machine labac

8/6/2019 Machine Labac

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AIM: No-load & Blocked-rotor Tests on

3-phase Squirrel Cage Induction Motor

AIM: Slip Test on 3-phase Salient Pole

Synchronous Machine

AIM: Voltage Regulation on Alternator

AIM: V-Curves of Synchronous

Machines

AIM: Speed Control of Induction Motor

by Variable Frequency Method


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APPARATUS:.


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PROCEDURE:

A) NO LOAD TESTMake the connections as shown in figure.

i) Keep the autotransformer in minimum

voltage position

ii) Keep belt on brake drum in looseposition (motor on no load) Switch on the

3 phase supply. Adjust autotransformer

and apply rated voltage to the stator.

Since the power factor of the induction

motor under no load condition is

generally less than 0.5, one wattmeter will

show negative reading. Then switch off

the supply and interchange the

connections of the pressure coil (orcurrent coil) of that wattmeter. Note down

the ammeter, voltmeter Reading


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B) BLOCKED ROTOR TEST

1) Make the connections as shown in

figure.2) Keep the autotransformer in minimum

voltage position

3) Rotor is blocked by tightening the belt

on the brake drum. Switch on the 3 phasesupply.Adjust the autotransformer so that

rated current (to get full load copper loss)

flows in the ammeter. Note down

voltmeter, ammeter and wattmeterreadings. (If any of the wattmeter reads

negative, switch off the supply and

interchange the connections


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Circuit diagram of No load test


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Circuit diagram of Blocked rotor test


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STATOR RESISTANCE MEASUREMENT


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APPARATUS:


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CIRCUIT DIAGRAM SLIP TEST ON 3-PHASE SALIENT POLE

SYNCHRONOUS MACHINE


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PROCEDURE:

SLIP TEST

1)Make the connections as shown infigure.

2) Keep the autotransformer at minimum

voltage position

3) Keep DPST, TPST and SPST switchesopen

4) Keep dc motor field rheostat at

minimum resistance position Switch

on the d.c. supply by closing the DPSTswitch. Using the three point starter,

start the motor. Run the motor at

synchronous speed by varying the

motor field rheostat.


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5)Close the TPST switch. By adjusting

the autotransformer, apply 20% to 30%

of the rated voltage to the armature ofthe synchronous machine.

6)Make sure that the direction of rotation

of the prime mover and the direction of

rotation of the magnetic field producedin the armature are the same by closing

the SPST switch. If the voltmeter

reading across the alternator field

winding is very small, both thedirections are correct.


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APPARATUS:


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OPEN CIRCUIT & SHORT CIRCUIT CHARACTERISTICS

(OCC & SCC)

Circuit diagram for Voltage Regulation on

Alternator


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ZERO POWER FECTOR CHARACTERISTICS


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PROCEDURE:

i) OPEN CIRCUIT & SHORT

CIRCUIT CHARACTERISTICS(OCC & SCC)

1)Make the connections as shown in

diagram.

2) TPST in open position3) DPST1 and DPST2 in open position

4) Motor field rheostat in minimum

position

5) Potential divider in minimum voltageposition


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ii) ZERO POWER FACTOR

CHARACTERISTICS (ZPFC)

Make the connections as shown indiagram.

i) TPST in open position

ii) DPST1 and DPST2 in open position

iii) Motor field rheostat in minimumposition

iv) Potential divider in minimum voltage

position


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APPARATUS


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CIRCUIT DIAGRAM FOR V CURVE OF SYNCHRONOUS

MACHINE


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PROCEDURE:

Make the connections as per the diagram.

1) Keep dc motor field rheostat inminimum position

2) Keep alternator field potential divider

in the minimum voltage position

3) Keep DPDT, DPST, TPST1, TPST2switches open

4) Keep the load on DC side in off

position.


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APPARATUS


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PROCEDURE:

1)Make the connections as shown in

diagram.2) TPST in open position

3) DPST1 and DPST2 in open position

4) Motor field rheostat in minimum

position5) Potential divider in minimum voltage

position

6) Autotransformer at minimum voltage

position7) Keep the belt on the brake drum of

induction motor in loose position

(induction motor on no load).

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