Transient dynamic analyses of presaturated core fault current limiters through flux and inductance versus current modelling

Abstract

Here, the outcomes of experimental measurements and finite-element simulations are used to develop MATLAB/ Simulink models for evaluating the transient dynamic behaviour of the well-known dual-core presaturated core fault current limiter (PCFCL), either for single-or three-phase configurations. These models are based on calculating the total flux linkagecurrent characteristics of the AC coils at different levels of DC biasing current, taking into consideration the induced voltage across the DC coil terminals due to significant flux variation during the fault condition. On the other hand, the time-varying selfinductance and the self-inductance-current characteristics of the PCFCL are directly developed through Simulink modelling. It is worth mentioning that the self-inductance-current characteristic enables an important and quick design optimisation tool for PCFCL, where the dynamic inductance term significantly contributes to the total voltage drop across PCFCL in comparison to the static inductance. These total flux linkage and inductance versus current models can be directly used for modelling the dynamic transient behaviour of PCFCL when attached to any electrical transient programme used for analysing complex electrical power systems, with remarkable accuracy, quicker, and easier for various network scenarios and fault conditions.

Compact designs of permanent‐magnet biased fault current limiters

“…The relative permeability of the magnetic iron core (μ r-core ) and consequently the associated time-varying inductance (L) can be expressed as follows [7,18,27]:…”

“…When the magnetic core is driven into saturation with the magnetic field and flux density as H sat and B sat , respectively, the inductance of the inductor decreases in comparison to the case when the BH working point is outside the saturation region. The inductances for the unsaturated and saturated case are given by (7) such that the value of μ r-core of the unsaturated core is much greater than that of the saturated case This is utilised to make the inductance of an FCL to be large enough to limit the fault current below a specified value and small enough so that the peak of the fault current is still detectable by present protective schemes of the system as the following [7]:…”

“…By assuming the FCL saturated insertion impedance and the transient impedance (≤ 1% of the base impedance and ≥ the source impedance of bus being protected, respectively), L min and L max can be calculated, respectively. Thereafter, from (7) and (8), N and l can be calculated. It is worth mentioning that dividing the AC coil into subcoils gives the opportunity to connect them in the differential mode and hence reducing L min and the voltage drop across FCL under normal operating condition.…”

“…Accordingly, the technology of fault current limiter (FCL), in particular, compromises a leading candidate for limiting these high levels of fault current to be within the operating limits of the switchgear [1][2][3][4][5][6]. Meanwhile, multishot ability and compatibility with re-closers encourage the request of such FCL technology for protecting sensitive equipment against growing levels of fault current and increasing the reliability of distribution networks [7].…”

“…Nevertheless, fault current limiting is achieved by the substantial increase of the magnetic iron core relative permeability, and consequently its impedance, due to the demagnetisation effect of the fault current. Such PCFCLs have enriched clipping performance of consecutive fault currents with reduced percentages of voltage drop and power losses during steady-state operation of the system [7].…”