15EE210L-ELECTRICAL MACHINES LAB-II
RECORD
ACADEMIC YEAR: ODD SEMESTER 2018-19
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 – 603 203
KANCHEEPURAM DISTRICT
SRM Institute of Science and Technology (Deemed to be University) S.R.M. NAGAR, KATTANKULATHUR -603 203 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 15EE210L Electrical machines Lab-II in SRM IST, Kattankulathur during the academic year 2017-2018.
Lab in-charge
Date: Year Co-ordinator
Submitted for end semester examination held in Electrical machines Lab, SRM IST, Kattankulathur.
Date: Examiner-1 Examiner-2
LIST OF EXPERIMENTS
1. Performance evaluation of single phase induction motor
2. 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 xd and xq for salient pole alternator using slip test
8. Characteristics of 3 phase induction generator
9. Single phasing in 3 phase induction motor
10. Armature reaction in synchronous generator
INDEX
Expe Date Viva Executi Calculation Pre and Total Faculty rime of Title of Experiment (10) on / Post Lab (50) Signatu nt No Experi (10) Evaluation (10) re ment (20) Performance evaluation of 1 single phase induction motor a) Performance evaluation 2 (a) of three phase induction motor b) Load test on three phase 2(b) squirrel cage induction motor using open lab system Speed control of rotating 3 transformer Synchronisation of 4 alternator to infinite bus bar Predetermination of voltage 5 regulation Determination of v and 6 inverted v curves of synchronous motor
Determination of xd and xq 7 for salient pole alternator using slip test Characteristics of 3 phase 8 induction generator Single phasing in 3 phase 9 induction motor Armature reaction in 10 synchronous generator
Average
PERFORMANCE EVALUATION OF SINGLE PHASE INDUCTION MOTOR
PRE LAB QUESTIONS
1. What are the types of single phase induction motor?
2. 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 1-phase Induction motor differ from a 3-phase Induction motor?
5. What is the rating of single phase machines? State its applications
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 1 VOLTMETER (0-300V) MI 1 (0-150V) MI 1 2 AMMETER (0-10A) MI 1 (0-5A) MI 1 3 WATTMETER (300V,10A,UPF) 1 (150V,10A, UPF) 1 (300V,5A,LPF) 1 4 TACHOMETER (0-10000 RPM) 1 5 Connecting wires As required
FORMULAE
Load test
1. Circumference of the brake drum = 2πR (m) R = Radius of the brake drum
2. Input power =W (watts) W = wattmeter readings
3. Torque (T) = 9.81x R x (S1 ~ S2) (N-m) S1, S2 = spring balance readings (Kg)
2NT 4. Output power = (watts) 60 N- Speed in rpm
output power 5. % Efficiency (η) = x100 input power W 6. Power factor, cos Φ= VI
Ns N 7. % Slip, s = 100 Ns 120 f NS = synchronous speed = (rpm) P P = no. of poles f=frequency of supply (Hz)
No load test
R1= 1.5x Rdc cos Ф = Wo / Vo Io
VAB = Io xo
xo = VAB /Io
Blocked rotor test cos Φsc =Wsc /Vsc Isc
Zeq = Vsc/ Isc 2 Req = Wsc /( Isc)
Req = R1 + R2
R2 = Req - R1 = rotor resistance referred to stator 2 2 Xeq =√(Zeq - Req )
X1 = X2
X2
Where W0 = no-load input power in watts (watts) Wsc = short circuit input power in watts (watts) V0 = line voltage on no-load I0 = line current on no-load
CALCULATIONS TO DRAW THE EQUIVALENT CIRCUIT Blocked rotor test
Zeq = Vsc/ Isc 2 Req = Wsc /( Isc)
2 2 Xeq =√(Zeq - Req )
R1= 1.5*Rdc
Req = R1 + R2
R2 = Req - R1
Xeq=X1 + X2
X1 = X2
x2 = X2 / 2
r2= R2 / 2
Where VSC= Short circuit voltage volts
ISC= Short circuit current in amps
WSC= Short circuit power in watts No load test
VAB = Io xo | | xo =
Where W0 = no-load input power in watts (watts)
V0 = line voltage on no-load
I0 = line current on no-load PRECAUTIONS
Load test
1. The auto transformer must kept at minimum voltage position. 2. The motor is started at no load condition. 3. The motor should not be stopped under loaded condition
No load test 1. Initially DPST Switch is kept open. 2. Auto transformer is kept at minimum potential position. 3. The machines must be started on no load.
Blocked rotor test 1. Initially the DPST Switch is kept open. 2. Auto transformer is kept at minimum potential position. 3. The machine must be started at full load (blocked rotor).
MODEL EQUIVALENT CIRCUIT
MODEL GRAPH
TABULAR COLUMN
No load test
V0 I0 W0 (volts) (amps) (watts) MF OBS ACT
Load test
Voltage Current Speed Wattmeter Spring balance Torque Output Power % efficiency %Slip(s) V I N reading readings (Kg) (T) Power factor (η) (volts ) Amps (rpm) (watts) S1 S2 S1~S2 (watts) (cos Φ) N-m OBS ACT
Blocked rotor test
VSC ISC WSC (volts) (amps) (watts) MF OBS ACT
CIRCUIT DIAGRAM
300V, 10A, UPF (0-10)A MI Fuse M L P A
15A C V D S1 S2 P M1 C Kg Kg
S
T
230V, (0-300)V
50Hz 1 S V
270) V 270)
- MI AC W Supply I
T 230/(0
Auto Transformer Auto C M2 H Rotor Brake Drum N
Link S1 S2
S , S - AUXILLARY WINDING FUSE RATING: NAME PLATE DETAILS: 1 2 M , M - MAIN WINDING 1 2 125% of rated current Rated Voltage : 220V Rated Current : 9.5A 125 x 9.5 Rated Power : 3HP ------= 15 A Rated Speed : 1470 RPM 100
PROCEDURE
Load test
1. Connections are given as per the circuit diagram 2. 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 1. Connections are given as per the circuit diagram. 2. The motor is kept at no load condition. 3. The DPST switch is closed 4. By adjusting the 1Φ auto transformer the machine is brought to rated voltage. 5. The ammeter, voltmeter and wattmeter readings are noted down.
Blocked rotor test 1. Connections are given as per the circuit diagram. 2. The rotor is made standstill (held tight) by applying Load to the motor. 3. Close the DPST switch. 4. By adjusting the 1Φ auto transformer rated current is allowed to circulate. 5. The ammeter, voltmeter and wattmeter readings are noted down.
RESULT
POST LAB QUESTIONS
1. What are the inherent characteristics of plain 1-Ø Induction motor?
2. 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?
PERFORMANCE EVALUATION OF THREE PHASE INDUCTION MOTOR
PRELAB QUESTIONS
1. What is slip of an induction motor?
2. 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?
PERFORMANCE EVALUATION OF THREE PHASE INDUCTION MOTOR
AIM
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 1 VOLTMETER (0-600V) MI 1 (0-300V)MI 1 2 AMMETER (0-10A) MI 1 (0-5A) MI 1 3 WATTMETER (600V,10A,UPF) 2 (600V,5A,LPF) 2 4 TACHOMETER (0-10000 RPM) 1
FORMULAE
Load test
1. circumference of the brake drum = 2πR (m) R = Radius of the brake drum
2. Input power W=W1+W2 (watts) W1, W2 = wattmeter readings
3. Torque (T) = 9.81* R * (S1 ~ S2) (N-m) S1, S2 = spring balance readings (Kg) 2NT 4. Output power = (watts) 60 output power 5. % Efficiency (η) = x100 input power W W 6. Power factor, Cos Φ = 1 2 3 VI
Cos Φ= Power factor
Ns N 7. %Slip, s = 100 Ns 120f NS = synchronous speed = (rpm) P P = no. of poles f=frequency of supply (Hz)
No load test
W0 Cos Φ0 = 3 V0 I 0
Where W0 = no-load input power in watts (watts) V0 = line voltage on no-load I0 = line current on no-load
Iw= Io Cos Φ0 Amps
V0( ph) V0 Ro= = Ω I w 3 I w
Iµ= Io Sin Φ0 Amps
V 0( ph) V0 Xo= = Ω I 3 I
Blocked rotor test
V ISN = I SC VSC 2 I SN WSN= Wsc (watts) I SC
WSC Cos Φsc = 3 Vsc Isc
2 2 X01= Z01 R01 ()
’ R2 = R01/ 2 Ω
’ ’ 1 s RL = R2 Ω s
Where
Wsc = short circuit input power in watts (watts) Iw= Working current in amps
Iµ= Magnetizing current in amps X0= No load reactance in Ω VSC= Short circuit voltage volts ISC= Short circuit current in amps WSC= Short circuit power in watts ISC=Line Current under blocked rotor condition for short circuit voltage ISN=Line Current under blocked rotor condition for rated voltage s= 5% (Assume
PRECAUTIONS Load test
1. The auto transformer is kept at minimum voltage position. 2. The motor is started at no load condition. 3. The motor should not be stopped under loaded condition
PROCEDURE
Load test
1. Connections are given as per the circuit diagram 2. 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
1. Connections are given as per the circuit diagram 2. 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
1. Connections are given as per the circuit diagram 2. 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.
CIRCUIT DIAGRAM
300V, 10A, UPF
300V, 10A, UPF
FUSE CALCULATION: 1.25x4.5= 10A
TABULAR COLUMN
Load test
V I Speed Wattmeter reading Spring balance T orque Output Power % % Slip volts Amps N (Watts) readings (Kg) (T) power factor efficien (rpm) W1 W2 S1 S2 S1~S2 N-m (Watts) (cos Φ) cy (s) Obs Act Obs Act W1+W2 (η)
No load test
V0 I0 W1 W2 W0 (volts) (amps) (watts) (watts) (watts)
Blocked rotor test
VSC ISC W1 W2 WSC (volts) (amps) (watts) (watts) (watts)
MODEL GRAPH
EQUIVALENT CIRCUIT
R X ’ 01 01 I1 P
’ Io
푅2(1/푠−1) RL’= V 1 퐾2
Ro Xo
N
CIRCLE DIAGRAM
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:
1. Take reference phasor V as vertical (Y-axis) 2. Select suitable current scale such that diameter of circle is 20-30cm.
3. From No load test, I0 and 0 are obtained. Draw vector I0, lagging V by angle 0. This is line OA
4. Draw horizontal line through extremity of I0 i.e., A parallel to horizontal axis.
5. Draw the current ISN calculated from ISC 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. 10. Torque line: The torque line separates stator and rotor copper losses.
The vertical distance BD represents power input at short circuit i.e., WSN which consist of core loss, stator and rotor copper losses.
FD = DE = fixed loss AF sum of stator & rotor copper losses. Pt ‘G’ is located as BG Rotor copperloss GD Statorcopperloss The line AG in called torque line
Power Scale: As AD represents WSN i.e., power input on short circuit at normal voltage, the power scale can be obtained as W Power scale = SN W / cm (BE)
(BE) = Distance BE in cm
Location of point E (slip ring induction motor) I K = 1 = transformation ratio I 2 2 AE Rotor copper loss I 2 R R I 2 2 2 2 2 EF stator copper loss I1 R1 R1 I1
1 R2 R2 = Rotor resistance referred to stator. K 2 BG R1 2 GD R1
' Thus pt G can be obtained by dividing the line BD in the ratio R2 R1
Location of point D (squirrel cage induction motor)
In a squirrel cage motor, the stator resistance can be measured by conducting resistance test.
2 i.e., Stator copper loss = 3I SN R1 where I SN is phase value. Neglecting core loss, WSN = stator Cu loss + Rotor Cu loss 2 i.e., Rotor copper loss = WSN 3I SN R1 2 BG WSN 3SN R1 2 GD 3I SN R1 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.
11. 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. 12. 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
LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR USING
OPEN LAB SYSTEM
AIM
To conduct load test on three phase squirrel cage Induction motor, 2 pole, 24 V, ∆- Connection.
APPARATUS REQUIRED
SL NO COMPONENT MODULE SPECIFICATION QUANTITY 1 3 phase cage rotor Open lab sys 24 V/5A AC (2pole) 1 2 Supply module DL 10281 Fixed 24 V/5A AC 1 Variable 42 V/5A 1 3 Measurement module DL 10282 AC voltmeter 1 (0-50)V AC ammeter 1 (0-5)A Wattmeter 2 75V/10A/300WUPF Speed sensor 1 4 Electromagnetic brake DL 10300A G=3.5N,g=1.5N 1
PRECAUTIONS
1. In the supply module DL10281,select the selector switch‛I’ to position‛ b’ for fixed AC supply 42/10A and switch L1/L2/L3 to position ‛0’. 2. In the supply module DL10281,select the selector switch‛ IV’ to position ‛c’ for variable DC voltage and control knob to 0%. 3. In the measurement module 10282,ensure the ammeter and voltmeter for AC measurements.
FORMULAE
INPUT POWER Pin = P1+P2 Watts
OUTPUT POWER Pout = 0.1047nM Watts
TORQUE M = G.b Nm
POWER FACTOR COS ɸ = Pin/√3 U I
EFFICIENCY % Ƞ = Pout/Pin × 100
Where, U = supply voltage in volts I = load current in Amps n = speed of cage rotor in Rpm
M = torque in Nm G = measuring weight b = distance of the arm in m
TABULAR COLUMN
U(V) I P1(W1) P2(W2) Pin COSɸ G b(m) M n Pout(W) %Ƞ (A) act obs act obs (W) (N) (Nm) (Rpm)
CIRCUIT DIAGRAM
MODEL GRAPH
PROCEDURE
1. Activate the supply modue by setting the switch L1/L2/L3 from position‛ 0’ to‛ 1’. 2. 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,P1,P2,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 L1/L2/L3 to a position to de-energize the brake.
RESULT
POST LAB QUESTIONS
1. What is the need for drawing a circle diagram?
2. 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.
SPEED CONTROL OF ROTATING TRANSFORMER
PRELAB QUESTIONS
1. Why is an induction motor not capable of running at synchronous speed?
2. 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?
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 1 Voltmeter (0-600V) MI 1 2 Ammeter (0-10A) MI 1 3 Tachometer 0-10000 (rpm) 1
TABULAR COLUMN
Voltage Current (A) Resistance () Speed (rpm) (V)
CIRCUIT DIAGRAM: ROTOR RHEOSTAT SPEED CONTROL OF 3ϕ SLIP RING INDUCTION MOTOR
MODEL GRAPH
Speed vs resistance
1480 1470 1460 1460 1450 1440 1440 1430 1420 1400 1390 Speed (rpm) 1380
speed(rpm) 1360 1340
46.6 32.2 21.8 5.88 12.12
Resistance (W) resistance(ohm)
PROCEDURE
1. The Connection are made as per circuit diagram 2. 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
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 1 Voltmeter (0-600V) MI 2 2 Ammeter (0-10A) MI 1 3 Tachometer (0-2)A MC 1 4 Frequency meter Digital 0-10000 (rpm) 1 5 . Rheostat Wire Wound (0-60Hz) 1 300Ω, 1.2A 2
PRECAUTIONS i) TPST in open position ii) DPST1 and DPST2 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
CIRCUIT DIAGRAM
Fuse calculation: NAME PLATE DETAILS: 125% of Rated current=1.25*19=30A Motor Alternator
Rated Voltage : 220V 415V Rated Current : 19A 4.2A Rated Power : 3HP 5KVA Rated Speed : 1500 RPM 1500 RPM
MODEL GRAPH
PROCEDURE
1. Make the connections as shown in diagram. 2. Switch on the DC supply to the DC motor by closing the switch DPST1. Start the DC shunt motor using 3-point starter. Adjust the field rheostat of the alternator and bring it to rated speed.(1500rpm). 3. Now, dc supply is given to the alternator field winding and adjust the potential divider so that the generated voltage is rated value (410V). 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 no- load.
RESULT
POSTLAB QUESTIONS
1. What does happen to the induction motor if supply frequency is reduced keeping the supply voltage constant?
2. 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?
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 1 VOLTMETER (0-600V) MI 2 2 AMMETERS (0-2A) MC 1 RHEOSTAT 300Ω,1.2A 1 350Ω,2A 1 3 SYNCHRONISING LAMPS 230V,15A 6
PROCEDURE
1) The DPST-1 is closed and the motor field rheostat is adjusted to make the alternator run at rated speed. 2) The DPST-2 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.
CIRCUIT DIAGRAM: SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR
RESULT
POSTLAB QUESTIONS
1. Three lights flashing rapidly in unison while paralleling alternators means that ______2. 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?
PREDETERMINATION OF VOLTAGE REGULATION
PRELAB QUESTIONS
1. Define the term voltage regulation of alternator.
2. 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?
PREDETERMINATION OF VOLTAGE REGULATION
AIM
To predetermine the regulation of alternator by EMF, MMF and ZPF methods
APPARATUS REQUIRED
SI.NO APPARATUS SPECIFICATIONS QUANTITY 1 VOLTMETER (0-600V) MI 2 2 AMMETER (0-5A) MI 1 3 RHEOSTAT 300Ω,1.2A 1 4 TACHOMETER (0-10000 RPM) 1 5 REACTIVE LOAD (1-15) amps 1
FORMULAE
EMF method OC voltage/ phase Synchronous impedance, Zs = (at constant If) SCcurrent/ phase
Synchronous reactance, Xs = Zs 2 Rac 2 () Where Rac = armature resistance For rated conditions, 2 2 EMF, E0 = (Vph cos IRa) (Vph sin IXs) + corresponds to lagging power factor - corresponds to leading power factor
E0 Vph % Regulation = x100 Vph
MMF method
If1 = field current corresponding to Isc E = Vph + IRa cosΦ If2 = field current corresponding to E from graph 2 2 If0 = (If 1 If 2 2If 1 If 2cos(180 (90))
E0 = open circuit voltage corresponding to If0 (from graph)
E0 Vph % Regulation = x100 Vph
ZPF method
2 2 EMF, E1 = (Vph cos IRa) (Vph sin IX L ) + corresponds to lagging power factor - corresponds to leading power factor IXL = RS (from graph) If2 = PS (from graph) If1 = field current corresponding to E1 (from graph)
If0 = (If 12 If 22 2If 1 If 2cos(180 (90)) E0 = open circuit voltage corresponding to If0 (from graph)
E0 Vph % Regulation = x100 Vph
PRECAUTION
1. The Motor field rheostat is kept at minimum resistance position. 2. The Generator field rheostat should be kept at maximum resistance position.
OC TEST
FIELD LINE PHASE CURRENT(If) VOLTAGE(VL) VOLTAGE (amps) (volts) (Vph)(volts)
CIRCUIT DIAGRAM
SC TEST
FIELD S.C.CURRENT CURRENT(If) (ISC)(amps) (amps)
ZPF TEST
If(amps) VZPF(VOLTS) ISC(amps)
VOLTAGE REGULATION
EMF method
COS Ø E0(volts) % regulation
LAG LEAD LAG LEAD
Unity
MMF method
cos Ø E0(volts) % regulation
LAG LEAD LAG LEAD
0.8
Unity
ZPF method
COS Ø E0(volts) % regulation
LAG LEAD LAG LEAD
0.8 Unity
MODEL GRAPH
MMF method
ZPF method
PROCEDURE
OC test
1. Connections are given as per the circuit diagram 2. The TPST switch of the alternator is kept opened. 3. The DPST-1 switch is closed 4. The motor field rheostat is varied such that the alternator runs at rated speed. 5. The DPST-2 switch is closed. 6. The Generator field rheostat is varied in step and the readings of If and V are noted, till 125% of the rated voltage is obtained.
SC test
1. Connections are given as per the circuit diagram 2. The DPST-1 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-2 switch is closed. 6. The Generator field rheostat is varied to bring rated current of alternator and the corresponding If is noted.
ZPF test (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 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 (IXL) PS represents armature reaction excitation (Ifa).
RESULT
POST LAB QUESTIONS
1. Why it is called as zero power factor method?
2. 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?
DETERMINATION OF V AND INVERTED V CURVES OF SYNCHRONOUS MOTOR
PRELAB QUESTIONS
1. Why synchronous motor is not self starting?
2. 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
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 1 VOLTMETER (0-600V) MI 1 2 AMMETERS (0-2A) MC 1 (0-10A)MI 1 3 RHEOSTAT 300Ω,1.2A 1 4 WATTMETER 600V,10A,UPF 2
FORMULAE
W W Φ = costan 1 3 1 2 W1 W2
Where W1 = wattmeter reading 1 W2 = wattmeter reading 1
PRECAUTION 1. The VARIAC is kept at minimum position. 2. The potentiometer should be kept at minimum voltage position.
TABULAR COLUMN
Ia If V W1(watts) W2(watts) W1+W2(watts) COSΦ Amps Amps Volts OBS ACT OBS ACT
CIRCUIT DIAGRAM
MODEL GRAPH
PROCEDURE 1. Connections are as per the circuit diagram 2. 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 If1, W1 and W2 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. 10. If any wattmeter shows negative deflection, change the current coil terminals of wattmeter.
RESULT
POSTLAB QUESTIONS
1. How synchronous machine does behave in under excitation?
2. 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
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DETERMINATION OF Xd AND Xq FOR SALIENT POLE ALTERNATOR USING SLIP TEST
PRELAB QUESTIONS
1. What are the two types of alternators?
2. 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.
Experiment No.
DETERMINATION OF Xd AND Xq FOR SALIENT POLE ALTERNATOR USING SLIP TEST
AIM To find the direct axis reactance Xd and quadrature axis reactance Xq by conducting slip test.
APPARATUS REQUIRED
SI.NO APPARATUS SPECIFICATIONS QUANTITY 1 VOLTMETER (0-300V) MI 2 2 AMMETER (0-5A) MI 1 3 RHEOSTAT 300Ω,1.2A 1 4 TACHOMETER (0-10000 RPM) 1
FORMULAE Xd = Maximum armature voltage/phase Minimum armature current/phase
Xq = Minimum armature voltage/phase Maximum armature current/phase
PRECAUTION 1. The Motor field rheostat should be kept at minimum resistance position
PROCEDURE 1. Connections are given as per the circuit diagram 2. 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 15-20% 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.
CIRCUIT DIAGRAM
TABULAR COLUMN
VMAX VMIN IMAX IMIN
MODEL CALCULATION
RESULT
POSTLAB QUESTIONS
1) Why does the pointer of ammeter and voltmeter oscillate at slip condition?
2) Which is higher Xd or Xq? Why?
3) Mention some application of synchronous motor
4) Can the slip condition achieved in non salient pole Synchronous machines? Why?