Power Research

B. Nageshwar Rao ¹, R. Arunjothi ¹, A. R. Srinivasan ¹, P. Rajashekhar ¹, A. Sudhindra ¹

Affiliations
1 Central Power Research Institute, Bengaluru, IN

Abstract

This paper presents and discusses heat release measurement, smoke and toxicity data obtained on cables: power, communication, automobile, wires and other materials used for various applications in power plants, petroleum refineries, metro rail, automobile industries. Fire survival cables intended to maintain electrical integrity under flaming conditions and flame retardant low smoke cables have been evaluated and their performance discussed. Fire safety assessment methods of cables and materials are reviewed and heat release rate, smoke, toxicity data and flammability characteristics obtained on materials like polystyrene, cellulosic fibre materials, upholstery, FRP/GRP laminate and others are discussed. Cushioning materials like polyurethane foam (slab stack, rigid PU, Expandable Graphite foam), thermally densified polyester block have been evaluated for HRR, smoke properties and the results are discussed. The toxicity of these materials evaluated as per NES 713/NCD 1409 are summarised.

Keywords

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Muhammed Faisal Rahman ¹, B. Nageshwar Rao ², Pradeep M. Nirgude ³

Affiliations
1 Senior Research Fellow, Cables and Diagnostics Division, Central Power Research Institute, Bangalore, IN
2 Additional Director, Cables and Diagnostics Division, Central Power Research Institute, Bangalore, IN
3 Joint Director, Ultra High Voltage Research Laboratory, Central Power Research Institute, Hyderabad, IN

Abstract

Corona discharge is one of the significant problem associated with power transformer and can occur due to sharp points or free conductive particles. The existence of sharp points at joints or terminals or conducting parts is very difficult to avoid completely during the manufacturing process of the transformer. The free conductive particles can arise from manufacturing process or can be developed during service period of the transformer. These free conductive particles can adhere to paper or pressboard insulation barrier or freely move in the bulk oil. In transformers highly non uniform fields are often present due to sharp points and free conducting particles, so detecting their effect on the transformer is very critical for the life of transformer. In the present investigation, to generate a high voltage corona in air or oil, a test chamber of dimension 50cm x 50cm x 50cm made from Perspex material and fitted with removable needle plane electrode arrangement has been used. The discharge measurements are carried out using Partial Discharge (PD) measurement technique according to IEC 60270. The results obtained are presented and discussed. Discharge pulse characteristics such as magnitude, rise time and decay time of different needle plane barrier configurations are analyzed. This paper also discussing pattern analysis and dominant frequency of discharges due to different needle plane barrier configurations.

Keywords

Corona in air, oil, pressboard barrier, partial discharge, pulse characteristics, pattern analysis.

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M. Jayakrishnan ¹, B. Nageshwar Rao ²

Affiliations
1 Junior Research fellow, Cables and Diagnostics Division, Central Power Research Institute, Bangalore, IN
2 Additional Director, Cables and Diagnostics Division, Central Power Research Institute, Bangalore, IN

Abstract

PD monitoring is an effective tool to evaluate the insulation condition of power electrical equipment. However, the major challenge during PD measurement at site is that PD signals are severely affected by external noises and disturbances like white noise, random noise, Discrete Spectral Interferences (DSI), which are generated due to broadcasting stations, stochastic noise and pulses from power electronics at site conditions. Extracting PD signals from these noises is a challenging task.This paper proposes a new method for selecting the mother wavelet based on the energy of the approximation coefficients. The coefficients are obtained using SWT by decomposing the extracted noisy signal to the maximum decomposition level which depends only on the length of the noisy signal. Hard thresholding is used as the threshold function and range dependent threshold estimator is used for obtaining the threshold value. For reconstruction of de-noised signal, the last level approximation coefficient and the thresholded ‘details coefficient’ are used. As most of the lower level details coefficients comprise of noises it can be discarded during reconstruction. A method for discarding noises during reconstruction is also proposed in this paper.

Keywords

SWT, partial discharge, DWT, noisy signal, signal to noise ratio.

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Ipsita Das ¹, B. Nageshwar Rao ², J. Sundara Rajan ², S. Seetharamu ², V. V. Rao ¹

Affiliations
1 Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur, West Bengal - 721302, IN
2 Central Power Reseach Institute, Bangalore - 560080, IN

Abstract

HTS (High Temperature Superconducting) cable has the ability of transmitting electrical power over long distances in an economical way, with improved stability and reliability. HTS Cable also provides a compact and low-loss transmission power line, in comparison with the conventional cable made out of copper or aluminium. The use of HTS tapes facilitates the cable operations with liquid nitrogen cooling system. A wide variety of HTS Cables with various cooling arrangements have been designed and developed. Their performance has been tested to obtain various thermo-hydaraulic and electrical data by installing the cables of different lengths in transmission and distribution networks. This paper reviews the cryogenic cooling aspects of previous and ongoing projects on superconducting cables for electrical power transmission around the world.

Keywords

Cryogenic cooling system, HTS cable, liquid nitrogen, termination

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K. P. Meena ¹, R. Arunjothi ¹, Thirumurthy ¹, G. K. Raja ¹, B. Nageshwar Rao ¹

Affiliations
1 Diagnostic, Cables and Capacitors Division, Central Power Research Institute, Bangalore-560 080, IN

Abstract

Flexible PVC Cables form the major part of Power distribution system within residential buildings, industrial buildings, and other commercial institutions. The ampacity of power cable depends upon the cross sectional area of conductor and the laying and installation of the cable in service. Generally two or more number of PVC cables are bundled together and inserted as a bundle in a conduit pipe for connecting to various load points. As the bundling of cables produce more heat than a single PVC Cable, and dissipation of heat is poor, the ampacity of these cables reduces considerably. Hence the exact selection of sizes and no. of cables are essential to avoid overheating of those cables and the resulting fire havocs.

PVC House wiring cables consists of copper conductor extruded with PVC insulation and are installed generally through a conduit pipe in a bundled manner. The steady state current rating of these cables depends on the way the heat generated in the cable due to current and the heat transmitted to the cable surface & then dissipated to the surroundings. The maximum conductor temperature is limited by the type of insulating material used. In this paper theoretical and experimental results of steady state ampacity ratings of bundles of house wiring PVC Cables laid in conduit pipes are compared.

Keywords

Ampacity, house wiring cables

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B. Nageshwar Rao ¹, J. Sundara Rajan ¹, B. Ramachandra ²

Affiliations
1 Central Power Research Institute, Bangalore, IN
2 PES College of Engineering, Mandya, IN

Abstract

No Abstract.

Keywords

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B. Nageshwar Rao ¹, K. Mallikarjunappa ¹, J. Sundara Rajan ¹, B. Ramachandra ², A. Sudhindra ¹

Affiliations
1 Central Power Research Institute, Bangalore, IN
2 PES College of Engineering, Mandya, IN

Abstract

This paper reviews the main ageing and failure mechanisms of stator winding and methods for extending the useful life of the machine. The symptoms for each failure mechanism are discussed and an overview of various electrical diagnostic techniques for condition assessment of stator winding insulation is presented

Keywords

Stator Winding Insulation, Degradation, Condition Monitoring Techniques.

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B. Nageshwar Rao ¹, K. Mallikarjunappa ¹, C. D. Keri ¹, T. R. Afzal Ahamed ¹, A. Sudhindra ¹, B. Ramachandra ²

Affiliations
1 Central Power Research Institute, Bangalore, IN
2 PES College of Engineering, Mandya, IN

Abstract

This paper presents the test results and analysis made on several machines at site. Case studies are employed to illustrate the usefulness of measurements on the stator windings in service.

Keywords

No Keywords.

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B. Nageshwar Rao ¹, K. P. Meena ¹, Thirumurthy ¹, G. K. Raja ¹

Affiliations
1 Central Power Research Institute, Bangalore-560080, IN

Abstract

Over the years both due to demand and technological advancements there has been a continuous transition from smaller operating voltages of 6.6. kV to higher voltages of 500 kV. The conventional technology like taping or fi eld moulding are in vogue and new technology like pre-moulded slip on cable accessories are gaining importance for jointing of polymeric high voltage cables up to voltages of 500 kV. The fl ammability characteristics of polymeric materials used in cable insulation and jacketing have been of great importance over the years. Evaluation techniques have become more stringent and both short term and long term tests are conducted in order to ensure the quality of materials used, the manufacturing processes, workmanship and reliability. In this paper the recent advances in HV and EHV power technology is summarized and the experiences in testing and evaluation of 220 kV cables is presented and discussed.

Keywords

Taping, Pre-moulded slip, High voltage (HV), Extra high voltage (EHV) polymeric cables.

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Dillip Kumar Puhan ¹, Rajat Sharma ¹, K. P. Meena ¹, B. Nageshwar Rao ¹

Affiliations
1 Central Power Research Institute (CPRI), Bengaluru – 560080, Karnataka, IN

Abstract

Power transformers are key components in the substation/switchyard and failure of transformer can have an enormous impact on reliability and availability of power supply and has financial implications. As there is ever increase in demand of power, the reliability of power equipment assumes high importance. Economic factors are the main consideration and in order to minimize capital expenditure on new equipment, it is a common policy among utilities to maximize the use of existing power transformers by operating at their design capability. This can be achieved by periodic diagnostic testing and adopting condition based maintenance practices. In this paper various condition assessment techniques for oil filled transformers are discussed and few case studies are presented.

Keywords

Condition Assessment, Generator Transformer, Insulation Diagnosis, SFRA

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