Interpreting Loss of Clamping Pressure and Axial Displacement in 1-Φ, 3-Φ Windings Using Effective Air-Core Inductance: An Experimental Study

Recently authors proposed an indirect method based on measured FRA to estimate an important electrical parameter of the winding, viz., effective air-core inductance (Leff), which together with winding capacitances creates the resonant frequencies. Since,Leffis directly linked to producing resonances, it is imperative that it possibly might be the right quantity to interpret frequency shifts observable in peaks and/or troughs when comparing two FRAs. The feasibility of such a possibility is investigated here. In the first part, a detailed study of uniformly distributed axial displacement (AD) viz., loss in clamping pressure on an actual single isolated winding is done to examine suitability ofLeffto not only detect it but also quantify it. Results revealed thatLeffhas exceptional sensitivity, bears a physical relation to AD, and most importantly is monotonic with respect to physical change$-$a unique feature. Thus, emerging as an ideal candidate to link frequency deviations in two FRAs to a measurable quantity. Encouraged by this success, the concept was next extended to interpret a localized AD of 5 mm introduced in one phase of a 3-Φwinding (Y orΔ) rated for 33 kV, 3.5 MVA. During these experiments, the phase position and extent of AD could be varied at will andLeffsuccessfully identified the phase containing AD, and its extent qualitatively. The method requires only measured FRA data, is applicable to any winding and does not need design data.