Increasing interest has been seen in condition monitoring (CM) techniques for electrical equipment, mainly including transformer, generator, and induction motor in power plants, because CM has the potential to reduce operating costs, enhance the reliability of operation, and improve power supply and service to customers. Literature is accumulated on developing intelligent CM systems with advanced practicability, sensitivity, reliability, and automation. A literature survey is felt necessary with an aim to reflect the state-of-the-art development in this important area. After introducing the concepts and functions of CM, this paper describes the popular monitoring methods for and research status of CM on transformers, generators, and induction motors, respectively. The paper also points out the potential benefits through the utilization of advanced signal processing and artificial intelligence techniques in developing novel CM schemes.

Condition monitoring techniques for electrical equipment-a literature survey

ower transformers are one of the most expensive elements in a power system, and their failure is a very costly event. Power transformers are mainly involved in energy transmission and distribution. Unplanned power transformer outages have considerable economic impact on the operation of electric power networks. To have reliable operation of transformers, it is necessary to identify problems at an early stage before a catastrophic failure occurs. In spite of corrective and predictive maintenance, preventive maintenance is gaining due importance in the modern era, and it must be taken into account to obtain the highest reliability of power apparatus such as power transformers. The well-known preventive maintenance techniques such as dissolved gas analysis (DGA), thermal monitoring, partial discharge measurement, capacitance and tan delta measurements, frequency response analysis, etc. are performed on transformers for a specific type of problem. DGA is a very efficient and reliable tool for the earliest detection of inception faults in transformer and other electrical equipment using insulating oil. Condition monitoring of electrical equipment, such as transformers, helps users in many ways such as planning of maintenance schedule, obtaining knowledge of the health of equipment, estimating the remaining service life of equipment, finding areas of further improvement, refining product specification, etc. Kraft paper (cellulose) immersed in mineral oil is used as the insulation system for the copper windings in large power transformers. As the system ages under load, the paper and oil can degrade, potentially leading to catastrophic failure. Partial discharge (PD) is an important tool for improving the reliability of HV insulation systems. It is a very sensitive and nondestructive method of evaluation of the health of the insulation of any HV equipment. PD always is associated with the degradation of insulation systems in HV equipment. Therefore, PDs need to be detected, measured, located, and reduced to a safe value so that the quality of the insulation system is not affected.

Condition Monitoring of Power Transformers - Bibliography Survey

Online transformer condition monitoring techniques based on transfer function methods, such as transmission-line diagnostics and swept frequency-response analysis, require the injection of a known test signal into the transformer On larger power transformers, a practical method is to use the available bushing tap connection In this paper, we will discuss a custom high-power signal generator that injects high-frequency signals on the bushing tap of the transformer under investigation, as well as a circuit to replace the bushing tap short and allow online operation of the system Finally, the system is demonstrated on a 650 kV transformer

Apparatus for Online Power Transformer Winding Monitoring Using Bushing Tap Injection

This paper presents an autotuning technique for the online selection of the cost function weight factors in model predictive control (MPC) The weight factors in the cost function with multiple control objectives directly affect the performance and robustness of the MPC The proposed method in this paper determines the optimum weight factors of the cost function for each sampling time; the optimization of the weight factors is done based on the prediction of the absolute tracking error of the control objectives and the corresponding constraints The proposed method eliminates the need of the trial-and-error approach to determine a fixed weight factor in the cost function The application considered is a capacitor-less static synchronous compensator based on the MPC of a direct matrix converter This technique compensates lagging power factor loads using inductive energy storage elements instead of electrolytic capacitors The result demonstrates that the proposed autotuning approach of cost function weights makes the control algorithm robust to parameter variation and other uncertainties in the system The proposed capacitor-less reactive power compensator based on the autotuned MPC cost function weight factor is verified experimentally

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Autotuning Technique for the Cost Function Weight Factors in Model Predictive Control for Power Electronic Interfaces

This paper presents the concept of a capacitorless static synchronous compensator (STATCOM) that uses a matrix converter (MC) and model predictive control (MPC) to compensate lagging power factor (p.f.) loads using inductors instead of electrolytic capacitors (e-caps) for energy storage. Although ubiquitous in power electronic converters, e-caps have well-known failure modes and wear-out mechanisms. In practice, the bus capacitors in a voltage-sourced inverter reactive power compensator may require monitoring and replacement, which can increase the cost of ownership of a traditional reactive power compensation method. The proposed MPC-MC-STATCOM uses a $3\times3$ direct MC, which when properly controlled using finite-set MPC, creates a phase shift of 180° from the input to output current, and thus supplies reactive power to the utility grid using inductors instead of the e-caps. This paper presents the fundamental concept and model derivation. The theoretical analysis is accompanied by simulation and experimental results that verify the intended operation of the controls and circuity in steady state under ideal grid conditions and dynamically to demonstrate robustness of the MPC control under step changes in grid voltage distortion and load characteristics. The conclusion is that the capacitorless STATCOM can provide the reactive power needed to compensate lagging p.f. load.

Model Predictive Control of a Capacitorless Matrix Converter-Based STATCOM

This paper describes the study of the reliability of capacitor units installed and operated in a distribution system during the period 1980 through 1990. Failures of capacitor units in distribution substations can be very costly to the supply of reliable power to consumers. To enhance utility reliability, failure analysis and rates, failure origin and physical damage causes were performed for these capacitor units. Two approaches, statistical and physical, were utilized in this study. In the statistical area, failure modes, reliability levels and failure causes are analyzed. The physical study mainly deals with the mechanism of deterioration of the composite dielectric, The results of the study on 2912 capacitor banks including 8736 capacitors installed at 153 distribution substations showed that the failure mode of capacitor units may be represented by a Weibull distribution and each capacitor manufactures has different failure rate. Analysis showed that partial discharge properties are a critical indicator for capacitor failure. Useful conclusions are presented both for power system operators and manufacturers. The methodology used in this study also applies to other equipment in the distribution system such as oil switches, transformers and insulators.

Failure analysis of composite dielectric of power capacitors in distribution systems

On-line partial discharge calibration and monitoring for power transformers

Failure analysis of composite dielectric of power capacitors used in distribution systems

This paper describes the study of the reliability of capacitor units installed and operated in distribution system during the period 1980 through 1990. Failures of capacitor units in distribution substations can be very costly to the supply of reliable power to consumers. To enhance utility reliability, failure analysis, and rates, failure origin and physical damage causes were performed for these capacitor units. Two approaches, statistical and physical, were utilized in this study. In the statistical area, failure modes, reliability levels and failure causes are analyzed. The physical study mainly deals with the mechanism of deterioration of the composite dielectric. This paper models capacitor's failure mathematical mode and calculates their failure rate. The results of the study of 2912 capacitor banks including 8736 capacitors installed at 153 distribution substations showed that the failure mode of capacitor units may be represented by Weibull distribution and each capacitor manufacturer has a diffe...

Failure Analysis of Composite Dielectric of Power Capacitors Used in Distribution Systems

This paper describes the study of the reliability of capacitor units installed and operated in a distribution system during the period of 1980 through 1990. Failures of capacitor units in distribution substations can be detrimental to the supply of reliable power to consumers. To enhance utility reliability, failure analysis and rates, failure origin and physical damage causes were studied for these capacitor units. Two approaches, statistical and physical, were utilized in this study. In the statistical area, failure modes, reliability levels and failure causes are analyzed. The physical study mainly deals with the mechanism of deterioration of the composite dielectric. This paper models the capacitor's failure mathematical mode and calculates the capacitor failure rate. The results of the study on 2912 capacitor banks including 8736 capacitors installed at 153 distribution substations showed that the failure mode of capacitor units may be represented by a Weibull distribution and that each capacitor manufacturer has a different failure rate. Analysis showed that partial discharge properties are a critical indicator for capacitor failure mechanisms. Useful conclusions are presented both for power system operators and manufacturers. The methodology used in this study also applies to other equipment in the distribution system such as oil switches, transformers and insulators.

C. Wang

Papers

Failure analysis of composite dielectric of power capacitors in distribution systems

On-line partial discharge calibration and monitoring for power transformers

Failure analysis of composite dielectric of power capacitors used in distribution systems

Failure Analysis of Composite Dielectric of Power Capacitors Used in Distribution Systems

Failure analysis of composite dielectric of power capacitors used in distribution systems