Compact designs of permanent‐magnet biased fault current limiters

Abstract

This study proposes two novel compact designs of three-phase permanent-magnet biased fault current limiters (PMFCLs), namely, delta-shaped and compact cross delta PMFCLs. The actual representation of neodymium permanent magnet (PM) is based on the Jiles-Atherton modelling for the demagnetisation behaviour in the second quadrant of its actual non-linear B-H hysteresis loop. This PM is a preliminary representation validated through experimental measurements to ensure the trends and behaviour of PMFCL during its entire pre-fault, fault and post-fault recovery durations. Comprehensive time-domain, electromagnetic finite-element simulations, through COMSOL multiphysics package, have been conducted to study the relative effect of the constructive controlling parameters on the general performance of these proposed PMFCLs. However, the general performance of PMFCL can be characterised through the voltage drop and power losses of normal operation, and the fault current clipping ratio during the fault condition. Results reveal that the compact cross delta design has superior performance and enhanced capability of limiting any type of fault current, either symmetrical or unsymmetrical, with leading advantages of significant reduction of the voltage drop across PMFCL and power losses during the normal operation of the grid.

Stacked Delta Design of Three-Phase Permanent-Magnet Fault Current Limiters

“…Some of the common electrical parameters for the proposed delta-shaped PMFCLs are shown in Table 1. The design arrangement of four AC coils and five NdFeB-N42 PM segments (4AC-5PM) three-phase delta-shaped PMFCL (Eladawy et al 2020) is shown in Fig. 2(a).…”

“…2(a). The subdivided coils of each phase are connected in series, with differential connection (Eladawy et al 2020), to carry the line current of the protected power line. The uniformly distributed PM segments are sandwiched and arranged between the two soft magnet triangles throughout the delta-shaped design.…”

“…This will in turn increase the voltage drop value, due to the increase of AC coil inductance, during the healthy condition of operation. However, this may exceed the maximum permissible value of the voltage drop (≈ 1%) stipulated by the utilities (Eladawy et al 2020). Another multi-storey design can be obtained by aligning the magnetization direction in all storeys in the same direction, as shown in Fig.…”

“…FCLs can be generally classified, according to their constructive technology, into solid-state FCLs (SSFCLs) (Radmanesh et al 2016), quench-type superconducting FCLs (SFCLs) (Jia et al 2016), and pre-saturated iron core FCLs (PCFCLs) Moscrop 2013;Eladawy et al 2019;Eladawy et al 2020;Pannu et al 2013;Yuan et al 2017;Xiao et al 2013, Zhao et al 2007). SSFCLs utilize the power semiconductor switches for controlling the current flow through the circuit.…”

“…The soft magnet (iron core), in such PCFCLs, is deeply saturated, which represents negligible impedance as the relative permeability µr ≈ 1 during the healthy operating condition. This deeper saturation state can be offered by either a DC coil or permanent magnet (PM) (Eladawy et al 2019, Eladawy et al 2020. During fault condition, the highly counter-magnetic flux created by the fault current can in turn desaturate the soft magnet towards higher relative permeability values, which corresponds to a sharp increase of the soft magnet impedance and hence limiting the fault current.…”