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Title: Application of EL CID to salient-pole electrical machines
Author: Ridley, G. K.
ISNI:       0000 0004 7425 6113
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2017
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Sutton introduced EL CID in the 1970's. This thesis records the development of EL CID theory, with particular reference to its application to large, salient-pole, water-turbine driven, electrical machines, known as hydrogenerators. Factors are identified and clarified which otherwise may cause misunderstanding of hydrogenerator stator core interlamination insulation condition. Features discussed, with reference to their impact upon the detected EL CID signal, are alternative forms of excitation winding of the stator core, its constructional features, including core build bars (or key bars), core segmentation, proximity of ferrous components, plus ancillary matters such as the location of brake/jack units, the degree of machine assembly, whether in or out of the operational situation, the extent of the machine enclosure, and the presence of the stator winding and rotor-mounted salient poles. Although satisfactory application of EL CID to turbogenerators was achieved in the 1970's, anomalies arose when applied to salient-pole machines, due to shorter stator winding end-overhang, its multi-parallel circuits, and also the disincentive of realignment of the rotor if removed, making access to the stator bore and accurate location of the excitation cable more difficult. When present, joints in very large hydrogenerator stator frames and cores, for transportation, made analysis of EL CID results particularly difficult. The problem presented by core joints arose in the initial factory demonstration of application of EL CID to hydrogenerators. The solution recognises the interdependence of the two orthogonal EL CID signal components, which indicate EL CID as analogous to a transformer, with two short-circuited secondary windings; one for interlamination fault current (designated "delta"), the other being the stator winding, when present. In order to draw the phasor diagram with reference to the secondary side of the analogous transformer, the direction of the excitation phasor is reversed, since the fault current is detected in a secondary circuit. Application of standard transformer theory produces an appropriate EL CID phasor diagram, in various forms, depending upon the particular test circumstance. In this context, the significant concept of a line for which interlamination fault current (delta) is zero (i.e. a zero delta line) was introduced. The two orthogonal EL CID signals, designated PHASE and QUAD, are plotted on equal scales; unless related appropriately by a technique described, which takes the difference into account, to ensure the highest accuracy. Evaluation of delta indicates the effectiveness of core repairs, which supports the usefulness of the EL CID technique when applied to hydrogenerators, as well as turbogenerators. At core joints, the detected maximum fault current (deltamax) is usually appreciably greater than the traditional acceptance criterion of 100 mA. This is discussed, and the conclusion drawn that the distribution of delta along the core length provides an adequate indication of any weak region of interlamination insulation. The practise of routinely resetting the Phase Reference for an EL CID test is examined, and found to be not acceptable, unless the results are subsequently referred back to the basic reference. As a final demonstration of the EL CID technique usefulness, the analysis of results from a core joint, where there was an imposed artificial fault, identifies the location concerned.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering