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Lab Manuals for Electrical Machines 2 - EM2 By ramesh bhattu

  • Electrical Machines 2 - EM2
  • Practical
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Note: - The standard symbols must be used in the circuit diagram in the report to be submitted. Precautions and Safety Measures: 1. All students should wear shoes with rubber sole. 2. Dress should be suitable for working safely near the rotating machines (Loose clothes are NOT allowed). 3. Get your circuit connections approved by the instructors, before switching the power supply ON. 4. Do not touch any live terminals or wires. For making any changes in the connections, you must switch-off the power supply. 5. Be alert and proceed with caution at all times in the laboratory. INSTRUCTIONS REGARDING CONDUCTION OF THE LAB COURSE NO. EEE/INSTR F211: Electrical Machines 1. General instructions will be given in the first lab session. 2. Familiarize yourself with the laboratory with the help of instructors. 3. Note down the Name Plate Rating (NPR) of the device(s) / machine(s) for the experiment to be conducted. 4. Read the procedure carefully and be prepared to conduct the experiment. 5. Before starting the experiment: (a) Draw the circuit diagram on a separate sheet of paper without consulting the manual. Get it verified by the instructor. (b) Write down the instruments and accessories that you need to conduct the experiment (along with their ranges, rating etc.). 6. Connect the circuit components as per the circuit diagram. Get the circuit connections verified by the instructor before you conduct the experiment. 7. Carry out the experiment as per the steps given in the manual and record the readings. 8. All the necessary computations are to be carried out in the laboratory itself. 9. Get the readings and subsequent computations verified by the instructor. 10. If you have any suggestions/queries regarding the conduction of the experiment(s), consult the lab instructor prior to the lab session. -2-

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EXPERIMENT No. 1 TESTS ON A SINGLE-PHASE TRANSFORMER Name _______________________________________ ID No.___________________________ Sec.No ______________________ Batch No.____________ Marks obtained________________ Date___________________________ Instructor’s signature_____________________________ --------------------------------------------------------------------------------------------------------------------1. Introduction Equivalent Circuit Taking into account each winding resistance and leakage reactance, magnetizing current and no-load losses, a transformer can be represented by the equivalent circuit shown in Fig.1.1. The equivalent circuit, though approximate, is quite accurate for practical purposes. Fig.1.1 Equivalent circuit of transformer Req  R1  R2' X eq  X 1  X 2' Here, R1 and X1 are resistance and inductance of primary winding. R2’ and X2’ are the resistance and inductance of secondary winding referred to the primary side. 2. Objective To determine the parameters of the equivalent circuit of a single-phase transformer and estimate the performance characteristics. 3. Name plate ratings of the transformer to be tested: ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. 4. Range of instruments and accessories (standard format) -3-

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S. No. DESCRIPTION TYPE RANGE MFR. NAME MFR. NO. Note: In O.C. test, voltage applied is rated while current drawn is 5-8% of full-load current. In S.C. test, full-load current is drawn while the voltage applied is 5-8% of rated-voltage. 5. Circuit Diagrams (a) Circuit diagram (b) Equivalent circuit Fig.1.2 O.C. Test; conducted from LV side (a) Circuit diagram (b) Equivalent circuit Fig.1.3 S.C. Test; conducted from HV side 6. Methodology -4-

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The parameters of the equivalent circuit of Fig.1.1 can be determined by the non–loading tests. Open Circuit Test – for determining shunt parameters (Gi and Bm) Short Circuit Test – for determining series parameters (Req and Xeq) a) Voltage ratio (≈ turns ratio) Test Now, temporarily connect a voltmeter (of appropriate rating) on HV side (open) and record V2. Then, voltage ratio (≈ turns ratio) = V2 = V1 (1.4) b) Open Circuit (O.C.) Test Connect the transformer as in Fig.1.2 (a), keeping the HV side open and LV side to be excited from mains. Switch on the mains and take the following readings. Readings Applied voltage (rated), V1 = No load current, I0 = No load power (= core loss), Pi = c) Short-Circuit Conduct the test from HV side with LV short-circuited as in the diagram of Fig.1.3 (a). To circulate full–load current through the transformer, reduced voltage of about 5 -8% of the rated voltage is needed. This supply is obtained from a variac. Turn the variac wheel to zero voltage output position and then switch on the supply for the transformer under test. Raise the variac voltage gradually till input current to transformer reaches it’s full –load value. Record meter readings. Readings Applied Voltage, VSC = Input current, ISC = Input power (=copper loss at rated current), PSC = 7. Calculations -5-

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