km for neural network methods and about 2.0 km for the conventional algorithms in staged field tests. The restriction of neural network methods is the huge training process needed because so many different parameters affect the amplitude and frequency of the transient signal. For practical use the conventional methods based on the faulty line impedance calculation proved to be more promising.

This thesis consists of an overview and of the following 7 publications:

  1. Hänninen, S. & Lehtonen, M. 1998. Characteristics of earth faults in electrical distribution networks with high impedance earthing. EPSR (Electric Power Systems Research), Vol. 44, No. 3, pp. 155-161.
  2. Hänninen, S., Lehtonen, M. & Hakola, T. 2001. Earth faults and related disturbances in distribution networks. Proceedings of IEEE PES SM2001, Vancouver, Canada, July 15-19, 2001. CD-ROM 01CH37262C. 6 p.
  3. Hänninen, S. & Lehtonen, M. 1999. Method for detection and location of very high resistive earth faults. ETEP (European Transactions on Electrical Power) Vol. 9, No. 5, pp. 285-291. http://www.ETEP.de
  4. Hänninen, S., Lehtonen, M. & Pulkkinen, U. 2000. A probabilistic method for detection and location of very high resistive earth faults. EPSR (Electric Power Systems Research), Vol. 54, No. 3, pp. 199-206.
  5. Hänninen, S., Lehtonen, M., Hakola, T. & Rantanen, R. 1999. Comparison of wavelet and differential equation algorithms in earth fault distance computation. PSCC'99. 13th Power Systems Computations Conference, Trondheim, Norway, June 28-July 2, Proceedings Vol. 2. Pp. 801-807.
  6. Eberl, G., Hänninen, S., Lehtonen, M. & Schegner, P. 2000. Comparison of artificial neural networks and conventional algorithms in ground fault distance computation. Proceedings of IEEE PES WM2000, Singapore, January 23-27, 2000. CD-ROM 00CH37077C. 6 p.
  7. Hänninen, S. & Lehtonen, M. 2001. Earth fault distance computation with artificial neural network trained by neutral voltage transients. Proceedings of IEEE PES SM2001, Vancouver, Canada, July 15-19, 2001. CD-ROM 01CH37262C. 6 p.

Keywords: power distribution, distribution networks, earth faults, detection, positioning, fault resistance, arching, neutral voltage, residual current, transients

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© 2004 Helsinki University of Technology

Last update 2011-05-26