The determination of ladder-network model parameters for transformer winding holds paramount significance in validating the design constraints of the transformer winding, with a particular emphasis on facilitating thorough analysis of its impulse behaviour. As these parameters cannot be measured directly, the majority of studies documented in the literature rely on iterative optimization techniques for estimation, and as of now, no analytical solution has been reported and implemented. To address this concern, this paper introduces an analytical approach for estimating unknown self and mutual inductances in equivalent ladder-network model of a homogeneous transformer winding, employing frequency response measurement. For this purpose, the method derived necessary linear and non-linear equations of unknown inductances pertaining to the coupled ladder-network model of the winding. The solution is directly obtained utilizing essential peak and trough frequencies extracted from three measured admittance magnitude responses along with series and ground capacitances determined separately. The practicality of the method has been verified using experimental results on three different transformer windings including one with iron-core. For improved precision, the estimated inductance values were fine-tuned further using conventional optimization technique. Results indeed demonstrate the practicality as well as efficacy of the method.

The frequency response analysis (FRA) technique is undoubtedly a sensitive diagnostic tool for assessing the mechanical and electrical integrity of transformers. Despite FRA measurement procedures being standardized by international bodies such as IEEE, IEC, and CIGRE, there is comparatively limited literature for identifying particular phase winding with localized faults in three-phase transformer. In this context, this paper proposed a series of new FRA measurements followed by their interpretation with no post-processing for identifying the faulty phase in star-connected HV windings. The method identifies the specific phase winding with a localized incipient fault in two stages. In the first stage, it determines whether the fault is in the middle phase winding or in one of the two outer phase windings. If the fault is in an outer phase, the second stage is employed to distinctly identify which outer phase winding has gone faulty. The philosophy of the proposed method has been validated by experimental results on a real three-phase 1MVA, 33/11kV, YnYn0, 50 Hz transformer. Results are found promising and encouraging.

A novel, indirect measurement technique for estimating equivalent inductance associated with multi-resonance behavior of an isolated transformer winding is reported for both healthy and inter-turn short-circuit fault-condition. For healthy winding, the authors proposed measuring two unique admittance magnitude responses of the winding followed by utilizing their natural frequencies for estimating the said inductance. Here, the one response is for line-end excitation with neutral-end grounded and the other one is for two equal and opposite polarity excitations from two ends of the winding. For inter-turn shorting, driving-point admittance magnitude response with neutral-end open is also utilized. This inductance seems to be one important parameter for verifying the design constraint mainly for impulse behavior as well as for identifying inter-turn shorting of the winding. The proposed method was also verified by experimental measurements on two actual transformer windings; one of which incorporated an iron core within it. All pertinent analytical derivations and the associated results are also included in the paper.

It is known that the frequency response analysis (FRA) method is the most sensitive for identifying any fault or mechanical damage in transformer windings. In FRA technique, a subsequently measured response needs to be compared with a 'reference measured response' for detecting any faults. But in practice, sometimes 'the reference measurement' may not be available for some reasons; in that case the measured response alone is not sufficient for identifying any damage in the windings. In this way a limitation has been existed for the conventional FRA method. For addressing this limitation, the author's research group recently published an innovative FRA based method for identifying the damage in single, isolated winding even in the absence of its' healthy reference response. In this paper a new method is proposed to overcome few limitations or constraints of the earlier method proposed by this research group. The validity of this newly proposed method was verified using both the simulation results of an equivalent ladder-network model and the experimental results on a 33 kV continuous-disk winding. The pertinent results shows that the method is simple and promising for identifying the fault in the winding even in the absence of its' healthy reference measurement.

Usually for controlling the speed of DC motor we use mechanical sensors like tachometers, encoders and Hall effect sensors which need to be coupled with the shaft of the DC motor for estimating the speed of the motor. But for small motors where miniaturization is required, these sensors will increase cost, mounting place and maintenance problems. In this work, a 'full-ordered state observer' based sensorless speed estimation of DC motor has been used. Since we take 'the speed of the DC motor' as a state variable, we will estimate it using the proposed observer. The effect of variations in load torque and input voltage on speed estimation are discussed. The observer works well in all dynamic variations on motor, for estimating the speed. The effect of placement of poles of observer on error of the estimated speed for the given variation on the motor are also been discussed. All these results are simulated in MATLAB.