CYME is now part of the Energy Automation Solutions (“EAS”) group within Cooper Power Systems

CYME is now part of the Energy Automation Solutions (“EAS”) group within Cooper Power Systems
Posted on December 5, 2008

Cooper announces the acquisition of CYME International. “This acquisition complements Cooper Power Systems’ ability to provide utility customers with comprehensive smartgrid solutions to improve power quality, reliability and efficiency in their transmission and distribution networks,” said Cooper Industries Chairman and Chief Executive Officer Kirk S. Hachigian.

“This is a natural integration of two companies who know that the smart grid is a business driver for utilities,” adds Marc Coursol, President and CEO of CYME. Press Release.

CYME International T&D is a world-class Power Engineering Solutions provider with an established reputation for customer responsiveness and technical expertise. Solutions stand behind thousands of T&D projects in over 100 countries around the world.

CYME offers an extensive line of Power Engineering Software that feature some of the most advanced analysis tools for transmission, distribution and industrial power systems.

Reference platform for simplifying 'smart' electric power metering

Paper source from: http://dataweek.co.za/news.aspx?pklNewsId=19121&pklCategoryID=46
Supplied by avnet kopp
www.avnet.co.za
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STMicroelectronics has introduced a reference design platform for the electronic power meter market. Electronic energy meters are replacing traditional electromechanical meters because their versatility and low-cost allows manufacturers to implement many features that were impractical with the older mechanical designs.

For example, an electronic design can protect against meter tampering and theft of service. It can also measure and record energy usage at different times of the day, so utilities can bill based on time of usage. Also, automatic meter reading (AMR) can be enabled, transmitted information to the utility over a power line communications link.The reference platform provides a modular solution that can be adapted by software to meet particular needs.

It comprises two PCBs, one dedicated to the mains power measurement functions and one implementing sophisticated computational and supervisory functions. The measurement board supports all current measurement technologies, from the most accurate Rogowski coils to inexpensive shunt resistors. It can monitor both Live and Neutral current for tamper detection and complies with international standards for metering equipment (AC).

The Measurement Board is based on ST's STPM01 power metering chip, which includes all necessary signal conditioning, processing, data conversion, input/output signals and voltage reference. The STPM01 can be used as a standalone device in 1-phase kWh meters or as a peripheral in microprocessor-based 1- or 3-phase energy meters, in which case active, reactive and apparent energy, Vrms, Irms, instantaneous voltage and current, and line frequency readings are available through the SPI bus. The Control Board is based on an ST7 microcontroller and is supplied with a library of C-code software, with many additional software routines (available free from the ST website).

The microcontroller communicates with the STMP01 ASSP via SPI interface, allowing easy customisation of metering functions with included PC software. The reference design also includes the M41ST87 realtime clock chip, a 256 Kbit serial SPI bus EEPROM and a dedicated 32-character alphanumeric LCD with on-glass driver.

Overview: Online Measurements of Transformer Fault Gases

Thomas, Waters, B.S. Chemist
Kristin Williamson, M.S. Chemist
Dr. Douglas Ritchie, PhD Physicist
SERVERON, INC

The dissolved gas analysis technique (DGA) is well known to the transformer engineering community. Equally well known are some of the limitations of this method for analyzing transformer fault gases (H2, O2, CO, CO2, CH4, C2H2, C2H4, C2H6). Further, it is widely knownthat knowledge of the concentrations of these gases dissolved in oil (especially the combustible gases) is critical to safe transformer operation and management.

Serveron has developed and deployed an online system that eliminates most of the aforementioned limitations and a system that provides near real time information on transformer gassing, with an ability to access this data from a remote location.

FUNDAMENTALS
If the transformer is a conservator design, there of course is no headspace. In these cases the analysis must be done by direct contact with the oil in the transformer main body. However, in the case of a headspace transformer, one has a choice. Measurements can be made utilizing a sample of gas taken from the headspace (especially if the transformer has a leak tight or low leakheadspace) or the measurements can be made from the oil.

Both will provide data on existing transformer fault gases. This paper presents data taken from a headspace transformer simultaneously outfitted with both types of analysis equipment – a headspace analyzer and an oilphase analyzer.

The questions of merit that are addressed in this paper are:
· Details on the instrumentation utilized
· Details concerning the subject transformer
· A clear description of the installations used to gather these measurements
· Precision measurements of gas-in-gas (transformed to oil equivalents) for all eight fault gases
· Precision measurements of gas-in-oil for all eight fault gases
· Comparisons of the two measurement techniques, with conclusions as to any differences seen between the two types of instrumentation, and conclusions about the dynamics oftransformer fault gases.

for INSTRUMENTATION UTILIZED and DATA ANALYSIS please visit EPRI or
http://www.bplglobal.net/eng/knowledge-center/download.aspx?id=206

SERVERON (EPRI Substation Equipment Diagnostics Conference (2/2001))

Comprehensive Links for transformer standard index

MSC provides indexed standards about transformers, which could be a good reference for standards index overview.

From the MSC link pages, both Chinese and English are arranged in columns, with simple description. vistors can view international standards index, such as IEC, IEEE, and national standards index, such as NF, EN, ANSI,BS,DIN,GB,JIS and so on.

Some of the latest standards index collected here are:
ANSI C12.9-2005
Test Switches for Transformer-Rated Meters

ANSI/IEEE C57.12.01-2005
Standard General Requirements for Dry-Type Distribution and Power Transformers Including Those with Solid-Cast and/or Resin Encapsulated Windings

ANSI/IEEE C57.125-2005
Guide for Failure Investigation, Documentation, and Analysis for Power Transformers and Shunt Reactors

ANSI/IEEE C57.13-2003
Standard Requirements for Instrument Transformers

ANSI/IEEE C57.13.2-2005
Standard Conformance Test Procedure for Instrument Transformers

ANSI/IEEE C57.13.6-2005
Standard for High Accuracy Instrument Transformers

ANSI/IEEE C57.94-2000
Recommended Practice for Installation, Application, Operation, and Maintenance of Dry-Type General-Purpose Distribution and Power Transformers

ASTM A 1009-2005
Standard Specification for Soft Magnetic MnZn Ferrite Core Materials for High Frequency (10 kHz-1 MHz) Power Transformer and Filter Inductor Applications

UL 1876-2001
Isolating signal and feedback transformers for use in electronic equipment

IEC 60044-1 Edition 1.2-2003
Instrument transformers - Part 1: Current transformers

IEC 60076-5-2006
Power transformers - Part 5: Ability to withstand short circuit

IEC/TS 60076-14-2004
Power transformers - Part 14: Design and application of liquid-immersed power transformers using high-temperature insulation materials

ANSI/IEEE C57.119-2002
Recommended Practice for Performing Temperature Rise Tests on Oil Immersed Power Transformers at Loads Beyond Nameplate Ratings

To view comprehensive index, please visit MSC links.

Carry out tests on power transformers

Abstracted standard from NZQA.

Purpose
People credited with this unit standard are able to: prepare for testing of power transformers for maintenance and/or acceptance; set up testequipment; carry out tests; interpret test results and complete compliance documentation; and place in, or return equipment to service.

Domain Electricity Supply - Testing
Status Registered
Status date 19 May 2006
Date version published 19 May 2006
Planned review date 31 December 2011

Entry information Recommended: Unit 14287, Use and maintain test instruments used within the high voltage electrical industry; Unit 14294, Carry out insulating oil sampling and voltage breakdown tests; or demonstrate equivalent knowledge and skills. Accreditation Evaluation of documentation and visit by NZQA and industry.

Standard setting body (SSB) Electricity Supply Industry Training Organisation Accreditation and Moderation Action Plan (AMAP) reference 0120This AMAP can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.

Standard setting body (SSB) Electricity Supply Industry Training Organisation

© New Zealand Qualifications Authority 2006

To access the full standard.

IET Activities Diagnosis Of The Condition Of Electric Components Using Transfer Funktions (transformer analyze)

by Søren Damsgaard Mikkelsen
RÉSUMÉ
In this report the performance of transfer functions in diagnosis of faults and ageing phenomena in components in electrical power systems has been tested. The basic principles of transfer function based diagnosis are explained in the following:

A low voltage test signal is applied to the device to be analyzed through a coupling circuit. This input signal is measured together with an output signal from the component and the obtained digitized data areused in a computer to calculate a dynamic input/output model of the device - the transfer function.

The calculated transfer function is subsequently compared with a reference model obtained when the device was new to determine whether differences has emerged. The differences, if they appear, are the key to evaluate the condition of the component and predict the time to breakdown.
Two transformer types are used as test basis in the research work....
The first step in the investigation is to survey the incipient failures and ageing phenomena to be detected by transfer functions.

Based on a systematic description of the most commonly appearing failures intransformers and ZnO surge arresters in electrical power systems a common pattern of symptoms for allthese irregularities is given.For transformers in electrical power systems four characteristic symptoms of incipient failures and ageing phenomena are set up:
a. Raised eddy current/magnetic losses.
b. Displaced turns/windings.
c. Decomposed or stressed winding insulation.
d. Acid, moisture and sludge in the insulating oil.

For ZnO surge arresters a single symptom is set up:a. Increased leakage current. These symptoms are the basic symptoms to be detected by transfer functions, if the method is going to be an effective tool in diagnosis of transformers and ZnO surge arresters in electrical power systems.

The second step in the research work is to set up the basic theoretical models describing the transformer and the ZnO surge arrester dynamic. An important demand for a descriptive model to be used in diagnosis is that - the model is closely connected to the physical operation of the component.

A mathematical description like a s-domain transfer function is thus less suited for diagnosis purposes than an equivalent circuit with RLC parameters related directly to the physical operation of specific parts within the component. Two basic equivalent circuit configurations describing the dynamic of single phase transformers and ZnO surge arresters, respectively, are set up for the project.The third step in the research work is to find the identification methods to identify the dynamic behaviourof transformers and ZnO surge arrester.

The most important demand for an identification method to be used in diagnosis is that- the identification result is stable and reproducible under unchanged conditions, i.e. the stochastic deviation of the identified model is small.

Basically, the available identification methods can be divided in two groups: non-parametric methods and parametric methods.The non-parametric identification methods determine a non-parametric model of the device under test.

The non-parametric model is usually a frequency domain model showing the amplitude gain and phasedisplacement of the component versus frequency. Such a frequency domain model forms together with an equivalent circuit a nearly complete basis to evaluate the dynamic (like the existence of resonant frequencies, impedance level, phase angle etc.) of a component.

The two most commonly used methods to determine the frequency response of a device is frequency sweep analysis and FFT analysis.

Both methods are thoroughly tested in this project by impedance identifications performed on the two singlephase transformer types and in the leakage region of the two ZnO surge arrester types. The result of these fundamental modelling tests are:- Frequency sweep analysis gives highly stable and reproducible models of transformers as well as of ZnO surge arresters.- FFT analysis gives stable and reproducible models of transformers, while the dynamic range of the available test equipment is too small to obtain reliable results on ZnO devices in the leakage region.

The parametric identification methods determines the parameter values of a parametric component model. The parametric model can be an equivalent circuit with RLC parameters or a general s-domain transfer function with a suitable number of coefficients. Several methods to solve the problem ofparameter identification in a given model from recorded test data are available.

In this project LeastSquares method is tested by impedance identifications performed on transformers and in the leakage andnormal operation region of ZnO surge arresters. The results of the these preliminary identification testsare:- Parametric identification gives stable and reproducible results on transformers and on ZnO surgearresters in the normal operation region. Contrary to this are the results of parametric identification in leakage region of ZnO arresters useless due to the same reason as stated for FFT analysis, i.e.limitations in the test equipment.

Three different identification methods are thus concluded to produce stable and reproducible results on transformers: frequency sweep analysis, FFT analysis and parametric identification.Two identification methods are similarly determined to give satisfactory results on ZnO surge arresters:frequency sweep analysis in the leakage region and parametric identification in the normal operation region.

The final but very important step in the research work is to determine the relation between the identified models and the condition of the devices concerned.Two test series are performed on the available transformers: sensitivity tests and ageing tests. The former test series is used to determine the sensitivity of the identified models to the condition of the insulating oil/grease, the magnetic circuit and the winding insulation. The latter test series is performed inorder to see whether or not the dynamic model of a transformer changes due to ageing phenomena andto determine whether or not it is possible to detect a development towards breakdown.

A single test series is performed on the available ZnO surge arresters: ageing tests. As the performed ageing tests on transformers, the ageing test series on ZnO surge arresters serves the purpose of investigating the development in the identified models towards breakdown.

The following results are obtained via the performed tests:- Detection of faults and ageing phenomena in a transformer is possible from the transfer function implied that changes in the lumped winding capacitances, the total losses, the reluctance of the core orthe geometry of the windings occurs.

However, a complete and precise condition evaluation of a transformer from the transfer function is impossible to obtain. The number of parameters included in the dynamic transfer function is thus insufficient.- Detection of faults and ageing phenomena in a ZnO surge arrester is also possible. However, in this situation it is the question, whether or not it is reasonable to use the described relatively complicated method.

A much simpler alternative is thus proposed in the project based on the experiences gained.

To view the full abstract.
To order the paper:
http://www.iet.aau.dk/

Selected feature of TTR application notes (power tranformer test)

APPLICATIONS
The TTR applies voltage to the high voltage winding of a transformer and accurately measures the resulting voltagefrom the low voltage winding. In addition to turns ratio,the unit measures excitation current, phase angle deviation between the high and low voltage windings and percentratio error.

Transformer Turns Ratio
Transformer turns ratio is the ratio of the number of turnsin the high-voltage winding to that in the low-voltagewinding. Complexity in the measured ratio versusnameplate ratio occurs with most three phase power transformers because multipliers such as √3 are required tomatch the measured ratio to the nameplate ratio. The three-phase TTR automatically applies the multiplier in a form which allows the operator a direct comparison to the nameplate (or expected) ratio. The TTR’s built-in calculator displays the % error versus nameplate for each tap and each winding, without the need of a computer or software.

Exciting Current
The TTR provides accurate measurement of exciting current (to 0.1 mA) which can help provide information about the condition of a transformer’s core. Unwanted circulating currents or unintentional grounds can increase the exciting current and indicate a problem.

Phase Angle Deviation and its Application
The phase angle deviation, displayed in either degrees(minutes) or radians, is the phase relationship between the voltage signal applied to the high voltage winding and the voltage signal extracted from the low voltage winding.The phase deviation together with ratio error can be used as a low cost method of verifying accuracy class of alltypes of PTs and CTs at “zero burden.”The phase deviation between the high and low side of atransformer is generally very small. If there is deteriorationor damage in the transformer core, however, the phase deviation can change significantly. The three-phase TTR can measure this phase relationship with the resolution of 0.1 minutes (equal to 1/600 of a degree), which is necessary to detect problems.

To view the comprehensive technical parameters and features, click here.
To view more information at www.megger.com

Problems on Transformer/LT coil evaluation

Abstracted from Agilent Effective Transformer/LF Coil TestingApplication Note 1305-3
Transformers and LF coils are used in power supplies, digital networks (forexample, ADSL) and various communication instruments to step up (or down)an AC voltage or for impedance conversion or filtering purposes. Thoughproduction of transformers is increasing year after year, there are problems thatQA test efficiency and production test throughput cannot be easily improvedbecause several different measurement instruments and setups need to be usedfor testing various transformer parameters. This application note introduces thecost-effective solutions to the transformer parameter measurements by usingthe Agilent 4263B LCR Meter.

Current Problems onTransformer/LF CoilEvaluation
The primary parameters that need to be known for transformer/LF coils areself-inductance, dc resistance, turns ratio and inter-winding capacitance.Conventional low-cost LCR meters have the following shortcomings when usedfor transformer/LF coil evaluation.

1. DC resistance of primary and secondary windings cannot be measured withLCR meters. (The DC resistance measurement requires using a separate testinstrument such as a multimeter.)

2. The turns ratio, a key transformer parameter, cannot be measured with LCRmeters.

3. The transformer parameters cannot be measured at 100 kHz because manylow-cost LCR meters do not cover high frequencies up to 100 kHz.

4. The test signal level is automatically selected according to the measurementrange, the test signal level cannot be user-defined for a specified level.

5. Total test throughput on production lines cannot be maximized because ofslow measurement
speed.

6. The connections of a transformer to the instrument (test fixture) must bechanged to measure parameters for the primary and secondary windings.The required connection changes make it difficult to enhance themeasurement efficiency.

To read more about solutions from Agilent.

Review of Several Free Electric Power Forums

Review of Electric Power Forums

Over the past two years, I have visited several electric power forums for problem solving, information collections and discussion. It might be happened that there exists lot of people looking for solutions but they may feel puzzled by large amout of data Googled or Yahooled by search engines.

I hope this brief review will be any help to reduce times cost for researchers, engineers...

1. http://www.eng-tips.com/

I take this is the best one of online forum. the website hosts large amout of subjects within industrial engineering, which attracts many visitors to show their problems. It also very good as you don't need to sign in before you browse the question and answers. Almost everything is open for guest visitors except when you want to start a new tread.

2. http://www.electricityforum.com/

Most of the time it is ranked No.1 on Google or Yahoo search list, it centrals on Electricity and Electrical Energy, for exchange of policy and technical information.
You can register for email notification of recent published news, they send you news almost every day, but I think most of them are advertizing or news information, which is very useful for marketing managers or product researchers looking for new products.

Note: You need sign in to look for further information.

3. PSAT forum (world famous but subject-limited and only for members)

http://tech.groups.yahoo.com/group/psatforum/

Actually it is a Yahoo Group that discuss information through mail lists. Even Though it is for membership sharing insights, the PSAT is opensource for everyone, and it is easy to join in the group. It is really powerful, full of intelligence mainly for academic research, but there also groups engineering technicians for soft-applications, below is brief introduction of PSAT.

PSAT is a Matlab toolbox for electric power system analysis and control. The command line version of PSAT is also GNU Octave compatible. PSAT includes power flow, continuation power flow, optimal power flow, small signal stability analysis and time domain simulation. All operations can be assessed by means of graphical user interfaces (GUIs) and a Simulink-based library provides an user-friendly tool for network design.

Note: The PSAT source code can be downloaded from here.

4. Forumelectric http://www.forumelectric.com/

With multisubject platform, posted over one thousand articles and hundreds of subjects.

I am not a register but views the Q&A, it really holds many interesting subjects.

Defects in Nonceramic Insulators: Can They be Detected in a Timely Manner?

Introduction: There are a multitude of designs, materials, formulations, and manufacturing processes that are used presently for nonceramic insulators. While this beneficial in terms of offering choices for the users, this also means that in case of problems, failure patterns could be different. It is fairly well known that most problems in NCI result originate from interfaces. The critical interfaces in this type of insulator are between the rod and housing, between hardware-rod-housing and different sheds of housing if unit is not manufactured in a single piece.
The presence of corona at the interfaces leads to sheath damage exposing the fiberglass rod, tracking the rod, thereby leading to insulator failure through interfacial flashover, rod burning and brittle fracture. Also, the presence of any contamination like water, salts, and dirt can intensify the field at those locations. Fig. 1 shows a picture of a failed NCI. It can be seen that the first few sheds have suffered corona cutting. Some degradation in the form of tracking and erosion is also visible. If the damage to the insulator is not in the line of sight, then this may not be identified as a problem during routine line inspection by road or helicopter patrols until the unit fails. The challenge is to identify such insulators at an early stage of degradation whe n there is still time to act.

Understanding the electric field distribution plays a vital role in insulator design and also can be useful for detecting internal defects. In ceramic insulators the voltage distribution is relatively more linear due to the presence of intermediate metal parts. The material does not degrade with corona, hence corona is not usually a problem in ceramic insulators. However in NCI’s the voltage distribution is highly non-uniform as shown in Fig. 2, and can give rise to corona. Corona rings are normally used for NCI at voltages above 230 kV in order to reduce the electric field near the line end.

There have been several recent publications that concluded that there is no fool-proof method for early detection of defects in nonceramic insulators. Among the methods examined were partial discharge detection, infrared thermography, corona and audible noise detection, leakage current measurement and electric field measurement. In the utility environment the electric field technique is being increasingly used as a diagnostic tool to ident ify defective porcelain units. Their use on nonceramic insulators appears to be the logical step. What types and degrees off defects can be detected by such a measurement? This study was undertaken to answer this question. The electric field distribution of a healthy insulator was taken as the reference.

Types of Defects Modeled: Several types of defects that can occur on a NCI were modeled. The various types of defects that are considered difficult to detect but critical are incorporated on to the healthy model and simulated. The size, position and conductivity of such defects are varied. The field values for locations close to the defect along the path of the probe are noted down. These values are then compared with the values obtained in the healthy cases. The presently used electric field probes are sensitive for field values above 2 kV/m. Hence defects that produce a difference of 2 kV/m and above are considered detectable while others were considered undetectable. The differences in field values thus obtained are plotted as a function of the shed number. A logarithmic trend line is fitted to the above plot for a better perception of the defect detection possibilities.

Various types of defects such as those occurring on the shed, shank, interface, external tracks from end fittings and tracks occurring on the rod sheath interface were considered. Most of the external defects could be observed during careful visual inspection. However, defects that occur inside the housing are not visible. Hence such defects are modeled for electric field distortion studies to verify the possibility of detecting such defects using field probes as shown in Table 1. A defect that occurs for the distance between any two consecutive sheds is named as the single shed defect. A single shed defect will have the shape of a cylinder with a 9.2 cm height and 5 mm diameter. A diagrammatic representation of various types of single shed defects modeled is as shown in Fig. 3. Similarly two-shed and three shed defects are simulated and analyzed.

It is likely that corona cuts or any other deformities in the insulator will give rise to corona, especially under humid conditions. The work reported last year showed that a combination of location specifics and quantitative data like brightness can provide useful information on making decisions such as problematic corona or nonproblematic corona. This should be explored further.

Conclusions:
The defect detection is position dependant and has the best possibility of being detected if it is closer to the high voltage electrode.Larger and longer defects produce higher field changes hence they are more easily detected than the smaller ones. The change in field value observed depends on the type of the defect. More conductive the defect is, greater is the possibility of detecting it. The range of the field probe can be greatly enhanced if measurements are taken radially instead of conventional axial measurements.
S. Gorur and S. Sivasubramaniyam Department of Electrical Engineering, Arizona State University, Tempe, AZ, USA
This work was performed under a PSERC funded project at Arizona State University

UGM,4-5-6 May,2009

UGM, 4-5-6 May, 2009
REGISTER NOW
The 6th UGM - UV inspection users group meeting will take place in Las Vegas NV USA during May 4th to May 6th, 2009. Attendees from all over the world are invited to participate and share their accumulated knowledge and exprience with the growing UV inspectors community.
The luxurious Tuscany Suites & Casino was selected to host the meeting, with special reduced rates for the group members. During the meetings breakfast, lunch and coffee breaks will be served. An informal dinner party is schedulled in the evening where spouses are welcome to attend.
The agenda will include lectures by keyspeakers, presentations by veteran users, tutorials by Ofil's engineers. The proceedings CD of the event will be given to attendees.
The five previous events were very successful and the list of users who register is getting filled up quickly. Space is limited and it is therefore recommended to reserve a seat in advance, and the earlier - the better.
To register download the form >>
Fill the form and fax it to Ofil1.888.950.5557 (USA toll free) +972.8.940.7873 (Israel)
Should you have any question or special request, please write to Hannah Barzilay - the UGM coordinator.

The objectives of the meetings
Expand aspects of using the UV inspection technology
Review, discuss and understand implications of corona discharge on lines, insulators substation components and grid hardware
Study from experts
Link between utilities, researchers, academy and industry
See what has been achieved by peers from around the world
Hands-on workshop

Who attends?
Potential users familiar with IR and Ultrasound inspection techniques wishing to learn about UV inspection
UV inspection users who want to expand their knowledge and understanding of corona
Users wishing to exchange information and know-how with colleagues
Utility executives
Electrical engineers, services providers, technicians, high voltage laboratory researchers, T&D engineers, predictive maintenance designers etc.
Researchers in search for projects and hot subjects

GIS Insulation Accident Concern

GIS (Gas-Insulated Switchgear) characterizes with many merits such as high reliability,easy-maintenance, small volume, and receives widely application in the world.
Even though, due to testing devices and techniques, there are still quite large amout of GIS never undergo strict fields test for earlier applications. it happens that insulation problem is still an improtant issue for fields maintenance, from which it aroses many methods to conduct insulation experiment, such as chemical analyzing method, pulse, ultrasonic and UHF method.

From the experience, there are certain kind of defect, which can not be anyharm and not easy to detect, will exemplify themselves in the later years, especially when CB operates, partial discharge occures that may result in large accident and maintenance has to be in power-off conditions so as to lead to large economic loss.

There are some insulation faults happened in Guangdong province, China:
Jiangmen 500kVGIS, DayaWan 400kVGIS, Shenzhen Huanggang station220kVGIS, ShajiaoA power plant220kVGIS.
Especially for Shajiao A plant, in the year of 1989, a 220kVGIS N.3 faults result in loss of 32GW.h.

Edited by J.Zh
IEEETM Center

On-site Sensitivity Verification for UHF PD Detection in GIS（NOTES）

Necessity of UHF Sensitivity Check
A article features with on-line check of Sensitivity, which rises an important issue.
S. Meijer1*, J.J. Smit11
Delft University of Technology, Mekelweg 4, 2628 CD, Delft, The Netherlands

In industry, partial discharge technology related to switchgear has been operational for many years. Partial discharge testing has been conducted on both new high voltage switchgear in the laboratory setup, as well as several older HV installations in the utility grid. The results clearly indicate that partial discharge analysis of HV switchgear is an excellent online tool to assess its dielectriccondition. “Dielectric windows” present on existing GIS offer the possibility to pick-up the signals by means of external couplers.In order to check the sensitivity or to prove the possibility to detect a certain PD level, a sensitivity check procedure has beenpublished by Cigre several years ago.

This procedure was mainly focusing on new equipment in which internal sensors are beinginstalled in the factory. In this case, it is possible to make comparison tests in the laboratory between the UHF technique andaccording to the IEC 60270 to get a relation between both readings.For older GIS with PD couplers retrofitted or using externalsensors, usually the laboratory step required in this sensitivity check procedure is not possible due to lack of spare parts. In this contribution, a solution to perform the laboratory test on-site is described.

Proceedings of the International Conference on
Electrical Engineering and InformaticsInstitut Teknologi Bandung, Indonesia
June 17-19, 2007

Why place more efforts on magnetizing characteristics for CT than VT?

Technical Notes of Instrument Transformers
The Role that Magnetizing Impedance Plays

Instrument Transformer is special transformer, due to its operation condition, the equivalent circuit differes with respect to tranfer parameters.

Difference in equivalent circuit between CT and VT
1.VT. due to its operation limit, the secondary voltage runs rarely out of the limit value (80%~120), even in fault conditions, protection equipment will prevent them long keep in the state of out-limit. so it is reasonable to assume that the magnetizing impedance during operation is constant with respect to protection, and linear with respect to metering.Also, as VT is connected in paralle with power lines, only voltage is considered. the magnetizing impedance has very little influence on the burden voltage.

2.CT, secondary current is considered, its operation range is (1%~120%,to say,S class), magnetizing impedance varies significantly thus bypass secondary current from the burden, and affect the state value from primary being transfered to secondary. especially in fault conditions, such as primary line short-circuit, magnetizing impedance is a very important parameters to be considered.

In consideration of metering accuracy:

Both CT and VT characterize their error graph by nonlinearity of magnetizing impedance (MI). In principle, MI bypasses burden current, which influence the voltage drop on secondary lines and thus affecting the signal supplied to the burden.

MI is an interesting parameter that still attracts big conern, both for metering and protections.

J.ZH
IEEETM Central Sources

Capacitive voltage sensor for measuring very fast transient overvoltages in GIS

What is the role that capacitive voltage sensor plays in GIS transient studies?
Masafumi Yashima, Hideo Fujinami, Tadasu Takuma§
Central Research Institute of Electric Power Industry

A reliable technique is needed for accurate measurement of very fast transient overvoltages such as disconnector-induced surges occurring in GIS which have very steep front and high-frequency oscillation. Recently, capacitive voltage sensors with very short response times have been proposed for this purpose. However, few studies have been made on the dielectric properties of materials used for a low-voltage-side capacitor, as well as the frequency bandwidth of the measuring system.

In this paper a thin mica plate is proposed for a low-voltage-side capacitor which has a surface coated with silver on both sides. This material has been shown to have stable and high static capacitance up to a high-frequency range. A quantitative estimate also is given for the frequency bandwidth of the measuring system. Furthermore, a practical-scale sensor of this type has been developed which can successfully measure simulated disconnector-induced surges of several hundred kilovolts under similar conditions in GIS.

Full Paper can be bought from Wiley Interscience.

I am wondering if and how it can be used for online condition assessment...
Discussion welcomed.

Retrofit and Field Test of Large Power Transformers with Fiber Optic Partial Discharge Sensors(Project Notes)

A tow-year project initiated by EPRI in 2006 has focus attention on Extending the useful life of power transformer so as to increasing the life of the power transmission and distribution infrastructure.
Central of the project features with effective transformer diagnostics and condition assessment.
The project aims to process data from testing in-tank, fiber optic partial discharge sensors and developing better transformer tank penetration methods for sensor insertion.
The project includes:
1. Develop a method and then manufacture and test prototypes of a cost-effective penetrator mechanism and sensor system suitable for retrofit into transformers
2. Obtain proof-of-concept of internal fiber optic pd sensors in an operating transformer with known pd
3. Establish an initial database to characterize the pd signals to the type of fault.

Abstracted and Summarized from EPRI

SF6 Insulated equipment Online Safety Issue

Online safety diagnostics of SF6 insulated equipment (Notes)
SF6 Gas is widely used in electric power industry, the internal metal kernel, dust and moisture content, are major reasons that lead to GIS fault. When there is conductive material within equipment, partial discharge produces abnormal noise, vibration and discharges with small light, in the phenomena of decomposition of SF6 gases.
Partial Discharge (PD) rises big concern for GIS, GCB and GIT.

Major Techniques employed for PD.
1. measuring electromagnetic wave to locate and judge the pd level.
2. UHF measurement and location.
3. High-frequency earthy current testing.
4. Sound tranmission and vibration test.
5. Chemical method, to analyze composition of sf6 Gases (HF/SO2/SOF2)

Actually there exists no effective method that can fix the problem well. There are both benefits and defects. among the methods, UHF is most popular at the present, but it is still difficult to measure the pd level and the cost is relative high.

Two extra research that complements the method
1. GIS discharge model or function( within or outside GIS)
2. Discharge Data Process to identify faults.

Also there are research that employs ultrasonic fault detection method which seldom sees the application.

J.ZH
Simplified Notes from
IEEETM Central Source

The Role short circuit impedance plays in Power Transformer Assessment

Short Circuit Impedance (SCI) refers to equivalent impedance from one side of Power Transformer (PT) with another side being short-circuited.
The main part of SCI is inductive value, so sometimes it can approximates to leakage inductance.
When testing the SCI, allow one side (ofen secondary) winding be short-circuited, and applies test voltage from another side winding (ofen primary), and then measure the impedance using VA or PQ method.

SCI can be used for frequency response test, with the help of equivalent model, to analyze defect of PT, such as winding deformation, internal insulation and core characteristics.

To analyze the data
Three phase comparision of impedance, periodic comparison and historic comparison are methods usually used to comprehensively characterize structural information of PT.
Also from a point of view to assess PT operation conditions, SCI is an improtant factor that help make medium or long time maintenance decisions.

J.ZH
Notes of Pusala Technology
成都普莎拉科技有限公司
IEEETM Central Source

How to enlarge leakage inductance for experiment

Leakage Inductance Issue
It is determined by structure of transformers, not easy for change. a possible way is adding inductance in series with the primary (high voltage side), so as to increase the voltage that applies on the transformers.
The principle behind this the series inductance be in series with equivalent capacitance, but it requires that the insulated voltage level of series inductance should be high enough.

Also increase the gap between winding and core, or between different windings can also enlarge leakage inductance.

Leakage inductance is supposed to be controlled in low value with consideration of applications. And in practice it is not easy to measure and assume, but most of the study and application consider that to be a constant value (due to what kind of use)

IEEETM Notes