Saturation Detection-Based Blocking Scheme for Transformer Differential Protection

Abstract

This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation period of the transformer core. At these instants, discontinuities arise in the first-difference function of the differential current. The second-and third-difference functions convert the points of inflection into pulses, the magnitudes of which are large enough to detect core saturation. The blocking signal is activated if the third-difference of the differential current is larger than the threshold and is maintained for one cycle. In addition, a method to discriminate between transformer saturation and current transformer (CT) saturation is included. The performance of the proposed blocking scheme was compared with that of a conventional harmonic blocking method. The test results OPEN ACCESSEnergies 2014, 7 4572 indicate that the proposed scheme successfully discriminates internal faults even with CT saturation from the magnetic inrush, over-excitation, and external faults with CT saturation, and can significantly reduce the operating time delay of the relay.

A Simple Method for Compensating Harmonic Distortion in Current Transformers: Experimental Validation

“…However, using ( 8) for reconstructing the primary current spectrum, requires an estimate I 1,e (1) of the fundamental primary current I 1 (1). For this purpose, let us consider (7); I 2 ( 1) is known since it can be directly measured.…”

“…The obvious method to mitigate this phenomenon is using a CT with a larger core cross-section and secondary winding area, but this translates into increased size and weight and higher manufacturing cost. Another possibility is applying proper processing techniques to the secondary current signal to detect the occurrence of saturation [ 1 ] and possibly reducing its impact [ 2 , 3 , 4 ]. In this respect, [ 2 ] employs the equations of the usual equivalent circuit model of the CT (with single-valued, polynomial magnetizing current-flux characteristics) to reconstruct the primary current from the measured secondary current, thus compensating nonlinear effects; preliminary model identification is required, and a least-squares (LS) approach is adopted.…”

Analysis and Improvement of Adaptive Coefficient Third Harmonic Voltage Differential Stator Grounding Protection

“…In recent years, technology related to power grid-side protection has been significantly improved [1,2], but generator protection as a power-side protection is still crucial in maintaining the safety and stability of the power system. Against the background of the rapid development of power systems, generator protection still has prospects for development.…”