DESIGN AND CONSTRUCTION OF 1500VA VARIABLE OUTPUT STEP DOWN TRANSFORMER

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1 DESIGN AND CONSTRUCTION OF 1500VA VARIABLE OUTPUT STEP DOWN TRANSFORMER OGUNDARE AYOADE B., OMOGOYE O. SAMUEL & OLUWASANYA OMOTAYO J. Department of Electrical/Electronic engineering, Lagos State Polytechnic, Ikorodu Abstract a statics device. The iron loss at both full load and In this work, 1500VA variable output step down transformer was designed and constructed. The voltage was stepped down from 230V A.C supply to 12V and 24V rectified D.C output. It finds application in the industries, laboratories and for charging batteries. The method used for the construction was a shell core type using the E-I section core and wire wound magnetic transformer winding which is air cooled. The design was accomplished with various equations and parameters to determine number of turns which were 900 in the primary, 90 and 45 for the 24volts and 12volts outputs respectively. The results of short circuit and open s at full load and half load were used to compute the efficiency which is 94.9% and 96% respectively. Thus, the efficiency of the transformer is high being half load remained fixed at 1.3watts. Keywords: shell core, open circuit, short circuit, winding, insulation, and lamination. 1.0 Introduction Transformer is a static (or stationary) piece of apparatus [1-4] by means of which electric power in one circuit is transformed into electric power of same frequency in another circuit. It can raise or lower the voltage in a circuit but with a corresponding decrease or increase in current [2]. The physical basis of a transformer is mutual induction between circuits linked by a common magnetic flow. In its simplex form it consists of two inductive coils, which are electrically separated but magnetically linked through a path of low reluctance. OGUNDARE AYOADE B. & OLUWASANYA OMOTAYO J. 1

2 The two coils possess high mutual inductance. One coil is connected to a source of alternating voltage, and alternating flow is set up in the laminated core which is mutually induced in the other coil according to Faraday s laws of electromagnetic induction [3] The coil in which energy is fed from is called primary winding and the other from which energy is drawn out is called secondary winding adjustment of the voltage ratio [5].The winding material depends on the application. 2.2 Insulation: The conductor materials must have insulation to ensure the current travels around the core and not through a turn-to-turn short-circuit. In power transformers, the voltage difference between parts of the primary and secondary windings can be quite large. Insulation is inserted between layers of windings to prevent arcing [6] The general practice in this country is to generate voltage of about 12-16KV, then step up by means of transformers to higher voltage of 132/330KV for the transmission lines[4]. These high AC voltages and current are then reduced to a much lower and safer voltage supply of 415/220V where it is needed in our homes and workplace and all this is possible by basic step down voltage transformer. 2.0 Transformers Overview 2.1 Winding: The primary and secondary conductors are coils of conducting wire because each turn of the coil contributes to the magnetic field, creating a higher magnetic flux density than would a single conductor. Windings on both primary and secondary of a power transformer may have external connections (called taps) to intermediate points on the winding to allow 2.3 Coolant: cooling medium is provided to remove heat from the core and coil to ensure that the insulating capacity of the transformer does not deteriorate. All transformers must therefore, have some circulation of coolant to remove heat produced. Small transformers up to a few kilowatts in size are usually cooled by air circulation. 2.4 Enclosure: Small transformers often have no enclosure. Transformers may have a shield enclosure. Larger units may be enclosed to prevent contact with live parts, and to contain the cooling medium (oil or pressurized gas). The enclosure, which protects the above components from dirt, moisture, and mechanical damage.[3] OGUNDARE AYOADE B. & OLUWASANYA OMOTAYO J. 2

3 2.5 Shielding: An ideal transformer is purely magnetic in operation, the proximity of the primary 2.6 Core: The core provides a path for the and secondary windings create a mutual capacitance between the windings. Magnetic lines of flux. Commonly used core materials are air, soft iron, and steel. Each of those materials is suitable for particular applications and unsuitable for others. % efficiency = Output (w) X 100 Output (w) + losses = n full load power factor n full load power factor + P oc + n 2 P sc 3.0 Losses in Transformer Where n is the fraction of the full load, P oc is the core loss and P sc is the copper loss Copper Loss: this is a loss of power in the transformer due to the resistance of the winding and the current flowing through them. It is termed I 2 R loss which is determined by short Iron Loss: There are two types of iron loss: Eddy current and Hysteresis loss. Iron loss remain constant irrespective of the load current but proportional to the apply frequency and depends on the flux density and the quality of the iron [6][7][8]. Its value is derived from open. 4.0 Efficiency This is the rated capacity of a transformer which is the product of the rated voltage and full load current on the output side. The power output depends upon the power factor of the load. The efficiency is defined as the product of useful power output to the input power. 5.0 Methodology In this work, wire wound magnetic transformers methods have been adopted. The wire wound could be core type or shell type transformer but the shell type was used because of its efficient characteristics. Each layer of the core consists of E- and I- shaped sections of metal. These sections are butted together to form the laminations. The laminations are insulated from each other and then pressed together to form the core. Two coils of wire (called windings) are wound on the core material. Both windings are on the centre limb, which has twice the cross sectional area of each of the outer limb. The objective is to place the windings in intimate contact with one another so as to reduce the leakage flux. At maximum efficiency, copper losses = iron losses. OGUNDARE AYOADE B. & OLUWASANYA OMOTAYO J. 3

In effect, the core material is air and the transformer is called an air cooled transformer. On the primary side of the former, SWG (standard wire gauge) 19 with 900 number of turns was used.

The secondary coil for 24V was wound with SWG 18 which was made up of 90 numbers of turns while the 12V secondary winding was implemented with SWG 17 using 45 numbers of turns. Fig.

44NPfØ (1) Where Np is the number of turns in the primary, f is the frequency =50Hz and Ø is the flux in Weber Core Area A = t x w Ø= AB - (2), Where A is the net area of the core and B is the flux

4 In effect, the core material is air and the transformer is called an air cooled transformer. On the primary side of the former, SWG (standard wire gauge) 19 with 900 number of turns was used. The primary coil was then covered with enameled paper to insulate it from the secondary. The secondary coil for 24V was wound with SWG 18 which was made up of 90 numbers of turns while the 12V secondary winding was implemented with SWG 17 using 45 numbers of turns. Fig.2 Transformer section showing the experimental set up. Constructional details 6.0 Design Calculations I Output Power P = 1500VA w E.m.f equation = 4.44NPfØ (1) Where Np is the number of turns in the primary, f is the frequency =50Hz and Ø is the flux in Weber Core Area A = t x w Ø= AB - (2), Where A is the net area of the core and B is the flux a density = 1.1 Wb/m 2 Substitute equation (2) in equation (1) E = 4.44 NpfAB - (3) b b E Section Window A=axb=2.6cmx3.85cm=10.01cm 2 =1.001x10-3 m 2 Fig 1) Core Dimensions and Winding Area The primary voltage = 230V 230 = 4.44Np x 50 x x 10-3 x 1.1 Np = x 50 x x 10-3 x 1.1 = 940 but 900 numbers of turns was used. OGUNDARE AYOADE B. & OLUWASANYA OMOTAYO J. 4

5 Secondary windings For 24V, Output, Ns = 24 = x 50 x x 10-3 x turns was used. for 12v output Ns = 12 = x 50 x x 10-3 x Tests and Results Table 1 Test results for full load Tests Volts Amperes Watts Short Open Output power = Secondary power = 1500VA Input power P in = 1.1 x P o = 1.1x1500=1650 VA Primary power = Input power = Primary voltage x primary current = Vp x Ip 1650 = 230 x Ip Ip = 1650 = 7.17A, 230 SWG (Standard Wire Gauge) 19 was used Secondary Power = Output Power 1500 = Vs x I s, When Vs = 24V, Is = 1500 = 62.5A 24 SWG 18 was used Is= 1500 = 125A 12 Table 2 Test results for half full load Tests Volts Amperes Watts Short Open Wattage output at 0.6 power factor = 1500 X 0.6 = 900W Efficiency at full load = 900 X ( ) = 94.9% Efficiency at half full load = 900 X ( ) = 96% SWG 17 was used. OGUNDARE AYOADE B. & OLUWASANYA OMOTAYO J. 5

6 8.0 Discussion of Results There are no rotational losses associated with transformer, so relatively little power is lost when transforming power from one voltage level to another. Since transformer is a statics device, it is expected to have high efficiency. This is evident in the calculation of efficiency both at full load and half load conditions which are 94.9% and 96% respectively. The iron loss at both full load and half load remained fixed at 1.3watts. [2] A.B Ogundare and A.S Alayande: Introduction to Electrical Machines : Jimsalaam, Lagos, 2012,(ISBN: ). [3] Alan Symonds: Electrical Power Equipment and Measurement, McGraw-Hill, Maidenhead, 1971(ISBN: ). [4] B.L. Theraja & A.K. Theraja: Electrical Technology, S.Chand, India, 2005 (ISBN: ) [5] G. Perica: Elimination of Leakage Effects Related to the use of Winding with Fractions of Turns : Proceedings of Power Electronics Specialists 9.0 Conclusion 1500VA variable voltage transformer has been designed and constructed. It has very high efficiency which is 94.9% at full load and 96% at half of full load. The output voltages are 24volts and 12volts. It can be used as transformer in inverter design and construction as well as battery charger. With the aid of rectifier, the output voltages could be set and use to supply d.c load. REFERENCES [1] James H. Harlow: Electric Power Transformer Engineering, CRC Press, LLC Publishing, Florida, United States, 2004 (ISBN: ). Conference (PESC), pp , 1984 [6] Nichola Chiesa: Power Transformer Modeling for Inrush Current Calculation : Norwegian University of Science and Technology, Faculty of Information Technology, Department of Electrical Power Engineering, Thesis for the Degree of Doctor of Philosophy: NTNU- trykk, June, 2010 (ISBN: ) [7] Haito Gan: On-chip Transformer Modeling, Characterization and Applications in Power and Low noise Amplifiers : A dissertation submitted for the Degree of Doctor of Philosophy: Stanford University, Department of Electrical Engineering, March, [8] Lorrain Paul: The Pointing Vector in Transformer : American Journal of Physics, Vol. 52, pp , November, 1984 OGUNDARE AYOADE B. & OLUWASANYA OMOTAYO J. 6

Walchand Institute of Technology. Basic Electrical and Electronics Engineering. Transformer

Walchand Institute of Technology Basic Electrical and Electronics Engineering Transformer 1. What is transformer? explain working principle of transformer. Electrical power transformer is a static device