DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

LABORATORY MANUAL (S7 EEE)

AC MACHINES

INDEX

SL.NO. NAME OF EXPERIMENTS PG.NO.

1Load test on 3 phase Slip Ring Induction Motor

3

2

Load test on 3 phase Squirrel Cage Induction Motor

8

3Regulation of Alternator by EMF & MMF method

11

4No Load & Blocked Rotor test on Slip Ring Induction method

18

5

No Load & Blocked Rotor test on Squirrel Cage Induction

method25

6Slip test on Salient Pole Alternator

31

7

Synchronous induction motor - V-curves and predetermination

offield current .35

8

No load and Blocked Rotor test on Single Phase Induction

Motor39

9Load test on Pole Changing Induction Motor

42

10Regulation of Alternator by Potier method

47

11V & Inverted V Curves of 3 Phase Synchronous Motor

53

12 Induction machine as motor &generator 56

EX. NO. : 1DATE :

LOAD TEST ON 3-PHASE SLIP RING INDUC-TION MOTOR

AIM:-

To obtain following performance characteristics. 1. Line current, torque, power factor, efficiency, speed and

slip Vs output. 2.Torque Vs slip.

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY

The slip ring induction motor has two separate parts, one is the stator and other is the rotor. The stator consists of a three phase winding. When 3 phase supply is given to the stator it produce a rotating magnetic field. The speed with which the magnetic field rotate is called synchronous speed.

synchronous speed Ns =120 f / P

ie; f = frequency of the supply

P = Number of poles

Rotor consists of star connected 3 phase winding. The three terminals of the star connected rotor are connected to three slip rings. These sliprings are used to connect external resistance to rotor circuit.

When three phase supply is given to the stator, a rotating magnetic field rotat-ing at synchronous speed is produced. This rotating magnetic field induse an emf and hence current in the stator winding.when current flows through the rotor wind-ing a torque is produced in the rotor conductors ( current carrying conductor placed in a magnetic field it will experience a torque) due to this torque the rotor starts ro-tating. Rotor accelerates in the direction of rotation of magnetic field reducing the relative speed between the magnetic field of stator and rotor.

If the motor attains synchronous speed the rotor will not be cutting the mag-netic flux and torque induced will be zero. Practically doesnot achieve synchron-ous speed.

The difference between synchronous speed and rotor speed is indicated using slip.Percentage slip ;s = NS-N/NS *100

Torque =K. E2Rr / Rr2+Xr2

From the torque equation it can be seen that starting torque can be measured by in-creasing rotor resistance..

PRECAUTIONS: 1. TPST switch is kept open initially. 2. The external resistance in the rotor circuit should be kept at max. value.

PROCEDURE: 1. Connections are given as per circuit diagram. 2. After observing precautions motor is started on no load. 3. As speed increases, the external resistance is gradually cut out. 4. The no-load readings are taken. 5. If watt meter reads nefgative, interchange its current coils terminals6. The meter readings are then noted for various load conditions.

FORMULAE USED: 1. Torque= (S1-S2)*9.81*100 N-m 2. O/P Power= 2πNT/60 watts 3. I /P Power = (W1+W2) watts 4. η % = (o/p power/ i/p power)*100 5. %s = (Ns-N)/Ns*10

CIRCUIT DIAGRAM

Sample Graph

OBSERVATION TABLE:

SL. NO

LOAD CUR-

RENT (A)

LOAD VOLTAG

E (V)

W1

W2

INPUT POWER

(W) W1+W

2

SPEED (N)

SPRING BAL-ANCE READ-

ING (Kg)

TORQUE (Nm)

OUT-PUT

POWER (w)

EFFI-CIENCY

SLIP

POWER FACTO

R

Calculation:

RESULT:

EX. NO. : 2DATE :

LOAD TEST ON 3 −φ SQUIRREL CAGEINDUCTION MOTOR

AIMTo conduct load test on the given 3-φ squirrel cage induction motor and plot the performancecharacteristics.APPARATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORYA squirrel cage induction motor essentially consists of a stator and a rotor. The stator is a hollow cylindrical structure with slots on the inner periphery and carries a three phase winding. The winding can be connected in star or delta and is con-nected across a 3-φ supply.The rotor is also a cylindrical structure with slots on the outer periphery. The slots carry thick Al or Cu bars. These bars are short circuited at both ends by means of end rings. When a 3-φ supply is given to a 3-φ winding displaced by 120◦ in space, a magnetic field of constant magnitude but rotating at synchronous speed is produced. This flux links with the stationary rotor, thus indu-cing an emf in it. As the rotor circuit is closed, a current flows through it.The direction of the induced current is such as to oppose the cause producing it. The cause is the relative motion between the stator magnetic field and the rotor. So

the rotor starts rotating in the same direction as the stator magnetic field and tries to catch up with it. But practically it is never able to do so. Because if it does so, there would be no relative motion, no emf and hence no torque. Thus an induction motor always runs at a speed slightly less than the synchronous speed. The termslip is of importance in an induction motor and is defined asAn induction motor can never operate at s=0. It always operates between s=0 and s=1(starting).

PROCEDURE1. The load on the motor is completely removed by loosening the brake drum.2. The motor is to be always started and stopped at no load, The supply is switched on andthe motor is started using a Direct On Line Starter (DOL Starter).3. The readings of the voltmeter, ammeter, wattmeters and spring balance are noted down.The speed is measured using a tachometer.4. The load is then increased in steps, each time noting down all the above read-ings.5. The experiment is repeated for different values of load currents till the rated cur-rent of themachine is reached.6. During the experiment, the machine may get heated up. It is cooled by pouring some waterinto the brake drum.At low loads,(when pf< 0.5) one of the wattmeters read negative, insuch cases, the supply is switched off and the connections to the M and L terminals of thewattmeter are interchanged.7. The meter now reads positive, but it is to be recorded as negative.8. The load on the machine is removed completely and the supply is switched off. The readings are tabulated and the performance characteristics are plotted.

FORMULAE USED-

Radius of Brake drum R=……………mNs= Synchronous speed in rpmN =Rotor speed in rpmS1&S2= Load of brake drum in kgVL=Line voltage in VoltsIL= Line current in Amps

1) % slip= [(Ns-N)/Ns]*100=……….%2) Input Power(W )= (W1+W2)=…………. watts3) Torque(T) = 9.81*(S1-S2)*R =…………….. N-m4) Output Power = 2πNT/60=……………… watts

5) % efficiency =[ output/input]* 100=……………..%6) Power Factor(PF) = Input Power/(√√3VLIL)=………………

CIRCUIT DIAGRAM:

SAMPLE GRAPH:

RESULT:

EX. NO. : 3DATE :

REGULATION OF 3–PHASE ALTERNATOR BY EMF AND MMF METHODS

AIM: To predetermine the regulation of 3-phase alternator by EMF and MMF methods

and also draw the vector diagrams.

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:

The regulation of a 3-phase alternator may be predetermined by conducting the Open Circuit (OC) and the Sort Circuit (SC) tests. The methods employed for determination of regulation are EMF or synchronous impedance method, MMF or Ampere Turns method and the ZPF or Potier triangle method. In this experiment, the EMF and MMF methods are used. The OC and SC graphs are plotted from the two tests. The synchronous impedance is found from the OC test. The regulation is then determined at different power factors by calculations using vector diagrams. The EMF method is also called pessimistic method as the value of regulation obtained is much more than the actual value. The MMF method is also called optimistic method as the value of regulation obtained is much less than the actual value. In the MMF method the armature leakage reactance is treated as an additional armature reaction. In both methods the OC and SC test data are utilized.

PRECAUTIONS:

(i) The motor field rheostat should be kept in the minimum resistance position. (ii) The alternator field potential divider should be kept in the minimum voltage position. (iii) Initially all switches are in open position.

PROCEDURE: (FOR BOTH EMF AND MMF METHODS)

1. Note down the name plate details of the motor and alternator. 2. Connections are made as per the circuit diagram. 3. Switch ON the supply by closing the DPST switch

4. Using the Three point starter, start the motor to run at the synchronous speed by adjusting the motor field rheostat. 5. Conduct Open Circuit test by varying the potential divider for various values of field current and tabulate the corresponding Open Circuit Voltage readings. 6. Conduct Short Circuit test by closing the TPST switch and adjust the potential divider to set the rated armature current and tabulate the corresponding field current. 7. The Stator resistance per phase is determined by connecting any one phase stator winding of the alternator as per the circuit diagram using MC voltmeter and ammeter of suitable ranges.

PROCEDURE TO DRAW GRAPH FOR EMF METHOD:

1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS Field current). 2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field current) 3. From the graph find the open circuit voltage per phase (E1 (ph) for the rated short circuit current (Isc). 4. By using respective formulae find the Zs, Xs, Eo and percentage regulation.

PROCEDURE TO DRAW GRAPH FOR MMF METHOD:

1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS Field current). 2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field current) 3. Draw the line OL to represent

FORMULAE:

1. Armature Resistance Ra = Ω

2. Synchronous Impedance Zs = O.C. voltage /S.C. current 3. Synchronous Reactance Xs = √ Zs2 – Ra2

4. Open circuit voltage for lagging p.f = √(VcosΦ + IaRa)2 + (VsinΦ + IaXs)2

5. Open circuit voltage for leading p.f. = √(VcosΦ + IaRa)2 + (VsinΦ – IaXs)2

6. Open circuit voltage for unity p.f = √(V + IaRa)2 + ( IaXs)2

7. Percentage regulation = (Eo – V)/V x 100

CIRCUIT DIAGRAM:-

CIRCUIT FOR RESISTANCE MEASURMENT:-

TABULAR COLUMNS

OPEN CIRCUIT TEST

SHORT CIRCUIT TEST:

EMF METHOD:

MMF METHOD:

EMF METHOD

MMF METHOD

RESULT:

EX. NO. : 4DATE :

NO LOAD AND BLOCKED ROTOR TEST ON SLIP RING IN-DUCTION MOTOR.

AIM:-1) To determine the equivalent circuit parameters.2) To draw the performace characterestics using data obtained from the circle

Diagram

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY :-A 3-phase induction motor consists of stator, rotor & other associated parts. In thestator, a 3- phase winding (provided) are displaced in space by 120. A3- phase cur-rent is fedto the winding so that a resultant rotating magnetic flux is generated. The rotor starts rotatingdue to the induction effect produced due the relative velocity between the rotor winding &the rotating flux.Slip ring motors are always started

with full line voltage applied across the stator terminals. The value of starting cur-rent is adjusted by introducing a variable resistance in therotor circuit.The controlling resistance is in the form of resistances connected in star. Theresistance is gradually cut out of the rotor circuit as the motor gathers speed.

CIRCUIT DIAGRAM:

FOR NO LOAD:-

FOR BLOCKED TOTOR:-

FOR STATOR RESISTANCE:

No load test:-If the motor is run at rated voltage and frequency without any mechanical load, it willdraw power necessary to supply the no load losses. The no load current will have twocomponents. The active component and the magnetizing component, the former being verysmall as the no load losses are small. The power factor at no load is therefore very low. Theno load power factor is always less than 0.5 and hence at no load one of the wattmeter atinput side reads negative.The no load input W0 to the stator consists of1. Small stator copper loss2. Core losses3. The loss due to friction and windage.

The rotor copper loss can be neglected, since slip is small at no load.Blocked rotor test :-The stator is supplied with a low voltage of rated frequency just sufficient to circu-laterated current through the stator with the rotor blocked and short circuited. The power input,current and the voltage applied are noted down. The power input dur-ing the blocked rotor testis wholly consumed in the stator and rotor copper losses. The core loss is low because theapplied voltage is only a small percentage of the normal voltage. Again since the rotor is atstand still the mechanical losses are ab-sent. Hence the blocked rotor input can be taken asapproximately equal to the cop-per losses.

PROCEDURE FOR NO LOAD TEST:-1. Connections are made as shown in the diagram for no load test.2. Brake drum is made free to rotate by loosening the belt.3. The autotransformer is placed in zero position. Then the supply is switched on and theauto transformer is adjusted to supply the rated voltage to the machine.4. Press green switch on the starter. The handle of the starter resistance switch is rotatedthree times in clockwise direction to cut out the rotor resistance.5. Readings of the two wattmeter, voltmeter and ammeter are noted and tabulated.6. Press red switch on starter and then switch off supply.

TABULAR COLUMN:

NO LOAD TEST:-

Voc= open circuit voltageIoc = open circuit current

BLOCKED ROTOR TEST:-

Vsc = short circuit voltageIsc = short circuit current

STATOR RESISTANCE:-

PROCEDURE FOR BLOCKED ROTOR TEST :-1. Connections are made as shown in the diagram for blocked rotor test.2. The rotor is blocked by tightening the belt on the brake drum.3. The auto transformer is set to the zero voltage position.4. Short circuit the terminals of rotor.5. Then the three phase supply is switched on.6. By adjusting the autotransformer, the ammeter reading is made equal to rated currentof the machine.7. Readings of the two wattmeter, voltmeter and the ammeter are noted and tabu-lated.8. Switch off supply.

CIRCLE DIAGRAM:-

EQUIVALENT CIRCUIT:

RESULT:

EX. NO. : 5

DATE :

NO LOAD AND BLOCKED ROTOR TEST ON 3 PHASE SQUIR-REL CAGEINDUCTION MOTOR.

AIM:-1) To draw the equavalant circuit pararmeters.2) Draw the circle diagram and obtain performance characteristics

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY :-A 3-phase induction motor consists of stator, rotor & other associated parts. In thestator, a 3- phase winding (provided) are displaced in space by 120. A3- phase current is fedto the winding so that a resultant rotating magnetic flux is generated. The rotor starts rotatingdue to the induction effect produced due the relative velo-city between the rotor winding &the rotating flux.No load test:-If the motor is run at rated voltage and frequency without any mechanical load, it willdraw power necessary to supply the no load losses. The no load current will have twocomponents. The active component and the magnetizing component, the former being verysmall as the no load losses are small. The power factor at no load is therefore very low. Theno load power factor is always less than 0.5 and hence at no load one of the wattmeter atinput side reads negative. The no load input W0 to the stator consists of1. Small stator copper loss2. Core losses3. The loss due to friction and windage.The rotor copper loss can be neglected, since slip is small at no load.Blocked rotor test :-The stator is supplied with a low voltage of rated frequency just sufficient to circu-laterated current through the stator with the rotor blocked and short circuited. The power input,current and the voltage applied are noted down. The power input dur-ing the blocked rotor testis wholly consumed in the stator and rotor copper losses.

The core loss is low because theapplied voltage is only a small percentage of the normal voltage. Again since the rotor is atstand still the mechanical losses are ab-sent. Hence the blocked rotor input can be taken asapproximately equal to the cop-per losses.PROCEDURE FOR NO LOAD TEST:-1. Connections are made as shown in the diagram for no load test.2. Brake drum is made free to rotate by loosening the belt.3. The autotransformer is placed in zero position. Then the supply is switched on and theauto transformer is adjusted to supply small voltage to the machine. Initially currentwill rise to high value. Wait until the current reaches to low current. Then increasethe voltage to rated value.4. Readings of the two wattmeter, voltmeter and ammeter are noted and tabulated.5. If the wattmeter reads negative, interchange current coil terminals and take wattmeterreading as negative.6. Switch off supply.PROCEDURE FOR BLOCKED ROTOR TEST :-1. Connections are made as shown in the diagram for blocked rotor test.2. The rotor is blocked by tightening the belt on the brake drum.3. The auto transformer is set to the zero voltage position.4. Then the three phase supply is switched on.5. By adjusting the autotransformer, the ammeter reading is made equal to rated currentof the machine.6. Readings of the two wattmeter, voltmeter and the ammeter are noted and tabu-lated.7. If the wattmeter reads negative, interchange current coil terminals and take wattmeterreading as negative.Switch off supply

FOR NO LOAD:-

FOR BLOCKED TOTOR:

FOR STATOR RESISTANCE:

TABULAR COLUMNS:-NO LOAD TEST:-

Voc= open circuit voltageIoc = open circuit current

BLOCKED ROTOR TEST:-

Vsc = short circuit voltageIsc = short circuit current

SAMPLE GRAPH:

OBSERVATIONS FROM CIRCLE DIAGRAM:

RESULT:

EX. NO. : 6

DATE :

SLIP TEST ON SALIENT POLE ALTERNATOR

AIM:-1) To determine Xd and Xq by conducting slip test.2) To pre-determine the regulation at upf different powerfactor and load3) To plot power Vs load angle graph

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:-If a synchronous machine runs at a slightly less than the synchronous speed, the fieldstructure is exposed to the rotating mmf of armature reaction. Hence the poles and armaturereaction mmf fall in phase and out of phase at slip frequency. Where the axis of twocoincides, the armature acts through the field magnetic circuit, in-cluding maximum voltage inthe field. The direct axis reactance Xd (and hence the impedance Zd) is maximum resulting inthe armature current being minimum. Where the field poles are in quadrature with armaturemmf, quadrature axis react-ance Xq (and hence the impedance Zq) will be minimum resultingin the armature current maximum. Hence,Zd = Max. voltage / min. currentZq = Min. voltage / max. current

PROCEDURE:-1. Make connections as shown in circuit diagram.2. Start the set and bring it to near synchronous speed keeping the field of the al-ternatoropen.3. Apply an AC voltage of reduced magnitude (about 25% of the rated value). The fieldpoles and armature mmf should rotate in same direction this can be verified bymeasuring the voltage across the field winding (It should be nearly equal to zero)Otherwise interchange the stator terminals.

4. Adjust the speed of the alternator to get sufficient oscillations (Maximum deflec-tion)in the meter.5. Note down the maximum and minimum value of ammeter and voltmeter.

CIRCUIT DIAGRAM:

Stator resistance measurement:

TABULAR COLUMN:

Slip test reading:

RESISTANCE CALCULATION:

SAMPLE GRAPH:

RESULT:

EX. NO. : 7DATE :

SYNCHRONOUS INDUCTION MOTOR

AIM: To draw the V and inverted V curves of a 3 phase Synchronous Motor.

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:-The variation of field current effects the power factor at which the synchro- nous motoroperates. For a syn motor, the armature current phasor is given by Ia=V-E where V is theapplied voltage .From the above equation it is clear that the mag-nitude and phase angle ofphasor Iadepends upon the value of DC excitation. When the syn. Motor is operated at constant loadwith variable field excitation, it is ob-served that:a) When the excitation is low, the armature current is lag in nature & the mag-nitude iscomparatively high.b) If the excitation is gradually increased, the magnitude of Ia is gradually decreas-ing and theangle of lag is gradually reduced.c) At one particular excitation, the magnitude of Ia corresponding to that load in minimumand vector will be in phase with V vector.d) If the excitation is further increased, the magnitude of Ia again gradually in-creased and Ia,vector goes to leading state and the angle of load is also gradually increased.

PROCEDURE:-

FOR DETERMINATION OF V AND INVERTED V CURVES:1. Connections are given as per the circuit diagram.2. The auto transformer is adjusted such that it reads the rated voltage.3. At no-load condition, the field excitation was varied and the corresponding linecurrent and the wattmeter readings are noted.

4. Then by keeping 75% load, the excitation was adjusted by varying the field rheostatand the above readings are noted.5. Same procedure was followed for full load.FOR LOAD TEST:-1. Connections are given as per the circuit diagram.2. By varying the auto-transformer, rated voltage was kept across the voltmeter.3. At no-load, the line current, the line current, wattmeter readings and the springbalance readings were noted down.4. Then by adding the load in steps, the above said readings were noted.5. The above procedure was followed until it reaches the rated current.

CIRCUIT DIAGRAM:

TABULAR COLUMN:

For motor:

For generator:

FORMULAE USED:

Motor ActionInput power =W1+W2=………..wattsOutput power =Idc*Vdc=…………..watts% efficiency = (output/input)*100 =………%Generator ActionInput power =Idc*Vdc =…………..wattsOutput power = W1+W2=………..watts% efficiency = (output/input)*100 =…………%

SAMPLE GRAPH:

RESULT:

EX. NO. : 8DATE :

NO LOAD AND BLOCKED ROTOR TEST ON SINGLE PHASE INDUC-TIONMOTOR

AIM:1) To obtain the equivalent circuit parameter of the single phase induction motor.2) To pre determine the line current, power factor, efficiency and the torque

developed at 4% slip.APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:-Single phase motors are similar in construction to poly phase squirrel cage induc-tionmotor with exception that the stator has single phase winding. Therefore in single phasemotors rotating magnetic field if not produced, but only a pulsating field is produced. Thetorque is also pulsating and hence single phase motors are not self starting. In order to makethem self starting, they are converted to two phase motors at starting. A centrifugal switch isused to cut off the starting winding after motor picks up full speed.

PROCEDURE:-FOR NO LOAD TEST:-1. Connections are done as shown in the diagram.2. Supply is switched on with dimmerstat in the minimum position.3. A low voltage is applied at starting.4. Gradually as motor picks up speed, the rated voltage is applied.5. The corresponding meter readings are noted.FOR BLOCKED ROTOR TEST:-1. For this test, starting winding is disconnected.2. A small voltage is applied so that the rated current of the motor flows.3. Corresponding meter readings are noted. (No physical blocking is required sincestarting windings is not connected).4. The resistance of stator winding is also measured.

CIRCUIT DIAGRAM:

FOR NO LOAD:-

FOR BLOCKED TOTOR:-

FOR STATOR RESISTANCE:-

TABULAR COLUMN:

RESULT:

EX. NO. : 9DATE :

LOAD TEST ON POLE CHANGING INDUCTION MOTORAIM:

1) 1) To study different modes of operation of three phase pole changing induction motor.2) Perform load test and obtain performance characteristics and compare the result-sobtained for different pole combination at different load condition.

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:- Pole changing motor is similar in construction when compared to stand-ard squirrelcage induction motor because of its simple construction and low cost. The only disadvantageis its single speed of running. But pole changing induction motor gives two speeds using asingle stator winding. The reliability and operating characteristics are identical to that ofstandard squirrel cage induction motor.In pole changing induction motor each phase winding is usually divided into equalparts provided with tappings. The direction in which current is passed through them can bereversed by switching, thereby number of pole becomes halved and will con-sequently lead todouble synchronous speed. In practice switch over from series to parallel connection isaccomplished by changing either from delta to double star or from single star to double star.

PROCEDURE:-1. For low speed, connections are made as per circuit diagram. Connect U2,V2 and W2to R, Y and B respectively. Make U1, V1 and W1 free.2. The rotor was made very much free to rotate. Adjust the autotransformer to zeroposition.3. Pour some water inside the brake drum so as to cool the rotor belt.4. 3-Φ induction motor started using auto transformer. Apply rated voltage slowly.5. Adjusted the load till current was made to rated value of motor.

6. Decrease the load step by step and note corresponding speed, load, current, voltageand wattmeter readings.7. At certain load, wattmeter W2 will show negative reading. Note down the cur-rent athis load. Interchange the connection of current coil of wattmeter W2 which wasreading negative after switching off supply by pressing red switch of starter.8. Rotor was made free to rotate by removing the load completely.9. 3-Φ induction motor started using autotransformer. Adjust the current to value instep710. Note down corresponding speed, load, current, voltage, wattmeter readings. Take the reading of wattmeter W2 as negative.11. Finally switch off supply.12. For high speed, connections are done as per the circuit diagram. Connect U1, V1 andW1 to R,Y and B respectivey. Short U2, V2 and W2.Repeat the above steps

CIRCUIT DIAGRAM:

Low Speed

High Speed

TABULAR COLUMN:

SAMPLE CALCULATION (For low and high speed):-

SAMPLE GRAPH:

RESULT:

EX. NO. : 10

DATE :

REGULATION OF ALTERNATOR BY POTIER AND ASA METHODS METHOD

AIM:To determine the voltage regulation of the given alternator by Potier and ASAmethods and also to draw the vector diagrams .

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:-The Zero Power Factor method is based on the separation of armature leakage re-actance drop and armature reaction effects. Hence it gives more accurate results .The experimental data required is :1. No load curve.2. Full load ZPF curve.This is also called wattles load characteristics. It is a curve of terminal voltage against excitation, when the armature is delivering full load current at zero power factor. The zero power factors lagging curve can be obtained by loading the alter-nator with pure inductive load. The reduction in voltage due to armature leakage reactance X2 is found from both the curves.E0 can be calculated from these two.Potier Triangle is drawn as follows. Point A is obtained from SC test, with full load armature current. Point B corresponds to voltmeter reading at full load armature current. From point B, BH is drawn parallel to line OA touching OCC to D The tri-angle BHD is obtained in the Potier triangle the triangle drawn from D to BH gives the armature leakage reactance drop. BE is the field current necessary to overcome armature reaction I,-2. In corresponding to E is obtained from OCC. The vector sum of If1 and If2 gives If. Now corresponding to If, Eo is found fromOCC.

PRECAUTION:

i) The motor field rheostat should be kept in the minimum resistance posi-tion.

ii) The Alternator field potential divider should be in the position of min-imum potential.

iii) Initially all switches are in open position.

PROCEDURE:-

PROCEDURE FOR BOTH POTIER AND ASA METHODS: 1. Note down the complete nameplate details of motor and alternator.2. Connections are made as per the circuit diagram. 3. Switch on the supply by closing the DPST main switch. 4. Using the Three point starter, start the motor to run at the synchronous speed by varying the motor field rheostat. 5. Conduct an Open Circuit Test by varying the Potential Divider for various val-ues of Field current and tabulate the corresponding Open circuit voltage readings. 6. Conduct a Short Circuit Test by closing the TPST knife switch and adjust the potential divider the set the rated Armature current, tabulate the corresponding Field current. 7. Conduct a ZPF test by adjusting the potential divider for full load current passing through either an inductive or capacitive load with zero power and tabulate the readings. 8. Conduct a Stator Resistance Test by giving connection as per the circuit diagram and tabulate the voltage and Current readings for various resistive loads.

PROCEDURE TO DRAW THE POTIER TRIANGLE (ZPF METHOD): (All the quantities are in per phase value) 1. Draw the Open Circuit Characteristics (Generated Voltage per phase VS Field Current) 2. Mark the point A at X-axis, which is obtained from short circuit test with full load armature current. 3. From the ZPF test, mark the point B for the field current to the corresponding rated armature current and the rated voltage. 4. Draw the ZPF curve which passing through the point A and B in such a way parallel to the open circuit characteristics curve. 5. Draw the tangent for the OCC curve from the origin (i.e.) air gap line.6. Draw the line BC from B towards Y-axis, which is parallel and equal to OA. 7. Draw the parallel line for the tangent from C to the OCC curve.

8. Join the points B and D also drop the perpendicular line DE to BC, where the line DE represents armature leakage reactance drop (IXL) BE represents armature reaction excitation (Ifa).

PROCEDURE TO DRAW THE VECTOR DIAGRAM (ZPF METHOD)1. Select the suitable voltage and current scale. 2. For the corresponding power angle ( Lag, Lead, Unity) draw the voltage vector and current vector OB. 3. Draw the vector AC with the magnitude of IRa drop, which should be parallel to the vector OB. 4. Draw the perpendicular CD to AC from the point C with the magnitude of IXL drop. 5. Join the points O and D, which will be equal to the air gap voltage (Eair). 6. Find out the field current (Ifc) for the corresponding air gap voltage (Eair) from the OCC curve. 7. Draw the vector OF with the magnitude of Ifc which should be perpendicular to the vector OD. 8. Draw the vector FG from F with the magnitude Ifa in such a way it is parallel to the current vector OB. 9. Join the points O and G, which will be equal to the field excitation current (If). 10. Draw the perpendicular line to the vector OG from the point O and extend CD in such a manner to intersect the perpendicular line at the point H. 11. Find out the open circuit voltage (Eo) for the corresponding field excitation current (If) from the OCC curve. 12. Find out the regulation from the suitable formula.

PROCEDURE TO DRAW THE POTIER TRIANGLE (ASA METHOD): (All the quantities are in per phase value) 1. Draw the Open Circuit Characteristics (Generated Voltage per phase VS Field Current) 2. Mark the point A at X-axis, which is obtained from short circuit test with full load armature current. 3. From the ZPF test, mark the point B for the field current to the corresponding rated armature current and the rated voltage. 4. Draw the ZPF curve which passing through the point A and B in such a way par-allel to the open circuit characteristics curve. 5. Draw the tangent for the OCC curve from the origin (i.e.) air gap line. 6. Draw the line BC from B towards Y-axis, which is parallel and equal to OA. 7. Draw the parallel line for the tangent from C to the OCC curve.

8. Join the points B and D also drop the perpendicular line DE to BC, where the line DE represents armature leakage reactance drop (IXL) BE represents armature reaction excitation (Ifa). 9. Extend the line BC towards the Y-axis up to the point O’. The same line inter-sects the air gap line at point G. 10. Mark the point I in Y-axis with the magnitude of Eair and draw the line from I towards OCC curve which should be parallel to X-axis. Let this line cut the air gap line at point H and the OCC curve at point F. 11. Mention the length O’G, HF and OA.

PROCEDURE TO DRAW THE VECTOR DIAGRAM (ASA METHOD) (To find the field Excitation current If) 1. Draw the vector with the magnitude O’G. 2. From G draw a vector with the magnitude of GH (OA) in such a way to make an angle of (90 ± Φ) from the line O’G [ (90 + Φ) for lagging power factor and (90 – Φ) for leading power factor] 3. Join the points O’ and, H also extend the vector O’F with the magnitude HF. Where O’F is the field excitation current (If). 4. Find out the open circuit voltage (Eo) for the corresponding field excitation cur-rent (If) from the OCC curve. 5. Find out the regulation from the suitable formula.

FORMULAE USED:

Percentage regulation = (Eo – Vrated)/ Vrated x 100

CIRCUIT DIAGRAM:

TABULAR COLUMN:

OC TEST

RESULT:

EX. NO. : 11DATE :

V AND INVERTED V CURVESOF 3–Φ SYNCHRONOUS MOTOR

AIM:To draw the V and inverted V curves of a 3 phase Synchronous Motor.

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:-

The variation of field current effects the power factor at which the synchro- nous motor operates. For a syn motor, the armature current phasor is given by Ia=V-E where V is the applied voltage .From the above equation it is clear that the mag-nitude and phase angle of phasor Ia depends upon the value of DC excitation. When the syn. Motor is operated at constant load with variable field excitation, it is observed that: a) When the excitation is low, the armature current is lag in nature & the mag-nitude is comparatively high. b) If the excitation is gradually increased, the magnitude of Ia is gradually de-creasing and the angle of lag is gradually reduced. c) At one particular excitation, the magnitude of Ia corresponding to that load in minimum and vector will be in phase with V vector. d) If the excitation is further increased, the magnitude of Ia again gradually in-creased and Ia ,vector goes to leading state and the angle of load is also gradually increased.

PROCEDURE:(1) Note down the name plate details of the motor. (2) Connections are made as per the circuit diagram..(3) Close the TPST switch.

(4) By adjusting the autotransformer from the minimum position to the maximum position the rated supply is given to motor. The motor starts as an induction motor. (5) In order to give the excitation to the field for making it to run as the synchron-ous motor, close the DPST switch. (6) By varying the field rheostat note down the excitation current, armature current and the power factor for various values of excitation. (7) The same process has to be repeated for loaded condition. (8) Later the motor is switched off and the graph is drawn.

PRECAUTION:(1) The Potential barrier should be in maximum position. (2) The motor should be started without load. (3) Initially TPST switch is in open position.

CIRCUIT DIAGRAM:

TABULAR COLUMN:

The graph is drawn for-(1) Armature current Vs Excitation current. (2) Power factor Vs Excitation current.

SAMPLE GRAPH:

RESULT:

EX. NO. : 12DATE :

INDUCTION MACHINE AS MOTOR AND GENERATOR

AIM:1. To operate the given 3 phase induction machine as i)induction motor and ii) induction generator.2. To obtain the overall efficiency vs. output charactereristics

APPRATUS REQUIRED:

Sl. No. Equipments Type Specification Quantity 1.2.3.4.5.

THEORY:-

An induction motor running above its synchronous speed (super synchronous speed) has negative slip and will act as a generator if the stator magnetizing current is supplied either from the synchronous mains or from a set of capacitors con-nected across its terminal. It’s seldom used for the purpose of generator operation but finds application in the electrical braking purpose.

PROCEDURE:

1. Connections are done as shown in the diagram.2. Keeping DPST in open position, start the set from the ac side using Υ/Δ starter. If the direction of rotation is opposite to the marked direction for the DC machine, restart the induction motor after interchanging any two phases.3. With the DPST open, the DC supply is switched on. Adjust the field rheostat such that the generated voltage and the DC supply voltage are equal in magnitude (check readings on V2 and V3 ). Also confirm that polarity is the same and if not interchange any two leads.4. Now close the DPST switch to bring the DC machine in floating condition. Ad-just the excitation in such a way that the DC machine acts as a generator and the

induction machine continues to run as a motor. For this effect reduce the field rheostat resistance.5. For different values of field current note all the meter readings. Now bring the field rheostat again to the floating condition and continue to decrease the excitation to make the DC machine run as a motor and the induction machine as a generator. The meter readings are noted for different values of field current.

PRECAUTION:

CIRCUIT DIAGRAM:

TABULAR COLUMN:

SAMPLE GRAPH:

RESULT: