# Fourth Lesson Im

## by guest74090e37 on Jan 11, 2010

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blocked rotor test IM

blocked rotor test IM

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## Fourth Lesson ImPresentation Transcript

• CLIL experience Content and Language Integrated Learning 4 th Fourth lesson
• Another test in order to have motor parameters is blocked rotor test . This test is similar to the short circuit test of transformer.
• Purpose of this test is to determine load dependant losses and stator & rotor reactance and rotor resistance .
• 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.
• Current, voltage and power are measured at the motor input and from this data motor parameters are calculated.
Three-phase induction motor OBJECT: To perform blocked rotor test of 3-phase Induction M.
• Theory
• Under blocked rotor condition the rotor is at rest and, therefore,
• the slip is unity. The load resistance R 1 (1-S)/S is zero.
• Thus the equivalent circuit of Fig.
I A
• 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: 
• R 1 can be measured by ammeter-voltmeter method by applying DC to
• the stator winding. To get AC resistance at 50Hz, the value of R 1 so
• obtained is to be multiplied by a factor, say, 1.5. Thus R 1 and R 2 ’ of
• R e ’ can be separated as R 2 ’ = R e ’- R 1 . There is no simple way of
• separating X 1 and X 2 ’ from X e ’ except arbitraly. X 1 may be taken
• equal to X 2 ’ so that X 1 = X 2 ’ = X e ’ / 2 .
• Thus the equivalent circuit elements as envisaged in Picture are
• found out. As mentioned earlier, all calculations regarding the
• performance of an induction motor can be done using the equivalent
• circuit with some approximations.
Theory The impedence And
• Elaborations otherwise
• 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.
• AIMS
• stator & rotor reactance
• rotor resistance
• Procedure
• Choose the apparatus and measuring instruments.
• Choose the connection: star or delta
• Make the circuit as shown in the picture.
• Keep rotor of induction motor pressed, so that it cannot
• rotate even upon energization.
• start increasing voltage slowly till at the 10% plus of the
• rated current is achieved.
• Note down the readings of all instruments connected.
• Repeat the test with decreasing current until zero.
• Results
• Results
• Diagram
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
• Observation - Results
• 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]
• 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
• 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]
• Results
• Diagram result
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
• Answer to the following questions
• How will the power factor vary if the voltage supply decreases?
• To what test is similar the blocked rotor test?
• What are the aims of the blocked rotor test?
• What instrument can the motor speed be measured with?
• How much is the voltage when the current is rated?
• Under blocked rotor condition, how is the slip?
• How much is the percentage on the voltage at blocked rotor test V S compared with rated current I R ?
• Under blocked rotor condition, how is the load resistance R 1 (1-S)/S ?
• What is the procedure in order to carry out blocked rotor test of 3-phase induction motor?
• How much the current will flow in the circuit when the rotor is blocked and rated voltage is applied to the stator terminals ?
• Fill the gaps
• Blocked rotor ……. is similar to short circuit test
• of ………..
• The …….. is blocked to prevent ………….
• Applied ………. is gradually increased till rated …………. is achieved
• From data input of current, voltage and ……… motor parameters are …………..
• Under ……….. rotor condition the slip is ……. and the load resistance R 1 (1-S)/S is ………..
• The applied ……….. V S under blocked rotor condition is about ………… to one-eight of the normal ………...
• Under reduced voltage the ………. I 0S flowing through the parallel branch is very small, and can be ………….