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1 ANADOLU UNIVERSITY DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING EEM 311 Principles of Energy Conversion Laboratory Fall 2016-2017 Experiment 4 : Determination of Transformer Parameters Determination of Transformer Performance (Load Test) ANADOLU UNIVERSITY EEM311 – Experiment 4 2 Purpose : To determine the equivalent circuit parameters of a single-phase transformer using open and shortcircuit test data and calculating the efficiency curves of a single-phase transformer under various loading schemes Background and Theoretical Discussion : The parameters of the transformer approximate equivalent circuit are readily obtained from opencircuit and short-circuit test. In the open circuit test, rated voltage is applied to high voltage (HV) side winding while low voltage (lv) side is open circuited. Instruments are connected to measure the input voltage, the no-load input current (excitation current), and the input power. If the secondary is open circuited, the secondary current will be zero and only the excitation current will be drawn from the supply. Also, the primary voltage drop due to the small excitation current is neglected, and therefore following equivalent circuit given in Fig. 1. is considered. Measurements performed on an unloaded transformer are open circuit voltage VOC , which is the rated high side voltage (HV), excitation current I ex , and open circuit power POC . The excitation current is inductive in nature and lags VOC by; POC VOC I ex OC cos 1 Knowing OC , I I ex cos OC I h e I ex sin OC ANADOLU UNIVERSITY EEM311 – Experiment 4 3 Next, shunt components are calculated as follows; RC VOC I he and X m VOC I The shunt elements can also be determined as; RC VOC 2 V , I he OC , POC RC I I h2e and X m since I ex is available we can calculate I 2 ex VOC I As mentioned before, no-load test is performed from the high voltage (HV) side of the transformer since HV side has a lower rated current than low voltage (LV) side. This prevents too high currents from flowing through instrumentations. Similarly short circuit test is performed from the LV side to avoid high voltages across instrumentations In the short-circuit test, a reduced voltage VSC is applied at terminals of LV winding while HV terminals are short circuited. Instruments are connected to measure the input voltage VSC , the input current I SC , and the input power PSC . The applied voltage is adjusted until rated LV side current is flowing. The voltage required to produce rated current in this case is just a few percent of rated LV side voltage. At such correspondingly low voltage and therefore flux, the exciting current and core loss are negligible and the shunt branch can be omitted. Thus, the power input can be taken to represent the winding copper loss. ANADOLU UNIVERSITY EEM311 – Experiment 4 4 Assume that LV side is the secondary while HV is primary, shorted and the approximate circuit referred to secondary is given in Fig.2. In this case, winding equivalent circuit elements referred to secondary are calculated as; Z eq 2 VSC I SC , and knowing the input power; Req2 PSC and X eq 2 2 I SC Z 2 eq Req2 2 An important aspect of transformer performance is the efficiency. Power transformer efficiencies are high and around 95 to 97 percent. The actual efficiency of a transformer is given by Output Power Input Power And the conventional efficiency of a transformer at n fraction of the full-load power is given by n S pf n S pf n 2 PCU Ph e Where S = Full-load rated volt-ampere PCU =Full-load copper loss n I I rated per-unit loading Equipment List : 1 DL 1013M2 Power Supply 1 DL 1031 Digital Power Measuring Unit 1 DL 1093 Single Phase Transformer 1 DL 1017R Resistive load bank 1 DL 1017L Inductive load bank 1 Wavetek Hand Multimeter ANADOLU UNIVERSITY EEM311 – Experiment 4 5 Procedure : Part 4A: Determination of Transformer Parameters Connect all necessary instrumentations to perform the open-circuit test. Perform the test and record the data. Practical Diagram for Open Circuit Test: Voc Ioc Poc ANADOLU UNIVERSITY 220 V EEM311 – Experiment 4 6 Make all necessary instrumentations to perform the short-circuit test. Perform the test and record the data. Practical Diagram for Short Circuit Test: Vsc Isc Psc 2.27 A Using the data recorded from open and short circuit tests, try to find out the elements of approximate equivalent circuit of the test transformer referred to primary winding. Draw your circuit. ANADOLU UNIVERSITY EEM311 – Experiment 4 7 Part 4B: Determination of Transformers Performance (Load Test) Using the R and L load banks provided, run the load test for the transformer to fill the following table. The load configuration will be given to you by your teaching assistant. Calculate and record I1rated. Calculate n. Using the results recorded from open and short circuit tests, calculate Ph+e and Pcu for each step. Calculate the efficiency for each step. Plot efficiency versus loading (x axis) curves for unity and lagging power factor cases. cos φ Load position I1 V2 P (Watt) I1-rated n (I/Irated) Ph+e Pcu η 1 2 3 1 (resistive) 4 5 6 7 1 2 3 _____ (inductive) 4 5 6 7 Position 1 2 3 4 5 6 7 DL 1017R DL 1017L Resistive load bank Inductive load bank 1050 Ω 4.46 H 750 Ω 3.19 H 435 Ω 1.84 H 300 Ω 1.27 H 213 Ω 0.90 H 150 Ω 0.64 H 123 Ω 0.52 H ANADOLU UNIVERSITY EEM311 – Experiment 4