Asset Management and Condition Maintenance

The effectiveness of expending maintenance resources can vary dramatically depending on the target and timing of the maintenance activities. The state-of-the-art in maintenance management offers at least three basic approaches for making maintenance management decisions:
(1) condition-based maintenance (CBM) initiates a maintenance activity when datafrom equipment monitors indicates a need;
(2) reliability centered maintenance (RCM) prioritizes maintenance activities based on quantification of likelihood and consequence of equipment failures; and
(3) optimization techniques offer methods for maximizing effectiveness of the maintenance activities subject to constraints on economic resources, available maintenance crews, and restricted time intervals.

A comprehensive and cost-effective system-wide maintenance allocation and scheduling system

Based on automated integration of condition monitoring with an RCM-based optimized scheduler. The maintenance allocation and scheduling system can reduce maintenance costs while increasing equipment reliability. It can also (1) extend equipment life; (2) cut costs for substation design, refurbishment and construction; and (3) ensure high levels of health and safety for operation and maintenance personnel, the public, and the environment.

The effect of a specified maintenance task can be quantified basedon the cumulative reduction in system risk obtained from it.
1. Mid-term maintenance selection and scheduling: Algorithms and related software applications were created for selecting and scheduling transmission-related maintenancetasks over a budget and labor-constrained time period (e.g., a year) such that the effect ofthose resources are optimized.
2. Long-term maintenance scheduling: an approach for planning longterm policies associated with inspecting and maintaining power transformers and circuit breakers. Results of this approach serve to provide a list of candidate maintenance tasks as input to the mid-term scheduler.
3. Data integration: A novel data integration method created to avoid the need to aggregate data into a centralized warehouse but rather to allow users to query multiple, related data sources simultaneously.
4. Software design approach: Multiagent systems use messaging to facilitate communication between software applications, provide for long-term maintain ability of the software system, and are particularly effective when data and applications are highly distributed as they are in the asset management problem ..
abstracted from
PSERC FINAL PROJECT REPOET 2006
www.pserc.org

Recursive Least Squares Method in Parameters Identification

Recursive Least Squares Method in Parameters Identification of DC Motors Models
Dedicated to Professor Mili´c Stoji´c on the occasion of his 65th birthdayRadojka Krneta, Sanja Anti´c, and Danilo Stojanovi´c
Abstract: The procedure of parameters identification of DC motor model using a method of recursive least squares is described in this paper. To identify the system an experimental measuring of signals was carrying out at input - supply of voltage and output of the system for identification - motor angle speed. For the needs of the experiment, a system has been configured with a motor and an optical encoder whose output is connected with the counter input of acquisition card LCK-6013 which overa block connector CB-68LP makes a connection with a computer. The speed of the motor measured by optical encoder is compared with the speed of identified system inorder to confirm the quality of the motor model's parameters estimation.

Conclusion:This paper has investigated the issues involved in applying Recursive Least Squares method in parameters identification of DC motor models. The issues have been considered both theoretically and experimentally. The experimental work was performed on a DC motor with an optical encoder as an output of the system. The validity of the proposed method was shown by simulation an experiments. By comparing a graphic of real motor speed and a graphics of speed of investigated models in a Z and S domains it can be concluded that a satisfying quality of DCmotor parameters identification has been achieved.

FACTA UNIVERSITATIS (NIS)
SER.: ELEC. ENERG. vol. 18, no. 3, December 2005, 467-478

Transformer winding defects identification based on a high frequency method

Transformer winding defects identification based on a high frequency method

frequency response analysis method is most frequently used technique employed to detecting fault of inductive apparatus. expecially for faults that are not so much significant but may enlarge in a certain period of time.

Below is an abstract from an article, I find that is a good representation of similar method.

Abstract. The transformer diagnostic methods are systematically being improved and extended due to growing requirements for reliability of power systems in terms of uninterrupted power supply and avoidance of blackouts. Those methods are also driven by longer lifetime of transformers and demand for reduction of transmission and distribution costs. Hence, the detection of winding faults in transformers, both in exploitation or during transportation is an important aspect of power transformer failure prevention. The frequency response analysis method (FRA), more and more frequently used in electric power engineering, has been applied for investigations and signature analysis based on the admittance and transfer function. The paper presents a novel approach to the identification of typical transformer winding problems such as axial or radial movements or turn-to-turn faults. The proposed transfer function discrimination (TFD) criteria are based on the derived transfer function ratios, manifesting higher sensitivity.

Print publication: Issue 9 (September 2007)Received 27 December 2006, in final form 8 June 2007Published 20 July 2007
Marek Florkowski1 and Jakub Furgał21 ABB Corporate Research, 31-038 Kraków, ul. Starowiślna 13A, Poland2 Electrical Power Institute, AGH University of Science and Technology 30-059 Kraków, al. Mickiewicza 30, PolandE-mail: marek.florkowski@pl.abb.com and furgal@uci.agh.edu.pl

In consideration of the basic techniques for the defects identification, I am also very interested in the frequency-vary power source, of how much power output should be considered in order to assure the accuracy of test....

Discuss welcomed.

Estimation of Partial Discharge Parameters

Estimation of Partial Discharge Parameters in GIS Using Acoustic Emission Techniques A Theoretical Approach
DOI No:
10.1142/S0218396X98000260
Source:
Journal of Computational Acoustics, Vol. 6, No. 4 (1998) 403-419
Author(s):
Nandini GuptaDepartment of High-Voltage Engineering, Indian Institute of Science, Bangalore-560 012, IndiaT. S. RamuDepartment of High-Voltage Engineering, Indian Institute of Science, Bangalore-560 012, India
History:
Received 15 October 1996Revised 2 September 1997
Abstract:
Electrical discharge activity within an electrical power apparatus has detrimental effects on the insulating components of the system, and thus its prognosis and diagnosis are of utmost importance. Traditional electrical methods have been replaced by newer techniques such as acoustic detection. Among these, acoustic methods possess certain inherent advantages, especially where complex electrical systems like GIS are involved. The major concerns therein are the estimation of the magnitude of the discharge level as well as location of the source of discharge. The present work addresses, on a theoretical basis, problems connected with identification, measurement and location of electrical discharges, in particular in GIS. Models for the inception and propagation of p.d. within GIS have been proposed. This study, based essentially on a numerical simulation model, corroborates many of the experimental findings reported in the existing literature, and in addition attempts to suggest newer directions in magnitude estimation and location of p.d.

INSTRUMENT TRANSFORMER ACCURACY TESTING BY DFT METHOD

Slobodan Škundrić, Dragan Kovačević, Slobodan Mikičić
Electrical Engineering Institute “Nikola Tesla”, Belgrade, Yugoslavia

Abstract -Instrument transformer accuracy testing bythe method based on integration of DFT and virtualinstrument concept, composed of standard hardware(osciloscope, PC) and specific software is outlined. Thestructure of the realized virtual instrument for accuracy testof current transformer by DFT method is shown. Themethod has experimentally verified and compared withmeasurements made with the classical complex Hohlecompensator.

Conclusion:
The main advantages of the VI-DFTmethod are that strong, flexible and standard hardware combined withpowerful, flexible and easily changeable software, resulting,compared to the classical concept in improvedperformances, reduced cost and time of development.The experimental test performed on the realised systemshow the validity of the followed approach and very gooddegree of coicidence with classical instruments.The concept proposed and the hardware and softwarestructures presented are strong enough to support laboratoryand on-site, standard and non standard, accuracy testing ofinstrument transformer.
To view detailed information:
http://www.imeko.org/publications/wc-2003/PWC-2003-TC4-113.pdf

Comments welcomed.

Measuring storm-restoration performance （Abstract from EEI Report)

Measuring storm-restoration performance
测量飓风恢复绩效
One of the challenges in attempting to compare past and present utility storm-restoration performance is that no two storms are the same.Ice storms can cause vastly different types of damage—depending on whether they hit whenleaves are still on trees, the thickness of the ice, how high the accompanying winds are andwhether the ice damages transmission lines as well as distribution lines.Similarly no two hurricanes are the same. One hurricane might wreak havoc on a utilitysystem with its high winds, while another creates considerable damage from flooding, andanother does both. Because of these differences, it is unrealistic to compare storms and utilityresponses to them without considering the wide variety of factors that can impact a utility’sstorm-restoration activities.The other major challenge of evaluating whether utility responses are getting better or worseis obtaining good data on utility storm-restoration activities. The industry does not have astandardized method for evaluating post-storm restoration effectiveness. Hence, there is noconsistent method of collecting data on utility storm-restoration activities.Most data regarding storm damage is collected and maintained by individual utilities, and isused primarily for tracking costs and preparing “major storm reports” for state public utilitycommissions. Once again, there is no formal or informal standard for preparing these reports,either at the regional or national level.To address this lack of comparable data, EEI designed a special survey to collectinformation on utility storm-restoration activities over at least a 10-year period of time.

Storm Restoration Survey Results
1) In recent years, survey respondents have improved the rate at which they are ableto restore power to customers following a major storm event.
3) The number of restoration workers deployed after major storms has decreasedfairly dramatically in recent years as the number of customers restored per workerhas risen.
4) Based on equipment damage, recent storms do not appear to have been any moreor less severe.
4) Based on equipment damage, recent storms do not appear to have been any moreor less severe.
Summary
These storm reports help clarify the tremendous impact of major storms on utility systems,and illustrate the huge effort utilities undertake to restore their systems as quickly as possible.The summaries indicate favorable performance trends when the companies’ most recent stormrestoration efforts are compared with previous significant storms.The North Carolina Utilities Commission reached similar conclusions regarding the DukePower and Progress Energy storm-restoration efforts. In its final report on the 2002 Ice Storm,the commission found no discernable increase in outage duration. The report illustrated howmuch more quickly Duke and Progress Energy customers were restored in 2002 than in theaftermath of a 1996 Ice Storm.The North Carolina Commission concluded that the companies’ restoration efforts were“diligent, effective and well managed as a whole.”10 The Maryland Public Service Commissionis currently evaluating BG&E’s storm report as well as those of the other Maryland utilities thataffected by Hurricane Isabel.

Taken from EEI (Edison Electric Institute) 2004 report 'Utility Storm RestorationResponse'

Current Transformer definition and principle（Continued from KAPPA)

Current transformers
Principle of operation
Definitions
Standards
Tests
Typical Specifications
Principle of operation
A current transformer is defined as "as an instrument transformer in which the secondary current is substantially proportional to the primary current (under normal conditions of operation) and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections." This highlights the accuracy requirement of the current transformer but also important is the isolating function, which means no matter what the system voltage the secondary circuit need be insulated only for a low voltage.
The current transformer works on the principle of variable flux. In the "ideal" current transformer, secondary current would be exactly equal (when multiplied by the turns ratio) and opposite to the primary current. But, as in the voltage transformer, some of the primary current or the primary ampere-turns is utilized for magnetizing the core, thus leaving less than the actual primary ampere turns to be "transformed" into the secondary ampere-turns. This naturally introduces an error in the transformation. The error is classified into two-the current or ratio error and the phase error.
Kappa CT s are designed to minimise the errors using the best quality electrical steels for the core of the transformer. Both toroidal (round) and rectangular CT s are manufactured.
Definitions
Rated primary current: The value of current which is to be transformed to a lower value. In CT parlance, the "load" of the CT refers to the primary current.
Rated secondary current: The current in the secondary circuit and on which the performance of the CT is based. Typical values of secondary current are 1 A or 5 A. In the case of transformer differential protection, secondary currents of 1/ root 3 A and 5/ root 3 A are also specified.
Rated burden: The apparent power of the secondary circuit in Volt-amperes expressed at the rated secondary current and at a specific power factor (0.8 for almost all standards)
Accuracy class: In the case of metering CT s, accuracy class is typically, 0.2, 0.5, 1 or 3. This means that the errors have to be within the limits specified in the standards for that particular accuracy class. The metering CT has to be accurate from 5% to 120% of the rated primary current, at 25% and 100% of the rated burden at the specified power factor. In the case of protection CT s, the CT s should pass both the ratio and phase errors at the specified accuracy class, usually 5P or 10P, as well as composite error at the accuracy limit factor of the CT.
Composite error: The rms value of the difference between the instantaneous primary current and the instantaneous secondary current multiplied by the turns ratio, under steady state conditions.
Accuracy limit factor: The value of primary current upto which the CT complies with composite error requirements. This is typically 5, 10 or 15, which means that the composite error of the CT has to be within specified limits at 5, 10 or 15 times the rated primary current.
Short time rating: The value of primary current (in kA) that the CT should be able to withstand both thermally and dynamically without damage to the windings, with the secondary circuit being short-circuited. The time specified is usually 1 or 3 seconds.
Instrument security factor (factor of security): This typically takes a value of less than 5 or less than 10 though it could be much higher if the ratio is very low. If the factor of security of the CT is 5, it means that the composite error of the metering CT at 5 times the rated primary current is equal to or greater than 10%. This means that heavy currents on the primary are not passed on to the secondary circuit and instruments are therefore protected. In the case of double ratio CT's, FS is applicable for the lowest ratio only.
Class PS/ X CT: In balance systems of protection, CT s with a high degree of similarity in their characteristics are required. These requirements are met by Class PS (X) CT s. Their performance is defined in terms of a knee-point voltage (KPV), the magnetizing current (Imag) at the knee point voltage or 1/2 or 1/4 the knee-point voltage, and the resistance of the CT secondary winding corrected to 75C. Accuracy is defined in terms of the turns ratio.
Knee point voltage: That point on the magnetizing curve where an increase of 10% in the flux density (voltage) causes an increase of 50% in the magnetizing force (current).
Summation CT: When the currents in a number of feeders need not be individually metered but summated to a single meter or instrument, a summation current transformer can be used. The summation CT consists of two or more primary windings which are connected to the feeders to be summated, and a single secondary winding, which feeds a current proportional to the summated primary current. A typical ratio would be 5+5+5/ 5A, which means that three primary feeders of 5 are to be summated to a single 5A meter.
Core balance CT (CBCT): The CBCT, also known as a zero sequence CT, is used for earth leakage and earth fault protection. The concept is similar to the RVT. In the CBCT, the three core cable or three single cores of a three phase system pass through the inner diameter of the CT. When the system is fault free, no current flows in the secondary of the CBCT. When there is an earth fault, the residual current (zero phase sequence current) of the system flows through the secondary of the CBCT and this operates the relay. In order to design the CBCT, the inner diameter of the CT, the relay type, the relay setting and the primary operating current need to be furnished.
Interposing CT's (ICT's) : Interposing CT's are used when the ratio of transformation is very high. It is also used to correct for phase displacement for differential protection of transformers.

Taken from KAPPA electricals.

Technical information on Instrument Transformers

Technical information On Instrument Transformers
For those who are interested in basic ideas of instrument transfomrers

Instrument transformers are used for measurement and protective application, together with equipment such as meters and relays. Their role in electrical systems is of primary importance as they are a means of "stepping down" the current or voltage of a system to measurable values, such as 5A or 1A in the case of a current transformers or 110V or 100V in the case of a voltage transformer. This offers the advantage that measurement and protective equipment can be standardized on a few values of current and voltage.
Voltage transformers
Current transformers
Kappa has published a reference manual on instrument transformers
Voltage transformers
Principle of operation
Definitions
Standards
Tests
Typical Specifications
Principle of operation
The standards define a voltage transformer as one in which "the secondary voltage is substantially proportional to the primary voltage and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections."
This, in essence, means that the voltage transformer has to be as close as possible to the "ideal" transformer. In an "ideal" transformer, the secondary voltage vector is exactly opposite and equal to the primary voltage vector, when multiplied by the turns ratio.
In a "practical" transformer, errors are introduced because some current is drawn for the magnetization of the core and because of drops in the primary and secondary windings due to leakage reactance and winding resistance. One can thus talk of a voltage error,which is the amount by which the voltage is less than the applied primary voltage ,and the phase error, which is the phase angle by which the reversed secondary voltage vector is displaced from the primary voltage vector.

To read more

Low voltage method characterize calibration for Instrument Transformer

Portable Electromagnetizing Instrument Transformer tester (calibrator) assumes first that there is no significant change of mechanical parameter.
Then it employs electric parameter to map the error model, and compute its error graph. all the error data is obtained from simulated test, including test power source and phatom electronic load, so as to lower down the test power significantly.

Because the simulation signal is applied from the secondary with primary being open circuited, the simulating voltage should assure that insulation between windings should not be damaged, which places high requirement for accurate measurement of feedback current from the secondary in response with the drive voltage.
But actually the feedback current can be as low as serveral miniamp, it is not easy to carry on accurate test without noise undercontrol.

From this point of view, frequency-response analyzing technique being used to complement that defect and focus attention on filters.
Data tested from simulation can be used to re-modify the original model that representing the error characteristics, among which one significant value is leakage inductance, a parameter not easy for direct measurement.

IEEETM website be blocked in China

IEEETM Can not be visited in China at the present, including its Chinese version Pusala, as it shares the same IP address.
The most recently published information will be copied to this blog.
IEEETM is also planning to establish a product panel that unfolds new tech and products from IEEETM (Pusala China), So customers in China can view the information as it is a different IP address.
Furthermore, IEEETM is considering transfer the server to load Pusala China website in 2009.