Transformer protection (report submit)

PROTECTION OF DISTRIBUTION TRANSFORMER USING MICROCONTROLLER A PROJECT REPORT Submitted by

SHAH BHARGAV YOGESHKUMAR (100374109101) PATEL SHAHIL RASHID

(110373109005)

SAVANI SANDIP JITUBHAI

(110373109006)

MEHTA AAKASH NAVINKUMAR

(110373109007)

In partial fulfillment of the award of the degree Of

BACHELOR OF ENGINEERING In ELECTRICAL ENGINEERING

PARUL INSTITUTE OF ENG. & TECH, P.O. LIMDA WAGHODIA, VADODARA

GUJARAT TECHNOLOGICAL UNIVERSI TY, AHMEDABAD DECEMBER – 2013 Page 1

PARUL INSTITUTE OF ENG. & TECHONLOGY ELECTRICAL ENGINEERING 2013

CERTIFICATE DATE:This is to certify that the dissertation entitled “PROTECTION OF DISTRIBUTION TRANSFORMER USING MICROCONTROLLER” has been carried out by SHAH BHARGAV YOGESHKUMAR (100374109101), PATEL SHAHIL RASHID (110373109005), SAVANI SANDIP JITUBHAI (110373109006), MEHTA AAKASH NAVINKUMAR (110373109007) under my guidance in partial fulfilment of the degree of Bachelor of Engineering in Electrical (7 th semester) of Gujarat Technological University , Ahmedabad during the academic year 2013-2014.

Guide: (INTERNAL) M/s Sweta Chauhan Assistant professor, P.I.E.T

(EXTERNAL) Chiragbhai Parmar Sr. Engineer Jayesh Electricals LTD.

Head of the department

Mrs. Falguni Bhavsar

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ACKNOWLEDGEMENT

We have great pleasure in presenting this group on “PROTECTION OF DISTRIBUTION TRANSFORMER USING MICROCONTROLLER” during our engineering project. We were bound to rely on the assistance to other persons. In our case many respected individual made contribution and we would like to hear by acknowledge their help for their valuable assistance in providing suggestions, constant guidance during the completion of our project.

We are also deeply obliged to M/s. SWETA CHAUHAN our internal guide, Mr. CHIRAG PARMAR our external guide and Mrs FALGUNI BHAVSAR (HOD electrical department Parul institute of engg. & tech.) for their competent guidance and encouragement.

We are also thankful to each and every professor and other staff members of our department who have been constant source of guidance, support and cooperation in the various related fields of our project directly or indirectly.

Last but not least we whole heartedly wish to thank to all the people, friends who gave us an unending support right from the beginning of project.

Name of students: SHAH BHARGAV YOGESHKUMAR

(100374109101)

PATEL SHAHIL RASHID

(110373109005)

SAVANI SANDIP JITUBHAI

(110373109006)

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MEHTA AAKASH NAVINKUMAR

(110373109007)

ABSTRACT

T h e a i m o f t h e p ro j e c t w o r k i s t o p ro t e c t t h e d i s t r i b u t i o n t r a n s f o r m e r o r a n y ot h e r p o w e r t r a n s f o r m e r, b u r n i n g d u e t o t h e o v e r l o a d a n d o v e r t e m p e r a t u re . N o r m a l l y m o s t o f t h e t r a n s f o r m e r s a re b u r n i n g b e c a u s e o f t h e s e re a s o n s ; h e n c e b y i n c o r p o r a t i n g t h i s t y p e o f m o n i t o r i n g a n d c o n t ro l c i rc u i t s , l i f e o f t h e t r a n s f o r m e r c a n b e i n c re a s e d . T h i s p ro j e c t i s u s e d f o r m u l t i - p u r p o s e l i k e p ro t e c t i o n , d a t a re c o rd i n g a n d a u t o re c l o s i n g o f t h e d i s t r i b u t i o n t r a n s f o r m e r f ro m o v e r l o a d . Th e e l e c t r i c a l p a r a m e t e r s l i k e l o a d c u r re n t o f t h e t r a n s f o r m e r s a re f e d a s b a s e v a l u e s , u s i n g a k e y p a d t o t h e P e r i p h e r a l I n t e r f a c e C o n t ro l l e r a n d t h e o u t p u t s i g n a l i s p ro v i d e d t o o p e r a t e a re l a y b y c o m p a r i n g t h e b a s e v a l u e s w i t h t h e o p e r a t i n g t h i s p a r a m e t e r s . T h e a p p l i c a t i o n c o n s i s t s o f a b o a rd o f e l e c t ro n i c c o m p o n e n t s i n c l u s i v e of a m i c ro c o n t ro l l e r w i t h p ro g r a m m a b l e logic.

It has been designed to work w i t h hi g h a c c u r a c y a n d s p e e d .

T h u s t h i s p ro j e c t i s v e r y a d v a n t a g e o u s f o r m a i nt e n a n c e department due to time saving as well as transformer m a n u f a c t u re r s f o r d e c i d e d w a r r a n t y p o l i c y f o r c u s t o m e r s t o serve better service.

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LIST OF TABLES

Table No

Table Description

Page No

4.1

Voltage signal from m/c or PC ………………………………25

4.2

ADC 0809 Channel Selection……………….………… 28

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LIST OF FIGURES Figure No

Fig Description

Page No

2.1

Graph for efficiency Vs load comparison …………………12

2.2

Graph for losses Vs load…………………….……………...14

4.1

Power supply block…………………….………………..…20

4.2

Step down transformer……………………………………...20

4.3

Diode symbol and device package………………………21

4.4

The pin out of 7805 IC………………………………..…….21

4.5

Basic principle of capacitor……………………….…….….22

4.6

Construction view of POT ………………………………..22

4.7

POT symbol………………………………………………....22

4.8

arrangement of all equipment for variable power supply.…23

4.9

Voltage regulator for 5 volt………………………….……...23

4.10

Contactor...…………………………………………..……...24

4.11

Relay internal connection…………………………………...25

4.12

LCD display……………………………………….….……..26

4.13

Keypad……………………………………………………...26

4.14

Pin out configuration of ADC 0809………….……….…….27

4.15

Block diagram of 0809……………………………………...28

4.16

Block diagram for NXP µc…………………………………29

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4.17

Entire pin out DIP package of P89v51RD2………..………..30LIST

OF SYMBOLS AND ABBREVIATIONS Symbol Name

Abbreviations

DT

Distribution Transformer

OL

Over Load

A.C

Alternating Current Supply

D.C

Direct Current Supply

RMS

Root Mean Square

LCD

Liquid Crystal Display

NO

Normally Open

NC

Normally Close

COM

Common

TOC

Total Owing Cost

µCU

Micro-controller Unit

ADC

Analog to Digital Converter

CT

Current Transformer

kVA

Kilovolt Ampere

KW

Kilo-Watts

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TABLE OF CONTENTS

Acknowledgement………………………………………..iv Abstract……………………………………………………v List of Figures……………………………………………..vi List of Tables……………………………………………. vii List of Abbreviations……………………………………...viii Table of Contents……………………………………….... ix Chapter: 1

Introduction……………………………………………… 01

Chapter: 2

Effects of distribution transformer………………………..11 2.1 How dose temrature affect the life of transformer……11 2.2 lower temperature rise means increase overload capability …………………………………....11 2.3 Desigining a transformer with lower temp. rise……….11 2.4 High efficiency and conditioned spaces ………………12 2.5 Transformer life cycle cost…………………………….12 2.6 How to calculate Transformer life cycle cost……….....12 2.7 Benefits of using Transformer life cycle cost …………13 2.8 What is premium efficiency transformer worth cost ….13 2.9 Transformer life vs insulation life……………………..10 2.10 Overloading limitation………………………………..11 2.11 Advantage of numerical relay……………………….17 2.12 Different types of relay characteristics……………….18 Page 8

Chapter: 3

Transformer Overloading guideline ………..……….19

Chapter: 4

Hardware specification…………………………………20 4.1 Power supply block diagram……………………….20 4.2 contactor……………………………………………24 4.3 Relay………………………………………………..24 4.4 LCD display………………………………………...25 4.5 Keypad…………………………….…………….….26 4.6 ADC IC 0809………………………….…………..28 4.7 microcontroller unit…………………………….….29

Chapter:5

Applications…………………………………….………..32

Chapter: 6

Conclusion…………………………………….…………33 Future Work……………………………………………..34 References………………………………………………35

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CHAPTER 1:- INTRODUCTION The Project Entitled “POWER TRANSFORMER PROTECTION USING MICROCONTROLLER-BASED RELAY� designed with Peripheral Interface Controller.

Utility companies have enormous amounts of money invested in power transformers and neglect distribution transformers, due to its low rating. But statically analysis says that more than 80% fault is occurred at distribution side. As we know Operating, maintaining, and inspecting all distribution transformers are not an easy work. In order to reduce burden on maintenance of such transformers a new idea has been discovered.

This project will consists of a P89V51RD2 Microcontroller programmed to monitor the load curve and take necessary action to control the overload condition under pre-defined limits. Load current will be sensed by CT then ADC converts analogue to digital thus obtained data will be processed and compared to set limit value. In case limit crosses the set value relay trip the contactor. After set duration auto-reclosing starts in our project its maximum 3 times can be done.

This project is used for multi-purpose like protection, data recording and auto reclosing of the distribution transformer from overload. The electrical parameters like load current of the transformers are fed as base values, using a keypad to the Peripheral Interface Controller and the output signal is provided to operate a relay by comparing the base values with the operating this parameters. The application consists of a board of electronic components inclusive of a microcontroller with programmable logic. It has been designed to work with high accuracy and speed.

This module is consists of microcontroller which requires external ADC and digital input/output pins, transistors and relays for load control and LCD display for user intimation.

Microcontroller has been programmed in C language with KEIL and same has been used for burning the HEX file in flash memory.

Thus this project is very advantageous for maintenance department due to time saving as well as transformer manufacturers for decided warranty policy for customers to serve better service.

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CHAPTER 2:- EFFECTS OF OVERLOAD ON DISTRIBTUION TRANSFORMER 

2 . 1 H o w D o e s Te mp e r a t u re Af f e c t t h e L i f e of a Tr a n s f o r me r ?

Temperature is one of the prime factors that affect a transformer's life. In fact, increased temperature is the major cause of reduced transformer life. Further, the cause of most transformer failures is a breakdown of the insulation system, so anything that adversely affects the insulating properties inside the transformer reduces transformer life.

Such things as overloading the transformer, moisture in the transformer, poor quality oil or insulating paper, and extreme temperatures affect the insulating properties of the transformer. Most transformers are designed to operate for a minimum of 20-30 years at the nameplate load, if properly sized, installed and maintained. Transformers loaded above the nameplate rating over an extended period of time may have reduced life expectancy. 

2 . 2 L o w e r Te mp e r a t u re R i s e M e a n s I n c re a s e d O v e r l o a d C a p a b i l i t y.

A lower-temperature-rise transformer results in a transformer with higher overload capability. For example, an 80C rise dry-type unit using 220C insulation has 70C reserve capacity compared to a 150C unit. This allows the 80C unit to operate with an overload capability of 15-30% without affecting the transformer life expectancy. Also, a cooler running transformer means a more reliable unit and more up-time. 

2 . 3 D e s i g n i n g a Tr a n s f o r me r w i t h L o w e r Te mp e r a t u re Rise

Transformers with lower temperature rise often use windings with lower resistance.

The low resistance per unit length of copper allows lower temperature rise transformers to be built without unnecessarily building a bigger transformer. For example, an aluminiumwound transformer coil requires conductors with approximately 66 per cent more crosssectional area than a copper-wound transformer coil to obtain the same current carrying capacity. 

2 . 4 H i g h E f f i c i e n cy a n d C on d i t i o n e d Sp a c e s

High-efficiency, low-temperature-rise (80C rise dry-type or 55 C liquid-filled) transformers are frequently found in confined spaces, like inside electrical rooms, underground vaults, and air-conditioned spaces in buildings. High efficiency means less waste heat generated thus lower ventilation and air-conditioning requirements. Selecting such a transformer, properly sized to the load requirements, assures greatest efficiency, longer life and increased overload capability.

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Fig. 2.1 Graph for efficiency vs. load comparison ďƒ˜

2 . 5 Tr a n s f o r me r L i f e - Cy c l e C o s t ( To t a l O w n i n g C o s t )

Transformers typically can be expected to operate 20-30 years or more, so buying a unit based only initial cost is uneconomical and foolish. Transformer life-cycle cost (also called "total owning cost") takes into account not only the initial transformer cost but also the cost to operate and maintain the transformer over its life. This requires that the total owning cost (TOC) be calculated over the life span of the transformer. With this method, it is now possible to calculate the real economic choice between competing models. (This same method can be used to calculate the most economical total owning cost of any longlived device and to compare competing models on the same basis.) The TOC method not only includes the value of purchase price and future losses but also allows the user to adjust for tax rates cost of borrowing money, different energy rates, etc.

A basic version of the TOC formula would look like this: TOC = Initial Cost of Transformer + Cost of the Load Losses + Cost of the Load Losses.

Since the formula includes the cost of losses, which will occur in the future, it is necessary to discount these future costs to equate them to present-day dollars (your company comptroller may be of assistance here). The transformer manufacturer supplies the bid price. If the A and B values are known, then the manufacturers should base the bid prices on the same A and B factors in all cases. The cost of Rated Load and over load losses are calculated using the following formulas: Cost of Rated load Losses = A x (Rated Load Losses) Cost of Over Load Losses = B x ( Over Load Losses) ďƒ˜

2 . 6 H o w t o C a l c u l at e Tr a n s f o r me r L i f e - Cy c l e C o s t

The A and B factors as described in an article titled, "Introduction to Transformer Losses," (elsewhere on this CD-ROM) has been determined on the basis of equivalent first cost and need no further manipulation. This has the benefit of allowing the manufacturer to design the transformer to meet the A and B factors specified by the customer. Rated Load losses are constant for each transformer design, being dependent on the core steel characteristics and design. Load losses, on the other hand, are variable and directly proportional to the load on the transformer, typically being stated at the full-rated nameplate loading.

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If the A and B values are not known, as is typical of smaller users, merely use the load loss and Rated Load loss in watts, multiplying each by the relevant hours and cost per kWh. (The case history of Herman Miller Company uses this method.)

2 . 7 B e n e f i t s of ( To t a l Owning Cost) ďƒ˜

U s i n g Tr a n s f o r me r L i f e - Cy c l e C o s t

Life-cycle cost (or total owning cost) analysis is a method that encompasses not only the initial purchase price but also the comparative operating costs of competing models, equalized to present-day dollars.

Since the operating cost of a transformer over its life may be many times its initial price, the only fair comparison with competing models must take operating costs into account.

Another benefit to owning a transformer with low life-cycle cost, results from the fact that it runs cooler Loss in the form of heat reduces the life of a transformer by causing damage to the insulation over time. It can also cause transformers to fail. Consequently, a transformer with lower life-cycle cost would be expected to have a longer life and lower failure rate, as well as lower losses. A transformer with lower losses (both core and coil) reduces the amount of power generation needed to accommodate the losses. This in turn reduces the emission of greenhouse gases, i.e. carbon dioxide (CO2), produced by fossil fuel generators.

2 . 8 W h y I s a P re mi u m- E f f i c i e n cy Tr a n s f o r me r Wo r t h the Cost? ďƒ˜

A premium-efficiency transformer costs more initially, but saves sufficient money over time to more than pay back the extra purchase cost. Pay a little more up front for a premium transformer and save money over the life of the unit, or save a few dollars on a low-first-cost standard-efficiency transformer and continue to spend more money on wasted electric power for 20-30 years. Premium-efficiency transformers have cores made of low-loss silicon steel with copper windings or amorphous steel with copper windings.

Copper windings have lower resistance per cross-sectional area than aluminium windings.

Thus, copper windings require smaller cores that produce lower Rated Load losses and offer greater reliability.

The transformer manufacturers have reduced the Rated Load losses of silicon steel transformers by over 60 percentages in the last 30 years. They have accomplished this reduction in four ways: (1) They have improved the construction of the silicon steel, itself; (2) They have improved the cutting of the laminations.

(3) They have improved the stacking or assembling of the laminations in the core of the transformer.

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(4) And finally, by using improved computer models of the Rated Load losses, they can better design the core to reduce Rated Load losses.

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Premium-efficiency transformers with cores made of amorphous steel with copper windings have even lower Rated Load losses than silicon steel transformers. Transformers with amorphous steel in their cores Manufacturers also reduce core losses by using thinner laminations in the core and by using step-lapped joints.

Rather than butting the laminations joints, they interleave laminations and increase the amount of steel that bridges the joint gap. This reduces the resistance between the laminations and thus reduces eddy current losses.

Example 1: Life-Cycle Cost Comparison of Two 75-kVA Transformers Using A and B Values (rated load VS overload) An example of the TOC of a more efficient (rated load) 75 kVA transformer to less efficient (overload) 75 kVA at 100% loading provided illustrates the lower TOC of the more-efficient copper-wound transformer: In this example, the A value is assumed to be $1.50 per watt, and the B value is $0.35 per kWh. TOC = Initial cost of transformer + Cost of the rated-load Losses + Cost of the over load Losses TOC of more efficient due to rated load = $2,064 + ($1.50/watt)(320 watts) + ($0.35)(1670 watts) = $3,128.502 Electrical: Energy Efficiency - Transformer Life Cycle Cost TOC of less efficient due to overload (125%over load) = $1,979 + ($1.50/watt)(350 watts) + ($0.35)(1874) = $3,159.90 In this example, the more efficient transformer costs $85 more initially, but has 30 watts less core loss, and 204 watts lower coil loss, so the total owning cost of the more efficient unit is less than the cheaper first-cost unit. Thus the transformer cost is increase due to overload condition. So accordingly this calculation breakeven point is 15 years of transformer life.

As we seen below graph losses increase due to overload so the efficiency is decrease.

Fig.2.2 Graph for Losses vs Load Page 15



2 . 9 Tr a n s f o r me r L i f e v s . I n s u l a t i o n L i f e

If an end-point of insulation life is to be defined, it must be done in terms of some measurable physical characteristic properties. This could be mechanical (RTS), chemical (DP) or electrical (dielectric strength) properties. Insulation dielectric strength is found to deteriorate slowly if insulation is not mechanically disturbed and bubbles are not present.

Initially a mechanical property “RTS” was chosen. Later, the “DP” is also accepted as another popular alternative. A number of end-of-life criteria have been suggested in the literature, namely 50% [20% suggested by others] RTS, and 200 DP. The DP of 200 which is equivalent to 20% retained tensile strength seems to be the most preferable. The direct measurement, when possible, of the RTS or DP on paper sample retrieved from transformer is the accurate method. However, removal of paper insulation is expensive and in many cases impractical. Reference [10] published the results of RTS and the DP of thermally upgraded paper aged in a sealed tube at 160°C. 

2 . 1 0 O v e r l o a d i n g L i mi t a t i o n

Although transformers are overloaded, there are some limits.

2.10.1 Hottest-Spot Limits The winding hottest-spot temperature at the top of the high or low voltage winding is the most critical parameter. It determines the loss-of-life and indicates the potential risk of Releasing gas bubbles on a severe sudden overload condition. If loss-of-life (of the solid insulation) is not tracked closely, the recent IEEE loading guide suggests a maximum continuous hottest-spot winding temperature limit of (with some loss-of-life), which the limiting temperature for long-term emergency is loading. During short-term emergency situations, hottest-spot temperature is allowed to exceed 140°C.

2 . 1 0 . 2 To p - O i l L i mi t s Due to convection and nature of cooling system design, the highest oil temperature in the transformer tank will be at the top-oil region. When the top-oil temperature exceeds 105°C, it is possible for oil to expand beyond the tank capacity and causes the pressure relief device to operate. Upon cooling, the reduced volume of oil may expose electrical Parts, including the bushing and the winding. Higher top-oil temperatures approaching Flash-point value of 145°C poses a much greater danger of sudden ignition and explosion.

IEEE recommends that the top-oil temperature under any overloading should not exceed 110°C.

2 . 1 0 . 3 I n s u l at i o n L i f e Insulation loss-of-life of power transformers is closely related to a time function of temperature, moisture, and oxygen content. From these parameters, the most significant determining factor to insulation deterioration is the temperature reached by the hottestspot in the winding.

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2 . 1 0 . 4 An c i l l a r y E q u i p me n t Overloading the transformer can have significant detrimental effects on associated equipment. The bushings, tap-changers, bushing-type current transformers (BCT’s) and leads may also be affected by the increased temperature.

2.10.5 Bushings They are designed for a hottest-spot temperature of 105°C for a normal top-oil Temperature limit of 95°C. Operating the bushing above these limits can have damaging effects such as internal pressure build up, aging of gasket material, bubble formation when the hottest-spot temperature exceeds 140°C. For bushings, the following guidelines are recommended: • Tr a n s f o r m e r t o p - o i l t e m p 11 0 ° C m a x i m u m • Maximum [continuous] current 2 x rated bushing current • Bushing insulation hottest-spot temp 150°C maximum

2.10.6 Tap changers Whether designed to change taps under load (LTC’s) or de-energized conditions, are subjected to carbon build-up at elevated temperatures. Transformers are normally designed so that the LTC rating is greater than the transformer rating. It has been seen from practice that, more frequent maintenance is required on LTC’s, which are subjected to operation at elevated temperatures compared to transformers running at lower temperature.

2.10.7 Bushing-type current transformers (BCT’s) The transformer top-oil as their ambient temperature. Overloading the transformer will result not only in higher top-oil temperature, but higher BCT’s secondary current as well. The manufacturer should be consulted regarding the BCT’s capability, if the transformer is loaded beyond its rating.

2 . 1 0 . 8 S t r ay F l u x H e a t i n g Stray flux produces localized heating in any metallic part. This heating results from induced eddy-current losses, harmonics losses, and some hysteresis losses. Under extreme conditions of transformer overvoltage, stray flux increases disproportionately due to core saturation.

Various methods for stray flux control include the use of insulated (non-metallic) supports at the top and bottom of the coil windings, vertical core-clamp configurations, special non-magnetic supports for LV bushings and BCT’s associated with high-current leads, and tank wall shields. Stray flux can also be controlled in a magnetic circuit design.

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2.10.9 Bubble Generation Gas bubbles within transformer oil are of a serious concern, since the dielectric strength of the gases is significantly lower than the dielectric strength of the oil or the cellulose. insulation. Bubbles can form in the transformer from gas generated during faults or from sudden overloading. The generated gas tends to re-dissolve after a long period of time (approx. 20 hours).

Three mechanisms are known by which gas can generate bubbles. IEEE recommends the absolute upper limit of 180°C winding hottest-spot temperature.

• Super-saturation of the oil with a blanket gas.

• Thermal decomposition of cellulose insulation.

• Va p o r i z a t i o n o f a b s o r b e d m o i s t u r e i n t h e c e l l u l o s e . 

2 . 11 A d v a n t a g e s of N u me r i c a l re l ay s

2.11.1 Compact Size Electromechanical Relay makes use of mechanical comparison devices, which cause the main reason f or the bulky size of relays. It uses a f lag system f or the indication purpose whether the relay has been activated or not. While numerical relay is in compact size and use indication on LCD f or relay activation. Digital protection can be physically smaller, and almost always requires less panel wiring than equivalent functions implemented using analogue technology.

2.11.2 Flexibility A variety of protection f unction’s can be accomplished with suitable modify citations in the software only either with the same hardware or with slight modify citations in the hardware.

2.11.3 Reliability A significant improvement in the relay reliability is obtained because the use of f ewer components results in less interconnections and reduced component failures.

2.11.4 Multi-Function Capability Traditional electromechanical and static protection relays off single-f unction and single characteristics. Range of operation of electromechanical relays is narrow as compared to numerical relay.

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ďƒ˜

2 . 1 2 D i f f e re n t t y p e s o f re l a y c h a r a ct e r i s t i c s

It is possible to provide better matching of protection characteristics since these characteristics are store in the memory of the microprocessor.

2.12.1 Digital communication capabilities The microprocessor based relay furnishes easy interface with digital communication equipment. Fibre optical communication with sub -station LAN.

2.12.2 Modular frame The relay hardware consists of standard modules resulting in ease of service.

2.12.3 Low burden The microprocessor based relays have minimum burden on the instrument transformers.

2.12.4 Sensitivity Greater sensitivity and high pickup ratio.

2.12.5 Speed With static relays, tripping time of ½ cycles or even less can be obtained.

2.12.6 Fast Resetting Resetting is less.

2.12.7 Data History Availability of fault data and disturbance record. Helps analysis of faults by recording details of: 1. Nature of fault, 2. Magnitude of fault level, 3. Breaker problem, 4. C.T. saturation, 5. Duration of fault.

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CHAPTER 3:-SIMPLIFIED TRANSFORMER OVERLOADING GUIDELINES 3.1 Understand Transformer Nameplate Rating and Design Fundamentals – Transformer Classification (Distribution and Power); Cooling; Average Winding Temperature Rise; Insulation Type (thermally upgraded vs. kraft paper) and Class; Allowable Hottest- Spot Temperature and Design Limits, Insulation Life vs.

Transformer Life; etc.

3.2 Determine End-of-Insulation Life Criteria and the Normal Insulation Life Value - RTS and DP or other. Typical industry standard for transformer life is between 20 to 40 yrs. 30 yrs., is the most commonly used number.

3.3 Moisture Content - Doubling of moisture content reduces insulation life by half.

3.4 Determine the Ambient Temperature - Worst possible condition over 24 hrs. period and estimate suitable correction. For every 1 °C ambient temperature decrement, loading capacity can be increases by 1% without any loss-of-life or vice versa.

3.5 Normal Life Expectancy Loading - Average (24 hrs.) maximum hottest-spot temperature of 110°C without exceeding the maximum value of 120°C with no additional loss-off life. Normal life is the transformer’s life when it operates at a constant hottest-spot temperature of 110°C. No limit for loading beyond nameplate rating as long as the hottest spot temperatures do not exceed 110°C. 3.6 Planned Loading beyond the Nameplate Rating - Average (24 hrs.) maximum temperature of 110°C without exceeding the maximum value of 130°C with limited loss-of-life. Aging rate is double for every 6-8°C hottest-spot temperature increment.

3.7 Long-Time Emergency Loading - It is recommended that the maximum hottest-spot temperature should not exceed 140°C, otherwise substantial loss-of-life is expected.

3.8 Short-Time Overloading - Usually last for a short-time (less than half-an hour), and the hottest-spot temperature may go up to 180 °C with severe loss-of-life. Transformer failure is expected due to the bubble and gas formation in the oil.

3.9 Maximum Overloading at any time - Limits to 2 times the highest rating.

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CHAPTER 4:- HARDWARE SPECIFICATIONS ďƒ˜ 4.1 POWER SUPPLY AND BLOCK DIAGRAM The ac voltage, typically 220V R.M.S., is connected to a transformer, which steps that ac voltage down to the level of the desired ac output. A diode rectifier then provides a full-wave rectified voltage that is initially filtered by a simple capacitor filter to produce a dc voltage. This resulting dc voltage usually has some ripple or ac voltage variation. A regulator circuit removes the ripples and also remains the same dc value even if the input dc voltage varies, or the load connected to the output dc voltage changes.

Fig 4.1 Power supply block A step down transformer, Diodes, Capacitor, Integrated Circuit, and a Variable resistor (POT). This will convert the 230V A.C supply into a 5V variable D.C. supply. This will act as a signal for electronic C.T. (current transformer) and it will sense the current and will process further.

4.1.1 Step down transformer (230v/12v) A Transformer is a device which transfers electrical energy from one circuit to another circuit through coupled conductors. A varying current in the primary winding creates a varying magnetic flux in the transformer’s core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force in the secondary winding. This effect is called mutual induction. If the load is connected on the secondary winding an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit to the load.

Fig 4.2 An example of step down transformer.

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4.1.2Diodes (IN4007) In electronics diode is a two-terminal electronic component that conducts electric current in only one direction. The most common function of a diode is to conduct current in one direction and to block the current in another direction.

Fig 4.3 Diode symbol and its device package view.

4.1.3 IC 7805 IC 7805 is a voltage regulator integrated circuit. It consists of 78xx series of fixed linear voltage regulator ICs. This voltage regulator IC maintains and gives the output voltage at constant value. 7805 provides +5v regulated power supply.

Fig 4.4 The pin out of 7805 IC.

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4.1.4 Capacitor A Capacitor is a passive electronic component consisting of pair of conductors separated by a dielectric medium (insulator). When there is a potential difference across the conductors, a static field develops across the dielectric, causing positive charge to collect on one plate and negative on other plate. Energy is stored in the form of electrostatic field.

Capacitors are widely used in electronic circuits for blocking direct current while allowing the alternating current to pass through.

Fig 4.5 The basic principle of capacitor.

4.1.5 Variable resistor (Potentiometer) A Potentiometer is an instrument for measuring the voltage in a circuit.

In this arrangement a fraction of known voltage from a resistive slide wire is compared with an unknown voltage. Potentiometers are commonly used to control the electrical devices.

Fig 4.6 Constructional view of POT. Page 23

Fig 4.7 POT symbol

Fig. 4.8 A complete arrangement of all the equipment for variable power supply

So the signal from the A.C. supply will be sensed by the ANALOG TO DIGITAL CONVERTER. It is the second part of the hardware.

Fig. 4.9 Voltage Regulator for 5 V

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ďƒ˜

4.2 Contactor

A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit.

Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a Contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amperes to thousands of amperes and 12 V DC to many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side.

Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.

Fig 4.10: Contactor ďƒ˜

4 . 3 R elay

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches. Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit.

There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical. The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil.

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available.

Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay. The animated picture shows a working relay with its coil and switch contacts. You can see a lever on the left being attracted by magnetism when the coil is switched on.

This lever moves the switch contacts. There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT. Page 25

Fig 4.11 Relay internal connection The relay switch connections are usually labelled COM, NC and NO : COM = Common, always connect to this. It is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

Working of relay: This circuit is designed to control the load. The load may be motor or any other load. The load is turned ON and OFF through relay. The relay ON and OFF is controlled by the pair of switching transistors (BC 547). The relay is connected in the Q2 transistor collector terminal. A Relay is nothing but electromagnetic switching device which consists of three pins. They are Common, Normally close (NC) and Normally open(NO).

The relay common pin is connected to supply voltage. The normally open (NO) pin connected to load. When high pulse signal is given to base of the Q1 transistors, the transistor is conducting and shorts the collector and emitter terminal and zero signals are given to base of the Q2 transistor. So the relay is turned OFF state.

TABLE -1 Voltage Signal from Microcontroller or PC

Transistor

Transistor

Q1

Q2

1

ON

OFF

OFF

0

OFF

ON

ON

ďƒ˜

Relay

4.4 LC D D IS PLAY

Liquid crystal displays (LCDs) have materials which combine the properties of both liquids and crystals. Rather than having a melting point, they have a temperature Page 26

range within which the molecules are almost as mobile as they would be in a liquid, but are grouped together in an ordered form similar to a crystal.

Fig 4.12 : LCD display An LCD consists of two glass panels, with the liquid crystal material sand witched in between them. The inner surface of the glass plates are coated with transparent electrodes which define the character, symbols or patterns to be displayed polymeric layers are present in between the electrodes and the liquid crystal, which makes the liquid crystal molecules to maintain a defined orientation angle.

One each polarizer’s are pasted outside the two glass panels. This polarizer’s would rotate the light rays passing through them to a definite angle, in a particular direction. When the LCD is in the off state, light rays are rotated by the two polarizers and the liquid crystal, such that the light rays come out of the LCD without any orientation, and hence the LCD appears transparent When sufficient voltage is applied to the electrodes, the liquid crystal molecules would be aligned in a specific direction. The light rays the LCD would be rotated by the polarizer’s, which would result in activating / highlighting the desired characters. The LCD’s are lightweight with only a few millimetres thickness. Since the LCD’s consume less power, they are compatible with low power electronic circuits, and can be powered for long durations. The LCD does don’t generate light and so light is needed to read the display. By using backlighting, reading is possible in the dark. The LCD’s have long life and a wide operating temperature range. Changing the display size or the layout size is relatively simple which makes the LCD’s more customer friendly. 

4 . 5 K E Y PA D

Keypad is used to enter the predefined values of the power transformer. Keypad with four keys is employed. The operations of the keys are to increment and decrement the values to be set.

Fig 4.13 : keypad  4.6 ANALOG TO DIGITAL CONVERTER (IC 0809)

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The outputs of the various parameters are fed to A/D converter. The channel selection depends upon the address selection sent by the Microcontroller. This ADC is having three address inputs to select one out of eight channels of the ADC. This ADC 0809 is a successive approx.

Analog to digital converter and the clock rate at which the conversion is fed from the IC 555 timer configured as a stable multi-vibrator. The digital output after the conversion is fed to Micro-controller. For ADC to start converting the data after selecting the channel by sending the address inputs, the start conversion signal is to be sent by Microcontroller.

Then ADC starts converting the analog signals voltage into corresponding digital data.

For Ex: The following table shows the digital data corresponding to analog input.

Fig 4.14 the pin out configuration of ADC IC 0809.

In the ADC0809, V ref (+) and V ref (-) set the reference voltage.

We use A, B, and C to select IN0 to IN7 and activate ALE to latch in the address.

SC is used for start of conversion which is same as WRITE function in other chips. EOC is the end of conversion OE is output enable which is nothing but READ function of the IC.

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4.6.1 Block diagram of ADC.

Fig 4.15 The Block diagram arrangement of ADC 0809 The various blocks of ADC are 8-channel selection multiplexer, comparator, 256R ladder register, switch tree, successive approximation register, output buffer, address latch enable and decoder.

The 8-Channel multiplexer can except 8 analog inputs in the range of 0 to 5V and allow one by one conversion depending upon the 3 address input.

Table 4.1 ADC 0809 Channel selection Selected analog channel IN0 IN1 IN2 IN3 IN4 IN5 IN6 IN7

C

B

A

0 0 0 0 1 1 1 1

0 0 1 1 0 0 1 1

0 1 0 1 0 1 0 1

The table represents how the channel is being selected for the particular multichannel features of the respective ADC 0809.

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The successive approximation register performs the 8 iteration to determine code for input value. The 256R ladder network has been provided instead of conventional R/2R ladder because of inherent monotonic.

ďƒ˜ 4.7 MICROCONTROLLER UNIT (P89V51RD2) A Microcontroller is a small computer on a single integrated circuit containing a core processor, memory, and programmable input/output peripherals.

Microcontrollers are used in automatically controlled products and devices such as remote controls, engine control systems, power tools, toys and other embedded systems.

There are various kinds of controllers available which differs from the application point of view such that high speed process with lesser instruments requires higher level microcontrollers which have different features than the other simple or conventional controllers.

The microcontroller which is used in the project that is PHILIPS SEMICONDUCTORS 8 bit microcontroller with 80C51 core. IC is named as P89V51RD2 with 64kB flash and 1024 bytes of data RAM.

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Fig 4.16 : Block diagrm of NXP controller4.7.1 DESCRIPTION

OF MICROCONTROLLER The entire microcontroller IC comes in different packages such as DIP, they all have 40 pins that are dedicated to various functions like I/O, RD, WR, address, data and interrupts. Some companies also offer 20 pin package which have lesser ports due to respective applications.

Fig 4.17 the entire pin out DIP package of P89V51RD2.

Each pin has different functions to serve as well as accept the data and also multiple functioning with single pin is available by programming the respective bits in software.

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4.7.2 PIN DESCRIPTION  XTAL1 and XTAL2:- The controller has on chip oscillator but requires an external clock to run it. The quartz crystal oscillator must be connected to these both pin for external source.

 EA: - (External access enable) This pin must be connected to Vss in order to enable the device to fetch code from external program memory. This pin must be strapped to VDD for internal program execution.

 ALE:- (Address latch enable) This is output signal for latching the low byte of the address during an acess to external memory.

 PSEN:- (Program store enable) This pin is a read strobe for external program memory. While the device is executing from internal program this pin is HIGH. When the device is executing code from external program memory this pin is LOW.

 PORT 0 :- It is an 8 bit open drain bi-directional I/O port. It needs the pull up resistors. It is also multiplexed lower address and data bus during accesses to external code and data memory.

 PORT 1:- It is a bi-directional I/O port with internal pull-ups. Because of internal pull-ups P1.5, P1.6, P1.7 have high current drive of 16mA.

 PORT 2:- It is an 8 bit bi-directional I/O port. Also designated as dual functions that when it is connected to external memory P2 is used as upper bits of 16bit address. i.e. A8-A15.

 PORT 3:- It is configured as a input port upon reset P3.0 AND P3.1 are used for receiving and transmitting the communication signals. P3.2 AND P3.3 are set aside for external interrupts. Bits P3.4 AND P3.5 are used for timers 0 and 1 and P3.6 AND P3.7 are used for read and write of the data to the microcontroller.

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AP P L I C AT I O N S



To protect distribution transformer from overload condition.



As auto-recloser in distribution transformer.



To record overload current for analysing purpose.



To counting annual switching operation of distribution transformer.

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CONCULSION

Protection of distribution transformer is a big challenge nowadays. By the help of microcontroller-based relay, protection of transformer is performed very quickly and accurately.

This system provides a better and safer protection than the other methods which are currently in use. The advantages of this system over the current methods in use are fast response, better isolation and accurate detection, auto even data recording also possible.

This system overcomes the other drawbacks in the existing systems such as reclosing problem due to temporary fault on load side. Thus burden of maintenance department is decrease. Even due to data recording and counting of switching operation due to overload manufacturers can decide warranty period policy and give better service to customers.

This project is used for multi-purpose like protection, data recording and auto reclosing of the distribution transformer from overload. The electrical parameters like load current of the transformers are fed as base values, using a keypad to the Peripheral Interface Controller and the output signal is provided to operate a relay by comparing the base values with the operating this parameters. The application consists of a board of electronic components inclusive of a microcontroller with programmable logic. It has been designed to work with high accuracy and speed.

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FUTURE WORK  Develop the android application for distribution transformer protection.  Develop logic for theft detection on distribution transformer.  Work for reducing price of device using different components and add more function.

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REFERENCES

ďƒ˜

FOR TEXT

[2] http://www.think-energy.net/KWvsKWH.htm [3] http://en.wikipedia.org/wiki/contactor [4] http://en.wikipedia.org/wiki/MCB [5] OVER LOAD PROTECTION OF TRANSFORMER [6] http://www.allinterview.com/showanswers/80596.html [7] http://wiki.answers.com/Q/Why_transformer_measured_in_kva?#Slide2 [8] http://www.measurlogic.com/EnergyManagement/maximumdemand.html [10] http://en.wikipedia.org/wiki/Diode [14] http://en.wikipedia.org/wiki/Analog-to-digital_converter http://8085projects.info/images/ADC0809-BD-Pic4(86).png [15] http://en.wikipedia.org/wiki/Microcontroller TARIFF PLAN https://www.google.co.in/url? sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CCgQFjAA&url=http%3A%2F %2Fwww.mgvcl.com%2FPeti%2520994%2520of%2520TO%2520APR%25200910%2520%26%2520ARR%2520FY%252010-11%2520010410%2520ht.pdf&ei=QkqkUrSCoWQrQeR6YDIAg&usg=AFQjCNEWxdJy2ao3I0SrUlfy5zyLUFNrqA&sig2=PIbmuho__zKVkWoUzw_KQ&bvm=bv.57752919,d.bmk

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ďƒ˜ FOR FIGURE A http://www.volt-on.in/protection of transformer.html B http://www.electricityforum.com/images/step-down-transformer.gif C http://vector-magz.com/wp-content/uploads/2013/10/diode-symbol.jpg D http://www.engineersgarage.com/sites/default/files/7805_1.jpg?1281349871 E http://upload.wikimedia.org/wikipedia/commons/c/cd/Capacitor_schematic_with_dielectric.svg F http://upload.wikimedia.org/wikipedia/commons/b/b5/Potentiometer.jpg G http://upload.wikimedia.org/wikipedia/commons/1/19/Potentiometer_symbol.svg H http://ugpro143.blogspot.in/2011/09/analog-to-digital-converter-module.html I http://8085projects.info/images/ADC0809-BD-Pic4(86).png J http://entesla.com/P89V51RD2-DIP

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