Fourth Lesson Im

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
load dependant losses
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 ………….

Fourth Lesson Im

by guest74090e37 on Jan 11, 2010

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