How to reduce transformer losses

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1. HOW TO REDUCE TRANSFORMER LOSSES Submitted to- Submitted by- Dr. Sandeep G upta Mr. kamal soni Assistant Professor B. Tech.- 6 th Sem (EE)

2. TANSFORMER INTRODUCTION A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. A varying current in one coil of the transformer produces a varying magnetic field, which in turn induces a voltage in a second coil. Faraday's law of induction discovered in 1831 described this effect. Transformers are used to increase or decrease the alternating voltages in electric power applications.

3. TANSFORMER INTRODUCTION Primary winding 1 - input (primary coil) –AC Source is connected to it. –Magnetizing current flows and establishes the flux in core . Primary winding 2 (secondary coil) –Load Magnetic circuit (core) Problems ? Stray flux, Transient, Heating, Vibrations, Noise, Losses, Regulation, Saturation, Human errors, D ielectrics (high voltage insulation), N on -linear magnetic, F luid dynamics, M aterial defects , Contamination , etc.

4. Transformers Classifications By Field Usage: Power transformer for transmission network Distribution transformer for distribution networks Power supply Isolation Rectifier Arc furnace

5. Transformers Classifications Number of phases: Single phase Three phase According to frequency: Low frequency (power and distribution transformer ) Very high, high frequency transformers (communication and power electronic devices ) Intermitted frequency transformer (communication)

6. Transformers Classifications Cooling : Self air cooled (dry type ) Air blast cooled (dry type) Liquid immersed, dry cooled Oil immersed, combination self cooled and air blast Oil immersed, water cooled Oil immersed, forced air cooled Oil immersed, combination self cooled and water cooled

7. Shell Type Transformer high voltage bushing tank top section cooling equipment oil circulating pump tank bottom section pancake coil inter -phase block L.V . coil group H.V . coil group tank shieldin g

8. TANSFORMER LOSSES Real transformer energy losses are dominated by winding resistance joule, eddy current and core losses. Transformers' efficiency tends to improve with increasing transformer capacity. The efficiency of typical distribution transformers is between about 98 and 99 percent .

9. TANSFORMER LOSSES No-load losses (iron losses) : No-load losses occur in the core material due to hysteresis and eddy currents , and are present almost continuously while the transformer is connected to the electricity supply (i.e. 8,760 hours per year). The hysteresis losses are proportional to the frequency and the induction. Eddy current losses are also proportional to the frequency and the amplitude of induction but mainly also to the thickness of the magnetic steel.

10. TANSFORMER LOSSES Load losses ( C opper losses) : Load losses occur in the windings, the connecting conductors and the tank. They are caused by the effects of Joule’s law ( Ohmic losses), eddy currents and ux leakages. Ohmic losses are equal to the product of the square of the current and the resistance of the conductor. The capitalization values for no-load losses are considerably higher than those for load losses , which is logical because no-load losses occur continuously.

11. Distribution Transformer Main Parts MAIN TANK RADIATORS BREATHER UNIT CONSERVATOR PRESSURE RELEIF SYSTEM OIL LEVEL INDICATOR TEMPERATUER DIAL TAP CHANGER HV /LV BUSHINGS OIL FILLING PLUG DRAIN PLUG CABLE BOX

12. Transformer Core This magnetic circuit, know more commonly as the “transformer core” is designed to provide a path for the magnetic field to flow around, which is necessary for induction of the voltage between the two windings . The two most common and basic designs of transformer construction are the Closed-core Transformer and the Shell-core Transformer . In the “closed-core” type (core form) transformer, the primary and secondary windings are wound outside and surround the core ring. In the “shell type” (shell form) transformer, the primary and secondary windings pass inside the steel magnetic circuit (core) which forms a shell around the windings.

13. Different types of Core

14. Reduction of High-Frequency Conduction Losses Using a Planar Litz Structure( Shen Wang ) IEEE 2005 Definitions for a Planar Litz Conductor Strand/s: Narrow conductors used to make up a planar litz conductor. Planar Litz Conductor: A planar conductor comprised of many isolated strands that are weaved together to form a single high-frequency, higher-current-carrying-capacity conductor. Strand Angle: The angle the strand makes with the direction of the planar litz conductor. Planar Litz Lines: The lines parallel to the direction of the conductor, which are spaced equidistant across the width of the planar litz conductor. Advantages Round litz wire is comprised of several insulated strands that are transposed along the conductor length so that they ideally occupy all the possible positions in the conductor cross section equally. Therefore, litz wire results in a more uniform current distribution across the conductor cross section so that losses due to the skin and proximity effects are effectively reduced, although usually over just a certain frequency range.

15. Core Losses Hysteresis Losses Transformer Hysteresis Losses are caused because of the friction of the molecules against the flow of the magnetic lines of force required to magnetize the core, which are constantly changing in value and direction first in one direction and then the other due to the influence of the sinusoidal supply voltage . This molecular friction causes heat to be developed which represents an energy loss to the transformer. Lowering the frequency of the supply will result in increased hysteresis and higher temperature in the iron core. So reducing the supply frequency from 60 Hertz to 50 Hertz will raise the amount of hysteresis present, decreased the VA capacity of the transformer.

16. Core Losses Eddy Current Losses The magnetic field surrounding a coil which is carrying AC current varies with time. This varying magnetic field induces voltages in nearby conductive material like metal equipment cabinets, transformer cores and so on. The resulting current is known as Eddy current. The currents flow in a circular manner like eddies in the brook, so they are called as eddy current. They create unwanted  power loss which is known as eddy current loss

17. Method to decrease Core losses Eddy current losses within a transformer core can not be eliminated completely, but they can be greatly reduced and controlled by reducing the thickness of the steel core . Instead of having one big solid iron core as the magnetic core material of the transformer or coil, the magnetic path is split up into many thin pressed steel shapes called “laminations” . The losses of energy, which appears as heat due both to hysteresis and to eddy currents in the magnetic path, is known commonly as “transformer core losses”.

18. Influence of Transformer Core Design on Power Losses ( Zvonimir valkovic ) IEEE MARCH 1982 The magnetic properties of a transformer core are influenced by three basic factors: quality (grade) of material processing of steel sheet during core manufacture core design Corner and T-Joint Design The influence of corner form on the building factor was investigated on the single-phase models. Besides the models with a 45" mitered overlap joint, similar models were made with a 90" butt and lap joint.

19. Stray Losses in Transformer Tank (Vogel and Adolphson ) IEEE 2005 In 1954, Vogel and Adolphson proposed a model to determine stray losses and heating of tanks for a core-type transformer. An oval-shaped tank is considered in this article, and the losses in the tank wall versus the distance for the top of the high-voltage coils are determined. ADVANTAGES:- The steel achieves the best performance among the three materials, which means that the shielding effect of the material with both high conductivity and high permeability is better than the one only with high conductivity and the one only with high permeability. The transformer enclosed by such material tanks can maintain the leakage magnetic field in a very small magnitude .

20. Transformer Core Grounds Power transformers are usually supplied with a ground from the core of the transformer to the tank. The core ground diverts this voltage safely to ground.

21. Copper Losses Transformer Copper Losses are mainly due to the electrical resistance of the primary and secondary windings. Most transformer coils are made from copper wire which has resistance in Ohms, (  Ω  ). This resistance opposes the magnetizing currents flowing through them . When a load is connected to the transformers secondary winding, large electrical currents flow in both the primary and the secondary windings, electrical energy and power ( or the I 2  R ) losses occur as heat. Generally copper losses vary with the load current, being almost zero at no-load, and at a maximum at full-load when current flow is at maximum.

22. Methods to reduce Copper Losses Transformers with high voltage and current ratings require conductors of large cross-section to help minimize their copper losses . Increasing the rate of heat dissipation (better cooling) by forced air or oil, or by improving the transformers insulation so that it will withstand higher temperatures can also increase a transformers VA rating.

23. TRANSFORMER OIL In 1887, the year after Stanley designed and built the first transformers in the U.S., Elihu Thompson patented the idea of using mineral oil as a transformer cooling and insulating medium (Myers et al.,1981). As per I.A.S. breakdown strength of oil used must be 50kv RMS One of the e.g. is chlorinated dephenyl is a synthetic oil its permittivity is 4.5

24. T he function of the oil in the Transformer Cooling Internal temperature rise in transformer if left could cause serious damage on transformer. Oil easily penetrates between windings and heat is transferred to oil. Heat is them being rejected out of the oil either through fans or radiators or through the contact between the transformer body and the oil itself. Insulation I nsulation between windings themselves and between the windings and the core.

25. T he function of the oil in the Transformer Protection Covers all metallic parts and prevents oxidation process which affects conductivity and prevents any other chemical reactions that causes corrosion. Fault diagnosis Used to detect many internal faults in the transformer . Fault cause changes in the chemistry of the oil due to the large energy accompanied by faults . Oil is analyses and results are used to determine the type of internal fault inside of the transformer

26. Radiator of Transformer Due to this flowing of electric current, heat is produced in the windings, this heat ultimately rises the temperature of transformer oil. Under loaded condition, warm oil increases in volume and comes to the upper portion of the main tank. Then this oil enters in the radiator through top valve and cools down by dissipating heat through the thin radiator wall. This cold oil comes back to the main tank through the bottom radiator valve. This cycle is repeated continuously till the load is connected to the transformer. These fans are fitted either on the radiator bank itself or fitted nearby the bank but all the fans must be faced towards the radiator. Sometime , the cooling rate of convectional circulation of oil is not sufficient. That time an oil pump may be used for speeding up oil circulation.

27. Fan Specifications All fans are very similar with only a few variations depending on the transformer requirements: Fan ratings(HP,CFM, dBA ) Electrical ratings(V, Phases ,FLA, etc.) One or two blades per fan Rotation of blades Mounting Adapter

28. Different Transformer Cooling Methods ONAN Cooling of Transformer This is the simplest transformer cooling system. The full form of ONAN is "Oil Natural Air Natural". Here natural convectional flow of hot oil is utilized for cooling . In convectional circulation of oil, the hot oil flows to the upper portion of the transformer tank and the vacant place is occupied by cold oil. This hot oil which comes to upper side, will dissipate heat in the atmosphere by natural conduction, convection & radiation in air and will become cold. In this way the oil in the transformer tank continually circulate when the transformer put into load.

29. Different Transformer Cooling Methods ONAF Cooling of Transformer The full form of ONAF is "Oil Natural Air Forced". As the heat dissipation rate is faster and more in ONAF transformer cooling method than ONAN cooling system, electrical power transformer can be put into more load without crossing the permissible temperature limits. Heat dissipation can obviously be increased, if dissipating surface is increased but it can be make further faster by applying forced air flow on that dissipating surface. Fans blowing air on cooling surface is employed. Forced air takes away the heat from the surface of radiator and provides better cooling than natural air.

30. Different Transformer Cooling Methods OFAF Cooling of Transformer OFAF means "Oil Forced Air Forced" cooling methods of transformer. In OFAF cooling system the oil is forced to circulate within the closed loop of transformer tank by means of oil pumps. The heat dissipation rate can be still increased further if this oil circulation is accelerated by applying some force. The main advantage of this system is that it is compact system and for same cooling capacity OFAF occupies much less space than farmer two systems of transformer cooling.

31. Different Transformer Cooling Methods OFWF Cooling of Transformer We know that ambient temperature of water is much less than the atmospheric air in same weather condition. So water may be used as better heat exchanger media than air. In OFWF cooling system of transformer, the hot oil is sent to a oil to water heat exchanger by means of oil pump and there the oil is cooled by applying sowers of cold water on the heat exchanger's oil pipes . ODAF Cooling of Transformer ODAF or oil directed air forced cooling of transformer can be considered as the improved version of OFAF. Here forced circulation of oil directed to flow through predetermined paths in transformer winding. ODAF or oil directed air forced cooling of transformer is generally used in very high rating transforme

32. Tank Losses Due to High-current Bushings ( Juan C.) IEEE 2008 There are few studies related to a single current-carrying conductor in the presence of conducting permeable surfaces. The means of preventing local overheating in the windings and other elements of transformers have been studied, but the means to prevent overheating on the structure surrounding the distribution transformer bushings are very scarce. Advantages:- Reduces eddy current losses. Its to use and easy to change the tapings to get desired voltages. Help transformer on low supply voltage to feed constant output voltage

33. Distribution Transformer Losses Harmonic Loads ( Sara Tancradi ) IEEE DEC. 2008 Harmonic currents and voltages are created by nonlinear loads connected on the power system. Harmonic distortion is a form of pollution in the electric plant that can cause problems if the sum of the harmonic currents increases above certain limits. A non-linear load is created when the load current is not proportional to the instantaneous voltage. Non-linear currents can be no sinusoidal, even when the source voltage is a clean sine wave. ADVANTAGES:- The harmonic losses factor for eddy current winding and other stray losses has been computed in order to evaluate the equivalent KVA of the transformer for supplying nonlinear loads. it is better to carry out monitoring on voltage and current, to reach to useful capacity of transformer based on available standards and the proposed model, if harmonic components exist.

34. Partial Interleaving (Michael Scofield ) IEEE 2004 A Method to Reduce High Frequency Losses and to Tune the Leakage Inductance in High Current, High Frequency Transformer Foil Windings . A conventional foil winding uses thickness optimized foils to reduce the skin effect losses and interleaving of the windings to reduce the proximity effect losses. we introduce a new way of interleaving called “Partial interleaving” . The main advantage of the partial interleaving is that it fulfills the requirements in the same time. would reduce the field strength in comparison with the conventional winding hence reduce the power losses keep the field strong enough to be able to achieve the required value of the leakage inductance keep the winding simple without using taps

35. Sudden pressure relay SPR The Sudden Pressure Relay is a device designed to respond to the sudden increase in gas pressure in a power transformer which would be caused by an internal arc. A pressure sensing bellows , a micro switch and a pressure equalizing orifice. All parts are enclosed in a sealed case and mounted on the outside of the transformer at the gas space.

36. BUCHHOLZ RELAY Placed when a conservator tank is used, as it indicated faults and errors such as oil loss when oil level goes low, improper oil flow between the oil tank and the transformer. Moreover , it shows gas emission inside transformer due to any unusual operation ( excessive loading or short circuit) and can issue a control signal which can be used to disconnect the transformer . It is equipped with a release valve in case oil exceeded its level.

37. OPERATION OF BUCHHOLTZ RELAY

38. PUMPS Transformer pumps allow for maximum cooling which allows for peak load operation of oil cooled transformers. There are two types of pumps generally used, axial and centrifugal, with centrifugal pumps being the most common.

39. Silica gel breather When the temperature changes occur in Transformer insulating oil, the oil expands or contracts and there an exchange of air also occurs when transformer is fully loaded. When transformer gets cooled, the oil level goes down and air gets absorbed within. This process is called breathing and the apparatus that pass through the air is called breather . Actually, Silica gel breathers controls the level of moisture, entering electrical equipment during the change in volume of the cooling medium and/or airspace caused by temperature increasing.

40. Pressure relieve device Mechanical device for relief of excessive pressure accumulation of large volumes of gas or fluid in transformer. Gasket system provides quick response time and automatically reseals after pressure has subsided. Options include local operation indication, contacts (switches) for operation alarming, and directional shield for hot oil and gas exhaust control

41. Core and clamp ground

42. Conclusion In above presentation we discuss about Transformer types , their losses and methods to reduce them. The typical transformer has the efficiency of 80-90%. We conclude that Transformer can achieve the efficiency of about 98-99% if the following things are applied successfully: Cooling the transformer properly. Shredding of core must be greater. Permeability of core material would be higher. Resistance of windings must be lesser. Proper structure of transformer core. Primary and secondary windings must be interleaving.

43. References M. Pavlovsky , S.W.H. de Haan , J.A. Ferreira Delft University of Technology Department of Electrical Power Processing Mekelweg4, 2628CD Delft, The Netherlands http:// www.edisontechcenter.org / Transformers.html http:// www.electronics-tutorials.ws /transformer/transformer- construction.html ‪ http://www.aast.edu/pheed/staffadminview/pdf_retreive.php?url=45_16255_EE543_2015_1__1_1_week_10_11.pdf&stafftype= staffcourses https://www.electrical4u.com/silica-gel-breather/ https://www.electrical4u.com/transformer-cooling-system-and-methods / https://www.electrical4u.com/radiator-of-transformer-function-of-radiator/