Partial discharge (PD) is one of the sources of insulation failures in Power transformers. Knowledge of the PD source locations are important for transformer maintenance and repair. Due to the complex structure of the transformer, it is very difficult to locate the PD accurately in transformer winding. Correlation methods are applied to locate the PD source across the winding. The PD across parts of the winding are simulated by applying voltage pulse across the sections. The winding response for a reference PD impulse across transformer sections are taken as base for correlation and correlated with winding response of PD impulse across any section with different PD pulse widths. In this paper the limitation of time domain correlation method in locating PD in transformer windings is found out. To overcome the limitation of time domain correlation method, frequency domain correlation with Gram Schmidt orthogonalization is proposed. Simulation and experiments are performed on layer, continuous disc and interleaved windings to prove the feasibility of the proposed method.

Frequency domain correlation technique for PD location in transformer winding

A correlation method is proposed for the location of partial discharge within a winding. Theoretical simulations and experimental results on a lumped parameter model of a winding are shown to prove the feasibility of the method.

A correlation method for detection of partial discharges in transformers

Future template numerical interpretation techniques for PD pulse location in transformer windings

A method is proposed for recognizing PD events within a winding during impulse tests using a lock-in amplifier technique. The resonant frequencies of the winding serve as the basis of selection of the lock-in amplifier reference frequencies. It is implemented with a virtual instrument and validated with an independent stand-alone lock-in amplifier. A physical model of a winding with discrete elements is used to demonstrate the results. A theoretical basis for the instrument is established using an 'abc' model of PD along with a linear discrete winding model. The influence of location of PD is also addressed. The method will provide online recognition of PD during the impulse test and can be adapted for onsite measurements.

A Lock-in Technique for PD Measurement during Impulse Tests

A fusion of hard and soft computing is proposed for the impulse analysis problem. An optimal hardware platform for the data acquisition and a minimal set of simulations form the hard computing element. As the number of simulations can become unbounded to cater to all types of faults, a soft computing approach based on fuzzy logic is proposed. This can lead to automation of impulse analysis function.

Fuzzy logic based impulse test analysis

An instrumentation scheme is proposed for the acquisition of waveforms during the lightning impulse test on transformers. Three filters segregate the response into distinct frequency bands. As partial discharge signals primarily influence the high frequency behaviour, experiments are reported on disc, interleaved disc and layer windings.

The influence of winding type on the recognition of partial discharges [power transformer testing]

An objective formulation of the impulse testing procedure is proposed based on models for winding response as well as fault models. Experimental validation of the fault models for breakdown and partial discharge (PD) is provided. A new adaptive filtering approach is proposed for analysis during impulse tests. The procedure is validated with experimental investigation on a 10 section lumped parameter network.

A. Palani

Papers

The influence of winding type on the recognition of partial discharges [power transformer testing]

Programmable continuous time filters for impulse testing of transformers