SRM Institute of Science and Technology (Deemed to be University)

Transcription

1 5EE0L-ELECTRICAL MACHINES LAB-II RECORD ACADEMIC YEAR: ODD SEMESTER 08-9 NAME : REG.NO. : DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING FACULTY OF ENGINEERING & TECHNOLOGY SRM Institute of Science and Technology (Deemed to be University) S.R.M. NAGAR, KATTANKULATHUR KANCHEEPURAM DISTRICT

2 SRM Institute of Science and Technology (Deemed to be University) S.R.M. NAGAR, KATTANKULATHUR KANCHEEPURAM DISTRICT BONAFIDE CERTIFICATE Register No Certified to be the bonafide record of work done by of EEE department, B.Tech degree course in the Practical 5EE0L Electrical machines Lab-II in SRM IST, Kattankulathur during the academic year Lab in-charge Date: Year Co-ordinator Submitted for end semester examination held in Electrical machines Lab, SRM IST, Kattankulathur. Date: Examiner- Examiner-

3 LIST OF EXPERIMENTS. Performance evaluation of single phase induction motor. a) Performance evaluation of three phase induction motor b) Load test on three phase squirrel cage induction motor using open lab system 3. Speed control of rotating transformer 4. Synchronisation of alternator to infinite bus bar 5. Predetermination of voltage regulation 6. Determination of v and inverted v curves of synchronous motor 7. Determination of x d and x q for salient pole alternator using slip test 8. Characteristics of 3 phase induction generator 9. Single phasing in 3 phase induction motor 0. Armature reaction in synchronous generator

4 INDEX Expe rime nt No Date of Experi ment Title of Experiment Performance evaluation of single phase induction motor Viva (0) Executi on (0) Calculation / Evaluation (0) Pre and Post Lab (0) Total (50) Faculty Signatu re a) Performance evaluation (a) of three phase induction motor b) Load test on three phase (b) squirrel cage induction motor using open lab system 3 Speed control of rotating transformer 4 Synchronisation of alternator to infinite bus bar 5 Predetermination of voltage regulation Determination of v and 6 inverted v curves of synchronous motor Determination of x d and x q 7 for salient pole alternator using slip test 8 Characteristics of 3 phase induction generator 9 Single phasing in 3 phase induction motor 0 Armature reaction in synchronous generator Average

5 PERFORMANCE EVALUATION OF SINGLE PHASE INDUCTION MOTOR PRE LAB QUESTIONS. What are the types of single phase induction motor?. Why single phase induction motors are not self-starting? 3. How the direction of a capacitor start Induction motor is be reversed? 4. In what respect does a -phase Induction motor differ from a 3-phase Induction motor? 5. What is the rating of single phase machines? State its applications

6 Experiment No. PERFORMANCE EVALUATION OF SINGLE PHASE INDUCTION MOTOR AIM To conduct open circuit, short circuit and load test on the given single phase induction motor and to plot its performance characteristics. APPARATUS REQUIRED: S.NO APPARATUS SPECIFICATIONS QUANTITY VOLTMETER (0-300V) MI (0-50V) MI AMMETER (0-0A) MI (0-5A) MI 3 WATTMETER (300V,0A,UPF) (50V,0A, UPF) (300V,5A,LPF) 4 TACHOMETER ( RPM) 5 Connecting wires As required FORMULAE Load test. Circumference of the brake drum = πr (m) R = Radius of the brake drum. Input power =W (watts) W = wattmeter readings 3. Torque (T) = 9.8x R x (S ~ S ) (N-m) S, S = spring balance readings (Kg) NT 4. Output power = 60 N- Speed in rpm (watts) output power 5. % Efficiency (η) = x00 input power W 6. Power factor, cos Φ= VI

7 Ns N 7. % Slip, s = 00 Ns 0 f N S = synchronous speed = (rpm) P P = no. of poles f=frequency of supply (Hz) No load test R =.5x R dc cos Ф = Wo / V o I o V AB = I o x o x o = V AB /I o Blocked rotor test cos Φ sc =W sc /V sc I sc Z eq = V sc / Isc R eq = W sc /( I sc ) R eq = R + R R = R eq - R = rotor resistance referred to stator X eq = (Z eq - R eq ) X = X X Where W 0 = no-load input power in watts (watts) W sc = short circuit input power in watts (watts) V 0 = line voltage on no-load I 0 = line current on no-load CALCULATIONS TO DRAW THE EQUIVALENT CIRCUIT Blocked rotor test Z eq = V sc / Isc R eq = W sc /( Isc) X eq = (Z eq - R eq ) R =.5*Rdc

8 R eq = R + R R = R eq - R Xeq=X + X X = X x = X / r = R / Where V SC = Short circuit voltage volts I SC = Short circuit current in amps W SC = Short circuit power in watts No load test V AB = I o x o x o = Where W 0 = no-load input power in watts (watts) V 0 = line voltage on no-load I 0 = line current on no-load PRECAUTIONS Load test. The auto transformer must kept at minimum voltage position.. The motor is started at no load condition. 3. The motor should not be stopped under loaded condition No load test. Initially DPST Switch is kept open.. Auto transformer is kept at minimum potential position. 3. The machines must be started on no load. Blocked rotor test. Initially the DPST Switch is kept open.. Auto transformer is kept at minimum potential position. 3. The machine must be started at full load (blocked rotor).

9 MODEL EQUIVALENT CIRCUIT MODEL GRAPH TABULAR COLUMN No load test V 0 (volts) I 0 (amps) W 0 (watts) MF OBS ACT

10 Load test Voltage V (volts ) Current I Amps Speed N (rpm) Wattmeter reading (watts) OBS ACT Spring balance readings (Kg) S S S~S Torque (T) N-m Output Power (watts) Power factor (cos Φ) % efficiency (η) %Slip(s) Blocked rotor test V SC (volts) I SC (amps) W SC (watts) MF OBS ACT

11 Auto Transformer 30/(0-70) V CIRCUIT DIAGRAM P 30V, 50Hz AC Supply N D P S T S W I T C H Fuse 5A Link V (0-0)A MI A (0-300)V MI 300V, 0A, UPF M L C V M M C Rotor S S S S Kg Kg Brake Drum FUSE RATING: 5% of rated current 5 x = 5 A 00 NAME PLATE DETAILS: Rated Voltage : 0V Rated Current : 9.5A Rated Power : 3HP Rated Speed : 470 RPM S, S - AUXILLARY WINDING M, M - MAIN WINDING

12 PROCEDURE Load test. Connections are given as per the circuit diagram. The DPST switch is closed and the single phase supply is given to the motor. 3. By adjusting the autotransformer, the rated voltage is applied and the corresponding no load values of speed, spring balance and meter readings are noted down. If the wattmeter readings show negative deflection on no load, switch of the supply & interchange the terminals of current coils (M & L) of the wattmeter. Now, again start the motor (follow above procedure for starting), take readings. 4. The procedure is repeated till rated current of the motor is reached. 5. The motor is unloaded, the auto transformer is brought to the minimum voltage position, and the DPST switch is opened. 6. The radius of the brake drum is measured. No load test. Connections are given as per the circuit diagram.. The motor is kept at no load condition. 3. The DPST switch is closed 4. By adjusting the Φ auto transformer the machine is brought to rated voltage. 5. The ammeter, voltmeter and wattmeter readings are noted down. Blocked rotor test. Connections are given as per the circuit diagram.. The rotor is made standstill (held tight) by applying Load to the motor. 3. Close the DPST switch. 4. By adjusting the Φ auto transformer rated current is allowed to circulate. 5. The ammeter, voltmeter and wattmeter readings are noted down. RESULT

13 POST LAB QUESTIONS. What are the inherent characteristics of plain -Ø Induction motor?. Why single phase induction motor has low power factor? 3. State double field revolving theory. 4. How the direction of a capacitor start Induction motor is reversed? 5. Why is the starting torque of a capacitor start induction motor high, when compared to that of a split phase induction motor?

14 PERFORMANCE EVALUATION OF THREE PHASE INDUCTION MOTOR PRELAB QUESTIONS. What is slip of an induction motor?. An induction motor is generally analogous to 3. What are the operating modes of 3-φ induction motor? 4. State the advantages of skewing? 5. How can the direction of rotation of the 3-φ induction motor be reversed?

15 AIM PERFORMANCE EVALUATION OF THREE PHASE INDUCTION MOTOR To conduct open circuit, short circuit and load test on the given three phase induction motor squirrel cage induction motor and to plot its performance characteristics. APPARATUS REQUIRED SI.NO APPARATUS SPECIFICATIONS QUANTITY VOLTMETER (0-600V) MI (0-300V)MI AMMETER (0-0A) MI (0-5A) MI 3 WATTMETER (600V,0A,UPF) (600V,5A,LPF) 4 TACHOMETER ( RPM) FORMULAE Load test. circumference of the brake drum = πr (m) R = Radius of the brake drum. Input power W=W +W (watts) W, W = wattmeter readings 3. Torque (T) = 9.8* R * (S ~ S ) (N-m) S, S = spring balance readings (Kg) NT 4. Output power = (watts) 60 output power 5. % Efficiency (η) = x00 input power 6. Power factor, Cos Φ = Cos Φ= Power factor W W 3 VI Ns N 7. %Slip, s = 00 Ns N S = synchronous speed = P = no. of poles f=frequency of supply (Hz) 0 f P (rpm)

16 No load test Cos Φ 0 = W 0 3 V I 0 0 Where W 0 = no-load input power in watts (watts) V 0 = line voltage on no-load I 0 = line current on no-load I w = I o Cos Φ 0 Amps R o = V 0( ph) I w = V 3 0 I w Ω I µ = I o Sin Φ 0 Amps X o = V 0 ( ph) = I V 3 0 I Ω Blocked rotor test I SN = I W SN = W V SC V sc SC I I SN SC (watts) Cos Φ sc = SC 3 W Vsc Isc 0 0 X 0 = Z R ( ) R = R 0 / R L = R s s Ω Ω Where Wsc = short circuit input power in watts (watts) I w = Working current in amps

17 I µ = Magnetizing current in amps X 0 = No load reactance in Ω V SC = Short circuit voltage volts I SC = Short circuit current in amps W SC = Short circuit power in watts I SC =Line Current under blocked rotor condition for short circuit voltage I SN =Line Current under blocked rotor condition for rated voltage s= 5% (Assume PRECAUTIONS Load test. The auto transformer is kept at minimum voltage position.. The motor is started at no load condition. 3. The motor should not be stopped under loaded condition PROCEDURE Load test. Connections are given as per the circuit diagram. The TPST switch is closed and the 3-phase supply is given 3. The motor is started with a Direct On-line (DOL) starter. 4. No load readings are noted down. 5. If any one of the wattmeter shows negative deflection, the connections of M and L in the wattmeter are interchanged after switching off the supply. 6. Gradually the motor is loaded and in each case all the meter readings are noted down and the procedure is repeated till the rated current is obtained. 7. The motor is unloaded. The DOL Starter is switched off and the TPST Switch is opened. 8. The radius of the brake drum is measured. No load test. Connections are given as per the circuit diagram. Initially the motor is kept at no load condition. 3. The TPST switch is closed 4. By adjusting the 3Φ auto transformer the machine is brought to rated voltage. 5. The ammeter, voltmeter and wattmeter readings are noted down. Blocked rotor test. Connections are given as per the circuit diagram. The rotor is made standstill (held tight) by applying Load to the motor. 3. Close the TPST switch. 4. By adjusting the 3Φ auto transformer rated current is allowed to circulate. 5. The ammeter, voltmeter and wattmeter readings are noted down.

18 CIRCUIT DIAGRAM 300V, 0A, UPF 300V, 0A, UPF FUSE CALCULATION:.5x4.5= 0A

19 TABULAR COLUMN Load test V volts I Amps Speed N (rpm) Wattmeter reading (Watts) W W Obs Act Obs Act W+W Spring balance readings (Kg) S S S~S Torque (T) N-m Output power (Watts) Power factor (cos Φ) % efficien cy (η) % Slip (s)

20 No load test V 0 (volts) I 0 (amps) W (watts) W (watts) W 0 (watts) Blocked rotor test V SC (volts) I SC (amps) W (watts) W (watts) W SC (watts) MODEL GRAPH EQUIVALENT CIRCUIT P I R 0 X 0 I o V R L = R (/s ) K R o X o N

21 CIRCLE DIAGRAM

22 PROCEDURE FOR CONSTRUCTION OF CIRCLE DIAGRAM By using the data obtained from the no load test and the blocked rotor test, the circle diagram can be drawn using the following steps:. Take reference phasor V as vertical (Y-axis). Select suitable current scale such that diameter of circle is 0-30cm. 3. From No load test, I 0 and 0 are obtained. Draw vector I 0, lagging V by angle 0. This is line OA 4. Draw horizontal line through extremity of I 0 i.e., A parallel to horizontal axis. 5. Draw the current I SN calculated from I SC with the same scale, lagging V by angle SC, from origion O. This is phasor OB. 6. Join AB. The line AB is called output line. 7. Draw a perpendicular bisector to AB Extend it to meet line AD at point C. This is the centre of the circle. 8. Draw the circle with C as a centre and radius equal to AC. This meets the horizontal line drawn from A at B. 9. Draw the perpendicular from point B on the horizontal axis to meet AF line at D and meet horizontal axis at E. 0. Torque line: The torque line separates stator and rotor copper losses. The vertical distance BD represents power input at short circuit i.e., W SN which consist of core loss, stator and rotor copper losses. F D = DE = fixed loss A F sum of stator & rotor copper losses. Pt G is located as BG Rotor copper loss GD Stator copper loss The line AG in called torque line Power Scale: As AD represents W SN i.e., power input on short circuit at normal voltage, the power scale can be obtained as Power scale = W SN W / cm ( BE) (BE) = Distance BE in cm

23 Location of point E (slip ring induction motor) I K = = transformation ratio I AE EF Rotor copper loss stator copper loss I R I R R R I I R R = Rotor resistance referred to stator. K R BG GD R ' Thus pt G can be obtained by dividing the line BD in the ratio R R Location of point D (squirrel cage induction motor) In a squirrel cage motor, the stator resistance can be measured by conducting resistance test. i.e., Stator copper loss = 3I SN R where I SN is phase value. Neglecting core loss, W SN = stator Cu loss + Rotor Cu loss i.e., Rotor copper loss = WSN 3I SN R BG WSN 3SN R GD 3I SN R Dividing line BD in this ratio, the point G can be obtained and hence AG represents torque line. To get the torque line, join the points A and G.. To find the full load quantities, draw line BK (=Full load output/power scale). Now, draw line PK parallel to output line meeting the circle at point P.. Draw line PT parallel to Y-axis meeting output line at Q, torque line at R, constant loss line at S and X-axis at T. RESULT

24 LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR USING AIM OPEN LAB SYSTEM To conduct load test on three phase squirrel cage Induction motor, pole, 4 V, - Connection. APPARATUS REQUIRED SL NO COMPONENT MODULE SPECIFICATION QUANTITY 3 phase cage rotor Open lab sys 4 V/5A AC (pole) Supply module DL 08 Fixed 4 V/5A AC Variable 4 V/5A 3 Measurement module DL 08 AC voltmeter (0-50)V AC ammeter (0-5)A Wattmeter 75V/0A/300WUPF Speed sensor 4 Electromagnetic brake DL 0300A G=3.5N,g=.5N PRECAUTIONS FORMULAE. In the supply module DL08,select the selector switch I to position b for fixed AC supply 4/0A and switch L/L/L3 to position 0.. In the supply module DL08,select the selector switch IV to position c for variable DC voltage and control knob to 0%. 3. In the measurement module 08,ensure the ammeter and voltmeter for AC measurements. INPUT POWER P in = P +P Watts OUTPUT POWER P out = 0.047nM Watts TORQUE M = G.b Nm POWER FACTOR COS ɸ = Pin/ 3 U I EFFICIENCY % Ƞ = Pout/Pin 00 Where, U = supply voltage in volts I = load current in Amps n = speed of cage rotor in Rpm

25 M = torque in Nm G = measuring weight b = distance of the arm in m TABULAR COLUMN U(V) I (A) P (W) P (W) P in act obs act obs (W) COSɸ G (N) b(m) M (Nm) n (Rpm) Pout(W) %Ƞ CIRCUIT DIAGRAM

26 MODEL GRAPH PROCEDURE RESULT. Activate the supply modue by setting the switch L/L/L3 from position 0 to.. Observe whether the motor runs in CW direction. 3. If not interchange any two phases. 4. Balance the brake by moving the balance weight g until the water level shows horizontal position and the speed measurement reads rated speed. 5. Now note down the No load measurements (U,I,P,P,n,G,b) 6. The motor is therefore loaded in steps by means of brake. (The load is increased by moving the weight g to a distance b from the No load initial position. Adjust the selector switch IV to balance the system again) 7. Perform the measurements as per previous step and repeat the procedure until rated current. 8. Stop the system by setting the load voltage switch L/L/L3 to a position to de-energize the brake.

27 POST LAB QUESTIONS. What is the need for drawing a circle diagram?. How to calculate the power scale for drawing a circle diagram? 3. What are the advantages and disadvantages of circle diagram method of predetermining the performance of 3 phase IM? 4. What are the effects of increasing rotor resistance on starting current and starting torque? 5. Draw the torque slip characteristics of 3 phase slip ring induction motor.

28 SPEED CONTROL OF ROTATING TRANSFORMER PRELAB QUESTIONS. Why is an induction motor not capable of running at synchronous speed?. What are the different starters needed for three phase induction motors? 3. The rotor core loss of an induction motor under running condition is usually neglected. Why? 4. Why are starters needed for induction motors? 4. What are the various methods of speed control of 3 phase induction motor? 5. What are the various methods of speed control of induction motor from the stator side?

29 ROTOR RESISTANCE SPEED CONTROL METHOD OF 3ϕ SLIP RING INDUCTION MOTOR AIM To vary the speed of the slip ring induction motor using rotor resistance speed control method. APPARATUS REQUIRED SI.NO APPARATUS SPECIFICATIONS QUANTITY 3 Voltmeter Ammeter Tachometer (0-600V) MI (0-0A) MI (rpm) TABULAR COLUMN Voltage (V) Current (A) Resistance ( ) Speed (rpm)

30 CIRCUIT DIAGRAM: ROTOR RHEOSTAT SPEED CONTROL OF 3ϕ SLIP RING INDUCTION MOTOR

31 speed(rpm) MODEL GRAPH Speed vs resistance Speed (rpm) Resistance (W) resistance(ohm) PROCEDURE. The Connection are made as per circuit diagram. The TPST switch is closed and three phase supply is given. 3. The motor is started with rotor connected with rotor resistance. 4. The rotor resistance is varied and corresponding values of speed, voltage and current are noted down. RESULT

32 VARIBALE FREQUENCY AND VOLTAGE SPEED CONTROL METHOD AIM To control the speed of the 3 phase induction motor by changing the supply frequency and to plot the speed Vs frequency curve. APPARATUS SI.NO APPARATUS SPECIFICATIONS QUANTITY Voltmeter Ammeter Tachometer Frequency meter Digital. Rheostat Wire Wound (0-600V) MI (0-0A) MI (0-)A MC (rpm) (0-60Hz) 300Ω,.A PRECAUTIONS i) TPST in open position ii) DPST and DPST in open position iii) Motor field rheostat in minimum position iv) Potential divider in minimum voltage position v) Autotransformer at minimum voltage position TABULATION Induction motor on no load Line voltage In volts Frequency In Hz Speed of IM In rpm

33 CIRCUIT DIAGRAM Fuse calculation: 5% of Rated current=.5*9=30a NAME PLATE DETAILS: Motor Alternator Rated Voltage : 0V 45V Rated Current : 9A 4.A Rated Power : 3HP 5KVA Rated Speed : 500 RPM 500 RPM

34 MODEL GRAPH PROCEDURE. Make the connections as shown in diagram.. Switch on the DC supply to the DC motor by closing the switch DPST. Start the DC shunt motor using 3-point starter. Adjust the field rheostat of the alternator and bring it to rated speed.(500rpm). 3. Now, dc supply is given to the alternator field winding and adjust the potential divider so that the generated voltage is rated value (40V). 4. Close the TPST switch. Increase the autotransformer. Induction motor starts running on no load. Apply rated voltage by adjusting autotransformer. Note down the frequency, voltage and speed of the induction motor. Now, decrease the frequency. Decrease the voltage and frequency in proportion and note down the frequency, voltage and speed of the induction motor each time. This procedure is continued till frequency decreases to 48Hz.Switch off the supply after bringing the motor to noload. RESULT

35 POSTLAB QUESTIONS. What does happen to the induction motor if supply frequency is reduced keeping the supply voltage constant?. Write down the main feature of v/f control? 3. Name some applications of speed control of induction motor? 4. Why external resistance is added in slip ring induction motor? 5. When does the induction motor behave as induction generator? 6. What is single phasing in induction motor?

36 Experiment No. SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR AIM To synchronize the 3Φ alternator to the infinite bus bar. APPARATUS REQUIRED SI.NO APPARATUS SPECIFICATIONS QUANTITY 3 VOLTMETER AMMETERS RHEOSTAT SYNCHRONISING LAMPS (0-600V) MI (0-A) MC 300Ω,.A 350Ω,A 30V,5A 6 PROCEDURE ) The DPST- is closed and the motor field rheostat is adjusted to make the alternator run at rated speed. ) The DPST- is closed and by keeping the TPST open, adjusts the alternator field rheostat to supply the voltage equal to infinite bus bar. 3) The phase sequence of the alternator is made as same as that of the infinite bus bar by observing the sequence of glowing of synchronizing lamps. If the phase sequence is not same, any of the two phases are interchanged. 4) The field rheostat is adjusted to bring the frequency of the alternator to same frequency of infinite bus bar. When the phase sequence of the two sides are same all the lamps will begin to glow bright and dark simultaneously. In this condition, when the frequencies are equal, the variation of lamps bright to dark is lowest. 5) At the dimmest point the TPST switch is closed thereby synchronizing the alternator to the bus bar.

37 CIRCUIT DIAGRAM: SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR

38 RESULT

39 POSTLAB QUESTIONS. Three lights flashing rapidly in unison while paralleling alternators means that. Advantage of paralleling of two machines? 3. How can the voltage and frequency be adjusted? 4. When the pointer of a synchroscope is stationary and points upward during the paralleling operation, the 5. List the factors that affect the load sharing in parallel operating generators? 6. What is the possible effect of wrong synchronization?

40 PREDETERMINATION OF VOLTAGE REGULATION PRELAB QUESTIONS. Define the term voltage regulation of alternator.. What is the necessity for predetermination of voltage regulation? 3. Name the various methods for predetermining the voltage regulation of 3-phase Alternator. 4. What are the causes of changes in terminal voltage of Alternators when loaded? 5. What is meant by armature reaction?

41 PREDETERMINATION OF VOLTAGE REGULATION AIM To predetermine the regulation of alternator by EMF, MMF and ZPF methods APPARATUS REQUIRED SI.NO APPARATUS SPECIFICATIONS QUANTITY VOLTMETER (0-600V) MI AMMETER (0-5A) MI 3 RHEOSTAT 300Ω,.A 4 TACHOMETER ( RPM) 5 REACTIVE LOAD (-5) amps FORMULAE EMF method Synchronous impedance, Zs = OC voltage/ phase (at constant If) SCcurrent / phase Synchronous reactance, Xs = Zs Rac ( ) Where Rac = armature resistance For rated conditions, EMF, E 0 = ( Vph cos IRa ) ( Vph sin IXs ) + corresponds to lagging power factor - corresponds to leading power factor MMF method E0 Vph % Regulation = x00 Vph If = field current corresponding to Isc E = Vph + IRa cosφ If = field current corresponding to E from graph If 0 = ( If If If If cos( 80 (90 )) E 0 = open circuit voltage corresponding to If0 (from graph) E0 Vph % Regulation = x00 Vph

42 ZPF method EMF, E = ( Vph cos IRa ) ( Vph sin IX L ) + corresponds to lagging power factor - corresponds to leading power factor IX L = RS (from graph) If = PS (from graph) If = field current corresponding to E (from graph) PRECAUTION OC TEST If0 = ( If If If If cos( 80 (90 )) E0 = open circuit voltage corresponding to If0 (from graph) E0 Vph % Regulation = x00 Vph. The Motor field rheostat is kept at minimum resistance position.. The Generator field rheostat should be kept at maximum resistance position. FIELD CURRENT(I f ) (amps) LINE VOLTAGE(V L ) (volts) PHASE VOLTAGE (V ph )(volts)

43 CIRCUIT DIAGRAM

44 SC TEST FIELD CURRENT(I f ) (amps) S.C.CURRENT (I SC )(amps) ZPF TEST I f (amps) V ZPF (VOLTS) I SC (amps) VOLTAGE REGULATION EMF method COS Ø E 0 (volts) % regulation LAG LEAD LAG LEAD Unity MMF method cos Ø E 0 (volts) % regulation 0.8 LAG LEAD LAG LEAD Unity

45 ZPF method COS Ø E 0 (volts) % regulation 0.8 Unity LAG LEAD LAG LEAD MODEL GRAPH MMF method ZPF method

46 PROCEDURE OC test SC test. Connections are given as per the circuit diagram. The TPST switch of the alternator is kept opened. 3. The DPST- switch is closed 4. The motor field rheostat is varied such that the alternator runs at rated speed. 5. The DPST- switch is closed. 6. The Generator field rheostat is varied in step and the readings of I f and V are noted, till 5% of the rated voltage is obtained.. Connections are given as per the circuit diagram. The DPST- switch is closed 3. The motor field rheostat is varied such that the alternator runs at rated speed. 4. The TPST switch is closed. 5. The DPST- switch is closed. 6. The Generator field rheostat is varied to bring rated current of alternator and the corresponding I f is noted. ZPF test (All the quantities are in per phase value). Draw the Open Circuit Characteristics (Generated Voltage per phase VS Field Current). 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 P 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 P 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 PX from P towards Y-axis, which is parallel and equal to OA. 7. Draw the parallel line for the tangent from R to the OCC curve. 8. Join the points R and S also drop the perpendicular line PX, where the line RS represents armature leakage reactance drop (IX L ) PS represents armature reaction excitation (Ifa). RESULT

47 POST LAB QUESTIONS. Why it is called as zero power factor method?. Why ZPF is called most accurate method? 3. Why the field rheostat is adjusted such that the voltmeter reads 380V. 4. Why voltage regulation on alternator is negative for leading power factor? 5. What are the advantages and disadvantages of estimating the voltage regulation of an Alternator by EMF method?

48 DETERMINATION OF V AND INVERTED V CURVES OF SYNCHRONOUS MOTOR PRELAB QUESTIONS. Why synchronous motor is not self starting?. Why a synchronous motor is a constant speed motor? 3. State the characteristic features of synchronous motor. 4. Name the methods of starting a synchronous motors

49 Experiment No. DETERMINATION OF V AND INVERTED V CURVES OF SYNCHRONOUS MOTOR AIM To determine the V and inverted V curve of synchronous motor APPARATUS REQUIRED SI.NO APPARATUS SPECIFICATIONS QUANTITY VOLTMETER AMMETERS 3 4 RHEOSTAT WATTMETER (0-600V) MI (0-A) MC (0-0A)MI 300Ω,.A 600V,0A,UPF FORMULAE Φ = cos tan W W 3 W W Where W = wattmeter reading W = wattmeter reading PRECAUTION. The VARIAC is kept at minimum position.. The potentiometer should be kept at minimum voltage position. TABULAR COLUMN Ia I f V W(watts) W(watts) W+W(watts) COSΦ Amps Amps Volts OBS ACT OBS ACT

50 CIRCUIT DIAGRAM

51 MODEL GRAPH PROCEDURE. Connections are as per the circuit diagram. The TPST switch is closed. 3. By varying auto synchronous motor starter the voltage is adjusted to 30-40% of rated voltage. 4. Close the DPST switch. 5. Adjusted the rheostat and bring for rated current. 6. Now the Voltmeter is adjusted for rated voltage values. 7. The values of If, W and W are noted down. 8. By adjusting the rheostat below rated current the corresponding reading are noted down. 9. At some point the value of Ia will increase and the above procedure is repeated till the rated value of current. 0. If any wattmeter shows negative deflection, change the current coil terminals of wattmeter. RESULT

52 POSTLAB QUESTIONS. How synchronous machine does behave in under excitation?. What is synchronous capacitor? 3. Distinguish between synchronous phase modifier and synchronous condenser. 4. Mention four applications of synchronous motor? 5. Define pull in torque in synchronous motor..

53 DETERMINATION OF X d AND X q FOR SALIENT POLE ALTERNATOR USING SLIP TEST PRELAB QUESTIONS. What are the two types of alternators?. Compare salient pole and Non salient pole rotor. SALIENT POLE ROTOR NON SALIENT POLE ROTOR (Smooth cylindrical type ) 3. What is meant by two reaction theory? 4. What is direct and quadrature axis reactance? 5. What are the normal values of Xq/Xd for the two types of syn. Machines.

54 Experiment No. DETERMINATION OF X d AND X q FOR SALIENT POLE ALTERNATOR USING SLIP TEST AIM To find the direct axis reactance X d and quadrature axis reactance X q by conducting slip test. APPARATUS REQUIRED SI.NO APPARATUS SPECIFICATIONS QUANTITY 3 4 VOLTMETER AMMETER RHEOSTAT TACHOMETER (0-300V) MI (0-5A) MI 300Ω,.A ( RPM) FORMULAE Xd = Maximum armature voltage/phase Minimum armature current/phase Xq = Minimum armature voltage/phase Maximum armature current/phase PRECAUTION. The Motor field rheostat should be kept at minimum resistance position PROCEDURE. Connections are given as per the circuit diagram. The DPST switch is closed 3. The rheostat is varied from the minimum resistance position so as to bring the speed to a value below or near to rated speed of the alternator 4. The TPST switch is closed keeping the variac in the minimum position. 5. The variac is varied to apply 5-0% of the rated voltage of alternator is observed. 6. Check the voltage in the field coil, if it reads high the phase sequence is changed so that the voltmeter reads zero. 7. The maximum and minimum deflections of voltmeter and ammeter are noted. 8. The variac is brought to minimum position and TPST Switch is opened. The field rheostat is brought to minimum position and DPST Switch is opened.

55 CIRCUIT DIAGRAM

56 TABULAR COLUMN V MAX V MIN I MAX I MIN MODEL CALCULATION RESULT

57 POSTLAB QUESTIONS ) Why does the pointer of ammeter and voltmeter oscillate at slip condition? ) Which is higher X d or X q? Why? 3) Mention some application of synchronous motor 4) Can the slip condition achieved in non salient pole Synchronous machines? Why?