Current signal processing-based methods to discriminate internal faults from magnetizing inrush current

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 20kVA 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 5ms to 10ms), particularly the minor internal faults such as the inter-turn 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.

Countermeasure to Prevent Transformer Differential Protection From False Operations

“…Category 3: Electrical parameter-based methods. They includes the current change ratio (CCR) and the percentage area difference (PAD) [11], the rate of phase angle [12], positive and negative sequence components [13], and the Sub-Cycle phase angle distance [14].…”