The Current Trends in Transformer Protection

A Seminar Report

Submitted by

Kinzang Wangmo

EDE2009044

Electronics and Communication Engineering

College of Science and Technology

Rinchending :: Phuentsholing

October 2012

ABSTRACT

Transformer protection is very important and essential in the

electrical power system to ensure a reliable power supply. In

the recent years, rapid changes and developments are being

witness in the transformer protection. This report presents the

current trends in transformer protection. The report also

presents there various transformer protective devices such as

thermal relay, Buchholz protection, differential protection, over-

current and distance protection, artificial intelligence, fuzzy

logic and artificial neural network. This study is particular aimed

to investigate the evolution of transformer protection and

forecast of future transformer protection.

i

ACKNOWLEDGEMENT

With immense pleasure, I take this opportunity to thank Royal University of

Bhutan (RUB) and the management, College of Science and Technology for

taking such initiative and for giving us an opportunity to present a report which

helped me to broaden the knowledge.

I wish to express my deep sense of gratitude to the Head of Institute Industrial

Relationship (IIR), Mr. Sonam Norbu for recommending the topic practically

applicable to our daily life.

I am highly indebted to Mr. Tashi, lecturer (Electronics and communication),

who had been the source of inspiration and for his timely guidance in the

conduct of the report presentation. I am extremely grateful for giving your time

in advising me and making this paper a wonderful accomplishment. Once more,

I would like to express my heartfelt thanks to each and every one for your help

and wishes for successful completion of the report.

ii

TABLE OF CONTENTS

Abstract........................................................................................................................................i

ACKNOWLEDGEMENT..........................................................................................................ii

Table of Contents.......................................................................................................................iii

LIST OF ABBREVIATIONS............................................................................................................iv

List of Figures.............................................................................................................................v

1 Introduction.......................................................................................................................1

2 Current Trends in Transformer Protection...................................................................2

2.1 Introduction..................................................................................................................2

2.2 First Protection Device.................................................................................................2

2.3 Thermal Relay..............................................................................................................3

2.4 Buchholz Protection.....................................................................................................7

2.5 Differential Protection................................................................................................11

2.6 Over-Current and Distance Protection.......................................................................14

2.7 Artificial Intelligence methods...................................................................................14

2.8 Fuzzy Logic approach................................................................................................15

2.9 Artificial Neural Network approach...........................................................................16

2.10 Summary.................................................................................................................17

3 Critical Analysis and Discussion....................................................................................18

4 Conclusion and Fucture Works.....................................................................................19

4.1 Future Works..............................................................................................................19

4.2 Conclusion..................................................................................................................19

References.................................................................................................................................21

iii

LIST OF ABBREVIATIONS

Sl. No. Terms Descriptions1 ANN Artificial Neural Network2 REF Restricted Earth fault3 CT Current transformer

LIST OF FIGURES

Figure 2. 1 First protection devices for transformer...................................................................3

Figure 2. 2. Bimetal relay, SSW, 1932.......................................................................................4

Figure 2. 3Limiitherm-relays, BIT, OERLIKON, 1950.............................................................5

Figure 2. 4Thermal models with thermostat or quicksilver remote thermometer (left) or

platinum resistance thermometer (right), alongside protective pipe...........................................6

Figure 2. 5Transformer protection RN1-CIT, Sprecher Energie, 1992......................................7

Figure 2. 6A Buchholz relays in a separated expansion tank.....................................................8

Figure 2. 7Buchholz relay, 1925...............................................................................................10

Figure 2. 8Buchholz relay, SSW, 1927.....................................................................................11

Figure 2. 9Buchholz relay, AEG, 1927.....................................................................................12

Figure 2. 10Tauber protection principle, 1934.........................................................................13

Figure 2. 11"Electronics Buchholz relay" University Hannover, Messko and SIEMENS, 1998

...................................................................................................................................................14

Figure2.12 ALSTOMtransformer, with Buchholz main tank, diverter switch and bushings...14

Figure 2. 13 Double pole differential protection with Petersen coil.........................................15

Figure 2. 14Differential protection with Scott-circuit..............................................................16

Figure 2. 15Zero sequence differential protection (REF), OERLIKON, 1954........................16

Figure 2. 16Differential relays RN1-DT, Sprecher Energie, 1992...........................................17

Figure 2. 17Simplified flow chart of the Fuzzy Logic protective relay....................................19

Figure 2. 18Application of the ANN technique to protective relaying.....................................20

1 INTRODUCTION

The increased growth of power systems both in size and complexity has brought about the

need for the fast and reliable relays to protect major equipments and to maintain system

stability. The power transformer is major and very important equipment in a power system. It

requires highly reliable protective devices to ensure a reliable power supply.

In the last few decades, there are tremendous evolutions are being witness in the transformer

protection device design and implementation. The technological leap is likely to continue for

the fourth coming years with simultaneous increase in the power rating and size of the

transformers. This leads to further revolution of the trends in transformer protection design

and analysis in the future.

Any failure of a transformer or its protective device will not only impair the system

performance but it also has a serious social impact. The reliability of transforms is major

concern to users and the manufactures for ensuring a trouble-free performance during the

service. One approach to improve the reliability of transformer for certain degree may be

improved by improving the quality and reliable transformer protective devices.

This study is aim to investigate the current trends in the transformer protection. The study also

focused on the investigation of merit and demerit of the different transformer protective

devices such as thermal relay, Buchholz projection, differential protection, over-current and

distance protection, artificial intelligence, fuzzy logic and artificial neural network.

The rest of the paper is organised as follows. Section 2 presents the current trends in

transformer protection. Section 3 discusses the critical analysis of this study. Finally, section 4

draws the conclusion and future works.

1

[2] TheCurrent Trends in Transformer Protection

1.1[2.1] Introduction

According to the patents of Karoly Zipernowski, Miksa Deri and Otto Blathy, the first

transformers were produced in 1885 by the company Ganz & Co. They were small alternating

current ring-transformers or shell-form transformers. The magnetic circuit was closed joint

less. The patentees in [1] used the word "transformer" for the first time [1].

Five years later Dolivo-Dobrowolsky invented the 3-phase-transformer. A new, improved

A.C. -system for "3-times diametric voltage" was his intention. A paper published in the

German ETZ in 1891 on "Transmission of force with alternating currents in different phases

[rotating current]" includes the first usage of the German word "Drehstrom" for "rotating

current". This paper has been translated into different languages and since then the term

“rotary currents” has been accepted. To use oil for isolation purposes was proposed by

Schwinburne in 1889 [1].

With the new century several companies started to produce high power and high voltage

transformers. Siemens - Schuckertwerke transformers with 12500 kVA (shell-form) and

Westinghouse's 100 kV are examples of leading edge transformers at this that time. With the

invention of transformers, the development of transmission grids could start. Rapidly

increasing demand for power forced this development in the 1920's. Huge transmission grids

have been connected, the amplitudes of short-circuit current reached substantial values,

several failures in windings occurred. Due to the dynamic impact of the initial symmetrical

short-circuit currents windings, arresters and bushing broke down.

The following sections will present trends in the transformer protection and its protective

devices or equipments used.

2

1.2[2.2] First Protection Device

The lack of protection devices resulted in fires and blackouts. The fuse, invented by Blathy,

O.T. (Germany) and the American Wurts in 1890 ("cell fuse") allowed fast interruption of the

short circuit. At first the fusible link was sufficient for the protection of lines, generators and

transformers. It starts operating if the current at the location of a fault was higher than the

nominal values. This works fine in case of small nominal values. With the increasing nominal

values of power this was not sufficient anymore, leading to the development of tripping

devices and relays.

The first switchgears have been "air-arm-"; mercury and tube-breakers. First oil circuit

breakers with fuses have been proposed in 1895. Brown, C.E.L., BBC, proposed in the

company’s headquarters "Porta Volta" in Milan in 1897 to put the 5kV circuit breaker directly

into an oil drum. This test was performed successfully, and so a new 16 kV breaker was built

for Paderno in the same year [1].

Kalamazoo's survey in 1901 showed the predominance of oil breakers. The first 2 kV oil-

circuit breakers (50 A) with direct release was produced in 1902 by S & H. Brown, C.E.L.,

BBC, applied in 1902 for a patent on current-dependent timing relay. The heating of the

transformer was supervised with thermal relays [6]. The first protective device for the

transformer is shown in Figure 2.1below.

3

Figure 2.1: First protection devices for transformer

1.3[2.3] Thermal Relay

To utilize transformers efficiently, short overloads have to be accepted (up to a multiple of

nominal values). To achieve this permanent supervision of the heating of the transformer is

necessary in order to avoid aging of the windings and their isolation. The German utility

OstpreuBenwerk tested thermal relays (v. Wiarda) with transformers in 1928.

In 1930 V.M.Montsinger investigated the behaviour of isolating material at higher

temperatures. He demonstrated the coherence of the aging of paper-oil isolation systems. The

rating life will be cut in half if the temperature of the asset increases with an amount of 8

Kelvin above the maximum operating temperature ("8-K-formula"). To avoid exceeding the

temperature of 115 °C in supervised substations, these devices are set up with a value of 80

°C (warning) and 90 (trip) [6].

Due to difficulties in measuring the temperature of the windings directly, a thermal model

emulates the winding temperature. This thermal relay is outside the transformer and closes a

contact at a certain level of temperature. Bimetals are used for thermal replicas of motors,

generators and transformer windings. An example is a bimetal relay produced by SSW in

1932 [1]. Figure 2.2 shows the bimetal relay.

Figure 2.2: Bimetal relay, SSW, 1932

Another example is OERLIKON's Limitherm- Relays (Type BIT, 1950) which is equipped

with a bimetal tripping device in a "thermal block". [6]. This device allows delay times

between 15 and 80 minutes. Due to safety reasons the delay time was selected smaller to

ensure that the temperature of the winding is not going to reach a critical value. The

4

calculated temperature was higher than the real one. A compensating winding considers

ambient temperature. The photographic image of the Limitherm-relay is shown in Figure 2.3.

Figure 2.3: Limiitherm-relays, BIT, OERLIKON, 1950

The thermal models could be used to protect against overload. Thermal relays are dipped into

the isolation oil and the functionality depends on the temperature of the oil. The higher the

temperature, the earlier the device will trip. Of course this takes into account the changes of

temperature of oil - at lower temperatures a higher load is possible. An advantage of these

thermal models was that it only considers the difference of temperature between winding and

oil, but not between oil and air. The thermal replica of the winding was mounted on protective

pipes that have been dipped into the oil. The thermal models are shown in the Figure 2.4.

Figure 2.4: Thermal models with thermostat or quicksilver remote thermometer (left) or

platinum resistance thermometer (right), alongside protective pipe

Measurement and supervision was the task of a thermostat, a resistive element with measuring

instrument for measurement of temperature or the quicksilver remote thermometer. The

5

thermostat was used for annunciation of an increased winding temperature. Well known are

"stick thermometers", system "Horn".

Oil-air cooling systems have been equipped with oil flow controllers that immediately detect

the failure of an oil pump. This was necessary because the rough walls of the tank do not get

even the capability to purge no-load losses for a longer time. Without a circulating pump,

these transformers had to be switched off as fast as possible. Very important stations have

been equipped with two circulating pumps for safety reasons. They have been connected in

parallel with stop valves.

A typical example for overload protection for oil transformers is the thermal relay RN1-CIT

by SPRECHER ENERGIE (1992) is shown in Figure 2.5.

Figure 2.5: Transformer protection RN1-CIT, Sprecher Energie, 1992

This device was a combination of staticalstatically over current protection with immediate

tripping and thermal overload. The part "T" contains a special circuit that models warming

and cooling of the transformer using the voltage proportional to the current. It contains two

delay times which could be set up in such a manner that the behaviour of the transformer

could be modelled. Now the transformer was safely protected against overheating. The short

time delay (5 min) was for high over currents; the longer one for small over currents

(temperature of oil). The nominal currents of the current transformers had to be adapted to the

nominal current of the transformer. This device could be used in small stations without

batteries as well. It could be supplied by AC with its tripping capacitor and trip with the

measurement transformer current. Mechanical bi-stable indicators showed the indication even

in the case of loss of power supply.

6

1.4[2.4] Buchholz Protection

Using oil for transformer isolation was an important milestone in the development of

transformers. Implementing expansion tanks (1910) decreases the aging of transformer oil.

These devices were at first mounted on the walls and later above the tank. Changes of volume

in case of change of load or change of temperature could be adjusted.

Since it was possible to adapt the over current protection to local needs, there still remains the

disadvantage that at the fault location the current has to be bigger than the nominal current of

the apparatus. Additionally, for selectivity reasons, the time delay was very long near the

source and in some complicated cases the system was not usable. Over-current protection was

only used for assets, where the impact of electric arcs was limited, for instance at transmission

lines. This is different for transformers. The material selected is not robust and the value of

the asset is very high. If a transformer is separated from the grid in case of a thunderstorm, it

does not show on the outside if it is damaged or not. Until the 1920's it was the decision of the

operator whether to switch the asset on after a failure. This was more a decision depending on

the character of the operator and less on his knowledge. If he was a careful guy, he would take

the transformer out of service and start opening and disassembling it. After two or three days

he would learn that the transformer is OK or damaged. This wastes a lot of time if the

transformer was without damage. Some brave engineers decided to switch on the transformer

without approval - it could happen that the transformer explodes. A typical installation of

Buchholz relay in a separate expansion tank is shown in Figure 2.6.

Figure 2.6: A Buchholz relays in a separated expansion tank.

7

Max Buchholz, while working in the Elektrizitatsamt Kassel (Germany) later, Preussische

Kraftwerke AG examined transformer damages. He figured out that the big heat of the arc

destroys insulation material and delivers gas. What to do with this important, but rudimental

awareness was probably unclear to Buchholz at this time. Some say that an experience in the

bath tub was helpful for him. He performed the first experiments in his son's aquarium.

The idea was to lead the gas bubbles under the transformer cover to an appropriate place.

There the quality and quantity of the gas can be estimated. After a lot of trials he found the

solution. The gas could be collected with a light inclination of the cover. A disposed pipe

should lead the gas to the expansion tank. Here its colour could be observed. In case of an

explosion the huge amount of gas produces a blast wave. Colour and Quantity of the gas

could be estimated outside the expansion tank, it could be checked if it is flammable or not.

This was sufficient to decide what happened in the transformer. Buchholz received his first

patent in 1921(DRP 386629) and his name is the name of the device until today. [1].

The Buchholz protection is the first device that does not detect the difference of a current,

voltage or power from a certain level - this device uses mechanical action. Now the changes

in the quality of oil could be detected easily and very early. The Buchholz relay was produced

in 3 varieties (1, 2 and 3 inches). This was a possibility to diversify the price according to the

size of the transformer. Following figures are Buchholz relays made in the 1920's. The

different types of the Buchholz relays used in 1920’s are shown in Figure 2.7, Figure 2.8, and

Figure 2.9.

Figure 2.7: Buchholz relay, 1925.

8

Figure 2.8: Buchholz relay, SSW, 1927.

Figure 2.9: Buchholz relay, AEG, 1927.

In the mid 20's the lower floater was realized in such a manner that even in case of strong

flow the floater moves the connected contact. Experience had shown that in case of serious

failures, the time from creation of the gas bubbles until reaching the relay was too long to

limit the danger of destroying the transformer. In the mid 30's the lower floater was connected

to a flow flap to achieve a higher sensitivity on flow. Tests performed by AEG with the

BEWAG (Berlin) showed that the start-up speed was 100 cm/s. After 1945 Buchholz relays

with small height have been developed and standardized in DIN 42566 in 1961 [2].

In 1934 Konrad Tauber proposed to implement a throttle control in the pipe between the tank

and the expansion tank. If the temperature of the gas increases, the increase of pressure could

be measured and a warning or tripping provided. A simple principle of the Tauber protection

is shown in Figure 2.10Fig. below. This differential pressure measuring device measured the

9

dynamic pressure (due to flow of oil) and the static pressure (due to oil on the installation

location).

Figure 2.10: Tauber protection principle, 1934.

This differential pressure measuring device measured the dynamic pressure (due to flow of

oil) and the static pressure (due to oil on the installation location).

[1.] 1 .Measuring Orifice

[2.] 2. Pressure Chamber

[3.] 3. Differential Pressure

After false tripping of the Buchholz relay during earth tremors or start of oil circulating

pumps, several further developments started. Aigner (Germany) reported a new development

in 1960’s- a shock-proof Buchholz device (up to 1 g). Reliability discussions in the 1960's

proposed redundant Buchholz relays (in series). Failures above the transformer cap should be

detected by fast differential protection. At the Hannover Fair 1998 an "electronic Buchholz

protection" was presented by the University of Hannover, Messko and SIEMENS which is

shown in Figure 2.11. Huge transformers are equipped with further Buchholz relays, e.g. for

bushings. [3] which is shown in Figure 2.12.

10

Figure 2.11: "Electronics Buchholz relay" University Hannover, Messko and SIEMENS, 1998

Figure 2.12: ALSTOM transformer, with Buchholz main tank, diverter switch and bushings.

11

1.5[2.5] Differential Protection

Petersen coils have been used for zero sequence current compensation since 1930. The double

pole differential protection with the Petersen coil is shown in Figure 2.13.

Figure 2.13: Double pole differential protection with Petersen coil.

The special case of a differential protection of a Scott-circuit transformer is shown in Figure

2.14.Figure below

Figure 2.14: Differential protection with Scott-circuit.

12

Residual current elimination during the grounding of the transformer's star point was realized

with interposing transformers with delta windings or with a filter in numerical relays. The

disadvantage of this solution was a reduced sensitivity for single phase short circuit current by

a value of 2/3. Transformer failures are more critical because the start up value decrease is not

linear as shown in Figure 2.15the figure below.

Figure 2.15: Zero sequence differential protection (REF), OERLIKON, 1954.

A solution for this issue was the Restricted Earth fault Protection (REF) that allows a more

sensitive setup. In English speaking countries the high-impedance principle for measurement

is quite popular. This is not valid for the German speaking countries where REF and low-

impedance principle do not play a major role. One of the reasons is the use of Petersen coils

in the neutral-point connection in the grids with voltages less than 110 kV. Due to this, the

unbalanced residual current is quite small. In 1992 SPRECHER Energie developed a static

differential relay RN1-DT shown in Figure 2.16 (Fig. 16) that allows usage without

interposing transformers for adaptation of transformers ratio and vector group (except for

YNyn0 and YNyn6 solid earthed). [6].

13

Figure 2.16: Differential relays RN1-DT, Sprecher Energie, 1992.

1.6[2.6] Over-Current and Distance Protection

Over current and later more and more distance protection is used as a backup protection for

the Buchholz and the differential protection, as a bus-bar protection or as a backup protection

of a line protection on the lower and higher voltage winding. In 1934 Walter, M., AEG,

proposed to extend the over current protection with a high-current stage and created a fast

backup protection for a big part of the transformer. This is also possible with a distance

protection on the higher-voltage winding.

In several countries distance protection with raised tripping time is also used to utilize a

busbar protection in transformer feeders. This is a fast backup protection for faults on the line

as well. Magyar Troszt Budapest (Hungary) developed in 1974 a stand-alone backup

protection AZT. This over current protection was located directly on the transformer – that is

why the connecting wires are very short. Redundancy was guaranteed as far as possible by

connecting to the measuring core of the current transformer and to a second coil of the circuit

breaker. The power supply of the relay and the tripping was realized with the higher-voltage

current transformer using energy stored in a capacitor. The operating time was dependent on

the pre-load and the type of failure. [6].

1.7[2.7] Artificial Intelligence methods

Regardless of their digital implementation, numerical relays basically emulate their analog

predecessors: they extract specified features of the signals such as magnitudes, active/reactive

powers, impedance components, and compare the signals with appropriate pre-set or

14

adaptable thresholds. Based on such comparisons they generate the tripping signal. The task

of protective relaying is, however, to distinguish between internal faults and other conditions

(pattern recognition), and consequently, to initiate or deny tripping (decision making). This

brings the application of Artificial Intelligence methods as an alternative or improvement to

the existing protective relaying functions.

1.8[2.8] Fuzzy Logic approach

The multi-criteria differential relay is a good example of the fuzzy logic approach to

protective relaying which is shown in Figure 2.17.

Figure 2.17: Simplified flow chart of the Fuzzy Logic protective relay.

In this technique, Criteria signals such as amplitudes, harmonic contents, etc. are fuzzified in

order to account for dynamic errors of the measuring algorithms. Thus, instead of real

numbers, the signals are represented by fuzzy numbers. Since the fuzzification process

provides a special kind of flexible filtering, faster measuring algorithms that speed up the

operation of protective relays may be used.

15

The thresholds for the criteria signals are also represented by fuzzy numbers to account for

the lack of precision in dividing the space of the criteria signal between the tripping and

blocking regions.

The fuzzy signals are compared with the fuzzy settings. The comparison result is a fuzzy

logic variable between the Boolean absolute levels of truth and false.

Several relaying criteria are used in parallel. The criteria are aggregated by means of formal

multi-criteria decision-making algorithms that allow the criteria to be assigned a weight

according to the reasoning ability.

The tripping decision depends on the multi-criteria evaluation of the status of a protected

element (sound vs. faulty). Additional decision factors may include the amount of available

information, or the expected costs of relay mis-operation.

This relaying frame may be self-organizing, i.e. it may be automatically tuned prior to its

installation using a large number of training cases, therefore resembling the Artificial Neural

Network (ANN) based approach. The prior tuning results in an algorithm that is simple and

traceable [4].

1.9[2.9] Artificial Neural Network approach

Since ANNs can provide excellent pattern recognition, they are proposed by many researchers

for implementation of power transformer relaying. The common application of the ANN

technique to power transformer protection is shown in Figure 2.18.

Figure 2.18: Application of the ANN technique to protective relaying.

16

The ANN is fed by all the currents either in the phase, or in the differential-restraining

coordinates. The sliding data widow, consisting of the recent and a few historical samples of

the signals, is fed to the ANN.

The output from the ANN encodes the tripping decision.

The training patterns exposed to the ANN cover usually inrush conditions, internal

and external faults. Only the selected data window positions are typically used for

training.

Additional pre- and post-processing may be applied. The ANN approach can also be

of either a global type or phenomena specific type. In the first case, the net is trained

to differentiate internal faults from all the other phenomena. In the second case, it is

trained to distinguish between internal faults and a specific non-internal fault pattern

(inrush, for example). Also, the ANNs are proposed for certain auxiliary functions

such as reconstruction of the secondary current waveforms distorted by saturation of

the CTs. The ANN based relays for power transformer show promising security and

dependability. [5].

1.10[2.10] Summary

The first transformer was produced in 1885 by the company Ganz and co. With the new

century several companies started to produce high power and high voltage transformers. With

the invention of transformers, the development of transmission grids could start. The huge

transmission grids have been connected; the amplitude of the short circuit current reached

substantial value, several failures in the winding occurred. These leads to the development of

transformer protection, and the first transformer protection device was a fuse invented by

Blathy in 1890. The fuse was able to protect only up to certain rated voltage and to overcome

the drawbacks of the fuse thermal, Buchholz relay, differential and over-current protection

relays were developed. Till now we have been using this relays for the protection of

transformers but due to advance in science and technology there is also a relay called

Artificial Neural Network which is more advance than the existing relays. Many researchers

are doing research on this relay.

The section will discuss the critical analysis and evaluation of this study and present depth

discussion and analysis.

17

2[3] CRITICAL ANALYSIS AND DISCUSSION

The power transformer is an essential component in the electrical power system. It is very

expensive and critical too. To have a reliable power supply for the customers’ one important

component is to have a better transformer protection system. There are different kinds of

transformer protections used nowadays.

By writing seminar on this topic “Current Trends in Transformer Protection”, I came to know

how the transformer protection came to exist. Till now I learned only the circuit diagrams and

the operations of the different types of transformer protections. But, I never realized that who

had invented the first transformer protection device. After writing this report, I came to know

the persons; they were Karoly Zipernowski, Miksa Deri and Otto Blath in the year 1885.

With the advance of science and technology the protection equipments keep on changed. The

first equipment to protect the transformer protection for the low rating was a fuse but fuse

didn’t work with the high ratings and to protect the high rating another protection schemes

like differential relays and Buchholz’s relays were introduced.

In Bhutan most of the protection scheme used is the Buchholz protection and of course fuse

for the low ratings. While writing this report, I also learned the history of Buchholz’s relay

and why it is known as Buchholz’s relay. Max Buchholz was the first person to introduce the

Buchholz relay and the protection relay was named as Buchholz’s relay. For future protective

scheme researchers are doing search on Artificial Neural Network approach which is far

better than the present protective schemes.

By doing seminar this, I could able to trace the current trends in the transformer protection.

There are lots of research project and works are undergoing on same topic. One day I also

would like to take opportunity to do research studies under same topic and will explore more

on software base transformer protection.

18

3[4] CONCLUSION AND FUCTURE WORKS

In 1885 the first transformer was developed. After development of transformer many

companies started to produce high power grids. While transmitting the power they faced lots

of problems like broken of arrester and bushings of the transformer. So to protect the

transformer for the reliable supply of power, protective devices were developed. Fuse was a

first protective device invented by Blathy. It couldn’t apply to a high rated power, so other

protective devices like thermal relay, Buchholz’s relay, differential relay and overcurrent and

distance relays were developed. It took so many years to develop a better transformer

protective device. With advance in technology now there is better relay than the existing ones.

Artificial Neural Network is one of the relay which is better and more sensitive than the other

relays. Many researchers are doing research on this relay and I hope after few years we would

able to see and learn more on this relay.

Future works related to these topics are as follows.

1. Optical CTs and other sensors

2. Intelligent transformer substation

3. To investigate software base transformer protection.

19

REFERENCES

[1] G. Walter Schossig, "Buchholz protection and relays for supervision oil," © PAC World , 14

March 2009. [Online]. Available:

http://www.pacw.org/no-cache/.../history/protection_history/.../print.html.

[2] B. k. a. M. kezunovic, "Improved power transformer protection using numerical relays," Texas A&M University, USA, [Online]. Available: http://www.elistas.net/cgi-bin/eGruposDMime.cgi?...qjd.

[3] B. a. D. N. Vishwakarma, Power system protection and switchgear, 7 West patel Nagar,New Delhi: Tata McGraw Hill, 2005.

[4] s. E. S. IEEE, "Intelligent Transformer substation in Modern Medium voltage," Siemens AG, Germany, 2011. [Online]. Available: http://www.ieeetmc.net/r9/el_salvador/concapan/descargas/memoria...11/.../P92.p....

[5] "Smart Grid," Siemens internet Website, 10 June 2010. [Online]. Available: http://www.energy.siemens.com/hq/en/energy-topics/smard-grid/,.

[6] W. schossi, "12"Electronic Buchholz relay"-PAC world magazine," PAC, 2009. [Online]. Available: http://www.pacw.org/fileadmin/doc/WinterIssue09/history_winter09.pdf.

[7] Edison, "The History of the transformer, the Edison Tech centre," [Online]. Available: http://www.edisontechcentre.

20