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# Fourth Lesson Im

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blocked rotor test IM

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• *A carico
• ### Fourth Lesson Im

1. 1. CLIL experience Content and Language Integrated Learning 4 th Fourth lesson
2. 2. <ul><li>Another test in order to have motor parameters is blocked rotor test . This test is similar to the short circuit test of transformer. </li></ul><ul><li>Purpose of this test is to determine load dependant losses and stator & rotor reactance and rotor resistance . </li></ul><ul><li>The rotor is blocked to prevent rotation and balanced voltages are applied to the stator terminals at rated frequency. Applied voltage is gradually increased till rated current is achieved. </li></ul><ul><li>Current, voltage and power are measured at the motor input and from this data motor parameters are calculated. </li></ul>Three-phase induction motor OBJECT: To perform blocked rotor test of 3-phase Induction M.
3. 3. Theory <ul><li>Under blocked rotor condition the rotor is at rest and, therefore, </li></ul><ul><li>the slip is unity. The load resistance R 1 (1-S)/S is zero. </li></ul><ul><li>Thus the equivalent circuit of Fig. </li></ul>I A
4. 4. Theory In an induction motor, if full voltage is applied across the stator terminals with the rotor not allowed to rotate, about six to eight times its full-load current will flow in the circuit. Blocked-rotor test is conducted at a reduced voltage V S so that current, I S equals to only the full-load current flow through the circuit. The applied voltage V S under blocked rotor condition is, therefore, about one-sixth to one-eighth of the normal voltage. At this reduced voltage the current I 0S flowing through the parallel branch is very small, and can be neglected. R e ’ and X e ’ are stationary resistence and reactance in series connected across the applied voltage, V S . If W S is the input power under blocked-rotor condition, I S is the current and cos φ S is the power factor, then as a result: 
5. 5. <ul><li>R 1 can be measured by ammeter-voltmeter method by applying DC to </li></ul><ul><li>the stator winding. To get AC resistance at 50Hz, the value of R 1 so </li></ul><ul><li>obtained is to be multiplied by a factor, say, 1.5. Thus R 1 and R 2 ’ of </li></ul><ul><li>R e ’ can be separated as R 2 ’ = R e ’- R 1 . There is no simple way of </li></ul><ul><li>separating X 1 and X 2 ’ from X e ’ except arbitraly. X 1 may be taken </li></ul><ul><li>equal to X 2 ’ so that X 1 = X 2 ’ = X e ’ / 2 . </li></ul><ul><li>Thus the equivalent circuit elements as envisaged in Picture are </li></ul><ul><li>found out. As mentioned earlier, all calculations regarding the </li></ul><ul><li>performance of an induction motor can be done using the equivalent </li></ul><ul><li>circuit with some approximations. </li></ul>Theory The impedence And
6. 6. Elaborations otherwise
7. 7. Three-phase induction motor CIRCUIT DIAGRAM APPARATUS 1. Voltmeter 2. Ammeter 3. Two wattmeters 4. Two Auto transformer OBJECT: To perform blocked rotor test of 3-phase Induction M. <ul><li>AIMS </li></ul><ul><li>load dependant losses </li></ul><ul><li>stator & rotor reactance </li></ul><ul><li>rotor resistance </li></ul>
8. 8. Procedure <ul><li>Choose the apparatus and measuring instruments. </li></ul><ul><li>Choose the connection: star or delta </li></ul><ul><li>Make the circuit as shown in the picture. </li></ul><ul><li>Keep rotor of induction motor pressed, so that it cannot </li></ul><ul><li>rotate even upon energization. </li></ul><ul><li>start increasing voltage slowly till at the 10% plus of the </li></ul><ul><li>rated current is achieved. </li></ul><ul><li>Note down the readings of all instruments connected. </li></ul><ul><li>Repeat the test with decreasing current until zero. </li></ul>
9. 9. Results
10. 10. Results <ul><li>Diagram </li></ul>V S [volt] 0 25 50 75 100 125 150 175 200 225 250 275 0 2 4 6 8 10 12 14 16 18 20 22 24 V S [V] V S V R I R I cc
11. 11. Observation - Results
12. 12. Results W S [watt] 0 50 100 150 200 250 300 350 400 450 500 550 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 W S [watt]
13. 13. Results cosf S 0,00 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 cosf S
14. 14. Results V S [volt] 0 10 20 30 40 50 60 70 80 90 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 V S [V]
15. 15. Results <ul><li>Diagram result </li></ul>V S [volt] 0 25 50 75 100 125 150 175 200 225 250 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 V S [V] V R V S I R I CC
16. 16. Answer to the following questions <ul><li>How will the power factor vary if the voltage supply decreases? </li></ul><ul><li>To what test is similar the blocked rotor test? </li></ul><ul><li>What are the aims of the blocked rotor test? </li></ul><ul><li>What instrument can the motor speed be measured with? </li></ul><ul><li>How much is the voltage when the current is rated? </li></ul><ul><li>Under blocked rotor condition, how is the slip? </li></ul><ul><li>How much is the percentage on the voltage at blocked rotor test V S compared with rated current I R ? </li></ul><ul><li>Under blocked rotor condition, how is the load resistance R 1 (1-S)/S ? </li></ul><ul><li>What is the procedure in order to carry out blocked rotor test of 3-phase induction motor? </li></ul><ul><li>How much the current will flow in the circuit when the rotor is blocked and rated voltage is applied to the stator terminals ? </li></ul>
17. 17. Fill the gaps <ul><li>Blocked rotor ……. is similar to short circuit test </li></ul><ul><li>of ……….. </li></ul><ul><li>The …….. is blocked to prevent …………. </li></ul><ul><li>Applied ………. is gradually increased till rated …………. is achieved </li></ul><ul><li>From data input of current, voltage and ……… motor parameters are ………….. </li></ul><ul><li>Under ……….. rotor condition the slip is ……. and the load resistance R 1 (1-S)/S is ……….. </li></ul><ul><li>The applied ……….. V S under blocked rotor condition is about ………… to one-eight of the normal ………... </li></ul><ul><li>Under reduced voltage the ………. I 0S flowing through the parallel branch is very small, and can be …………. </li></ul>