A simulation model of a continuous disc type 6.6 kV transformer winding was used to study the propagation behaviour of partial discharge (PD) pulses. The model based on multi-conductor transmission line theory uses a single turn as a circuit element with the capacitance, inductance, and losses calculated as distributed parameters. Transfer functions that describe how the location of the PD source affects the current signals measured at the terminals of the winding were calculated. The paper shows how the position of the zeros in the frequency response of the measured current signals can be used to locate the source of the discharge. Sensitivity studies on the parameters of the model were used to investigate the effect of inaccuracies in the model on the position of the zeros and hence the location of the discharge.

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Simulation of a transformer winding for partial discharge propagation studies

Partial discharges are well known as a source for insulation degradation in power transformers. A hybrid transformer model is introduced to simulate the transformer winding transient response. Transformer structural data is used to determine the hybrid model parameters. Calculations of the hybrid transient model parameters are based on the parameters of the lumped parameter equivalent transformer model and electromagnetic rules. Modern computation techniques and optimizations are employed beside this model for PD location using the multi conductor transmission line model and also to analyze its propagation aimed at achieving (i) more reliable simulation results (ii) less computational time (iii) accurate results for a wide range of frequency. The simulation results on a 66 kV, 25 MVA fully interleaved winding are presented. The measurement results on this winding are employed to validate this model

A hybrid transformer model for determination of partial discharge location in transformer winding

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

Proposed method of partial discharge allocation with acoustic emission sensors within power transformers

Partial discharge (PD) is an important indicator of insulation condition in a power transformer. The PD phenomenon is exhibited in various observable forms such as electrical, mechanical, optical and electromagnetic energy. Many modern systems use a combination of these techniques, because electrical detection is a proven technology, combining it with modern techniques gives the conformity and the advantage of modern digital signal processing. This paper discusses the evolution of various techniques in partial discharge measurement as a condition monitoring tool available for online measurement of field transformers. This paper also discusses the recent techniques used for partial discharge analysis with its advantages and suitability over conventional method for proper condition monitoring of large power transformers.

Online partial discharge detection and location techniques for condition monitoring of power transformers: A review

A matched filter approach is proposed for the location of a partial discharge within a winding. The approach is very general and does not need isolation of the capacitively transferred components. Simulations are performed on a lumped parameter model of a layer winding to prove the feasibility of the method. Experiments are also performed on a layer winding in order to validate the method. It is possible to extend the method to the determination of location of PD during impulse tests.

Location of partial discharges in transformers

It is possible to estimate the location of the fault based on a study of the resonant frequencies of the winding current. It is shown that the nearest neighbourhood rule based on a clustering approach provides a good framework for fault location. Additional signal acquisition in the form of the tank current can considerably simplify the identification of a fault to ground. Experimental investigations are performed in order to identify and locate breakdown in windings.

M. Gopalakrishnan

Papers

Location of partial discharges in transformers

Identification and location of breakdown in windings