a3-101 hybrid chamber with vacuum and gas …
TRANSCRIPT
A3-101
HYBRID CHAMBER WITH VACUUM AND GAS INTERRUPTERS FOR HIGH-VOLTAGE CIRCUIT-BREAKERS
by
D. DUFOURNET* C.LINDNER
ALSTOM T&D
(France)
Summary SF6 technology for high-voltage circuit-breakers was introduced during the 1960’s in the transmission voltages range. In the 1970’s it soon became the dominant medium in this range due to its excellent arc quenching and dielectric withstand capabilities. In spite of continuous researches for alternative gases, some are conducted at the present time, no other gas has been found yet that could combine both the arc quenching capability required for high voltage applications and the dielectric withstand necessary to have a reduced number of chambers per pole. Among the alternative technologies for high-voltage circuit-breakers, the application of vacuum technology has already been investigated and several contributions were presented during the CIGRE session of 2002.
This report intends to present another interrupting principle were a vacuum interrupter is combined in series with a gas blast chamber to provide the required performances. During interruption of high breaking currents, the thermal interrupting capability is given by the vacuum interrupter and the withstand of the peak TRV is mainly provided by the gas blast interrupter. Both interrupters contribute to the dielectric withstand required for switching tests and for the insulation level.
After a brief history on the matter, the report explains the interrupting principle and shows some examples of geometry where this principle has been implemented for testing. A necessary requirement for practical use is that both interrupters must be operated by the same operating mechanism. Special arrangements had to be designed in order to obtain ratios of up to 10 between the strokes and velocities of the two interrupters.
Tests results obtained on a full scale mock up are presented, showing the potential and limitations for the main type test duties.
Comparisons are made with present interrupting techniques for high-voltage circuit-breakers. They are commented and perspective on their possible use is given in the report. It is shown that this technology allows to reduce the size and the operating energy of high-voltage circuit-breakers, and can be an alternative to present technologies in some high-voltage applications.
PCB ROGOWSKI COILS – HIGH PRECISION LOW POWER SENSORS
Ljubomir A. Kojovic*
Cooper Power Systems
USA
This paper presents high precision printed circuit board (PCB) Rogowski coil (RC) designs andcharacteristics suitable for advanced protection, control, and metering systems with new multifunctionrelays and fiber optic communication. The RCs consist of two PCBs located next to each other. EachPCB contains one imprinted coil wound in opposite directions (clockwise and counter-clockwise).The top and bottom sides of each PCB are imprinted to form a coil around the center of the board.The conductive imprints on the upper and lower sides of the PCB are interconnected by conductive-plated holes. High precision is obtained because the manufacturing process is computer controlled,providing accurate geometry of the coils.
PCB Rogowski coils can be designed with different shapes to adjust for the application. Besidescircular shape, they have been designed in an oval or rectangular shape to embrace all three-phaseconductors (for measurement of residual currents) or to embrace parallel conductors that carry heavycurrents. PCB coils can also be designed in split-core style for installation without the need todisconnect primary conductors.
PCB Rogowski coils have the following characteristics: measurement accuracy reaching 0.1 %;measurement range from 1 A to over 100 kA; frequency response linear up to 700 kHz; unlimitedshort-circuit withstand; galvanically isolated from the primary conductors; can be installed aroundbushings or cables, avoiding the need for high insulation. PCB Rogowski coils can be connected inseries to increase output signal.
High power tests confirmed that both the split-core and non-slit-core RC output signals are almostidentical to signals obtained by high-precision laboratory current sensors. Influence from nearbyconductors on the coil performance was smaller than 0.01%, confirming superb rejection of theexternal electromagnetic fields. The PCB RCs have excellent performance for applications inadvanced protection, control, and metering systems.
A3-102
LONG-TERM DIELECTRIC STRENGTH OF CAST EPOXY
AND COMPOSITE INSULATORS by
E. OSTAPENKO* V. TRIFONOV V. VARIVODOV
All-Russian Electrotechnical Institute named after V.I. Lenin (VEI) Moscow, Russia
Summary In report the results of experimental statistical investigations of long-term electrical strength of cast epoxy insulators as well as insulating characteristics of composite polymer isolators to be used in HV and EHV equipment are presented. The cast epoxy insulators are very popular for application in high voltage apparatus at rated voltage up to 1200 kV (for example - in SF6 - filled equipment). One of the main features of the up-to-date HV equipment is the usage of cast epoxy design with appearance of quasi- uniform electrical field at applied voltage. As a result the investigation of electrical strength at mentioned conditions is very important. The main value of long – term electrical strength of epoxy insulation in quasi – uniform electrical field may be estimated as function of service term and some aging factor. The analysis of results of experimental statistical investigations of long-term electrical strength for small probability of breakdown leads to conclusion that in case of applied voltage duration more than few months there is a trend for increase of electrical strength compared to calculated data according to traditional approach. As a result it was shown that time to breakdown of epoxy insulation at different probability in quasi- uniform electrical field may be calculated well by means of proposed relationship. The maintenance of long-term electrical and mechanical strength at the conditions of climatic and electrical ageing - the basic problem over development of polymer high-voltage isolators for outside installation. The existing accelerated tests of materials do not allow to predict with high reliability the behaviour of polymer isolators during service life - therefore there is a necessity of direct long - term tests in the special facilities . The carried out laboratory researches have allowed to determine the most perspective materials for high-voltage isolators of outside installation. Samples of these materials (epoxy resin, cycloaliphatique resin and silicone rubber) as well as insulating design on their basis were putting for long-term direct tests at simultaneous affect of electrical and mechanical load in the outside stand. The results of tests of material samples and various types of insulating designs have allowed to establish that silicone rubber is the steadiest against the atmospheric and electric affect; cycloaliphatique epoxy resin can be used for devices of outside installation at moderate pollution; for polymers it is reasonable to use aluminium hydrat as filler. Tests have shown, that even at designs based on the most perfect polymer materials during service the decrease of breakdown voltage is observed. During rain tests of isolator with cycloaliphatique protective coating and epoxy core there was full destruction owing to electric breakdown in the border of core and coating. It is reasonable to conclude, that application of rigid cycloaliphatique epoxy resins in the composite designs of isolators does not provide the reliable jointing. Key words - Electrical Strength - Epoxy Insulation - Breakdown Probability - Partial Discharges - Electrical Field Stresses - Statistical Investigations - Parameter of Dispersion- Composite Outdoor Insulators - Long-term Tests - Pollution .
A3-103
1
Silicone rubber composite insulators have become more frequently used for HV equipment like surgearresters, bushings and breakers. However, the often discussed possibility of using shorter creepagedistances than for porcelain insulation has, in most cases, not been realised in spite of encouragingresults. This is maybe due to some conservatism in the market but also due to the lack of long-term fieldtest results. It is important to distinguish between pollution performance (i.e. risk for flashover) andageing of composite insulators. Detailed inspections of tested apparatus during 2-7 years as well as asophisticated data acquisition system at three test stations located in heavy polluted areas have made itpossible to cover both these aspects. The test stations used are Dungeness, on the South East coast ofEngland; Kelso, on the North East coast of South Africa and Beer Sheva in the Negev desert of Israel.In addition results are reported from an inland test station in central Sweden. This station representstypical clean environment, considered as representative of the majority of all high-voltage installations.The pollution performance of silicone rubber apparatus insulators is compared with the pollutionperformance of porcelain apparatus insulators. The ageing performance of 22 apparatus insulators iscompared with the ageing performance of 15 line insulators tested at the same site.
Based on the experience from the long-term testing of the apparatus silicone rubber insulators thefollowing conclusions can be drawn regarding ageing characteristics and pollution performance.
With regard to ageing characteristics, the results of 2-7 years of field testing show that there is only slightdeterioration for the apparatus insulators even with rather short creepage distance and in severe coastalenvironment. This is a much better performance than that of silicone rubber line insulators tested at thesame site. The most important explanation of less ageing is a lower and differently located maximum E-field in the vicinity of HV flanges and lower current density due to a large diameter in comparison withline insulators.
With regard to pollution performance, the short-term and long-term hydrophobicity characteristics ofsilicone rubber apparatus insulators are better than of the porcelain insulators at the same site. Thenumber of the high pulses of the leakage current provoking a flashover is much lower for silicone rubberapparatus insulators than for the porcelain insulators at the same site.
Considering both ageing as well as pollution performance, it is possible to reduce creepage distance incoastal areas with, as a minimum, one pollution level according to IEC 60815.
Key words: Insulator - Composite - Apparatus - Line - Field - Experience - Pollution - Ageing
Optimized use of HV composite apparatus insulators: field experience from coastal and inland test stations
I. Gutman* L. Stenström, D. Gustavsson, D. Windmar W.L. VoslooSTRI ABB Power Technologies ESKOM
(Sweden) (Sweden) (South Africa)
A3-104
A3-105
MODERN ZNO SURGE ARRESTERS UNDER SHORT-CIRCUIT CURRENT STRESSES:
TEST EXPERIENCES AND CRITICAL REVIEW OF THE IEC STANDARD R.P.P. SMEETS, H. BARTS, W.A. VAN DER LINDEN* L.STENSTRÖM KEMA HIGH-POWER LABORATORY ABB POWER TECHNOLOGIES (the Netherlands) (Sweden) Summary Metal-oxide surge arresters housed in polymer silicon rubber enclosure are the state-of-the-art for primary protection of high-voltage equipment against overvoltages of various origin. Specific requirements are formulated in the standards to ensure that possible failures, leading to short-circuit, will not give consequential damage on other equipment or lead to injury of personnel. In the present contribution, various design types are discussed (open or cage design, closed design and tubular design types) with respect to their short-circuit behaviour. The new IEC standard 60099-4 of 2001 prescibes (as “informative”), the short-circuit conditions to which arresters should be subjected, in order to verify a sufficiently rapid pressure relief associated with the transition from the high-current arc from the inside of the enclosure to the outside. One of the key requirements is the passage of asymmetrical current after deliberate establishment of an arc by suitable preparation (fuse wire) or sustained overvoltage stress ("pre-failing"). The latter method requires very careful high-voltage application since by the non-linear nature of the arrester, it is difficult to obtain the required asymmetrical peak value. In the contribution methods developed by the authors for testing arresters with very high current (up to 80 kA) will be presented, along with methods to solve the problem of timely arc initiation immediately following the pre-failing procedure. In addition, the short-circuit features of the IEC 60099-4 (2001) standard are summarized, together with a critical review of the requirements based on practical laboratory experience. The following conclusions emerge: • The asymmetrical current is not the most onerous condition for the pressure relief performance of
the arrester, given a more rapid rise of arc energy during symmetrical current passage. • Asymmetrical current tests alone are not representative of the operational situation, in which one
can expect an arrester to fail at any system voltage angle. • Asymmetrical current does not automatically necessarily generate the most severe situation, since
high current tends to elongate the externally burning arc away from the arrester. • Due to limitations of testing stations, full asymmetrical current is very difficult to realise. Failure modes of ZnO blocks are presented and it is shown how they affect the test severity. Realistic scenarios for failure in real service are summed up. Keywords Surge arrester - Protection - Short-circuit - Testing - Standard
* KEMA High Power Laboratory, Utrechtseweg 310, 6812 AR Arnhem, Netherlands ([email protected])
SUMMARY
Spring mechanisms have demonstrated their high reliable performance by operating safely thousands of circuit breakers all over the world for decades under the most severe conditions. This well-known technology could be improved, when merged with a servo motor system. The result is a hybrid drive, which offers the accuracy and flexibility of servomechanisms and the reliability of spring operating mechanisms. A prototype of a hybrid drive attached to a 145 kV life tank circuit breaker is demonstrated. The archi-tecture description emphasizes the reliability aspects due to the independent tripping systems. Exten-sive tests have shown an excellent technical performance of hybrid drives. The following of preset travel curves is possible within a wide range. The scattering of the operating time and speed can be kept within very narrow ranges even when influenced by provoked variations such as ambient tem-perature, increased friction, manufacturing tolerances and others. The applications of such a hybrid technology will be restricted to specific applications in a first step. In the future, the architecture of operating mechanisms could be dramatically modified and tighter merged with the circuit beaker. Integration of different auxiliary equipments like monitoring systems and synchronous relays within the hybrid drive are possible and the benefits of the adaptability could be used to optimize breaking characteristics. The drawback is, that the actual cost of a hybrid drive exceeds the cost of a today's spring operating mechanism. This is mainly due to the cost of low inertia motors, whatever the technology, brushless or flat rotor. It is also caused by the reliability considerations, implying the use of redundant systems with associated costs. On the other side, the integrated functionality could be used not only to perform the breaker duty, it could help to provide monitoring data of the breaker and drive itself. The situation could change if a breakthrough would occur in the technology of low inertia motors. Therefore we will continue our investigations on the hybrid drives, keeping in mind the high reliabil-ity, simplicity and cost effectiveness of the spring operating mechanisms as a guideline. KEY WORDS
Circuit breaker – High Voltage – Operating mechanism – Spring – Hybrid – Drive – Servo motor – Reliability – Energy – Electronics – Tripping – Closing
THE MERGING OF AN ACCURATE SERVO CONTROLLED MOTOR WITH A RELIABLE SPRING OPERATING MECHANISM
R. LUESCHER*, M. CASTIGLIONI J.P. DUPRAZ, S. PLANTE, S. POULLAIN, E. COURBON
ALSTOM T&D ALSTOM T&D (Switzerland) (France)
A3-106
A3-107
INCREASED PERFORMANCE OF CAPACITOR BANK CIRCUIT BREAKERS BY CONTROLLED OPENING
U. KRÜSI* P. M. JONSSON High Voltage Laboratory ABB Power Technology Products AB Swiss Federal Institute of Technology Ludvika ETH Zurich (Sweden) (Switzerland) Abstract—In IEC 62271-100 (Ed. 2001)—replacing IEC 60056—the severeness of the test duties for capacitive load switching was greatly increased and the concept of a “restrike-free” circuit breaker was replaced by two more appropriate categories C1 “low” and C2 “very low” expected probability of restrike during capacitive current breaking. In the test procedures a certain number of breaking tests have to be performed without a restrike. This affords the conclusion that the restrike probability is below a certain level, but does not provide the real restrike probability of the breaker, which might be much lower and would therefore require significantly more tests to be identified. Until now the influence of the arcing time on these probabilities could not be quantified neither by calculation nor by economically justifiable tests. For the first time a statistical model of the dielectric withstand of the CB opening has been developed to assess the restrike characteristic and to allow quantitative statements of the influence of controlled opening on the restrike probability. The calculation is based on the statistical variance of the rate of rise of dielectric strength and of the instant of contact separation. For given statistical properties of a circuit breaker – determined from the cold gas characteristic – its restrike probability can be calculated as a function of arcing time. The influence of the interrupted current on the dielectric strength can be neglected as verified by small inductive current interruption tests. The standard deviations of the rate of rise of dielectric strength and of the instant of contact separation were varied to investigate how these statistical properties affect the restrike probability. The calculations show that even with conservative assumptions about the standard deviations, the restrike probability varies by several orders of magnitude with arcing time. Hence, prolonging the arcing time by controlled opening minimizes the risk of a restrike significantly. In order to verify the theoretical findings, the cold gas characteristic of an SF6 circuit breaker was measured by the use of a 160 Hz 1-cosine wave for different arcing times. The results indicate that a fixed arcing time of 2.8 ms allows for an increased test voltage by 15% at an increased frequency of 66 Hz (compared to 50 Hz) as predicted by the calculation of the restrike probability. The results encourage a new view on the application of controlled switching since modern controllers seem not to decrease the reliability of such a controller-breaker system. A C1 circuit breaker equipped with a controller can pass the C2 tests. Alternatively, the class could stay the same while the tests are conducted at higher voltages and/or frequencies. Furthermore, the given test procedure in connection with the mathematical model of the recovery withstand allow the real assessment of the restrike probability of a circuit breaker. Keywords: Circuit Breaker – Controlled Switching – Restrike Probability – Rate of Rise of Dielectric Strength RRDS
6
A3-108
TEST AND APPLICATION OF NON-CONVENTIONAL MULTI-PURPOSE VOLTAGE AND CURRENT TRANSDUCERS
H.-D. SCHLEMPER*, D. FÜCHSLE G. RAMM J. WIDMER ABB SWITZERLAND LTD. PTB LANDIS+GYR LTD. (Switzerland) (Germany) (Switzerland)
Session Summary Non-conventional instrument transformers (NCITs) for encapsulated high voltage systems have been deployed in modular (hybrid) GIS installations in significant volumes since a couple of years. In the past, the NCIT’s digital data or analogue low voltage interfaces towards control, protection and metering equipment have been manufacturer specific designs. Also, requirements (signal fidelity, type tests) were not standardized. Today, the standards IEC 60044-7, IEC 60044-8 and IEC 61850-9-x define type tests and signal interfaces. Their application enables interoperability between NCITs and secondary equipment of different manufacturers. The paper describes the design of a NCIT for control, protection and metering applications according to these standards. It is a multi-purpose voltage and current transducer for metal-clad switchgear based on a capacitive voltage sensor and a Rogowski coil. National and international metrology regulations require provisions for protection against fraud and for control over legally relevant components. The requirements are met by a suitable system design with separated data connections (IEC 61850-9-x protocol) for metering and control/protection and a suitable sealing system. Accuracy tests of NCITs with digital interfaces require “digital bridge circuits”. A digital bridge measures phase and amplitude errors of the NCIT compared to conventional reference instrument transformers. The paper describes the design of the bridge circuit and discusses the influence of quantization noise introduced by the digital interface. A calibration facility developed by the German national metrology institute PTB is used to verify and calibrate the bridge circuits. The calibration procedure yields an uncertainty of 0.005% and 0.007 crad. The NCIT has been subjected to a complete set of type tests according to IEC 60044-7/-8. The paper reports the experience gained during testing. In general, the tests are adequate and provide the user with a comprehensive assessment of accuracy, transient behaviour and robustness. The items that may need improvement are • The definition of the signal-to-noise ratio, i.e. the definition of the considered noise
bandwidth • The definitions of transient performance requirements for ECTs with TPZ-alike characteristic. • The definition of crosstalk tests for combined voltage/current NCITs.
High precision meters with digital inputs are the best choice for interfacing the metering system to the existing remote data acquisition units. Meters are tested with a digital test pattern generator able to provide polyphase test patterns with variable levels, frequency and harmonic content.
Novel Application of Optical Current and Voltage Transducers on High Voltage Switchgear
Roberto Boero Chris Jones* Andrew Klimek VA TECH VA TECH NxtPHase (Italy) (United Kingdom) (Canada)
This paper describes some applications of the latest optical current and voltage transducers (OCT and OVT) onto high voltage switchgear which are capable of use with the latest digital IEC 61850 communication protocol, low energy analogue (LEA) connections or indeed conventional high energy analogue (HEA) metering equipment dependent on customer requirements. An OCT system mounted on conventional live tank breakers opens wide opportunities for application where space constraints are of concern and installation of separate CT devices in AIS substation is difficult. The optical current transducers (OCTs) are in-line fibre optic interferometers that measure current using the Faraday effect in a vibration-immune architecture. The system consists of OCT heads mounted on the breaker, insulator for the OCT sensor fiber, a set of electronic modules associated with the optical sensors, and a fiber optic cable system to connect the HV OCT heads to the electronics. The OCTs are all IEC & IEEE compliant, and can have metering class better than 0.2S and 0.3% and protection class better than 5P (5TPE) and 10% (IEC60044-1,6,8 and ANSI/IEEE C57.13 respectively). An output of OCT electronics can be 1A HEA to interface with conventional revenue meters, 200 mV LEA to relays having such an interface and digital interface to relays and meters following the IEC 61850 standard. The OCTs are rated and tested to maintain accuracy over ambient temperature from -40°C to +50°C and withstand vibrations caused by breaker opening and closing maintaining accurate readings of current. The OCT on LTB have an environmentally friendly design with the particular design features and advantages described. This arrangement can exploit the OCT’s wide dynamic range for protection and metering applications, and be able quantify the accuracy of energy metering and conventional current measurement at low currents (e.g., <10% of rated current). Initial applications are also being used to monitor the accuracy and selectivity of low energy analogue connections and the emerging digital interfaces to relays. The OCT is fully tested and has shown that it maintains accuracy over a wide temperature and vibration range and the results of these stringent tests will be discussed. The paper contains information on system design, features and benefits of the solution, mechanical/electrical design issues as well as OCT performance tests (with specific data and discussion on laboratory test results). The same technology is also capable of being applied in a range of substation applications including GIS equipment where a novel combined OCT/OVT provides considerable advantages when compared to conventional measurement technologies.
*VA TECH Transmission & Distribution, Hebburn, Tyne and Wear, NE31 1EJ, UK; [email protected]
A3-109
LONG TERM PERFORMANCE OF POLYMER HOUSED MO-SURGE ARRESTERS B. RICHTER*, W. SCHMIDT K. KANNUS, K. LAHTI ABB SWITZERLAND LTD. TAMPERE UNIVERSITY OF TECHNOLOGY (Switzerland) (Finland)
V. HINRICHSEN C. NEUMANN W. PETRUSCH K. STEINFELD DARMSTADT UNIVERSITY RWE NET AG FGH MANNHEIM SIEMENS AG OF TECHNOLOGY
(Germany)
The standard IEC 60099-4, Ed.1.2, 2001-12, “Surge arresters – Part 4: Metal-oxide surge arrester without gaps for a.c. systems”, is, besides the general testing, dealing with test procedures for polymeric housed MO arresters. Besides mechanical tests, climatic tests, and the short circuit test (which is still under consideration), the long-term tests have led to controversial discussions. One reason is that it is virtually almost impossible to define a test procedure for the outer insulation, which considers the features of hydrophobic and non-hydrophobic polymer materials in the same time. Polymers, which do not recover after severe pollution stresses (complete loss of hydrophobicity, e.g. EPDM) should preferably be tested by a 1000 h salt fog test, while polymers, which recover after a severe pollution stress (e.g. silicone) should be tested by cyclic tests. MO-surge arresters with polymeric housings can be differentiated according their internal structure and their production process. For high voltage arresters it is suggested to make a differentiation between designs using a hollow core insulator and such designs, where the housing is moulded directly onto the internal parts, without any gas volume in the arrester. A similar differentiation can be made for medium voltage MO-surge arresters. Here the designs are grouped according to the manufacturing process and the internal structure. The difference in the design differentiation is due to the fact that for high voltage arresters the mechanical strength of the design is of more importance, for medium voltage designs the production process is of more importance. In research institutes test procedures have been developed to prove the validity of existing test methods, to develop new tests, and to compare artificial laboratory tests with real existing stresses in the system. It is obvious that especially in long-term tests complete arresters have to be tested, because not only the material itself is decisive for the performance of an arrester, but also the design and the quality of the production process. Long-term tests (testing time longer than two years) under high humidity proved, that directly moulded (e.g. by silicone) designs show the best performance. Large field studies on medium voltage arresters in Finland, and the experience from outdoor test stations with severe pollution stresses show that no problems are to be expected with polymeric housed MO-surge arresters. The overall experience with polymer house MO-surge arresters in medium voltage, high voltage and extra high voltage systems is very good. The arresters have performed in very different places and under severe ambient conditions without any problem. The different designs, developed for different applications, allow special solutions for overvoltage protection and insulation coordination in general.
A3-110
A3-111
FIELD EXPERIENCE WITH HIGH-VOLTAGE COMBINED OPTICAL VOLTAGE AND CURRENT TRANSDUCERS
FARNOOSH RAHMATIAN*1, GREG POLOVICK2, BRENT HUGHES2, and VIORIKA ARESTEANU3
NxtPhase Corporation1, British Columbia Hydro2, and Hydro Québec3
(Canada)
Three-phase combined optical voltage and current transducer systems (NXVCTs) for accurate energy metering at transmission level voltages are described. Laboratory tests and field data are presented with emphasis on stability and reliability of the installed systems. Experiences with an early 145 kV prototype and a more recent 550 kV system are presented. The 145 kV system has been installed near downtown Montreal, Canada, on Hydro Quebec’s transmission system since October 2001. The 550 kV system has been installed near Vancouver, Canada, in a BC Hydro substation since March 2003. The optical voltage transducers (OVTs) use a distributed electric field sensor system together with resistive shielding to measure voltage accurately. The optical current transducers (OCTs) are in-line fibre optic interferometers that measure current using the Faraday effect in a vibration-immune architecture. The OVTs and OCTs are all IEEE 0.3% class (ANSI/IEEE C57.13) instrument transformers and are connected to three-phase energy meters. They are rated and tested to maintain accuracy over ambient temperature from −40°C to +50°C. They are environmentally friendly, do not use oil, cellulose, or SF6; rather, they use composite insulators filled with dry nitrogen. In both installations, NXVCT systems are compared with conventional revenue metering class instrument transformers. The rated accuracy currents for the 145 kV and 550 kV systems are 600 A and 1500 A, respectively (with an over current factor of 1.5). The 145 kV system has been running at extremely low currents, typically ~ 2 A, whereas the 550 KV system has been running at higher currents, typically ~ 450 A. The data obtained from both installations confirm the accuracy and stability of the NXVCT system with respect to time, dynamic range, and environmental conditions. Keywords: Optical Sensors, Instrument Transformers, Stability, Reliability, High Voltage, Energy Metering, Voltage Measurement, Current Measurement, Fibre Optic.
A3-112
A New Measurement Method of the Dynamic Contact Resistance of HV Circuit Breakers
M. Landry*, A. Mercier, G. Ouellet, C. Rajotte, J. Caron, M. Roy
Hydro-Québec
Fouad Brikci Zensol Automation Inc.
(CANADA)
To assess the condition of the breaker contacts, the main contact resistance measurement is usually
performed by all utilities around the world. However, the static resistance measured when the breaker remains in a closed position does not give any indication of the condition of the arcing contacts. To evaluate the latter’s condition, an internal inspection can be done, but time-consuming and costly maintenance procedures must be followed in order to securely handle the SF6 gas and arc by-products. It is well known that breaker performance can be impaired by such maintenance action if some defects or incorrect adjustments are involuntary introduced.
The dynamic contact resistance measurement (DRM) was developed over 10 years ago to assess the condition of the arcing contacts without dismantling the breaker. This method is no longer widely used since the interpretation of the resistance curve remains ambiguous. Previously published test results usually depicted several spikes in the resistance curve which could be the result of a partial contact part during the contact movement.
The following paper presents a new dynamic-contact-resistance measurement method that has been validated by field tests which were performed on air-blast and SF6 gas circuit breakers. The unique measurement method allows reproducible resistance curves to be obtained, which is not the case with the conventional method. Dynamic contact resistance curves obtained by using both the conventional technique and the new method are compared. By applying the novel measuring method, the dynamic contact resistance curve is easy to interpret.
Furthermore, when superimposing the dynamic contact resistance curve and that of the contact travel, criteria for assessing the breaker contact conditions are derived such as the average main contact resistance, average arcing contact resistance, main contact and arcing contact wipes, and position of the breaker contacts at the contact part. Finally, by plotting the contact resistance as a function of the contact travel, a simple mathematical algorithm for determining contact wear and/or condition has been developed. One advantage of this algorithm is that the output value is comparable for breakers of the same technology type even when they come from different manufacturers.
Using this new measuring method, arcing contact anomalies were detected on several interrupting chambers of SF6 gas circuit breakers. Internal inspections revealed significant damage to the arcing contacts that could be caused by contact misalignment.
To summarize, it is believed that the new measuring method can be used as a diagnostic tool for SF6 gas circuit breakers whenever contact anomalies are suspected. This new measurement method allows for an accurate evaluation of both main- and arcing-contact conditions without dismantling the circuit breaker. Moreover, it provides the maintenance crew with relevant criteria for selecting the interrupting chambers that should be internally inspected.
Keywords: Circuit Breaker – Dynamic Contact Resistance – Contact Wear – Diagnosis
METROLOGICAL PROPERTIES OF HIGH-VOLTAGE INSTRUMENT TRANSFORMERS AFTER MANY YEARS’ SERVICE
E. Anderson* A. Hyrczak J. Karolak A. Ratajczak J. Wróblewski R. Zając
Institute of Power Engineering Polish Power Grid Company
(Poland)
About seven thousand of current transformers, voltage transformers and recently exploited
combined transformers are installed in Polish power networks of 110, 220, 400 and 750 kV. They are in service from several years to maximum forty years for use with protective devices and energy measuring systems, being the base of settlement of accounts between the different users of the networks.
The research program developed for last ten years in Poland in the scope of determining the metrological properties of instrument transformers has shown, that some part of transformers doesn’t fulfill the requirements of measuring accuracy. In principle it concerns all types of transformers but especially the capacitor voltage transformers. For those transforms it was stated in many cases, that voltage error in extreme cases reaches ten to twenty percent – so they are useless for energy measurements as well as the co-operation with protective devices is doubtful. It concerns mainly the units with the longest time of exploitation.
In the paper the age structure of the instrument transformers installed in Polish grids and the results of research in the range of metrological properties of tested transformers are presented. The test results are shown in relation to type of transformers, to exploitation time and to rated voltages. The separate analysis was made for voltage transformers, in particular capacitor transformers, which have presented high inaccuracy.
Taking into consideration the number and the economic value of capacitor voltage transformers installed in Polish networks, the studies concerning the modernization of those transformers in order to attain the conformity with IEC 60044 – 7 and 8 requirements have been undertaken. It was proposed the way of modernization by installing the low voltage correction units (countershafts) making possible the elimination of measuring errors, the complete suppression of dynamic errors caused by inductive part of the transformer and the exact transferring of higher frequency transients. Application of proposed solution assures the correct operation of distance protection devices in particular during auto-reclosing and the correct measurements of quantity and quality of energy and also eliminates the necessity of replacement of voltage transformers (this operation could be relatively expensive) under condition, that the general state of transformers is not questionable. Keywords: High Voltage - Instrument Transformer - Exploitation Time – Class – Accuracy - Electronic Transformer – Modernization.
A3-113
A3-114
Factory and Field testing of controlled switching systems and their service experience
H. Ito, H. Kohyama, B. R. Naik, R. G. Asche, H. Wilson, S. Billings TMT&D Corporation, Portland General Electric, Mitsubishi Electric Power Products Inc.
(JAPAN) (United States)
Controlled switching systems (CSS) with 145kV, 245kV, 362kV and 550kV independent- pole-operated gas circuit breakers and controller have demonstrated their performance. The circuit breaker, sensor and controller, and integrated system were verified according to CIGRE recommendations for routine and type tests. The characteristics of circuit breakers such as the rate of decrease of dielectric strength, the mechanical scatter of the operating times and the idle time dependence are essential to the success of a CSS.
Variations of the operating times due to operating conditions such as ambient temperature, control voltage and stored energy of the drives can be compensated by the controller using the measured dependence of variations of the operating times for these conditions. The drifts of the operating times over a number of consecutive operations due to wearing of the parts can be compensated using the adaptive control. The effective compensation of adaptive control during 10000 operations of the circuit breaker was demonstrated.
Idle time dependence of the drive is one of the major causes for controlled switching failure. A few milliseconds delay of the closing time can occur after only a few hours of idle time since the last opening operation. This indicates that even a daily-operated CSS requires idle time compensation if the circuit breaker shows this dependence. CIGRE WG13.07 proposed a detailed test procedure for the determination of the relationship between the idle time and the operating times and also provided some typical results. It can be seen that the requirement of idle time compensation can be judged from the measurement up to 100 hours. Innovative spring operating mechanisms do not show any delay of the operating times for idle time up to 1000 hours.
Field verification is required to ensure satisfactory in-service performance of the complete CSS. The CSS applied to a capacitor bank and a reactor bank was tested in the field. Since the commissioning tests are limited to the minimum possible to avoid inconvenience in the utility's network, the tests consist of a limited number of point-on-wave operations of a breaker by means of a controller. Controlled shunt capacitor switching in the field showed more successful results of controlled closing to the voltage zero targets because the adaptive control reduces the prediction error caused by the design tolerance after learning from the previous operation results. The CSS also demonstrates successful reactor opening without any reignition and accurate operation consistency over one year period. Therefore, CIGRE WG13.07 recommendation successfully covers all the testing requirements and their procedures.
A Algorithm for the Three-Pole Controlled Auto-Reclosing of Shunt Compensated Transmission Lines with a Optimization for the second and
third Pole
G. Pilz*, P. Schegner Technical University of
Dresden (Germany)
C. Wallner Siemens AG Berlin,
(Germany)
H. M. Muhr, S. Pack, Technical University of
Graz (Austria)
SUMMARY ∗
The controlled closing of shunt compensated transmission lines by an auto-reclosing is a reliable method to reduce the switching overvoltage and starting current. The transient phenomena after disconnection depend on the parameter of the transmission line and the level of compensation. The floating voltage and the variance of compensation level complicate the prediction of the optimal switching instant. In a first step an algorithm was developed, which predicts the future voltage across the switching contacts of the circuit-breaker during the dead time of an auto-reclosing.
State of the art applied methods are using pattern recognition algorithms. In the case of an auto-reclosing of shunt compensated transmission lines these methods estimate no satisfactory solutions. Especially the switching instants are too inaccurate for a three-pole auto-reclosing, because the influence of the individual poles among themselves can not be taken into consideration.
The new algorithm is based on the Prony Method. The Prony Method composes the voltage over the circuit breaker by a sum of sinusoidal and exponential damped functions. The lowest recognizable frequency is independent of the evaluation window of the Prony Method. Another advantage of the Prony Method is a high resolution in the frequency domain. Signals with small frequency differences will be exactly determined. Via the estimation of the signal components it is not only possible to calculate accurately the voltage zero crossing across the switching contacts of the circuit-breaker as possible switching instant, but also the rate of voltage rise in this point.
By a single pole auto-reclosing it is now possible to shift the switching instant, if the rise of voltage in the zero crossing is greater than the characteristic curve of strength recovery of the circuit breaker. Thereby the best results will be achieved with a variable time shift parameter.
The closing of the second and third pole during a three-pole auto-reclosing is more complicated. After closing the first pole the estimated zero crossing for the second and third pole is no more valid, because a voltage from the first closed pole is induced to the other phases. A first algorithm for selection of switching instants is optimized for a standard processor. The second algorithm is more complex and calculates optimized switching instants for the second and third pole.
The simulations of auto-reclosings with controlled closing operations take place in ATP. The real-time algorithms were developed in MATLAB.
Keywords
Controlled Closing, Switching Overvoltage, Shunt Compensated Transmission Lines, Pattern Recognition, Prony Method ∗[email protected]
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13
A3-201
The concept of disconnecting circuit-breakers (DCB) for air-insulated substations (AIS) has been discussed in several Cigré papers since the middle of the 1990’s. The DCB is aimed at replacing the traditional combination of a circuit-breaker (CB) and its associated conventional disconnectors (DS). The long intervals between maintenance of the DCB, compared with the conventional open-air DS, provide high availability also with simplified substation configurations. The main advantage of the DCB compared to a conventional disconnector is that the electrical contacts are enclosed in SF6 gas, thereby protecting them from the influence of ambient conditions including the effects of pollution. The protected environment provides improved reliability and prolonged intervals between de-energisation for maintenance of the DCB. The possibility of excluding the conventional disconnectors is based on the reduced maintenance demands of modern circuit-breakers; one major traditional function of the disconnector has been to isolate the breaker for maintenance of the breaker itself. With the prolonged maintenance intervals associated with modern circuit-breakers (de-energisation required typically only every 15 years), this isolating function of the disconnector is becoming obsolete. Furthermore, other major functions of the conventional disconnector, e.g. the isolation of lines, transformers, etc., for operational or maintenance purposes, can be equally well handled by the DCB, as shown in the paper. Since 1999, the DCB concept has been applied in several transmission and sub-transmission substations in various countries, from 72 to 420 kV. A recent example is the application of DCB for rehabilitation of a major 400/130 kV substation in the south of Sweden, owned by Svenska Kraftnät and Sydkraft Nät, respectively. The reasons for selecting the DCB concept for both the 400 kV and the 130 kV voltage levels are discussed. An important aspect of the DCB is its ability to provide safe working conditions during maintenance and repair work in substations. When the DCB is used as a disconnector for this purpose, it has to be assured that the open contacts are not closed unintentionally, or bridged by a disruptive discharge. This important aspect has been considered in the design and specification of the DCB. The safety locking system of the DCB is described, and an analysis of the insulating properties of the DCB in the open position is presented, taking into account the voltage stresses and the risks and consequences of a disruptive discharge. The importance of the safety aspects is reflected in the upcoming IEC standard for combined function disconnecting circuit-breakers. Results of the standardisation work are briefly described in the paper. Keywords: Disconnecting – Circuit-Breaker – Disconnector – Substation – Insulation – Interlocking
APPLICATIONS OF DISCONNECTING CIRCUIT-BREAKERS
P-O Andersson H-E Olovsson B Franzén U Lager J Lundquist*ABB Power Technologies Svenska Kraftnät Sydkraft Nät STRI
(Sweden)
14
A3-301
CURRENT INTERRUPTION WITH HIGH VOLTAGE AIR-BREAK DISCONNECTORS
D.F. PEELO* DF PEELO & ASSOCIATES
J.H. SAWADA BC HYDRO
B.R. SUNGA BC TRANSMISSION CORP.
(Canada)
R.P.P. SMEETS KEMA HIGH-POWER LAB
J.G. KRONE HAPAM B.V.
L. VAN DER SLUIS S. KUIVENHOVEN
DELFT UNIVERSITY
(The Netherlands)
Summary High voltage disconnectors are intended for use as isolators. However, disconnectors are operated under energized conditions and therefore are expected to interrupt current, the type being dependent on the switching circumstances and individual utility practices. Particularly in North America, disconnectors are used to switch out unloaded transformers and short transmission lines, and also for loop switching between transmission lines.
For modern low loss power transformers, the high voltage side magnetizing current is generally less than 2 A and often less than 1 A. The transformer side transient recovery voltage is a critically or overdamped oscillation at low frequency. Since the peak of the oscillation is unlikely to coincide with the source side voltage peak, the latter voltage tends to dominate the switching event. Successful switching is dependent primarily on achieving a sufficient contact gap spacing to withstand the transient recovery voltage. Multiple restriking will occur and the possible impact of the restriking overvoltages on the transformer insulation is a serious consideration. Restrikes may result in inrush current which prolongs the arcing period by its duration without contributing to propagation of the arc.
For capacitive currents of about 1 A or less, the interruption is also dependent on achieving a contact gap spacing to withstand the applicable recovery voltage. Above 1 A, arc thermal effects start to influence the interruption process by providing a remnant arc channel for energy injection by restrikes. Interruption is also dependent on the ratio of the source (CS) to load side (CL) capacitances, the longest arc durations and highest load side overvoltages occurring when CS/CL < 1.
Loop switching is a complex event and varies from the busbar transfer case of 1600 A and 300 V to the transmission lines case of 100 to 200 A and up to 10 kV. The event is one of commutating the current from the disconnector circuit to a parallel circuit. As the arc propagates and grows in length, it forces more and more of the current to the parallel path until interruption is achieved. It can be shown that the arc will continue to propagate only as long as its power input is increasing. Eventually this condition can no longer be met and the arc will become unstable and collapse.
Keywords: Disconnectors - High Voltage - Current Interruption
CONSEQUENCES ON THE VOLTAGE STRESSES IMPOSED ON STEP-UP TRANSFORMERS DUE TO THE USE OF GENERATOR CIRCUIT-BREAKERS
DIETER BRAUN GEORG S. KOEPPL
ABB SWITZERLAND LTD. KOEPPL POWER EXPERTS (Switzerland) (Switzerland)
Today the use of generator circuit-breakers is widespread because this offers many advantages when compared to the unit connection such as simplified operational procedures and better protection against the effects of faults. The insertion of a switching device in the connection between the generator and the step-up transformer however exerts an influence on the type and magnitude of overvoltages that will occur. It therefore raises the question of the possibility of overvoltages being generated by the generator circuit-breaker itself during switching operations and also by its sole presence while being in the open state. The present paper specifically examines the voltage stresses occurring on the low-voltage side of the step-up transformer in power stations equipped with generator circuit-breakers. It differentiates between temporary overvoltages, switching overvoltages and transient overvoltages transferred through the step-up transformer. Examples for temporary overvoltages, which are influenced by the presence of a switching device in the connection between the generator and the step-up transformer, are overvoltages due to ferroresonance and stuck-pole conditions. Examples for switching overvoltages are overvoltages due to the interruption of fault currents, the interruption of load currents and the interruption of the magnetising current of the step-up transformer. Overvoltages due to the initiation of earth faults on either side of the open generator circuit-breaker are considered, too. The impact of surges transferred through the step-up transformer is also influenced by the presence of a generator circuit-breaker, the highest voltage stresses occur when the generator circuit-breaker is open. In most power stations the step-up transformers are protected by surge arresters fitted at or close to their high-voltage terminals. These surge arresters may not provide in all cases a sufficient overvoltage protection for the equipment on the low-voltage side and additional steps must be taken to protect the generator busbar and the equipment connected to it. Such measures can comprise the use of surge capacitors and surge arresters as well as devices, which prevent the occurrence of ferroresonance. Finally, the paper explains the procedures applied for the starting-up or shutting-down of a unit when the relevant switching device is located either on the low-voltage side of the step-up transformer or on the high-voltage side of the step-up transformer and compares the voltage stresses imposed on the major power station equipment resulting from these different procedures. Keywords: Power Station - Generator Circuit-Breaker - Overvoltage - Surge Protection
A3-302
16
A3-303
ASSESSMENT OF NON-SUSTAINED DISRUPTIVE DISCHARGES
(NSDD) IN SWITCHGEAR.
TEST EXPERIENCE AND STANDARDISATION STATUS R.P.P. SMEETS, A.G.A. LATHOUWERS* L.T.FALKINGHAM KEMA HIGH-POWER LABORATORY AREVA T&D MVB (The Netherlands) (The United Kingdom) Summary A non-sustained disruptive discharges (NSDD), by definition, causes a very short lasting bridging of the insulation of a switching gap relatively long (up to 1 s) after interruption of current. The authors report their experience with NSDD during one year of current interruption with vacuum switching devices. Based on tests with more than one hundred different vacuum switching devices, it is concluded that NSDDs occur during more than a third of all (current interruption) test series and can thus be considered as inextricably bound up with the interruption process in vacuum. Using simulation techniques, it is demonstrated that a NSDD can only cause significant overvoltages in 'standard' circuits with a capacitive load when the duration of the NSDD is long enough to develop a oscillation through the load capacitance. Measurements have shown that the duration of NSDDs under realistic circuit conditions is below 10 µs (in the tested breakers). Hence it is concluded that in "standard" distribution circuits the risk of overvoltages as a result of NSDDs is very small. For capacitive current interruption tests the authors propose to make a distinction between restrike and NSDD based on the discharge of the load capacitance: if it discharges as a result of a late breakdown, then the late breakdown is termed "restrike", if not, then "NSDD". Keywords Electrical breakdown - Circuit breaker - Capacitive current switching - Standards - Testing
* KEMA High Power Laboratory, Utrechtseweg 310, 6812 AR Arnhem, Netherlands ([email protected])
THE STATISTICS behind the ELECTRICAL ENDURANCE TYPE TEST for HV CIRCUIT-BREAKERS
applied by CIGRE SC A3/WG13.08 and IEC SC 17A/WG29
A.L.J. Janssen* C.E. Sölver NUON Assetmanagement ABB Power Technologies
the Netherlands Sweden KEYWORDS Circuit-breakers, short-circuit currents, electrical stresses, electrical endurance test SUMMARY For medium voltage circuit-breakers (up to 52 kV) an electrical endurance type test, non-mandatory, has been defined already in the old IEC-Standard 60056 and the present IEC-Standard 62271-100. In addition the specification of an electrical endurance type test for circuit-breakers with a rated voltage of 72,5 kV and above is already since decennia under consideration. In order to study the necessity of an electrical endurance type test for modern circuit-breakers and to specify such a type test, when necessary, IEC SC 17A has established a task force at its 1996 meeting in Jakarta (later transformed into a regular Working Group, WG29). As shortly before CIGRE SC13 had formed a new WG 13.08 to study Life Management of Circuit-Breakers, this working group has been asked to collect information about short-circuit currents in service. Now IEC SC 17A is about to publish a Technical Report on Electrical Endurance Type Tests for circuit-breakers with a rated voltage of 72.5 kV and above: in IEC Publication 62271-310 a dedicated type test sequence will be defined, based on data collected by CIGRE WG 13.08 and IEC 17A/WG29. Although in the CIGRE survey the populations of circuit-breaker-years and OH-line-km-years are quite large, the number of answers used for the statistical evaluation is rather small. Nevertheless the average values and 90% percentiles for the number of faults per OH-line show some consistency and are in line with publications on much smaller populations. The information collected about the maximum expected short-circuit currents in the substations shows that these are rather low in comparison to the rated short-circuit current of circuit-breakers. The real value of the short-circuit current level in service is even lower. Given the statistical distribution of the number of faults per 100 km OH-line and given the statistical distribution of the short-circuit powers, a chessboard can be built with the percentiles of both distributions. Each square of a 10 by 10 chessboard thus represents 1% of the whole population of circuit-breakers. As for each square (combination of probabilities) the total electrical wear can be calculated and translated into T100 operations, a complete distribution of electrical stresses can be achieved. The distribution of electrical stresses can be split into 90%-10%: 90 squares with lower total wear and 10 squares with higher total wear than the borderline (i.e. the 90% percentile of electrical wear). The exercise results into a substantial reduction in electrical wear (90% percentile) in comparison to the values used by the IEC SC 17A/WG29.
A3-304
1. In the years to come experience with the new IEC Technical Report will be collected and evaluated, leading to further considerations to the topic of electrical endurance type tests for circuit-breakers rated 72,5 kV and above.
2
* Landgraf-Georg-Str. 4, D-64283 Darmstadt; [email protected]
A3-305
EVALUATION OF FAILURE DATA OF HV CIRCUIT-BREAKERS FOR CONDITION BASED MAINTENANCE
G. Balzer * D. Drescher
Darmstadt University of Technology (Germany)
F. Heil ABB Schweiz AG
(Switzerland)
P. Kirchesch Alstom Energietechnik
GmbH (Germany)
R. Meister
EnBW Regional AG (Germany)
C. Neumann
RWE Transportnetz Strom GmbH (Germany)
SUMMARY
Permanently new ideas are investigated to optimize maintenance strategies and measures to reduce
expenses with constant quality of power supply. Therefore most German network operators attempt to expand the time interval of maintenance. The overall question is how long such intervals for electrical equipment can be expanded without reducing the quality of power supply? In this report a new method is presented which evaluates the future failure frequency coming from disturbance statistics of equipment. It is a direct anticipation from results, how long maintenance intervals can be extended by a tolerated failure frequency.
As a result of the evaluation it can be stated that in many cases the maintenance interval can be extended depending on the type of circuit-breaker, especially on the type of drives in use. Due to the teething problems, which are relevant for high voltage components as well as for hydraulic drives, the maintenance measures should be performed more carefully. Furthermore it is recommended to monitor the condition of components. As a consequence the possibilities of manual interventions on the circuit-breakers thus increasing the risk of teething problems can considerably be reduced. Regarding the hydraulic drives it is obvious that the maintenance intervals can be extended up to 12 or 15 years. Whereas the interval of a mechanic drive should be about 10 years. But due to the low number of recorded failures this value is a rough estimation. In principle the network operator has to make sure that the failure rate does not exceed the level he is willing to accept. The main goal is to observe the failure behavior continuously and built up a proper data collection it is also necessary to define levels of importance at any point where a circuit breaker is installed [4]. From the correlation between failure behavior and mentioned levels the network operator can define the risks depending on the time interval of maintenance and can decide which risk level at the different system points is acceptable. Together with the relation between maintenance costs versus new equipment costs it will be possible to find a reasonable time for replacement. . In a next step this procedure will be applied für power transformers.
FAILURES OF VOLTAGE GRADING CAPACITORS IN GIS CIRCUIT BREAKERS
M. RUNDE* J. SLETBAK J.-T. ERSDAL SINTEF Energy Research Sira-Kvina kraftselskap A. MJELVE B. SKYBERG L. SØREIDE E. ÅKRA Viken Nett Statnett BKK Produksjon Statkraft
(Norway)
Voltage grading capacitors have over a five-year period been responsible for several serious failures on Norwegian GIS circuit breakers operating in the 300 and 420 kV grid. Five grading capacitors have exploded, hundreds leaked oil and/or SF6, and several cases of severe mechanical fatigue in the metal foils connecting the capacitor elements have been found. Only 36 GIS are in service at these voltage levels in Norway, so these problems significantly impaired the overall reliability record of this equipment. In fact, nearly all the major and minor failures occurring in GIS were in this period originating in the grading capacitors. Furthermore, the malfunctions were not limited to equipment provided by certain manufacturers. All the major grading capacitors manufacturers and all GIS vendors were involved, signifying that this was a broader and consequently, more severe problem. Apparently, the lifetime for grading capacitors installed in the 70-ies and 80-ies is shorter than for the rest of the GIS. Test procedures and standards that take into account the stresses grading capacitors are exposed to in service, particularly during circuit breaker operations, need to be developed. (Keywords: Circuit breaker – Voltage grading capacitor – Failure mechanism – Reliability)
A3-306
E-mail: [email protected], [email protected]
A3-307
Feature, technical problem and application of surge arrester using high gradient zinc-oxide elements
K. Ikebe, M. Kan, M. Yamaguchi, S. Watahiki Tokyo Electric Power Company, TMT&D Corporation, Japan AE Power Systems Corporation (JAPAN)
To improve reliability of surge arrester by decreasing the number of components and increase the flexibility in optimizing the GIS layout, miniaturization of a metal-enclosed type surge arrester has been desired. The size of the surge arrester is determined by the number of ZnO elements. To miniaturize the surge arrester, it is the effective way to decrease the number of the ZnO elements by increasing the varistor voltage of the ZnO element per unit of thickness. The non-linear voltage-current characteristic of ZnO elements depends on the boundary layers between ZnO grains. The smaller the ZnO grain size, the greater the number of the grain boundary layers per unit element length, thereby increasing the varistor voltage of the elements. However, it is also desirable to improve energy absorption capability of the ZnO elements because the energy absorption capability per unit volume of the ZnO elements needs to be increased when the varistor voltage is increased. As a consequence of continuous study of improvement in energy absorption capability in parallel with increase in varistor voltage, in the middle of 1990s, high gradient zinc-oxide elements (HG elements) with varistor voltage of 400 V/mm have been first developed in the world. This was achieved by controlling the ZnO grain growth due to changing the combination ratio of the additive.
These elements began to have been applied to a metal-enclosed type surge arrester and oil-immersed surge arrester in Japan, whose size are desirable to be reduced. At the present, they have been widely used from distribution lines up to 800 kV transmission systems as the mainstream product. More than 6 years have passed since a metal-enclosed type surge arrester using the HG elements was applied to 154 kV system for the first time. However, failures causing serious damage to transmission system have never been occurred. In addition, the verification test has been carried out to confirm that the HG elements are applicable to Ultra High Voltage (UHV) systems since 2000 prior to service application. No abnormalities in leakage current have been found for 3 years. The total amount of supply of the surge arrester using the HG element is about 5,450 units. The HG elements have been widely used in almost all fields in surge arrester applications, including station, distribution and transmission.
This paper describes the HG elements, and the feature, technical problem and applications of surge arresters using the HG elements.
A3-308
HIGH SPEED GROUNDING SWITCH FOR EXTRA-HIGH VOLTAGE LINES
G.E. Agafonov, I.V. Babkin∗, B.E. Berlin Y. F. Kaminsky, S. V. Tretiakov, Y. I. Vishnevsky
NIIVA Russia
J.H. Yoon, J.H. Kang, B.H. Choi
HHI Korea
Summary At a single-phase short-circuit in extra-high voltage lines after breaking of faulty phase from both sides by the circuit breakers the secondary arc can exist for a long time in a place of a short-circuit, roused by electrostatic induction from the "sound" phases. One of possible ways of a secondary arc elimination is employment of grounding switches, which are capable during a dead time at autoreclosing of circuit breakers at first to short-circuit purposely a faulty phase from both sides, thus having shunted and eliminated an arc in a fault location, and then to open it, by breaking of the induced currents, and to make a phase ready for making of the circuit breakers, i.e. renewal of power supply. The basic requirements to a switching performance of a grounding switch result from the transient analysis in power lines and include the requirements to switching of capacitive and inductive currents, including currents, which up to 100 ms have no zero value.
The design of a high speed grounding switch (HSGS), meeting the given requirements was realized within the framework of GIS 800 kV project for KEPCO - Korean electric power company creating nowadays a system with such rated voltage.
HSGS represents the single-break, puffer type device. For arcing capacity ensuring at large times the dead zone is provided for in compressed volume, sufficient for an intensive blow after the stopping of a moving contact. The distinctive feature of the given device is the usage of the stationary nozzle on the side of the moving contact. The given solution allows to lower the flow rate of SF6 on an initial stage of an arc blowout and to increase a gas pressure at bigger arc durations.
For checking of the switching performance at large arc durations the new synthetic circuit was built, where the high-power rectifying installation was used as the current source permitting to obtain the unipolar currents up to 14 кА by amplitude and up to 100 ms by duration.
Keywords: High speed grounding switch – Extra high voltage – Switching performance test.
∗ I.Babkin, [email protected]