G. Rabach

Frequency-response analysis of power transformers by means of fuzzy tools

A novel Fuzzy algorithm for the automatic analysis of frequency response of power transformers is described in this paper. It relies on the values of two parameters able to quantify the difference between the present and a reference frequency response, over three frequency ranges. These ranges are associated with different defect types, i.e., short circuits between turns, radial and axial displacements. Training examples obtained mainly from experimental results have been used to select the different ranges. Fuzzy-Logic has been adopted to reflect the uncertainty in the analysis of the differences between the two curves in the defect-identification results. Practical applications are also discussed to show the efficiency of the proposed diagnostic method.

Computer-aided partial discharge amplitude distribution measurement system for large electrical machines diagnosis

The authors describe a distributed intelligent measurement system for partial discharge amplitude distribution (PDAD) detection for large rotating machinery, such as power generators. The equipment design is based on a modular adaptive technique, which allows the flexibility required for applications to different types of generators. The partial discharge acquisition and computing system is based on two main units. The remote unit is located close to the system to be tested and is designed to supervise the dynamic conditioning process as well as the acquisition and fast preprocessing of the probe signals. The second unit has no specific location and is linked with the first one by means of a fiber-optic data link. The second unit mainly consists of a PC (personal computer) having properly designed software tools to assist acquisition and perform real-time information analysis and diagnostics. This measurement system was used to perform tests on a nonloaded hydrogenerator equipped with a directional coupler. Experimental results are presented.<<ETX>>

Evaluation of LV insulating systems in inverter fed electric motors by means of partial discharges

A synthetic description of the phenomena induced by PWM inverter drive systems are reported and the parameters related to motor reliability are evaluated. The winding quality of brand new motors is addressed, specifically the integrity of the turn or the conductor insulation is checked by applying surge voltage stresses. Finally Partial Discharge (PD) measurements are carried out on an aged 800 kW motor: the outcomes are reported and discussed.

On turbogenerator H.V. stator winding condition assessment by the analysis of PDHD detected on phases and insulated coils after untimely failure

The paper deals with the results of investigations performed in order to verify whether diagnostic tests, based on Partial Discharge Height Distribution (PDHD) analysis, are able to identify the causes of deterioration and to guide the repair of the insulation system of HV rotating machine stator windings. The insulation system of a turbogenerator was tested after a breakdown occurred in service. Partial Discharge (PD) measurements were performed both on the windings and on single coils. The analysis of the results of PD measurements evidenced that the breakdown was due to a defective impregnation of the winding.

Partial discharge amplitude distribution analysis for the evaluation of ageing progression in voltage endurance tests

The use of partial-discharge amplitude distribution (PDAD) analysis for monitoring the aging trend in accelerated tests on insulation systems is proposed. The PDAD technique was found to be more reliable than traditional nondestructive diagnostic tests. The calculation of a merit index of aging progression is also discussed.<<ETX>>