Projects:2015s1-11 Estimation of Transformer Parameters

Aims & Motivations

The transformer is an essential component in the electrical world, especially in a power systems network. Currently, available transformer models do not accurately portray the actual behaviour of the transformer, due to the non-linearity of the transformer at higher frequencies. Although there are several models that have been developed for modelling the transformers, most of these models neglect the existence of non-linearity phenomenon [1].

Thus, current approximations have plenty of room for improvement in terms of accuracy. A non-linear model does not accurately plot the behaviour of a transformer, as the equivalent transformer exhibits non-linear behaviours such as generation harmonics, saturation and other conditions. Developing a model which will accurately showcase the behaviour of the transformer, minimising the difference between the estimated and exact transformer parameters is the primary motivation for this project.

Additionally, determining the limits of applicability of the linear model will be a major focus of this project. By driving the transformer into the non-linear region and observing its behaviour, it is possible to determine how well the developed model copes with non-linearity and to what extent is it able to do so. By driving the transformer to its extremes, the team will be able to work out the power loss model for the transformer. Doing so, will bring aid in getting the complete transformer model.

Outline of Main Tasks

To achieve the above stated objectives, the project has been modularised into 3 major components – Power source, Sensors, and Analysis.

1) Power source – Using the available power source in the school labs, a power amplifier will be built to take that power source and amplify it to a reasonable amount which will allow the team to gather measurements from the transformer. A filter connected to the output of the power source may be necessary, but that will be the secondary objective of this module.

2) Sensors – To accurately measure the incoming and outgoing currents, which will be relatively small, Instrumentation amplifiers will be built to determine the current.

3) Getting measurements - 2 loading conditions are used which are open circuit and short circuit measurements at 2 different frequencies. These data are stored using a systematic approach.

4) Analysis – Once measurements have been taken, the limits of applicability of the linear model and the exploration into the non-linear characteristics of the transformer can be analysed using special techniques such as Least Squared Spectral Analysis. At the end of the analysis, a set of complete estimated transmission parameters are obtained to be used in the calculation of 7 transformer parameters.

Significance

This project is of great significance as there are many high frequency electrical appliances and devices that are regarded to be non-linear loads in the industry. This phenomenon leads to harmonic pollution which may cause the reduction of life span of the transformer [2]. Therefore, the study and analysis of non-linear load loss transformer is significant to the electrical world to encounter that problem. Furthermore, standard tests which give the linear approximation are unable to show the behaviour of the transformer at saturation point and can cause significant errors when estimating the non-linear behaviour of the transformer [3]. This is why an analytical and accurate method is needed to develop the non-linear model which gives better estimation.

Amplifier

An isolation transformer is used as it allows an AC signal or power to be taken from one device and fed into another without electrically connecting the two circuits. Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass.

Isolation transformer also block interference caused by ground loops. Isolation transformers with electrostatic shields are used for low power supplies for sensitive equipment such as computers or laboratories.

File:Amplifier.jpg

Sensors - Instrumentation Amplifier

The measuring devices that are used in measuring voltage and current at primary and secondary terminal is the instrumentation amplifier. Instrumentation Amplifier is a Differential Amplifier which means it measures the voltage difference across the two inputs. Measuring voltage is straightforward which is just across the transformer terminals. However to measure current accurately without getting noise, a known resistor is used. The Instrumentation Amplifier measures the voltage across the resistor, and Ohm's Law is used to calculate the current. For this project, a 332ohms resistor with 0.1% tolerance was used.

Shielded Box

The Instrumentation Amplifier needs to be shielded to reduce ingress of noise. Unshielded sensors and power amplifiers will cause the measurements to pick up signals and noises from the surrounding.

Team

Group Members

1) Kartthikeyen Sivananthan

2) Matthew Harding

3) Nurliyana Khazali

4) Adib Rashidin

Supervisors

1) Dr. Andrew Allison

2) Dr. Rastko Zivanovic

Workplace

Bench 19 of EEE Projects Lab, University of Adelaide

Future Work

1) Develop a Non-Linear Model

2) increase the output of the Power Amplifier

3) Add fuses to the Power Amplifier and Instrumentation Amplifier

4) Improvise the automation process to become faster.

References

[1] JD Greene, C.A Gross, “Non-linear modelling of transformers” IEEE Transactions on Industry Applications, Vol. 24, No.3, May/June 1988.

[2] Pan Chao et al, “Analysis Based on Improved Method for Transformer Harmonic Losses”, in 2012 Int. Conf. on Future Energy, Environment, and Materials, 2012, Energy Procedia.

[3] S. Bogarra et al, “Parameter Estimation of a Transformer with Saturation Using Inrush Measurements”, in Electrical Power Systems Research, 2008 © 2008 Elsevier B. V.