Current signal processing-based methods to discriminate internal faults from magnetizing inrush current
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ORIGINAL PAPER
Current signal processing-based methods to discriminate internal faults from magnetizing inrush current Adel Ali Amar Etumi1
· Fatih Jamel Anayi1
Received: 18 December 2018 / Accepted: 26 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Two new methods, current change ratio (CCR) and percentage area difference (PAD) were proposed to solve a problem of how to distinguish between internal faults and inrush condition when transformer is switched on. This problem may delay operation or may mal-operate some protection schemes like deferential protection. The methods were concluded after observing and analyzing the behavior and shape of large number of both inrush and internal fault signals that had been obtained using a model transformer in a laboratory. The methods were practically tested on a three-phase transformer with rated power of 20 kVA at Cardiff University’s laboratory and the data were processed using LabVIEW and MATLAB programs. The results showed that internal faults can be correctly distinguished from inrush condition within a short time (from 5 to 10 ms), particularly the minor internal faults such as the interturn fault which is submerged to inrush current and make it is too difficult to be detected. The advantages of these algorithms are simple in design and faster than the second harmonic method which is the most popular method used for solving this problem. Keywords Internal fault · Inrush current · LabVIEW and MATLAB programs · Current change ratio · Percentage area difference · Transformer protection
1 Introduction Protection system is an important part in any power system as it continually monitors the status of the equipment and can act almost immediately to any fluctuations occur in the power system. This is important as it can isolate any faulty unit within the system to a localized area and minimize as much damage as possible to the faulty equipment or any equipment in the vicinity without disrupting power flow to unaffected areas. Power system equipment repairs can be lengthy and expensive as well as replacement difficulties and fire risk to other equipment surrounding. Therefore, any protection system must be reliable, dependable and secure to ensure that any damage due to a fault is kept to a minimum [1]. For some decades, the differential protection is the main protection system for most power transformers. It is implemented to avoid any mal-operation may occur in protection relays. The 2nd harmonic restraint is commonly used as a
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Adel Ali Amar Etumi [email protected] Wolfson Centre for Magnetics, Cardiff University, Cardiff CF24 3AA, UK
protection technique to prevent the differential protection systems from operating during either external faults or inrush condition [2, 3]. Nevertheless, this method cannot be relied on for all cases, including internal transformer winding faults and for power transformers that their cores are built using the amorphous material which are characterized by low power loss. In this case, there
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