Informatics Publishing Limited

Y. Agrawal ¹, M. K. Wadhwani ¹, B. V. Raghavaiah ¹

Affiliations
1 Switchgear Testing and Development Station, Central Power Research Institute, Bhopal, IN

Abstract

Transformers are basic electrical machines and they form a very vital link in any electrical power transmission networks. During its service life, a transformer may experience number of short circuits in the system in addition to the abnormal overloading and switching impulses. Such abnormal conditions can cause the movement of the windings and failure of the supporting structures due to electro – mechanical forces and may result in total failure due to inadequacy in design and defective manufacturing process. Further, the rapid growth of fault level in the system network is major a concern for short circuit withstand capability of a transformer in service for a long period of time. With advanced modern technology and available short circuit test facilities, transformer manufacturing industry is now enabling to produce the reliable and safe transformers. Performance evaluation during ability to withstand short circuit test in a fully equipped testing laboratory is still final measure of checking the overall quality of the transformer from the point of design, material used, production process and quality control. Central Power Research Institute (CPRI), is having an experience of more than fifty years in the fi eld of short-circuit testing. The roles of various factors which affect the performance of transformers under short-circuit conditions are discussed along with the analysis of the failure cases during the short circuit testing.

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G. Venkateswarlu ¹, Yugal Agarwal ¹, M. S. Takkher ¹, M. K. Wadhwani ¹, B. M. Mehra ¹

Affiliations
1 Switchgear Testing and Development Station, Central Power Research Institute Govindpura, Bhopal – 462023, Madhya Pradesh, IN

Abstract

Capacitor banks are installed in an increasing number to control power quality issues and improving the power factor to counteract the reactive power in the transmission and distribution networks. Due to load fluctuations switching of capacitor banks is a typical phenomenon. Capacitor bank is normally having concentrated capacitance in contrast with distributed capacitance. It generally draws more current than unloaded cableor line in practical cases up to several hundred amperes. Hence, switching of capacitor bank causes a very high rate of rise of transient recovery voltage across circuit breaker contacts. This scenario can be simulated in testing laboratories by a voltage source connected to a circuit breaker which again is connected to a large capacitance in terms of IEC called capacitive current switching test. Non-sustained disruptive discharge (NSDD) is a voltage breakdown after the vacuum circuit-breaker open the fault current which will not cause the recovery of power frequency current. Restrike is different from NSDD, the recovery of power frequency current between the contacts will make the breaker failed. It’s not easy to show the distinction between NSDD and restrike during some type tests. The paper presents the study of performance evaluation of the circuit breaker during the capacitor current switching duties. A statistical analysis of failure of circuit breaker during capacitor current switching tests are included in the paper to help the manufacturers & utilities, so that the care can be taken for trouble free services. The paper also discusses the changes made in the IEC 62271 – 100, Amendment1:2012 for conducting the capacitive current switching tests.

Keywords

Capacitor Switching Duty Cycle, Non-sustained Disruptive Discharge (NSDD), Voltage Breakdown, Capacitive Current Switching Test,Current Switching Test, Inadequate Synchronization.

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K. Sharath Kumar ¹, Diptiranjan Sahoo ¹, Yugal Agarwal ¹, Manoher Singh Takkher ¹, M. K. Wadhwani ¹

Affiliations
1 Central Power Research Institute, Govindpura, Bhopal – 462023, Madhya Pradesh, IN

Abstract

Among several switchgear equipment largely used in high voltage Transmission systems, which change the grid configuration, isolates faulty parts from the grid, etc. circuit breaker is a remarkable one. For the reason to analyse the interrupting capabilities, a circuit breaker has to undergo various test duties according to IEC 62271-100 among which Test duty T100a is considered as the most onerous one. During this test the breaker has to prove its Interrupting capability during maximum arc energy condition. This article focuses on the Performance evaluation of circuit breaker under asymmetric condition Test duty T100a.

Keywords

Asymmetrical Fault, Circuit Breaker, IEC 62271-100, Luminous Electric Discharge, Test Duty T100a.

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T. Prabakaran ¹, M. K. Wadhwani ¹, Sumbul Munshi ¹, Himangshu Roy ¹, Saumitra Pathak ¹

Affiliations
1 CPRI, Bhopal - 462023, Madhya Pradesh, IN

Abstract

Emerging modern technologies and ever-changing demands compete with each other to bring new changes to the sociotechnical life of human beings. OLTC is one such equipment connected as an integral part of the transformer to change the turns ratio while the transformer is in energized condition, to adjust the output voltage. Changing times and technology brought many changes in the OLTC techniques, design and operation. Traditionally OLTC is a complex mechanical device, which has some deficiencies. OLTC design elements are checked during the transition resistor test. Thus, OLTC testing for transition resistors is a method to enhance the reliability of OLTC design. This paper discusses a typical failure case of OLTC during the transition resistor test conducted in CPRI.

Keywords

On Load Tap Changer (OLTC), Transition Resistor and Mechanical Device.

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