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ELECTRICAL MACHINES – II LAB

ELECTRICAL MACHINES-II

LABORATORY

DEPT. OF EEE, PSCMRCET ELECTRICAL MACHINES – II LAB

LIST OF EXPERIMENTS PAGE NO

1. Brake test on three phase Induction Motor 1 - 7

2. No-load & Blocked rotor tests on three phase Induction motor 8 - 15

3. Regulation of a three –phase alternator by synchronous 16 - 23 Impedance & M.M.F. Methods

4.V and Inverted V curves of a three- phase synchronous motor 24 - 30

5.Determination of Xd and Xq of a salient pole synchronous 31 - 36 Machine

6.Regulation of three–phase alternator by Potier triangle method 37 - 45

7.Equivalent Circuit of a single phase induction motor 46 - 54

8.Speed control of induction motor by V/f method. 55 - 63

9.Determination of efficiency of three phase alternator by 64 - 70 loading with three phase induction motor.

10.Power factor improvement of single phase induction motor 71 - 75 by using capacitors and load test on single phase induction

motor

DEPT. OF EEE, PSCMRCET ELECTRICAL MACHINES – II LAB

INDEX

EXPT PAGE STAFF

S.NO DATE NAME OF THE EXPERIMENT MARKS

NO. NO SIGN.

DEPT. OF EEE, PSCMRCET ELECTRICAL MACHINES – II LAB

CYCLE OF EXPERIMENTS

CYCLE - I

1.Brake test on three phase Induction Motor

2. No-load & Blocked rotor tests on three phase Induction motor

3. Regulation of a three –phase alternator by synchronous Impedance & M.M.F. Methods

4.V and Inverted V curves of a three- phase synchronous motor

5.Determination of Xd and Xq of a salient pole synchronous Machine

CYCLE – II

6.Regulation of three–phase alternator by Potier triangle method

7.Equivalent Circuit of a single phase induction motor

8.Speed control of induction motor by V/f method.

9.Determination of efficiency of three phase alternator by loading with three phase induction motor.

10.Power factor improvement of single phase induction motor by using capacitors and load test on single phase induction motor

DEPT. OF EEE, PSCMRCET

ELECTRICAL MACHINES – II LAB (R13)

EXPT.NO. : DATE :

BRAKE TEST ON THREE PHASE INDUCTION MOTOR

AIM: To obtain the performance curves of a three phase induction motor by conducting brake test.

NAME PLATE DETAILS:

3Ø INDUCTION MOTOR

APPARATUS:

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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CIRCUIT DIAGRAM :

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PROCEDURE:

1. Connect the circuit as per the circuit diagram. 2. The supply is given and the stator button is pressed down, the motor stars from rest. 3. The readings as all meters and speed are noted in the table. The load on the motor is gradually increased up to its full load value by tightening the belt over the brake drum. 4. At each load the ratings of all meters, spring balances and speed of rotor are noted. 5. The load on the motor is removed, the supply is cut off. 6. Calculations are made as shown and draw the graphs for O/P versus speed, versus current, O/P -efficiency, O/P- slip, O/P- Torque, O/P-Power factor .

Formulae Used :

1. Torque = ( S1~ S2 ) ( R ) x 9.81 N-m Where, S1, S2 - Spring Balance readings in Kg R - Radius of the brake drum in ‘m’

2. Output Power = 2πNT/60 Watt

N - Rotor Speed in RPM T - Torque in N-m

3. Input power = ( W1 + W2 ) Watts W1, W2 - Wattmeter Readings

Output Power 4. Percentage efficiency = ------X 100 Input Power Ns - Nr 5. Percentage Slip = ------X 100 Ns Where, NS - Synchronous Speed Nr - Rotor Speed 6. Power Factor = Cos[Tan-1 {√3(W1 - W2)/( W1 + W2)]

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OBSERVATIONS:

Power Factor

Slip

Efficiency(%)

Output

Torque(N-M)

Speed (RPM)

(kg)

Readings

Spring Balance

(kg)

+ W +

= W =

(Watts)

+ W +

1 1

W W

W W W =

W (Watts)

InputPower

W (Watts)

Current(Amps)

Voltage(Volts)

S.No

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PRECAUTIONS: 1. Connections should be tight, avoid loose connections. 2. Correct rated meters should be selected from the name plate details. 3. While during the experiment see that the meter readings should not be exceed its rated values. 4. Note down the readings without any parallax error.

MODEL GRAPHS: S

%S CosΦ N IL T %η %η T in N-m

CosΦ

N In rpm

IL in Amps

RESULT :

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VIVA-QUESTIONS: 1. Define Slip in Induction Machine?

2. Why Induction Machine always runs below synchronous speed ?

3. How direction of 3 phase Induction Motor can be changed ?

4. What are the different starting methods of 3 phase induction motor?

5. When we can get Maximum Torque in Induction Motor while starting?

6. What are the different losses in 3 phase induction motor?

7.What is the relation between torque and supply voltage in 3 phase induction

motor?

8. Why skewing is done in squirrel cage Induction motor?

DEPT. OF EEE, PSCMRCT 7 ELECTRICAL MACHINES – II LAB (R13)

EXPT.NO. : DATE :

NO-LOAD & BLOCKED ROTOR TESTS ON THREE PHASE INDUCTION MOTOR

AIM : To conduct the no load test and Blocked rotor test on three phase squirrel cage induction motor and to draw the equivalent circuit.

NAME PLATE DETAILS :

3-Ø INDUCTION MOTOR AUTOTRANSFORMER

APPARATUS REQUIRED:-

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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CIRCUIT DIAGRAM FOR NO LOAD TEST :

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CIRCUIT DIAGRAM FOR BLOCKED ROTOR TEST :

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PROCEDURE:

NO LOAD TEST:

1. Make the connections as per the circuit diagram. 2. The 3- autotransformer is kept in zero voltage position and see that the brakedrum rotates freely. 3. TPST switch is closed. By adjusting the 3- auto transformer variable knob, increase the applied voltage gradually until the voltmeter reads the rated voltage of the motor.

4. Note the voltmeter (V0), Ammeter (I0) & Wattmeter (W1, W2) readings. 5. Bring the 3- autotransformer to zero output voltage position and open the supply TPST switch.

BLOCKED ROTOR TEST:

1. Tight the belt around the brake drum to block the rotor of induction motor. 2. The applied voltage is increased slowly by varying 3- autotransformer variable knob until the ammeter reads rated current.

3. Note down Voltmeter (Vsc), ammeter (Isc) & wattmeter (Wsc) reading. 4. Bring the 3- autotransformer to zero output voltage position and open the supply TPST switch.

PRECAUTIONS:-

1. The auto transformer should be kept at minimum voltage position 2. Initially all switches are in open position 3. Note down the readings without parallax error.

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MODEL GRAPH

OBSERVATIONS:

TABLE 1:

FOR NO LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR

No load No load Wattmeter readings 1 Po  P = W – W  = Cos   voltage Current 0 1 2   (W)  3V0I0  V (V) I (A) W1(W) W2 (W) 0 0 Degree

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TABLE 2:

FOR BLOCKED ROTOR TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR

 P   = Cos1 o  VSC (V) ISC (A) Wsc (Watt) SC    3VSCISC 

RESULTS:

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VIVA-QUESTIONS:

1. Name the tests to be conducted for predetermining the performance of 3-phase induction machine.

2. What are the information’s obtained from no-load test in a 3-phase I M?

3. What are the information’s obtained from blocked rotor test in a 3-phase I M?

4. What is circle diagram of an I M?

5. What are the advantages of 3-phase induction motor?

6. What are the methods adopted to reduce harmonic torques?

DEPT. OF EEE, PSCMRCT 15 ELECTRICAL MACHINES – II LAB (R13)

EXPT.NO. : DATE :

REGULATION OF A 3- ALTERNATOR BY SYNCHRONOUS IMPEDANCE AND M.M.F METHODS AIM: To predetermine the regulation of an alternator by i) Synchronous Impedance & ii) M.M.F method.

NAME PLATE DETAILS:

3Ø Alternator DC Shunt motor

APPARATUS REQUIRED:-

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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CIRCUIT DIAGRAM :

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PROCEDURE:

1. Connect the circuit as per the circuit diagram. 2. Start the motor with the help of 3-point starter and adjust the field regulator of a Motor till rated speed obtained. 3. Keep the TPST knife switch open position and by varying the excitation of the Alternator, note down the ammeter and voltmeter readings in (table-1) till rated field Current of the alternator. 4. Now, close the TPST knife switch and by varying the excitation of the alternator note down field current short circuit current (in table-2) till rated field current of the Alternator. 5. Draw the graphs and calculate the regulation.

PRECAUTIONS:-

1. Avoid loose connections. 2. Correct rated meters should be used from the nameplate details. 3. While doing the experiment see that meter readings should not exceed its rated value. 4. Note down the readings without any parallax error.

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OBSERVATIONS:-

OPEN CIRCUIT TEST:

Terminal voltage V = V / 3 in S.No Field current ph 1 VL in volts Volts

SHORT CIRCUIT TEST:

S.No Field current in A Short Circuit current in A

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CALCULATIONS :-

FORMULAE USED :

1. Armature Resistance, Ra = 1.2Rdc Where, Rdc – is the resistance arranged with D.C.

Open Circuit Voltage per phase 2. Synchronous Impedance, Zs = ------Short Circuit Current

2 2 3. Synchronous Reactance, Xs = √ (Zs -Ra )

2 4. Open Circuit Voltage, Eo = √ (Vrated CosØ + IaRa) + (Vrated SinØ + IaXs)2 --- (For Lagging PF)

2 5. Open Circuit Voltage, Eo = √ (Vrated CosØ + IaRa) + (Vrated SinØ - 2 IaXs) ----(For Leading PF)

2 6. Open Circuit Voltage, Eo = √ (Vrated CosØ + IaRa) + 2 (IaXs) -----(For Unity PF) Eo - Vrated 7. Percentage Regulation = ------X 100 Vrated

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MODEL GRAPH :

RESULT:

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VIVA-QUESTIONS: l. What is an alternator?

2. What are the types of alternator’?

3. Define voltage regulation of an alternator?

4. Mention the methods by which voltage regulation can be determined.?

5. Which method gives the result nearer to the actual value?

6. How synchronous impedance is calculated from OCC and SCC?

7. Why is the synchronous impedance method of estimating voltage regulation considered as pessimistic method?

8. Why is the MMF method of estimating the voltage regulation considered as the optimistic method?

DEPT. OF EEE, PSCMRCT 23 ELECTRICAL MACHINES – II LAB (R13)

EXPT.NO. : DATE :

V AND INVERTED V CURVES OF A THREE PHASE SYNCHRONOUS MOTOR

AIM: To study the effect of excitation on Armature Current and Power Factor and to plot V and Inverted V Curves

NAME PLATE DETAILS:

SYNCHRONOUS MOTOR

APPARATUS :

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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CIRCUIT DIAGRAM :

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PROCEDURE: 1. Connect the circuit as per circuit diagram. 2. Set the excitation of synchronous motor to 40% of its rated field current and move the switch to position 1. 3. Switch ON the supply and press the start button and swift the excitation switch from position 1 to position 2. 4. Now the motor runs as a synchronous motor. 5. Vary the excitation of synchronous motor and note down the readings of Voltmeter, Ammeters and Power Factor meter. 6. Press the stop button and switch off the supply.

7. Draw the graph for Ia versus If and cosØ versus If.

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OBSERVATIONS:

Armature current Armature current Voltage (V) Power Factor S.No in Volts (Ia) (If) (CosØ) in amps in amps

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MODEL GRAPHS:

RESULTS:

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VIVA-QUESTIONS: 1. With what condition synchronous motor can be used as a synchronous condenser?

2. What are the special applications of an over excited synchronous motor?

3. Explain the effect of change of excitation of a synchronous motor on its armature current?

4. Explain the effect of change of excitation of a synchronous motor on its power factor.?

5. what are the starting methods of synchronous motor?

DEPT. OF EEE, PSCMRCT 30 ELECTRICAL MACHINES – II LAB (R13)

EXPT.NO. : DATE :

DETERMINATION OF Xd and Xq OF A SALIENT POLE SYNCHRONOUS MACHINE

AIM: To Conduct the Slip test on three phase alternator and to determine the The direct and quadrature axis reactance.

NAME PLATE DETAILS :

D.C.SHUNT MOTOR ALTERNATOR

APPARATUS :-

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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CIRCUIT DIAGRAM :

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PROCEDURE:

1. Connect the circuit as per the circuit diagram 2. Ensure that external resistance in field circuit of a dc motor is maximum and resistance in field circuit of an alternator is maximum. 3. Switch on DC supply to DC motor.. 4. Adjust the speed of the DC motor slightly increased synchronous speed of the alternator by varying the resistance in the field winding of DC motor 5. Ensure that setting of 3-Φvariac is at zero position 6. Switch on 3-ΦACsupply to the stator winding of an alternator. 7. Ensure that the direction of rotation of an alternator when run by dc motor and when run as 3-Φinduction motor at reduced voltage is the same. 8. Adjust the voltage applied to stator winding till current in the stator winding is approximately full load rated value. 9. Under these conditions current in stator winding applied voltage to stator winding and induces voltage in open field circuit will fluctuate from minimum value to maximum value which are recorded by using meters. 10. Reduce the applied voltage to stator winding of an alternator and switch off 3-Φ ac supply 11. Decrease the speed of dc motor and switch off dc supply

PRECATIONS:

1. Loose connections are avoided. 2. Note down the readings with out parallax errors. 3. Correct rated meters should be used.

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OBSERVATIONS:-

Voltmeter reading Ammeter reading Xq

v min v min Xd S.NO Xd= Xq= in min max min max i max i max

CALCULATIONS:

1. Armature Resistance = V min 2. Direct Axis Impedance per Phase(Zd) = in Ohms Im ax 3. Quadrature Axis Impedance per Phase (Zq) = V max in Ohms Im in 4. Direct Axis Reactance per Phase(Xd) = (Zd 2  Ra 2 ) in Ohms 5. Quadrature Axis Reactance per Phase (Xq) = (Zq 2  Ra 2 in Ohms Eo Vrated 6. Percentage regulation = 100(For both EMF and MMF method) Vrated

RESULT:

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VIVA –QUESTIONS: 1. What is the purpose of slip test on 3 phase alternator?

2. What is meant by direct axis reactance?

3. What is meant by quadrature axis reactance?

4. How is the regulation of alternator predetermined by slip test?

5. What is the difference between salient pole alternator and cylindrical rotor type alternator?

DEPT. OF EEE, PSCMRCT 36 ELECTRICAL MACHINES – II LAB

EXPT.NO. : DATE :

REGULATION OF THREE–PHASE ALTERNATOR BY POTIER TRIANGLE METHOD

AIM:- a) Perform open circuit and short circuit test on a 3-Φ alternator. b)Perform load test on 3-Φ alternator with highly lagging load (Approximately zero power factor) when rated voltage and rated current flowing in the starter winding. c) Find out regulation of alternator by using zero power factor method. NAME PLATE DETAILS:

DC MOTOR THREE PHASE ALTERNATOR

APPARATUS:-

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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37 ELECTRICAL MACHINES - II LAB

THEORY: Zero power factor saturation curve method is most reliable for determining the regulation of alternators because it properly takes into account of the effect of armature leakage reactance drop and the saturation. The following experimental data is needed to determine the regulation by this method. 1. Open circuit characteristic at rated speed of the alternator. 2. Field current corresponding to full load short circuit current. 3. Field current corresponding to full load, rated voltage, zero power factor. 4. AC resistance of the stator winding per phase of the alternator.

To plot zero power factor characteristic from the experimental data and to determine the regulation of the Alternator proceed as follows: Plotting of zero power factor characteristic

G OCC Air gap line D

T P

C E V

ZPF curve

D’

P’ C’

O B Ifsc Ifzp Field current Fig-1 Zero power factor characteristic of alternator  Draw the open circuit characteristic to proper scale and draw the air gap line as shown in Fig-1.

 Draw the field current, Ifsc corresponding to full load short circuit current (line OB).

 Draw the field current, Ifzp at rated voltage which corresponding to full load zero power factor, thus obtaining a point P on the zero power factor, full load characteristic (line TP).  From the point P draw a horizontal line PC representing the field current corresponding to full load short circuit current i.e. PC=OB.  From the point C draw a line CD parallel to air gap line.

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38 ELECTRICAL MACHINES - II LAB

 Join D and P. Now PCD is a triangle, which normally called as Potier triangle.

Determination of leakage reactance  Drop a perpendicular from the point D, meeting the line PC at the point E. then line ED represents the leakage

reactance drop, which is also called as Potier reactance drop (Ex).

Determination of Regulation

Fig-2 Determination of saturation effect

 Draw the current phasor, Ia as shown in Fig-2 horizontally, which is a reference phasor.  Terminal voltage phasor, V is drawn at power factor angle Φ with respect to current (line OA).

 Add armature resistance drop IaRa (line AB) to the terminal voltage phasor V.

 Potier reactance drop, Ex is added in quadrature to the current phasor (line BC).  Join O and C, line OC represents the internally generated emf, Eg.  Phasors OA and OC are projected by arc to vertical line.  Intercept DE shown by dotted horizontal line in Fig-2 represents the field current, Ifg corresponding to rated no load voltage.  The portion GH of the intercept FH represents the field current, Ifs which takes into account the effect of saturation.

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c s If

Fig-3 Phasor diagram for ZPF method  Draw the field current Ifg horizontally (line OS) as shown in Fig-3.  Add the field current Ifsc (line ST) at power factor angle Φ with the vertical as shown in Fig-3.  Join OT and add the field current Ifs (line TU), thus giving a total field current Ifl.

 No load emf, Eo corresponding to field current Ifl is found out from the open circuit characteristic. Then 

CIRCUIT DIAGRAM:

3 point starter

L F A

A1 + F1 R V Y FUSE 500 , 3 A DC SUPPLY M ALT. 0 – 300 V 220 Volt. B N

- F2 DPST A2 SWITCH F1 F2

+ A

FUSE , + A DC SUPPLY 220 Volt. 0 – 5 A 0 7

- DPST SWITCH Fig- 4 Circuit Diagram for O.C Test on alternator

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Fig- 5 Circuit Diagram for S.C Test on alternator

Fig- 6 Circuit Diagram for armature resistance measurement of alternator A

5 , 0 7

Fig-7 Zero power factor, full load test on alternator

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PRECAUTION: Before starting the dc shunt motor ensure that, the armature rheostat of the motor is kept in maximum position and field rheostat at minimum position.

PROCEDURE: 1. Open-Circuit characteristic: 5. Connect the alternator as shown in Fig-4. 6. The prime mover in this experiment is a D.C. shunt motor coupled with alternator. The speed of the alternator is adjusted to rated speed by varying field resistance of DC shunt motor. 7. Adjust the speed of alternator to rated speed with No-load for each setting of the field current of alternator and record the alternator terminal voltage.

8. Record readings [field current (If ) verses terminal voltage(Voc) of alternator] still open circuit voltage reaches 120% of the rated voltage of the machine in the observation table-1.

2. Short-Circuit characteristic: 5. Connect circuit diagram as in Fig-5, but short-circuit the armature terminals through an ammeter. 6. The current range of the instrument should be about 25-50 % more than the full load current of the alternator. 7. Starting with zero field current, increase the field current gradually and cautiously till rated current flows in the

armature and note down the readings( If versus Isc) in observation table-1 8. The speed of the set in this test also is to be maintained at the rated speed of the alternator.

3. Armature resistance measurement: 5. Connect the circuit as in Fig-6. 6. Switch ON the power supply. 7. Note down the readings ammeter(I) and voltmeter(V) correctly in the observation table-1 for different supply voltages. 8. Switch OFF the power supply.

4. For zero power factor test: 1. Connect the circuit as in Fig-7. 2. Set the field rheostat of alternator, so that the field current of alternator is minimum. 3. Switch on the dc supply and start the dc shunt motor with the help of starter. 4. Vary the field current of motor to obtain rated speed. 5. Switch on the dc supply to the field of the alternator. 6. Vary the field current of the alternator to obtain rated voltage. 7. Load the alternator gradually in steps and adjust the rated terminal voltage across the load at each step by increasing the field current, till full load of the alternator. 8. Decrease the load on the alternator gradually and side by side, reduce the field current of the alternator. 9. Switch off the dc supply to the field of the alternator and dc motor.

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OBSERVATION: Table – 1 (OC & SC Test and Ra Measurement)

Open Circuit Test Short Circuit Test Armature Resistance Sl. No. If Voc If Isc V I Radc Mean Radc Ra= 1.2*Radc

Table – 1 (ZPF Test)

Sl. No. Stator Current Terminal voltage Field current

REPORTS: 4. Plot on the same graph sheet, the O.C.C (open circuit terminal voltage per phase versus the field current), and the short-circuit characteristic (short-circuit armature current versus the field current). 5. Calculate the unsaturated value of the synchronous impedance, and the value corresponding to rated current at short circuit. Also calculate the corresponding values of the synchronous reactance. 6. Calculate regulation of the alternator under the following conditions: d) Full load current at unity power factor. e) Full load current at 0.8 power factor lagging. f) Full -load current at 0.8 power factor leading.

CALCULATIONS:

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CONCLUSION:

DISCUSSION:

1. What are the preconditions necessary for performing the Open Circuit characteristics test? 2. What is the power factor of alternator on Short Circuited condition? 3. Why is the Short Circuit characteristic a straight line? Up to what range of Short Circuit current the linearity is maintained? 4. Why do you think ZPF method is more accurate method as compared to synchronous impedance method? 5. By which other methods can you load the alternator for watt less current? 6. Discuss how it enables to separate the armature reaction drop from the leakage reactance drop. 7. Write in brief construction of the Potier triangle.

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VIVA-QUESTIONS 1. What is meant by alternator?

2. What are the applications of alternator?

3. What are the types of regulation of alternator?

4. Which method is the best of regulation of alternator?

5. Why do you think ZPF method is more accurate method as compared to synchronous impedance method?

6. What are the preconditions necessary for performing the Open Circuit characteristics test?

DEPT. OF EEE, PSCMRCT 45 ELECTRICAL MACHINES – II LAB (R13)

EXPT.NO. : DATE :

EQUIVALENT CIRCUIT OF A SINGLE PHASE INDUCTION MOTOR

AIM: To determine the Parameters of a single phase squirrel cage induction motor and to draw the circuit diagram of motor.

NAME PLATE DETAILS:

IØ Induction motor Autotransformer

APPARATUS:-

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

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CIRCUIT DIAGRAM :

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PROCEDURE :

NO-LOAD TEST:

1. Connect the circuit as per the circuit diagram. 2. Auto Transformer is set in zero output voltage position and supply is switched ON. 3. Set the autotransformer to read rated voltage of single phase induction motor 4. Note down all the meter readings at this position. 5. Calculate Zo from no-load test and hence estimate magnetizing reactance and also find Power factor from No-Load data.

BLOCKED ROTOR TEST:

1. Connect the circuit as per the circuit diagram. 2. Switch ON the DPST switch and adjust the autotransformer till the ammeter reads rated current. 3. Note down ammeter, voltmeter & wattmeter readings. 4. Calculate the leakage reactance & total resistance. 5. Finally calculate the efficiency & net torque, input power, output power.

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48 ELECTRICAL MACHINES – II LAB (R13)

PRECAUTIONS:

1. Avoid loose connections. 2. Correct rated meters should be used. 3. Meter readings should not exceed rated value. 4. Note down reading without parallax error.

OBSERVATIONS :-

NO-LOAD TEST:

S.No Open circuit voltage Open circuit current Open circuit o/p power Wo in watts

BLOCKED ROTOR TEST:

S.No Short circuit voltage Short circuit current short circuit o/p power Wsc in watts

CALCULATIONS:

No-Load Test data:

Vo No-Load equivalent Impedance = ZO = Io Wo No-Load equivalent resistance = RO = Io 2 2 2 No-Load equivalent reactance =XO = Z O  RO

DEPT. OF EEE, PSCMRCET Page 36

49 ELECTRICAL MACHINES – II LAB (R13)

From equivalent circuit,

Zo=Ro+jXo. 1 R2 Ro=R1 + 4

1 1 Rsc=R1+R2 R2 = Rsc – R1

Rsc = Wsc Isc 2 1 1 Xm X 2 1 Xsc Vsc Xo=X2 +  ; X1=X2 = ; Zsc = ; 2 2 2 Isc

Rotational Losses:

Rotational Losses(Wr) = Wo – (no load ”cu” Losses)

2 = Wo – IO RO 1 2 R2 = WO-IO (R1+ ) 4 % slip:

%slip = Ns  Nr X100 Ns

DEPT. OF EEE, PSCMRCET Page 37

50 ELECTRICAL MACHINES – II LAB (R13)

EQUIVALENT CIRCUIT :

X1 I1

R2’/2s V Xm 2 Ef X2’/2s

R2’/2(2-S)

X2’/2 Eb

DEPT. OF EEE, PSCMRCET Page 38

51 ELECTRICAL MACHINES – II LAB (R13)

RESULT:

DEPT. OF EEE, PSCMRCET Page 39

52 ELECTRICAL MACHINES – II LAB (R13)

DEPT. OF EEE, PSCMRCET Page 40

53 ELECTRICAL MACHINES – II LAB

VIVA - QUESTION: 1. What is a 1-phase induction motor?

2. Write the classification of 1-phase induction motor?

3. Why do we draw the equivalent circuit of 1-phase induction motor?

4. Explain double-field revolving theory?

5. Why 1-phase induction motor is not self-starting?

DEPT. OF EEE, PSCMRCT 54 ELECTRICAL MACHINES -II LAB

SPEED CONTROT OF 3 PH INDUCTION MOTOR BY VARIABLE FREQUENCY METHOD

AIM:To control the speed of the 3 ph induction motor by changing the supplyfrequency and to plotthe speed Vs frequency curve.

APPARATUS :

st.No APPARATUS SPECIFICATIONS qTY 01 VFD DRIVE 7.s HP (DETTA C2000) 01 02 MD METER 01 03 EXPERIMENT PANEL 01 3 PH MOTOR 5HP 01 05 RPM METER DIGITAL 01

THEORY:

AC Motor

The AC electric motor used in a VFD system is usually three-phaseinduction motor. Some types of single-phase motors or synchronous motors advantageous in some sitlations

can be used, but three-phase induction motors are usually generally preferred as the most economical motor choice. Motors that are designed for fircd-speed operation are oftea

used. Elevated-voltage stresses imposed on induction motors that are supplied by VFDS

require that such motors be designed for defioite-purpose inverter-fud duty in accordance with such requirem€nts as Part 31 of NEMA Standard MG-l.

CON1ROLLER

The VFD controller is a solid-state power electronics conversion system consisting of three distinct sub-systems: a rectifier bridge converter, a direct current (DC) link, and an ,Generic inverter. Voltage-source inverter (VSl) drives (see topologies' sub-section below) are by far the most common type of drives. Most drives are AC-AC drives in that they cont ert AC line input to AC inverter output However, in some applications such as common DC bus or solar applications, drives are configured as DC-AC drives. The most basic rectifier conveter for the VSI drive is configured as a three-phase, sir(-pulse, full-r.6ve diode bridge. ln a VSI drive, the DC link consists of a capacitor which smooth,s out the converter,s DC

55 ELECTRICAL MACHINES-II LAB output ripple and provides a stiff input to the inverter. This filtered DC voltage is converted to quasi-sinusoidal AC voltage output using the inverter's adive switching elements. VSI drives provide higher pow€r fu.to. and lower harmonic distortion than phase-controlled current-source inverter (CSl) and load-commutated inverter (LCl) drives (see 'Generic topotogies' sub-section belowl. The drive contloller can also be configured as a phase converter having single-phase converter input and three-phase inverter output.

Controller advances have exploited dramatic increases in the voltage afid current ratings and switching frequenry of solid-state power devices over the past six decades. lntroduced in 1983, the insulated-gate bipolar transistor (lGBTl has in the past two decades come to dominate VFOS as an inverter switching device.

ln the various industrial applications the induction motor is mostly used. The loads on induction motor always vary as per its application but speed of induction motor is

constant & cannot match with the load demand. lf load on induction motor decrease, the speed of inductioE motor .annot be dec.eased as per the load. Hence it takes rated

power from supply so the energy consume by the motor is same. Hence there is energy

consumption is same during load varying condition also, To overcom€ this problem a VFD is used in industrial application to save the energy consumption and eledricity billing. Variable frequency drive (VFDI usage has increased dBmatically in industrial applications. The VFD5 are now commonly (VFD). This device uses power electroniE to vary the frequency of input power to the motor, thereby controlling motor speed.

lnpLrt supply

This more generic term appliesto devices that controlthe speed ofeitherthe motor

or tlle equipment driven by the motor {tan, pump, compressor, etc,). This device can be either electronic or mechanical

Again, a more generic term applyingto both mechanicaland electriaal means of controlling speed

16 56 ELECTRICAL MACHINES - II LAB

DESCRIPTION:

It load need large speed variation, variable frequency drive (VFD) come with significant energy saving, if not, may be difficult to sustain VFD cost/ investment. First candidates to VFD are pump / fan systems, Vfd do provide some advantages, but there are also some disadvantages as well, like harmonic5 injection, motor insulation premature fails, cable reflection for lengths more than 10m. These issues must be controlled / put in balance. 5o, there are not advantages only by using a VFD.

Foa sure VFDS are big energy enablers. Yet official data ahnounced that only 10 to

20% of motors are equipped worldwide. And even with new motor classes, we will not reach the same level of savings. The trend is now motor being embedded intellitence for ener8y savings, this push VFD manufacturers enhan.e the saving rates of the VFD. Finally, people and earth will benefrt of their capabilities.

For the area where there is only single phase power supply available but you have three phase plant, in case ol less than 5 HP, by far the most efficient and easy way to convert single phase to three phase are the variable frequency drives out that can be equipped with sintle phase front ends, and provide variable lrequency three phase power. i have olle 5hp VFD on my water pump and could not be happier, not just for the ability to use a three phase motor, but also soft start, dynamic breaking, speed .ontrol, and direction control.

A variable-frequency drive is a device used in a drive system consisting of the following th.ee main sub-systems: AC motor, main drive controller assembly, and drive/operator interface.

Sine Vvave Variable M echanical Power Frequency Power Pou/er 1lariable AC [,{otor Frsguency .|Lt..r' Controller

Power Converslon Power Conversion Operator I nterface VFD system

57 ELECTRICAL MACHINES - II LAB

aLe€K q|Aq84!4

POWER MCB CONTACTOR METER

VFD

PROMMffi INDUCTION

SENSOR MOTOR

58 ELECTRICAL MACHINES - II LAB

PARAMETERS LIST DELTA C2OOO VFD PARAMETER PARAMETER PARAMETER PARAI,'iETEA SERIES NUMBER SETTING FUNC}!O},I 00 04 4 Di.hrlr e-ryq( s0 _. -.-r.1r ^,,L.n,.-. YUr.dEe 04 0 r'rirni-.. -..-.,,. ..._ 00 04 6 iri

o0 2a 1 Motor ON/OFF Command throu€h extemal 00 ..is{g!::*:iir," 21 2 M-t^r rlnl /^EE .^**-, , . _-.--:t :tr::l:Y11llE,,o -'.nroriSn r|L--l oa 20 0 so*.€e of :.eq uer':! .or,.trra; C tirouA; 00 zo _vsrlor.Erajds 2 so,utce of f requency rommand through rxler$atAnaiu6 I np 1 tirErrjff} 00 - " {iJ.j 20 1 5our.e _.l or rrequency !9m-9_$ ilfq !q- 01 0ol 50 I Hz Marim,,h-'---- ^--,-+L^*-,{ert I.---..i- rsqu

59 ELECTRICAL MACHINES - II LAB

\-\,<, )\ (-l Lt-

r I {

\ \ 7 t" on <\ L) ZI-+ oi i.'Jl "( i. S['

2_ Yil I 6u_*] al$

UL /: o.lt, -nt a l

60 ELECTRICAL MACHINES - II LAB

EXPERTMENT PROCEDURE:

1. Connedions are made as per the circuit diagram, 2. Switch ON the input supply Usin8 MC8. 3. Adiust the VFD Settings to desired speed. 4. Now run the motor using run button on the VFD. 5, Note down different parameters from multifundion meter 5. Note down the readings at different adjustments of VFD 7. Observe the speed variations with the corresponding rrariations in VFD 8. After all the parameters are taken stop the motor using stop button on the VFD 9, Now sw'rtch OFF the MCB,

OBSERVATIONS:

sL. NO. FREQUENCY SPEED

EFFICIENCY: sl.No I W=S1-S2 N T=9.8lxwxr olP= vP n=oP/lPxloo Kgs rpm N-M 2,,NT16A (watts)

61 ELECTRICAL MACHINES -II LAB

TABULATION Ia!d!!*tio$ tli4tor oq ao ktad Line voltage In volts F.€qlleirc]' In Hz Speed ofIM Ilr rpm

MODEL GRAPH:

streed Vs frequency curve on load 1*AO 1600 14 * 1 200 1000 800 6011 400 200 o 40 60 Freq e[cy fur Hz

62 ELECTRICAL MACHINES – II LAB

VIVA-QUESTIONS: 1. In what respect does a 1-phase Induction motor differ from a 3-phase Induction motor?

2. What happens if the air gap length is doubled?

3. What are the advantages and disadvantages of large air gap length in induction motor?

4. What would happen if a 3 phase induction motor is switched on with one phase disconnected?

5. What are the methods of speed control of three-phase induction motor?

6. How does controlling the speed of the motor using the v/f method give a constant current?

7. What are the advantages and disadvantages of v/f speed control method of induction motor?

8.Why should we maintain V/F ratio constant in induction motor?

DEPT. OF EEE, PSCMRCT 63 ELECTRICAL MACHINES -II LAB EFFICIENCY OF A THREE PHASE ALTERNATOR LOADING WITH 3PH INDUCTION MOTOR

AIM: To Conduct a suitable test on the given alternator and to determine the efficiency of a three phase alternator loading with induction motor.

APPARATUS :

SL.NO ITEM TYPE RANGE QUANTITY 01 AMMETER (DC) MC 5ADC 01 02 AMMETER (DC) MC 20ADC 01 03 VOLTMETER (DC) MC 500VDC 01 04 AMMETER (AC) MI 20AAC 01 05 VOLTMETER (AC) MI 500VAC 01 06 EXPERIMENT PANEL 01 07 SHUNT MOTOR COUPLED TO 01 ALTENATOR SET 08 INDUCTION MOTOR 01 09 CONNECTING WIRES Required

THEORY :

Whenever we convert one form of energy into another there are bound to be losses. No machine is perfect. Power is supplied to an alternator both in the form of electrical energy and in the form of mechanical energy. The electrical energy is supplied to the field coil. This energy is used to set up the main magnetic field. This field is constant. There is no energy taken from it in the generation of electricity. Therefore, since none of the power out comes from this energy, the power by the field must be counted as a loss.

Most of the power comes from the prime mover. Some of this mechanical power is lost to the windings and friction of the alternator. The mechanical losses do not depend on the alternator’s load. To find these losses it is necessary to determine the overall mechanical losses then subtract the losses of the prime mover.

Another class of losses that does not vary with load is the core losses. We are speaking here about the armature’s core. Since there is an alternating voltage generated, the core is contin- ually becoming magnetized with one polarity, de-magnetized, then magnetized with the other polarity each cycle. All of this magnetic activity in the core causes eddy current and hysteresis losses. These core losses depend on the alternator’s voltage, not on load.

As load current flows through the armature coils the resistance of the wire causes a power loss. This copper loss is proportional to the square of the current, P= Copper losses, therefore, increase rapidly with load.

Percent efficiency is the ratio between the power out and the power in. % Eff. = x 100. If the load has unity power factor, = E x I x 1.73. Regardless of load, = + losses.

64 ELECTRICAL MACHINES -II LAB

CIRCUIT DIAGRAM :

65 ELECTRICAL MACHINES - II LAB

TO FINDOUT THE ARMATURE RESISTANCE

ARMATURE RESISTANCE DETERMINATION:

S.No V I Rdc= V/I

Ra = 1.25 x Rdc (For one winding) Total armature resistance=3 x Ra (For three windings).

66 ELECTRICAL MACHINES- II LAB

PROCEDUCER : A. ROTATIONAL LOSSES:

1. Connect the DC machine as a shunt motor. 2. Clamp the motor but do not couple the alternator. 3. Give the 220VDC supply to the DC shunt motor. 4. Run the DC shunt motor to the above synchronous speed (1600RPM). 5. Read the motor’s voltage and current and record these readings in TABLE 6-1. 6. Turn off the DC supply to the motor. 7. Multiply voltage and current values of motor this value is rotational losses in motor (PML). 8. Couple the alternator to the motor. 9. With no connections made to the alternator. 10. Run the DC shunt motor to the above synchronous speed (1600RPM) 11. Read the motor’s voltage and current and record these readings. 12. Turn off the DC supply to the motor. 13. Multiply voltage and current values of motor to find total rotational losses in the motor and alternator (PMAL). Record this value in TABLE 6-1. 14. Compute the alternator’s rotational losses, PAL, by subtracting PML from PMAL, Record in TABLES 6-1 and 6-5.

B. DETERMINE THE FIELD LOSS:

1. Run the DC shunt motor to the synchronous speed (1500RPM). 2. Slowly increase the excitation voltage until the terminal voltage of the alternator is 400 (L to L volts). 3. Read the field voltage and amps of alternator and record in TABLE 6-3. 4. Multiply field volts and amps of alternator to find field loss PFL. Record in TABLE 6-3 and 6-5.

C. CORE LOSSES :

1. Read the motor’s voltage and current readings at alternator rated voltage condition and record these readings in TABLE 6-4. 2. Multiply the voltage and current readings of motor to find total no-load losses of motor PNLL. Record in TABLE 6-4. 3. Compute the alternator’s core losses, PCL, by subtracting the total rotational losses PMAL from the total no-load losses, PNLL. Record in TABLE 6-4 and TABLE 6-5.

D. OUTPUT POWER :

1. Load the alternator by using 3 phase induction motor load. 2. Break the induction motor drum to load the alternator. 3. Read the terminal voltage and the load current of the alternator at load condition . Record these values in TABLE 6-6. 4. Calculate the output power of the alternator using following formula ( √ퟑ × VL IL × cos∅) 5. Find out the full load armature copper losses (퐼 R) by using full load alternator armature current and total alternator armature resistance Ra. 6. Add the rotational, field, core, and armature losses and record the value in TABLE 6-5 .

67 ELECTRICAL MACHINES - II LAB

7. Determine the power input =power out put +total losses

Note :  PML =Motor Rotational Losses  PAL =Alternator Rotational Losses  PMAL = Motor Alternator Rotational Losses  PFL = Alternator Field Copper Losses  PNLL = Motor No Load Losses  PCL = Alternator Core Losses  P푰ퟐR = Alternator Armature Copper losses  Ra = Total Armature Resistance

CALCULATIONS :

Note: Total losses in alternator :  Iron or core losses (W1)

 Copper Losses (W2&W3) 1. Field Copper Losses (W2) 2. Armature copper losses (W3)

 Rotational Losses (W4)

W1 = CORE LOSSES (PCL) W2 = FIELD LOSSES (PFL) W3 = ARMATURE COPPER LOSSES (푰ퟐR) W4 = ROTATIONAL LOSSES(PAL)

POWER INPUT = POWER OUT PUT +TOTAL LOSSES POWER OUTPUT = ( √ퟑ × VL IL × cos∅)

TOTAL LOSSES =W1+W2+W3+W4

DETERMINATION OF THE ALTERNATOR EFFICIENCY FROM THE EQUATION:

퐏퐨퐰퐞퐫 퐨퐮퐭퐩퐮퐭 % Efficiency = × ퟏퟎퟎ 퐏퐨퐰퐞퐫 퐨퐮퐭퐩퐮퐭퐓퐨퐭퐚퐥 퐥퐨퐬퐬퐞퐬 68 ELECTRICAL MACHINES - II LAB

OBSERVATION TABLES :

RESULT :

69 ELECTRICAL MACHINES – II LAB

VIVA-QUESTIONS: 1. What are the types of three-phase induction motors?

3. why the three phase induction motor draws heavy current at starting?

4. What are the effects of increasing rotor resistance on starting current and starting torque?

5. How to keep the synchronous speed of rotor in alternator?

6. How to determination of efficiency of alternator?

DEPT. OF EEE, PSCMRCT 70 ELECTRICAL MACHINES - II LAB

Experiment No.

LOAD TEST ON SINGLE PHASE INDUCTIO1Y MOTOR AIM: To conduct load test on the given single phase induction motor and to plot its performance characteristics.

APPARATUS REQUIRED:

S.NO APPARATUS SPECIFICATIONS QUANTITY 1 VOLTMETER (0-300v) Mr 1 l .AMME'TER {0-10rq} MI t a J WATTMETER (300v,10A,uPF) 1

4 TACHOMETER (0-10000 RPM) 1

FORMULAE:

1. Circumf-erence of the brake drum :21-IR (m) R = Radius of the brake drum

2. Input power:W (watts) W : wattmeter readings

3. Torque (T):9.81* R * (S, - Sz) ("Il-m) Si. S: : spring balance readings {Kg)

4. output power :'y'(wans) 60 N- Speed in rpm

u-.u'F'd 5. 7o Efficiency (rl) = l'*'"'" ,rca tnput power

CI. Folter factor, **, &: I VT Ns 7. %Slip.s:--'--Ar xl00 l29J Ns : slnchronous speed,I - (rpm) P : ns. of poles tsfrequency of supply (Hz)

71 ELECTRICAL MACHINES - II LAB

PRECAUTIONS:

I. The auto transformer is kept at minimum voltage position. 2. The motor is started at no load condition.

PROCEDURE:

i. Connections are given as per the circuit diagram 2. The DPST switch is closed and the single phase supply is given i. By adjxsting tlre variac the rated vrltage is applie,d anri thr corresp*r:iling n* luaii values of speed, spring balance and meter readings are noted down. If the wattmeter re*dings shct'negative dei.-lectioil on nc i*ad, sulteh oi'the supply & interchange th* terminals of current coils (M & L) of the wattmeter. Now, again starting the motor (f*llarv above procedure lcr sta*ing), take readings. +.I The procedure is repeated till rated current of the motor. 'I-he 5. mator is unloaded, the auto transf*rcer is br*ught ro the voitage position, and the DPST switch is opened. "I'he 6. radius oithe brake drum is measured"

72 a ( i t/ J '6'aIf k -c

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1_ L rt) I I h .J br a) I El (t +r l,- .-\ l> \q. T 1l rtO t: l1r \-/ -r-\. 2\a\ ! 4> C) a-) .b 6J I lolr \_Jo

vr rA,r gUDl) E>oo qd $

-) AN P -?.+'l tn t- t> Xre\ \tr Ys i1 c{ " y{. 73 ELECTRICAL MACHINES - II LAB

df, r I>

:, Z ?ZEts$ 4 rJl== uq(! ,'{

_; g.RV F'A gI - A

-a> q

74 ELECTRICAL MACHINES – II LAB

VIVA-QUESTIONS:

1. Why is the power factor of a single-phase induction motor low?

2. What is the function of centrifugal starting switch in a single-phase induction motor?

3. Why is the starting torque of a capacitor start induction motor high?

4. Which type of torque is developed in single phase motors?

5. How the speed of rotation of a split phase induction motor is reversed?

6. How to determine the efficiency of single phase induction motor?

DEPT. OF EEE, PSCMRCT 75