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Intermediate results from ongoing Cigré Enquiry
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FIRST
RESULTS FROM ON-GOING CIGRÉ ENQUIRY ON RELIABILITY OF HIGH VOLTAGE EQUIPMENT
C.E. SÖLVER*, on behalf of CIGRÉ WG A3.06**Abstract:
CIGRÉ
WG A3.06 in cooperation with WG B3.02 is presently carrying out a worldwide
survey of failures in service on high voltage equipment rated for voltages
greater than or equal to 60 kV. The survey covers circuit breakers (only SF6
technology), disconnectors, earthing switches, instrument transformers and GIS.
The collection of information from utilities about their equipment populations,
and about failures that occur in these populations, started in January 2004, and
will go on until December 2007. At present (April 2005) 36 utilities from 18
countries have submitted information about their apparatus populations, together
with a total of 1446 failure cards, each describing one failure. Many more
utilities are currently collecting information for the survey, and a large
number of extra cards will be submitted. The information will, when the data
acquisition has been completed, be subjected to extensive statistical analyses
with the purpose of obtaining trustworthy information on reliability and
failures for the considered component types. Keywords: High voltage
apparatus - Failure statistics - Reliability survey - Service experience *ABB Power Technologies, Dept. PTPH/HV/MT, SE-771 80 Ludvika, e-mail: carl-ejnar.solver@se.abb.com **Members of WG A3.06: Bill Bergman, Antonio Carvalho, Stefano Dessanti,
Hiroshi Furuta, André Giboulet, Wolfgang Grieshaber, Antoni Hyrczak, Dagmar
Kopejtkova, Johan G. Krone, Matthias Kudoke, Torsten Kuntze, Manuel Lopez
Cormenzana, Dirk Makareinis, Kresimir Mestrovic, Yasuhiko Nakada, Jan Ostlund,
Kyong-Yop Park, Jashavant Patel, Magne Runde, John E. Skog, Carl E. Solver (convenor),
Bob Sweeney, Francis Waite Accurate
information about service experience of high voltage equipment is of significant
value for both electric utilities and for manufacturers of such equipment. It
helps the manufacturers improve their products, and provides important inputs
for the utilities when buying equipment and when organizing maintenance.
Equipment reliability data are also required when assessing of the overall
reliability of an electric power system, including studies of the electric
energy supply security. Furthermore, international standards applicable to high
voltage equipment are being improved on the basis of service experience and
reliability data. Hence,
CIGRÉ has considered collecting, analyzing and publishing reliability data
important tasks. A number of years have now passed since the previous surveys on
high voltage equipment. For example, in the previous study on circuit breaker
service experience, the data collection ended in 1991. Deregulation and new
technologies, among other things, have caused the service and maintenance
practises to change significantly, and it is thus time for renewed studies. Against
this background, CIGRÉ decided to launch a new worldwide enquiry on service
experience on high voltage equipment. The survey is fairly comprehensive in that
it includes several types of high voltage components: circuit breakers,
disconnectors and earthing switches, instrument transformers and gas insulated
substations (GIS). Information is collected by asking utilities to complete and
return equipment population and equipment failure forms to a CIGRÉ working
group, which in turn analyses the data and reports the findings. This
paper starts by briefly reviewing the previous CIGRÉ enquiries on high voltage
equipment. Then some essential features of the new survey are summarised,
including a brief description of the applied data collection forms and
procedures. Some data showing the initial 2.
PREVIOUS SERVICE EXPERIENCE ENQUIRIES The first circuit
breaker survey was carried out in 1974 - 77 and concerned nearly 79,000 circuit
breaker years of service. The results were published in 1981 [1] and had a
significant impact on IEC standardization work, including mechanical and
environmental test procedures. The
second circuit breaker survey covered almost the same number of circuit breaker
years, but was limited to single pressure SF6 technology. Service
data were collected in the period 1988 – 91. The very comprehensive and
detailed 180-page report [2] remains a very valuable source of information for
the circuit breaker community, and a CIGRÉ bestseller. A
first failure survey of conventional instrument transformers was published in
1990 [3]. It covers failures from the time interval 1970 - 86. Both
manufacturers and users contributed. There was no age limitation to the overall
population. A
second failure survey has also been performed, covering the years 1985 - 95.
This survey only made use of contributions from users. These results are
unpublished. As for the first survey, there was no age limitation to the overall
population. Two
enquiries on GIS reliability have been conducted. The first enquiry covers
service experience up to 1990, and the second up to 1996 [4]. Both surveys
address not only the GIS as a whole, but also the apparatus inside. Failures
were collected without age limitation and users and manufacturers (only in first
survey) contributed. No
previous service experience enquiries have been performed for disconnectors and
earthing switches. 3.
THE PRESENT ENQUIRY The
present study is a cooperation between CIGRÉ Study Committees A3 and B3. A
working group, “A3.06: Reliability of high voltage equipment”, was
established to organize the work and analyze the results. The
enquiry comprises equipment rated for voltages greater than or equal to 60 kV.
For circuit breakers only single pressure SF6 technology is included,
thus in practice excluding equipment installed before around 1970. For
disconnectors, earthing switches and instrument transformers there is no such
limitation in age or technology. Only
failures occurring in a four-year period starting January 2004 are collected. To
be able to determine failure rates, the numbers and details of the equipment
populations that are covered by the survey also have to be recorded for the same
time interval. Thus for each of the four equipment types included, the enquiry
employs two types of forms or cards or questionnaires: one for equipment
populations and one for failures. Population cards are to be completed annually
(i.e., one for each year 2004 - 07), whereas a failure card should be filled in
each time a failure occurs. The
population cards ask for the age and number of components being covered, grouped
by voltage level, application, technology, design and maintenance strategy. The
failure cards request the same type of information about the failed component,
together with information describing the failure itself, such as its origin and
cause, what sub-assembly failed, whether this is a minor or major failure, if
environmental stress contributed, etc. Furthermore, a few questions addressing
the service history of the failed component as well as repair and consequential
measures, are included. A
main objective of the present survey is to identify trends by comparing the
findings from the present survey with those from the previous ones.
Consequently, the majority of the definitions and questions are completely or
nearly identical to those applied earlier. For example, the division into minor
and major failures follows the procedures used in the previous circuit breaker
surveys. A few new topics that have attained a substantial attention in recent
years, like asset management and diagnostics issues, have been addressed in the
questionnaires. A specific new item for circuit breakers is that information
regarding type of service is to be included, e.g. line breaker, transformer
breaker, etc. All questions in population and failure cards are of the check box
types, or they require numbers or dates as input. The
data collection is carried out by means of a specially developed Excel
spreadsheet tool, containing the four population and the four failure cards. In
addition, a separate questionnaire related to maintenance and operation issues
of GIS is included in the tool. The tool is multi-lingual; at present it is
possible to choose among, and even switch between, 11 different languages.
Moreover, a comprehensive “help function”, including all relevant
definitions is included in the tool and is easily accessed by “push buttons”
next to the relevant questions. The
Excel tool is distributed by e-mail to utilities worldwide interesting in
participating in the survey. They fill in the forms, and return a file with the
answers to the working group member responsible for the country. After a quality
check, the responses are forwarded and compiled in a database for subsequent
statistical analysis. The information is collected directly and solely from the
utility sector, not from manufacturers or others as in some of the previous
surveys. All incoming information is treated as confidential. Some
utilities are, on a permanent basis, collecting information about the service
experience of their high voltage equipment by using forms and procedures similar
to those adopted by CIGRÉ. Hence, in a few cases population and failure data
can be more or less directly loaded into the database. 4. PARTICIPATION The
questionnaire was distributed to utilities worldwide by mid 2004, with the
objective to receive the first data at beginning of 2005. By the time of writing
(April 2005) 36 utilities from 18 countries have submitted one or more completed
cards. Tables I and II show the received cards sorted by component for
population cards and failure cards, respectively. It has to be emphasized that
these numbers are far from the final ones. The number of submitted cards is
steadily growing. It
may be noted from the work with the survey, that many contacts and discussions
between participating utilities and the members of the CIGRÉ WG are necessary.
Such contacts help to clarify some of the questions asked and to avoid
misunderstandings. Table
I. Population cards received by April 2005.
Table
II. Failure cards received by April 2005.
Thus,
so far the WG has received 1446 failure cards. More
interesting than the number of population cards is the number of apparatus
included in these populations. Table III shows these numbers, again as by April
2005. The number of GIS circuit breaker bays included in the total population is
10470. This means that 38% of the reported number of circuit breakers is of
GIS-type. Table
III. Number of apparatus included in
the population cards of Table I.
5. DEFINITION
OF FAILURES
Failures
of high voltage equipment may be considered either from a system, or from an
equipment point of view. With a system approach, the important issue is whether
a fault caused a system outage or not, and related consequences such as transfer
of power to other paths, or even loss of supplied power. With an equipment
approach, the focus is on failure mechanisms, properties of the equipment, etc.
In the present survey, as in the previous ones, the equipment approach is
applied. The definitions of “Major failure” and “Minor failure” relate
to the performance of the equipment. Individual
utilities and organizations sometimes use the system approach. Their internal
failure statistics will be different from what a CIGRÉ approach would
give. For example, an unplanned system outage, caused by failure of a high
voltage apparatus, per definition means that the apparatus suffered a major
failure. There are, however, several types of major failures that do not
automatically lead to system outages (example: “Does not close on command”,
for a circuit breaker). This means that a utility, which only records system
outages due to faults, will not necessarily “detect” all major failures that
occur. Minor failures may not be registered at all. This
discrepancy between different ways to define failures is a factor that will be
kept in mind in the future analysis of failure data within the survey. 6. FUTURE ANALYSIS OF
DATA Incoming
data will be analyzed and presented as far as possible in the same manner as in
the previous surveys. This will make it possible to compare the outcome and to
identify any trends or similarities. It is still too early to present any
conclusions since there is at this point not a complete consistency between the
population and failure cards. That is, failures may have been reported for
equipment that has not yet been included in the population cards, and vice
versa. 7. CONCLUSION A
new CIGRÉ survey on reliability of high voltage equipment was launched in 2004.
It covers circuit breakers, disconnectors and earthing switches, instrument
transformers and GIS. Data from participating utilities, on equipment
populations and failures, is being collected by the responsible WG A3.06. At present
(April 2005) 36 utilities from 18 countries have submitted information about
their apparatus populations, together with a total of 1446 failure cards, each
describing one failure. Many more utilities are currently collecting information
for the survey, and a large number of extra cards will be submitted. It is still
too early to present any trends or results. The compiled information will, when
the data acquisition has been completed, be subjected to extensive statistical
analyses with the purpose of obtaining trustworthy information on reliability
and failures for the considered component types. 8. REFERENCES [1].
G. Mazza, and R. Michaca, The first international enquiry on
circuit-breaker failures and defects in service, Elektra no. 79, 1981, pp.
21-91. [2].
Final report of the second international enquiry on high voltage
circuit-breaker failures and defects in service, CIGRÉ Technical Brochure no.
83, 1994. [3]. The paper-oil
insulated measurement transformer, CIGRÉ Technical Brochure no. 57, 1990.
[4].
Report on the second international survey on high voltage gas insulated
substations (GIS) service experience, CIGRÉ Technical Brochure no. 150, 2000. |