Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance
Paper presents method of earth faults detection in electric power cables based on measurement and analysis of the short circuit resistance value in transient under mechanical bumps exerted on the faulty cable line during detection procedure. Discussed investigated results and formulates conclusions...
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| Дата: | 2014 |
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| Мова: | English |
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Інститут проблем матеріалознавства ім. І.М. Францевича НАН України
2014
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| Назва видання: | Электрические контакты и электроды |
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| Цитувати: | Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance / P. Wojtas, A. Kozłowski, M. Kryca, B. Miedziński // Электрические контакты и электроды. — К.: ИПМ НАН України, 2014. — С. 246-250. — Бібліогр.: 3 назв. — англ. |
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irk-123456789-1040102016-06-29T03:02:21Z Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance Wojtas, P. Kozłowski, A. Kryca, M. Miedziński, B. Paper presents method of earth faults detection in electric power cables based on measurement and analysis of the short circuit resistance value in transient under mechanical bumps exerted on the faulty cable line during detection procedure. Discussed investigated results and formulates conclusions for use in practice. Предложен метод обнаружения дефектов заземления в электрических силовых кабелях, основанный на измерении и анализе сопротивления короткого замыкания при кратковременных механических ударах (толчках), прикладываемых к дефектному кабелю в процессе испытаний. Обсуждаются полученные результаты и формулируются практические рекомендации. Запропоновано метод виявлення дефектів заземлення в електричних силових кабелях, заснований на вимірюванні та аналізі опору короткого замикання при короткочасних механічних ударах (поштовхах), що прикладаються до дефектного кабелю в процесі випробувань. Обговорюються отримані результати і формулюються практичні рекомендації. 2014 Article Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance / P. Wojtas, A. Kozłowski, M. Kryca, B. Miedziński // Электрические контакты и электроды. — К.: ИПМ НАН України, 2014. — С. 246-250. — Бібліогр.: 3 назв. — англ. 2311-0627 http://dspace.nbuv.gov.ua/handle/123456789/104010 621.3.06 en Электрические контакты и электроды Інститут проблем матеріалознавства ім. І.М. Францевича НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| description |
Paper presents method of earth faults detection in electric power cables based on measurement and analysis of the short circuit resistance value in transient under mechanical bumps exerted on the faulty cable line during detection procedure. Discussed investigated results and formulates conclusions for use in practice. |
| format |
Article |
| author |
Wojtas, P. Kozłowski, A. Kryca, M. Miedziński, B. |
| spellingShingle |
Wojtas, P. Kozłowski, A. Kryca, M. Miedziński, B. Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance Электрические контакты и электроды |
| author_facet |
Wojtas, P. Kozłowski, A. Kryca, M. Miedziński, B. |
| author_sort |
Wojtas, P. |
| title |
Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance |
| title_short |
Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance |
| title_full |
Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance |
| title_fullStr |
Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance |
| title_full_unstemmed |
Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance |
| title_sort |
detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance |
| publisher |
Інститут проблем матеріалознавства ім. І.М. Францевича НАН України |
| publishDate |
2014 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/104010 |
| citation_txt |
Detection of earth faults in electric power cables by analyzing changes in the short-circuit resistance / P. Wojtas, A. Kozłowski, M. Kryca, B. Miedziński // Электрические контакты и электроды. — К.: ИПМ НАН України, 2014. — С. 246-250. — Бібліогр.: 3 назв. — англ. |
| series |
Электрические контакты и электроды |
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| first_indexed |
2025-07-07T14:40:38Z |
| last_indexed |
2025-07-07T14:40:38Z |
| _version_ |
1836999497036595200 |
| fulltext |
246
UDK 621.3.06
Detection of earth faults in electric power cables
by analyzing changes in the short-circuit resistance
P. Wojtas, A. Kozłowski, M. Kryca, B. Miedziński
Institute of Innovative Technologies EMAG, Poland
Paper presents method of earth faults detection in electric power cables based on
measurement and analysis of the short circuit resistance value in transient under
mechanical bumps exerted on the faulty cable line during detection procedure.
Discussed investigated results and formulates conclusions for use in practice.
Keywords: electric cable, earth fault, detection method.
Introduction
Effective ground fault detection and fast clearing in mine supplying cable
network of both LV and MV is of great importance in view of both economic
issue as well as safety requirements (hazard of fire and/or explosion in methane
and coal dust environment). Commonly use methods and devices in electric
power networks can not be therefore directly adapted to working conditions of
underground mines, where such, aspects have to be carefully considered like:
onerous microclimate of coal mine, specific environmental conditions and
safety requirements that have to be met. One has to keep, in among other,
elevated temperature (up to 45 oC), high humidity around 95% (at 45 oC),
exposure to unexpected mechanical disturbances (shocks, vibrations, bumps)
cramped spice, high noise level, insufficient lightning and necessity of
limitation of a single phase short circuit current value as much as
possible [2, 3]. As a result there is urgent need to develop new methods and to
employ reliable protection devices applicable under underground coal mine
conditions of operation.
Paper presents suitable method and arrangement developed by authors to
detect high resistive earth faults in electric power cable lines used in mine,
discusses preliminary laboratory test of investigations.
The project is realized by consortium companies and supported by Polish
governmental institution –The National Centre for Research and Development.
The project consortium consists of research institutes (Institute of Innovative
Technologies EMAG, Tele and Radio Research Institute, Central Mining
Institute GIG-KD “Barbara”), Silesian University of Technology and a private
company MARTECH PLUS. The main objective of the project is improvement
in work safety at coal mines.
Single phase ground faults in mine cables and ways of their identification
Simple phase ground faults that occur the most frequently in practice
(around 85% of total faults in electric power networks — not only in mines) are
particularly difficult to localize due to high short-circuit resistance value and
related small fault current to measure efficiently. Commonly used methods
basing on increasing discharge power value through faulty place to around
0,5—1 kW (forcing electric arc discharge) is in mines not acceptable. Therefore
© P. Wojtas, A. Kozłowski, M. Kryca, B. Miedziński, 2014
247
T a b l e 1. Leakage earth resistance (maximum value) that must results
in interruption of power supply in low voltage network
Tripping (setting) resistance value, kΩ
Rated voltage, V Central protection
(on-line)
Blocking protection
1000
500
230
133
36,0 (30)
18,0 (15)
8,4 (7)
8,4 (7)
60,0 (50)
30,0 (25)
18,0 (15)
18,0 (15)
T a b l e 2. Setting resistance value for central ground-
fault protection in medium voltage network
Rated voltage, kV Setting
1 < Un ≤ 3,3
3,3 < Un ≤ 6
220 kΩ ± 20%
360 kΩ ± 20%
the ground fault location in underground cable lines is based mostly on control
of their insulation resistively value. Sometimes inductance or capacity value to
the ground is controlled as well; it is called a rough localization of a faulty
place. Usually two systems are employed: central leakage protection and local
earth leakage protection. Basic physical parameters taken into account for
leakage protections are: setting resistance value (table 1 and 2) and operation
time provided that long lasting fault current is not higher that 25 mA.
Therefore, if only the isolation resistance value (to the ground) is found to be
lower, the electric supply is immediately disconnected by the central leakage
protection and further precise fault localization in the cable is performed under
dead (no load) conditions. One of the useful method that can be used in
underground mines is an impulse reflection method (IRM). However, the wave
propagation speed along the cable line under test is in the range of 160—
250 m/s and is not constant in time. Besides, it is varied during cable ageing and
under influence of humidity and/or temperature fluctuations. However,
interpretations of received (reflected) waveforms parameters without knowing
topology of a grid is difficult. Therefore, effective detection of ground faults of
resistance over a few hundreds ohms is almost impossible in practice.
Method based on measurements of variation of the fault resistance value
and associated electromagnetic noise
Method developed by authors is based on measurement and analysis of
variation of an insulation resistance value at the faulty point under the influence
of external mechanical disturbances (bumps) exerted on the cable line under
detection procedure [1]. To detect rapid fluctuations of the metering DC current
(resulting from fast changes of insulation resistance value in transient between
the cable cores and protection screen) a fast working ohmmeter device of a high
sensitivity has to be employed.
The measuring equipment is able to indicate rapid changes in insulation
resistance value between the cable cores and the protection screen. It is
composed of a transmitter RAKn and receiver unit RAKo (fig. 2).
Fig. 1. Illustration of fault localization
system (T — transmitter; R — receiver;
F — external mechanical force).
248
Fig. 2. View of RAKn and RAKo units.
Both units are designed with use of the same microcontroller board. The
transmitter that is used as the ohmmeter provides DC measuring current of a
very small value (around 30 μA) and low frequency waves withacoustic
frequency modulation for communication as well. The receiver in turn is
equipped with antenna to detect maximum intensity level of electromagnetic
radiation (cable tracing) and to receive data from transmitter. Communication
link between the transmitter (ohmmeter) and the receiver is provided by
a transmission channel using the cable under testing as a distributed antenna.
Laboratory test results
The fault location procedure requires cooperation of two persons and
disconnection from supplying source of the damaged cable from the both ends.
RAKn and RAKo units are battery powered — charging can be performed only
within a safe area. The intrinsically safe battery has rated voltage of 12 V and
capacity equal to 0,7 Ah. The system can be used in the temperature range
between –0 o to +40 oC. The cases are made of glass fiber reinforced with
polyester and are suitable for use under coalmine conditions (certified) —
suitable for zones I and II. The leakage resistance is measured in the range of
0—300 kΩ with resolution of 100 Ω.
Investigations were carried out in circuit as in fig. 3. Measuring DC current
value was about 250 μA for cable (~40m long) of total capacity equal to 20
μF. Observations of measuring signal at the beginning and at the end of open
cable line have indicated negligible effect of distributed cable capacity on signal
deformation (fig. 4).
Earth
RF
T
R FF R
Cable
Rf
T
Fig. 3. Sketch of testing system.
249
Fig. 4. Comparison of wave deformation in cable.
-61 mv 20 ms Ch2500 mv 10 ms
In
su
la
tio
n
re
si
st
an
ce
, k
Ω
Time, s
Fig. 5. Insulation resistance changes at the point of insulation
damage under external force (bumps) applied.
By progressive reduction of measurement sensitivity or force (bumps) being
applied one can find maximum effect (resistance fluctuations) just at the faulty
(short circuit) point (fig. 5).
Conclusions
Localization of the faulty cable line in underground coal — mines with
hazard of explosion (methane and/or coal dust) requires the use of special non-
standard methods. The method developed by authors that is based on
measurements and following analysis of leakage (ground fault) resistance
variation under influence of external mechanical disturbance (bumps) exerted
on the cable during measuring procedure is combined with detection of intensity
level of electromagnetic radiation due to injected low voltage waves.
250
The advantage of this method is the possibility of detection of the high
resistive earth-faults around 200—300 kΩ with resolution of about 1 kΩ and
sufficient (with practical point of view) high accuracy of localization in power
cable lines used particularly in underground mines. The developed system
successfully passed laboratory tests and is now being prepared for research
under working conditions of mine.
1. Kozłowski A. Underground cable fault location under hazard of methane and coal
dust explosion / [A.Kozłowski, M. Kryca, T. Gąsior et al.] // Proc. 23rd World
Mining Congres Montreal, 2013.
2. Kozłowski A., Wojtas P., Kryca M. Lokalizacja uszkodzeń kabli i przewodów
oponowych w strefach zagrożonych wybuchem — aspekty związane z poprawą
bezpieczeństwa / A. Kozłowski, P. Wojtas, M. Kryca // Materiały konf. EMTECH
2013 Konferencja Naukowo-Techniczna EMTECH 2013. 20-22.05.2012,
Zakopane (in polish).
3. Wojtas P. Działania instytutu badawczego EMAG w zakresie poprawy bezpiec-
zeństwa pracy w kopalniach // XV konf. "Problemy Bezpieczeństwa i Ochrony
Zdrowia w Polskim Górnictwie", Jaworze k/Bielska, WUG, 9-10.04.2013 r. (in
polish).
Обнаружение дефектов в заземлении в силовых
электрических кабелях
П. Войтас, А. Козловский, М. Круса, Б. Медзинский
Предложен метод обнаружения дефектов заземления в электрических силовых
кабелях, основанный на измерении и анализе сопротивления короткого замыкания
при кратковременных механических ударах (толчках), прикладываемых к
дефектному кабелю в процессе испытаний. Обсуждаются полученные
результаты и формулируются практические рекомендации.
Ключевые слова: электрический кабель, дефект заземления, метод обнаружения.
Виявлення дефектів у заземлюванні в силових
електричних кабелях
П. Войтас, А. Козловський, М. Круса, Б. Медзинський
Запропоновано метод виявлення дефектів заземлення в електричних силових
кабелях, заснований на вимірюванні та аналізі опору короткого замикання при
короткочасних механічних ударах (поштовхах), що прикладаються до
дефектного кабелю в процесі випробувань. Обговорюються отримані результати
і формулюються практичні рекомендації.
Ключові слова: електричний кабель, дефект заземлення, метод виявлення.
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