Single phase earth faults in high impedance grounded netwotrks

Characteristics, indication and location: Dissertation

Research output: ThesisDissertationCollection of Articles

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 kW. 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.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Lehtonen, Matti, Supervisor, External person
Award date17 Dec 2001
Place of PublicationEspoo
Publisher
Print ISBNs951-38-5960-6
Electronic ISBNs951-38-5961-4
Publication statusPublished - 2001
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

method
artificial neural network
wavelet
snow
extinction
disturbance
distribution
calculation
parameter
test
analysis
thesis

Keywords

  • power distribution
  • distribution networks
  • earth faults
  • detection
  • positioning
  • fault resistance
  • arching
  • neutral voltage
  • residual current
  • transients

Cite this

@phdthesis{9a71e999bddf48839bc532e805b75548,
title = "Single phase earth faults in high impedance grounded netwotrks: Characteristics, indication and location: Dissertation",
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 kW. 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.",
keywords = "power distribution, distribution networks, earth faults, detection, positioning, fault resistance, arching, neutral voltage, residual current, transients",
author = "Seppo H{\"a}nninen",
year = "2001",
language = "English",
isbn = "951-38-5960-6",
series = "VTT Publications",
publisher = "VTT Technical Research Centre of Finland",
number = "453",
address = "Finland",
school = "Aalto University",

}

Single phase earth faults in high impedance grounded netwotrks : Characteristics, indication and location: Dissertation. / Hänninen, Seppo.

Espoo : VTT Technical Research Centre of Finland, 2001. 143 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - Single phase earth faults in high impedance grounded netwotrks

T2 - Characteristics, indication and location: Dissertation

AU - Hänninen, Seppo

PY - 2001

Y1 - 2001

N2 - 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 kW. 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.

AB - 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 kW. 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.

KW - power distribution

KW - distribution networks

KW - earth faults

KW - detection

KW - positioning

KW - fault resistance

KW - arching

KW - neutral voltage

KW - residual current

KW - transients

M3 - Dissertation

SN - 951-38-5960-6

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -