Current Injection Transformer Research Articles

Rational approach for self-limiting current injection transformers confirmed by coupledelectromagnetic–thermal FEM simulation

Current injection transformer (CIT) systems are within the major group of thestandard-type test of high current components in the electrical industry. The presentprecious approach contemplates an arrangement for a rational design of a self-currentlimiting transformer (SLT) being integrated by a single unit 25 kA CIT system for fastovercurrent detection in stipulated current tests. This paper describes mathematicalformulations based on an electric models and the dominant effects of an auxiliary windingon the rate of the self-limiting process of the system. This requires the evaluation ofmultiphysical (i.e. coupling of the electromagnetic and thermal parts) finite elementmodelling and simulations for three different approaches to suit the designer’s choice.An overcurrent causes a considerable distortion of axial leakage flux, which in turnproduces high radial forces. The transient analysis of the leakage flux densities and thecorresponding electromagnetic forces on windings of the CIT and proposed SLT are theother objects of this paper. Moreover, the distribution of the flux density and thecorresponding localized losses within the SLT core are further objects of this paper.However, this paper will mark another important event in superconductor technology andaugment efficiency and compactness from which a lower overall cost of the CIT systemcould be attainable.

REDUCTION OF LEAKAGE MAGNETIC FIELD IN ELECTROMAGNETIC SYSTEMS BASED ON ACTIVE SHIELDING CONCEPT VERIFIED BY EIGENVALUE ANALYSIS

Leakage flelds are one of the main issues in design of electromagnetic systems. Some of these flelds close their paths through the core and air, giving rise to non-ideal behavior of the magnetic systems. This paper explains a novel concept of active shielding which consists of two compensation coils in series and generates a counter fleld opposite to the leakage flelds leaking from an iron-core system. As the method is based on physical reasoning of electromagnetic coupled circuit theory, the design criterions for the compensating coils parameters, their number of turns and their adaptation to the systems, were considered. The state of the art is presented by a model which is verifled by roots of system characteristic equations, using state equations. In a case study, this method was investigated in a 25kA (125kVA) current injection transformer (CIT) system delivering a secondary current as closely proportioned to the primary current as possible, using flnite element method (FEM) simulation. This paper will also push the state of the art by reducing the age efiect of the CIT through mechanical force reduction.

Superconducting technology for overcurrent limiting in a 25 kA current injectionsystem

Current injection transformer (CIT) systems are within the major group of thestandard type test of high current equipment in the electrical industry, so theirperformance becomes very important. When designing high current systems, thereare many factors to be considered from which their overcurrent protection mustbe ensured. The output of a CIT is wholly dependent on the impedance of theequipment under test (EUT). Therefore current flow beyond the allowable limit canoccur. The present state of the art provides an important guide to developingcurrent limiters not only for the grid application but also in industrial equipment.This paper reports the state of the art in the technology available that could be developedinto an application of superconductivity for high current equipment (CIT) protection withno test disruption. This will result in a greater market choice and lower costs for equipmentprotection solutions, reduced costs and improved system reliability. The paper willalso push the state of the art by using two distinctive circuits, closed-core andopen-core, for overcurrent protection of a 25 kA CIT system, based on a flux-lock-typesuperconducting fault current limiter (SFCL) and magnetic properties of hightemperature superconducting (HTS) elements. An appropriate location of the HTSelement will enhance the rate of limitation with the help of the magnetic fieldgenerated by the CIT output busbars. The calculation of the HTS parameters forovercurrent limiting is also performed to suit the required current levels of the CIT.

CONVOLUTIONAL CODES ACTING AS EMI VIRTUAL SHIELDS IN CURRENT INJECTION SYSTEMS

In order to design high current devices, there are many factors to be considered, such as the compatibility of these devices with internal and external propagation, as well as the generation of lowand high-frequency disturbances within electromagnetic environments. This paper reports the simulation and measurement results of the electromagnetic interference (EMI) due to the fields inside and outside a Current Injection Transformer (CIT) and its control system during short circuit tests. This paper also pushes the state of the art by proposing a synthetic algorithm based on a channel coding technique for error free EMI shielding to increase the performance level of the CIT against the unpredictable events of the likelihood of transient states accompanying EMI which may result in the malfunctioning of the control system and data exchanges through the connectors.

A new approach for AC loss reduction in HTS transformer using auxiliary windings, casestudy: 25 kA HTS current injection transformer

AC loss is one of the important parameters in HTS (high temperature superconducting)AC devices. Among the HTS AC power devices, the transformer is an essential partin the electrical power system. The AC losses in an HTS tape depend on themagnetic field. One of the techniques usually adopted to mitigate the unwantedmagnetic field is using a system of coils that produce a magnetic field oppositeto the incident one, reducing the total magnetic field. In this paper adding twoauxiliary windings to the HTS transformer to produce this opposite magneticfield is proposed. The proper use of these auxiliary windings could reduce theleakage flux and, therefore, the AC loss. A mathematical model is used to describethe behaviour of a transformer operating with auxiliary windings, based on thetheory of electromagnetic coupled circuits. The influence of the auxiliary windingson the leakage field is studied by the finite element method (FEM) and the ACloss of an HTS transformer was calculated. Also, the simulation results showthat employing auxiliary windings will improve the HTS transformer efficiency.

Single-Phase Operation of a Three-Phase Induction Generator Using a Novel Line Current Injection Method

By using two capacitances and a current injection transformer, a three-phase induction generator can operate with good phase balance and line power factor while delivering power to a single-phase power grid. This paper presents a systematic analysis on this novel induction generator configuration. The solution of the system's inspection equations using the method of symmetrical components enables the steady-state generator performance at any speed to be computed. The conditions for achieving perfect phase balance are deduced from the phasor diagram. It is shown that the capacitances that result in perfect phase balance depend on the generator admittance, power factor angle, as well as the turns-ratio of the current injection transformer. Where possible, the computed results are verified by experiments conducted on a 2-kW induction machine. An experimental investigation on the system waveforms and harmonics is also carried out.