1. Magnetization Characteristics of DC Shunt Generator

Transcription

1 im: 1. Magnetization Characteristics of DC Shunt Generator To conduct an experiment on a D.C shunt generator and draw the magnetization characteristics (OCC) and to determine the critical field resistance and critical speed. pparatus: S. No pparatus Type Range Qty 1 Voltmeter M.C 0-250/500V 1 2 mmeter M.C 0-1/2 1 3 Rheostats Wire 400 /1.7 1 wound 4 Tachometer Digital Circuit diagram: 3 point starter DPST Switch L F DPST Switch 230 V DC Supply F 400Ω/ 1.7 M (0-500)V V G (0-2) MC F DC Excit- F Fuse FF Fuse

2 Shunt Field Resistance (Rsh):- DPST FUSE 400Ω/1.7 (0-2) 230 V DC Sup- F FF V (0-250V) Theory: Open circuit characteristics or magnetization curve is the graph between the generated emf and field current of a dc shunt generator. For field current is equal to zero there will be residual voltage of 10 to 12V because of the residual magnetism present in the machine.if this is absent there the machine can not build up voltage to obtain residual magnetism the machine is separately excited by a dc source from OCC we can get critical field resistance and critical speed. Critical field resistance: It is the resistance above which the machine cannot build up emf. Critical speed: It is the speed below which the machine cannot build up emf. Procedure: 1. Connections are made as per the circuit diagram. 2. Start the motor and bring it to rated speed.. 3. The switch SPST is opened and If=0 4. For the different values of excitations (If) the generated voltage (Eg)from the voltmeter is taken at rated speed, with increasing and decreasing orders. 5. Calculate average Eg from increasing and decreasing orders. 6. graph is drawn between vg Eg & If. From the graph (OCC) Critical field resistance and critical speed are calculated.

3 Tabular column: S.NO Field current If Generated Voltage (Eg) Increasing Decreasing verage Eg Graph: Eg (V ) R Rf Q O C P If ()

4 Critical field resistance (Rc) Field resistance (Rf) The maximum voltage the Generator can induce With this field resistance. Critical Speed = O/OC = OR = OM = PQ/PR * N Result:

5 2. BRKE TEST ON DC SHUNT MOTOR. DETERMI- NTION OF ITS PERFORMNCE CURVES im: To conduct brake test on DC Shunt motor. nd to determine its performance curves. pparatus: S. No Equipment Range Type Qty 1. Voltmeter 0-250V M.C mmeter 0-20 M.C 1 3 mmeter 0-1/2 M.C 1 4 Rheostat 400 /1.7 Wire wound 1 5. Tachometer Digital type 1 6. Connecting wires

6 Circuit diagram: (0-20) 3 point starter DPST Switch MC L F 400Ω/ S 1 S (0-2) 230 V V (0-250)V MC DC MC Sup- F M FF Fuse

7 Theory: When if is required to determine directly efficiency if comparatively small motors, the motor is loaded directly by means of Mechanical Break. Hence in the case of shunt motor there is no drastic change in speed. The Torque T = (S1 ~ S2) g. r Nm. where S1 S2 is the spring balance reading, r = Break drum Radius and g=9.81. P = Power developed. Efficiency of DC motor = Po/ Pi x 100 Procedure:- 01. Make Connections as per the circuit diagram. 02. Start the motor with the help of the starter. 03. Then bring the motor to rated speed by adjusting field rheostat. 04. Put the mechanical load on the motor in steps and note down corresponding readings of all meters. 05. Do calculations accordingly. Tabular columns : S.No Voltage (V) Current (I) Spee d (N) Spring Balance Readings S1 S2 Torque= 9.8 1(S 1 ~ S 2).r -Nm P out = 2 nt/60 -Watts P in = Vi - Watts Eff = op/ip x100.

8 EXPECTED GRPHS: T T sh T a 0 X Ia Ta vs Ia. X N 0 I a N vs Ia

9 N vs T T X η O/P Vs O/P Result:

10 3. BRKE TEST ON DC COMPOUND MOTOR DE- TERMINTION OF PERFORMNCE CURVES im: To conduct brake test on dc compound motor. pparatus: S. No Equipment Range Type Quantity 1 Voltmeter (0-250V) M.C. 1 No 2 mmeter (0-20) M.C 1 No. 3 Rheostat 400 /1.7 Wire wound 1 4 Tachometer digital No 5 Connecting wires Circuit diagram: Cumulative: (0-20) DPST Switch MC 3 point starter L F 230 V DC Sup- V (0-250)V MC M 400Ω/ 1.7 (0-2) MC F S1 S2 FF Fuse

11 Differential: (0-20) DPST Switch MC 3 point starter L F 230 V DC Sup- V (0-250)V MC M 400Ω/ 1.7 (0-2) MC F S1 S2 FF Fuse Theory: Compound motor has a shunt field winding as well as series field winding. If the series field mmf and shunt field mmf help each other it is a cumulative compound motor. If the series and shunt fields appose each other it is a differentially compound motor. The operation of differential compound motor is unstable In a cumulative compounded motor the fluxes are add each other at light loads the shunt field is stronger than series field so motor behaves shunt motor. t high loads series field is stronger than shunt field so the characteristics like nearly to series motor. Procedure: 1. Connections are made as per the circuit diagram. 2. Start the motor with the help of the starter. 3. Then bring the motor to rated speed by adjusting field rheostat. 4. Put the mechanical load on the motor in steps and note down all the meter readings.

12 Tabular columns: s.no Voltage (V) Current (I) Speed (N) Spring balance readings S1 S2 Torque= 9.81xS1 ~S2xr - Nm Output power 2πNT/60- Watts Input power VI- Watts Efficiency Pout/P in x 100.

13 Graph: Draw graphs O/P Vs Speed, Current, Torque, Efficiency. Cum Diff N 0 X T N vs Ia

14 X T Diff Cum 0 I a T vs Ia Cum Diff N vs T T

15 X η Cum Diff O/P Vs O/P Result:

16 4. LOD TEST ON DC SHUNT GENERTOR. im: To conduct a load test on the given DC Shunt generator and to obtain the performance characteristics. pparatus required: 1 mmeter 0-20, MC 1 0-1, MC MC 1 2 Voltmeter 0-250V, MC V, MC 1 3 Rheostat 400 / Rheostat 100 /5 1 5 Load 3 Kw / 220V 1 6 Tachometer 1 5 Connecting wires Circuit diagram:

17 rmature Resistance (Ra):- DPST FUSE 100Ω/5 (0-5) 230 V DC Supply M V (0-30V) Theory:. By conducting load test on DC shunt generator we can get load characteristics i.e, Internal & External characteristics. By exciting the m/c, the field current increases and voltage build up. fter the machine has attained 220V the rated load is switched on. With increase in load, the voltage will be dropped Procedure: 1. Connections are made as per the circuit diagram. 2. Start the machine with the help of starter and bring to rated speed by varying field rheostat of motor, then by varying field rheostat of the generator set the rated voltage of the generator.. Then close the DPST switch of the load and increase the load by step 0.125Kw, up to full load of the generator. 3. Note down all the meter readings at every step. 4. Do necessary calculations. Observations: S no IL, in amps If, in amps Ia= ILif in amps Vt in volts Ia Ra in volts EG = Vt IaRa in volts

18 Graph: X E& Internal External P E& vs I I E&V vs I Result:

19 5. LOD TEST ON DC SERIES GENERTOR im: To conduct load test on the given DC series generator and to obtain its performance characteristics. pparatus required: S.NO Equipment Range Type Qty 1 mmeter M.C MC 1 2 Voltmeter V M.C V MC 1 3 Rheostat 400 /1.7 Wire wound /5 Wire wound 1 4 Load 5,Kw 1 5 Tachometer Digital 1 Circuit diagram:- 3 point starter (0-20) DPST Switch L F 400Ω/ 1.7 DPST Switch 230 V DC Sup- M F FF G V (0-250v) Resistive Load Fuse rmature Resistance (Ra):-

20 DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- M V (0-30V) Series Field Resistance (Rse):- DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- V (0-30V) Theory: The load characteristics curve of DC series generator shows the relation b/w its terminal voltage and load current. The characteristics are rising in nature and excitation increases with load. t large values of load current, the terminal voltage must be start decreasing owing to the saturation of the machine iron & rapidly increasing voltage drop of armature and armature resistance.

21 Procedure: 1. Make connections as per the circuit diagram. 2. djust the speed of the motor to its rated value using field rheostat.(motor). 3. Connect the load to generator with the help of load box, and increase the load 0.125Kw at every step and note the corresponding readings. 4. Plot the graph b/w terminal voltage Vs current and generated voltage Vs armature current. Observations: Sno Terminal voltage, in volts Speed of the motor, N = Load current, IL =Ia=Ise in amps IaRa In volts IaRse In volts Eg=VIaRaIaRse In volts Graph: Plot the graph b/w terminal voltage and load current by taking V on - axis and IL on X-axis, and Eg on axis and Ia on X axis. X OCC E g & V Internal External Eg & V vs Ia= Ise I a = I se Result:

22 6. SPEED CONTROL OF DC SHUNT MOTOR im: To conduct speed controls on DC shunt motor. The methods are 1. rmature voltage control method 2. Flux control method pparatus: S.No Equipment Range Type Qty 1 mmeter MC MC 1No 1No 2 Voltmeter 0-250V MC 1No 3 Rheostats 100 /5 Wire wound 1NO 400 /1.7 Wire wound 1No 4 Tachometer rpm Digital 1No 5 Connecting Wires LS Nameplate Details (To be noted Down from the Machine) Circuit diagram: DPST FUSE L F 100Ω/5 400Ω/ V DC Supply (0-5) F (0-2) (0-250V) V M FF

23 rmature Resistance (Ra):- DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- M V (0-30V) Theory: i) rmature voltage control method: For a load of constant Torque, the speed is proportional to the applied to the armature. Therefore speed voltage characteristic is linear and is a straight line. s the voltage is decrease across the armature the speed falls. This method gives speeds less than rated speeds. Eb α ΦN Eb α N V-Ia(RaR) α N s the voltage is decreased speed decreases. ii) Flux Control Method: With rated voltage applied to the motor, the field resistance is increased i.e field current is decreased. I t is observed that speed increases. Eb/Φ α N N α Eb/If The characteristics If Vs N is inverse (or) if it is hyperbola. Procedure: i) rmature Voltage Control Method 1) Make connections as per the circuit diagram. 2) Show the connections to the lab instructor. 3) Keeping both rheostats at minimum, Start the motor with the help of starter and by adjusting field rheostat bring the motor to rated speed. 4) By increasing armature circuit rheostat in steps note down voltage, Ia and speed at every step. 5) The corresponding graph is draw between armature Voltage Vs speed.

24 ii) Flux Control method: 1) The machine run at its rated speed and rated voltage obtained. 2) The voltage is kept constant and for different values of field current the speed are noted. Tabular Column: rmature Voltage Control Method: S.No rmature Voltage in volts rmature current=ia in amps Speed in RPM Eb=V-IaRa in volts Flux Control Method: S.No Field Current in amps Speed in RPM Expected graphs:- N O If(I) N Vs If X

25 N O Va(V) N Vs Va X N vs Va(rmature voltage) Result:

26 6. SWINBURNE S TEST ON DC SHUNT MCHINE PREDETERMINTION OF EFFICIENCIES im: To perform no load test on dc motor and to predetermine the efficiencies of the machine acting as a motor and generator. Equipment: S.No pparatus Type Range qty 1 Voltmeter MC 0-250v 1 2 Voltmeter MC 0-30V 1 3 mmeter MC mmeter MC Rheostats Wire wound 400 /1.7 1 Wire wound 100 /5 1 Circuit diagram: (0-5) DPST Switch MC 3 point starter L F 230 V DC Supply V (0-250)V MC M 400Ω/ 1.7 F (0-2) MC FF Fuse

27 Circuit diagram to find out Ra: DPST Switch 230 V DC Supply 100Ω/5 M (0-5) MC V (0-30)V MC Theory: Fuse It is simple indirect method in which losses are measured separately and the efficiency at any desired load can be predetermined. This test applicable to those machines in which flux is practically constant i.e. shunt and compound wound machines. The no load power input to armature consist iron losses in core, friction loss, windage loss and armature copper loss. It is convenient and economical because power required to test a large machine is small i.e. only no load power. But no account is taken the change in iron losses from no load to full load due to armature reaction flux is distorted which increases the iron losses in some cases by as 50% Procedure: 1. Make connections as per the circuit diagram. 2. Show the connections to the lab instructor. 3. Keeping both rheostats at minimum, Start the motor with the help of starter and by adjusting field rheostat bring the motor to rated speed. 4. Note down all the meter readings at no load.. 5. Do necessary calculations and find out the efficiency of the Machine as a motor and as a generator. 6. Draw the graphs between output Vs efficiency of the Machine as a generator and as a motor.

28 Observations: IL IF I V N For Ra S.NO V I Ra=V/I Expected graphs:- η Generator Motor O Out- Efficiency Vs Output

29 Tabular Column to find out efficiency: GENERTOR: S.No Voltage in volts Load Current in amps rmature Current Ia = (ILIf) rmature Cu loss= Ia XIaXRa Total losses Wt=Wc IaXIaXRa Input- VxIL Output- Input-total losses= VxIL-Wt = Outpu Input. Motor: S.N o Voltag e in volts Load Current in amps rmature Current Ia =(IL-If) rmature Cu loss= Ia XIaXRa Total losses Wt=Wc IaXIaXRa Output= VxIL Input=output total losses= VxILWt = Outpu Input. t

30

31 Model calculations: No load input=v IL No load armature copper losses =Ia 2 Ra =(Il If) 2 Ra Constant losses Wc=V l (Il-If ) 2 Ra Efficiency as a motor: I= ssumed load current Motor i/p=vi Ia=IL-If Motor armature losses=i 2 a.ra Total losses=i 2 a Ra Wc Efficiency of motor= VI- I 2 a Ra Wc / VI x 100 Efficiency as generator: I=assumed load current Generator O/P =VI Generator armature cu. Losses= I 2 a.ra Total losses= I 2 a Ra Wc Efficiency of generator=vi / VI I 2 a Ra Wc Results:

32 7. LOD TEST ON COMPOUND GENERTOR im: To conduct load test on DC compound generator and to determine its characteristics. pparatus: S. No Equipment Range Type Qty 1. Voltmeter V M.C mmeter 0-2 M.C M.C Rheostats 400 /1.7 Wire wound 2 4. Tachometer Digital 1 5 Connecting wires Circuit diagram for cumulative compound generator: DPST Switch 3 point starter L F 400Ω/ Ω/ 1.7 (0-2) (0-20) DPST Switch 230 V DC Sup- M F FF F FF G V (0-250v) Resistive Load Fuse

33 Circuit diagram for differential compound generator: DPST Switch 3 point starter L F 400Ω/ Ω/ 1.7 (0-2) (0-20) DPST Switch 230 V DC Sup- M F FF F FF G V (0-250v) Resistive Load Fuse rmature Resistance (Ra):- 100Ω/5 (0-5) M (0-30V) Series Field Resistance (Rse):- DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- V (0-30V)

34 Theory: NSCET LB MNUL D.C. Compound generator consists of both series and shunt field wind- ings. The shunt and series fields can be connected in two ways. 1. Short shunt. 2. Long shunt. When the MMF of series field opposes the MMF of shunt field, the gener- ator is differentially compound. The terminal voltage decreases sharply with in- creasing load current. Evidently this connection is not used. In cumulative compound the connections of the two fields are such that their MMF s added and help each other. If the series field is very strong, the termi- nal voltage may increase as the load current increases and it is called over com- pounding. When terminal voltage on full load and no load are equal, it is known as flat compounded generator. If the series field is not strong, the terminal voltage will decreases with increase in load current (under compound) Procedure: 1. Connections are made as per the circuit diagram. 2. The machine is run at rated speed and the rated voltage is obtained by varying field excitation 3. There the switch is closed so that load is connected across the generator. 4. Increase the load step by step with 0.125Kw and note down all the meter readings and calculations are made accordingly and the characteristics are obtained. 5. Plot graph for internal external characteristics.

35 Tabular Column:- S.No IL, mps VL Volts If, mps Eg = vli (rnrsc) Model graphs:- Internal characteristics Cumulative Differential E (V) O Ia () E (V) Vs Ia X

36 External characteristics Cumula- Differential V O Ia () V Vs Ia X Result:-

37 8. FIELDS TEST ON TWO IDENTICL DC SERIES MCHINES im: To determination the efficiency of two mechanically coupled series machines by conducting field s test. pparatus: S.No Equipment Range Type Qty 1. Voltmeter 0-250V 2-30V 2 mmeter Resistive load 5Kw 4. Connecting wires M.C. MC M.C. M.C Circuit diagram: DPST Switch (0-20) 2 point starter (0-20) L DPST Switch 230 V DC Sup- V (0-250v) M V (0-250v) G Resistive Load Fuse

38 rmature Resistance (Ra):- DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- M V (0-30V) Series Field Resistance (Rse):- DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- V (0-30V) Theory: This test is applicable for two series machines which are coupled mechanically. Series machines cannot be tested on no load conditions due to dangerous high speeds. One machine normally run as motor and drives generator whose out put is wasted in a variable load R. The fields of two machines are connected in series in order to make iron losses of both the machines equal. Model calculations: Generator output = V3.I2 Watts (1) Total input = V1.I1 Watts (2) Total losses Pt of both machines = ( V1.I1)-(V3.I2) Watts - - (3) Motor Field Cu loss = I1.I1.Rsem (4) Motor rmature Cu loss = I1.I1.Ram (5)

39 Generator Field Cu loss Generator rmature Cu loss P2,Total Ra and Se,Cu losses = = I1.I1.Rseg (6) I2.I2.Rag (7) NSCET LB MNUL Of both machines = (4)(5)(6)(7) (8) Ps, Stray losses of both m/c = (Pt-P2) Watts (9) Ps/2, Stray losses of each m/c = (Pt-P2)/2 Watts (10) Efficiency calculations for Generator:- Output of Generator =V3. I2 Watts (11) Stray losses of Generator = (Pt-P2)/2 Watts (12) Field Cu loss of Generator. = I1. I1.Rseg (13) rmature Cu loss of Generator. = I2.I2.Rag (14) Input to Generator. = (11)(12)(13)(14) (15) Efficiency of Generator =Output/Input =(11)/(15) Efficiency calculations for Generator:- Motor in put. =V2.I1 Watts (16) Motor Field Cu loss = I1.I1.Rsem (17) Motor rmature Cu loss =I1. I1.Ram (18) Motor Stray losses =(Pt-P2)/2 Watts (19) Motor Output =(16)- (17)(18)(19) (20) Efficiency of Motor =Output/Input=(20)/(16) Model graphs:- η Genera- Motor O Out- Result: By conducting the field s test we found the efficiency of series machines (motor and generator).

40 9. REGENERTIVE (OR) HOPKINSON S TEST NSCET LB MNUL im : To conduct a Hopkinson s test on a two similar D.C shunt machines and find out the efficiency. pparatus Required: S.no Equipment Range Type Qty 1 Volt meter 0-250V M.C. 1 2 mmeter M.C M.C Rheostat 400 /1.7 Wire wound 2 4 Connecting wires Name Plate Details (To be noted Down from the Machine) Circuit Diagram: 3 point start- DPST Switch 230 V DC L F (0-230)V V MC M V 400Ω/ 1.7 (0-500)V MC (0-2) MC F M (0-2) MC 400Ω/ (0-20) 1.7 MC F FF Fuse FF

41 rmature Resistance (Ra):- DPST FUSE 100Ω/5 (0-5) 230 V DC Sup- M V (0-30V) Theory: Hopkinson s test is also called as regenerative test or back-to-back test. It is an indirect test or full test, which is used to determine the efficiency of the two identical shunt machines. The two machines are mechanically coupled and are also adjusted electrically that are of then run as motor and other as a generator. The two-shunt machines are connected in parallel. The power input from the mains is only that needed for supplying the losses of the two machines. The two machines can be tested under full load conditions (for determining the efficiency and maximum temperature rise). Procedure: 1. Connected the circuit as per the circuit diagram. 2. Keep the field regulator minimum resistance position and start the motor by using starter, Keeping S.P.S.T switch open. 3. djust the regulator on generator side until the rated voltage equal to both in magnitude and polarity as that of main supply. i. e; voltmeter reads zero. 4. The S. P. S.T switch is closed to parallel the machines, by adjusting the re- spective field regulators, any load can how be thrown on to machines. 5. Calculate efficiency by applying load.(changing excitation) Observations: S. No Input Voltage in volts Input Current=I 1 Gen Ia=I 2 Gen If=I 3 Motor If=I 4

42 To find out efficiency: Motor: S. No Motor input Motor rmature Cu loss Motor Field Cu loss Stray loss Total losses of motor Out put Of Motor of Motor Generator: S. Generator No output Generator rmature Cu loss Generator Field Cu loss Stray loss Total losses of generator Input Of generator of generator Calculations: rmature Resistance of each machine =Ra Generator rmature cu loss =I1 x I2 x Ra Watts. Motor rmature cu loss =(I1 I2)(I1 I2)Ra Watts. rmature power input to the set. =VL x I1 Watts. Ps, Stray losses of both machines = VL x I1 rmature Cu loss of (Gen Motor) Stray losses of each machine = Ps/2 Efficiency of Generator: Generator output Generator Losses Pg Efficiency of Generator =VL. I2 Watts = V.I3 I2 x I2(Ps/2) =( VL.I2 )/ (VL.I2 Pg) Efficiency of Motor : Motor in put: =VL (I1 I2 I4). Motor losses Pm =(I1 I2)(I1 I2)Ra VxI4 Ps/2. Motor Efficiency = {VL (I1 I2I4)}-Pm/ VL (I1I2I4) Plot the following graphs:- (a) Output Vs Efficiency for Generator. (b) Output Vs Efficiency for Motor.

43 Model graphs:- η Genera- Motor O Output Result:

44 10.SEPRTION OF STR LOSSES IN DC MCHINE im : To conduct the No-load Test at various speeds at two different excitations on a DC shunt machine and to determine following losses:- (a) Hysteresis Loss (b) Eddy Current Loss (c) Mechanical Loss. pparatus Required: S.no Equipment Range Type Qty 1 Volt meter 0-250V M.C V M C 1 2 mmeter M.C M.C Rheostat 400 /1.7 Wire wound / 5 Wire wound 1 4 Connecting wires 5 Tachometer digital Name Plate Details (To be noted Down from the Machine) Circuit Diagram: DPST FUSE L F 100Ω/5 400Ω/ V DC Supply (0-5) F (0-2) (0-250V) V M FF

45 Circuit diagram to find out Ra: DPST FUSE 100Ω/5 (0-5) 230 V DC Supply M V (0-30V) Procedure: 1. Connected the circuit as per the circuit diagram. 2. Keep both field and armature rheostats at minimum position and start the motor by using starter, and bring to rated speed by adjusting field rheostat. 3. Note down all the meter readings, repeat this by varying armature rheostat. The field current to be kept constant. 4. djust the field to another suitable value and repeat step Find the armature resistance by conducting the experiment. Observations: Field current (if)= S. No rmature Voltage= Va rmature Current= Ia Speed N Back EMF Eb rmature input rmature Cu loss Stray loss

46 Evaluation of friction, Hysterisis and Eddy current losses(different speeds) S. No Speed N Friction loss NBN 2 Hysterisis Loss CM Eddy current loss DN 2 Calculations:- Stray losses (Ps)= Mechanical loss Eddy current loss Hysterisis loss t constant normal excitation: Ps=NBN 2 CNDN (1) t constant reduced excitation (Ps/N)=(C 1 )(BD 1 )N (2) Plot the graph between speeds Vs Ps/N From the graph at two different speeds determine the values of Ps/N, for normal and reduced excitations and find the values (C),(BD),(C 1 ) and (BD 1 ) nd from these values calculate the values of C-C 1,D-D 1. The co-efficient of hysteresis loss C is proportional to 1.6, and the co-efficient of eddy current loss D is proportional to 2. If and are the fluxes corresponding to the normal and reduced excitation,the:- (C /C) = ( / ) 1.6 (D /D) = ( / ) 2 at the same speed lso, ( / ) = (E,E) at any speed. From the above equations evaluate the equations the constants,b,c&d. Hence evaluate the friction, Hysteresis and Eddy current losses at various speeds up to the rated speed and tabulate the results in the table:-

47 Model graphs:- Normal Excitation PS / N 3/4 Excitation O Speed (N) X Ps/N Vs N Result

48 11. Brake Test On DC Series Motor IM: To draw the performance characteristics of DC series motor by performing Brake PPRTUS: S.no Equipment Range Type Qty 1 Volt meter 0-250V M.C. 1 2 mmeter 0-20 M.C 1 3 Connecting wires 4 Tachometer digital 1 Name Plate Details (To be noted Down from the Machine) Circuit Diagram: DPST Switch (0-20) MC 2 point starter L 230 V DC Supply V (0-250)V MC M S1 S 2 Fuse

49 THEOR : DC series motor is having high starting torque and its speed will be decreases by increasing of load.series motor runs on load only. It implies that the motor starts only when the load is applied on it. If S1, S2 are spring balance reading force T= (S1-S2)*G*r r- brake drum radius o/p power P=T*W = 2πNT/60 Input power Pin =VIL efficiency η = Pout/Pin*100 SPECIFICTION RTINGS OF DC SERIES MOTOR : PROCEDURE: 1) Construct the circuit as shown in the figure 2) pply some load and then switch on DPST switch 3) Take down the readings of N,S1,S2,IL 4) Calculate the efficiency under different loads 5) Plot the graph between o/p and i/p PRECUTIONS: Efficiency vs o/p Torque vs IL Speed vs IL Speed vs T 1) See that before switching on DPST whether some load is applied or not. If not apply some load 2) Pour water on brake drum whenever you are changing the load

50 TBLE: S.NO. VOLTGE LOD CURR ENT SPEED S1 S2 TORQUE P=2ΠNT/60 (out put power) Input power η = Pout Pin 1) ) ) Model Graphs T T sh T a 0 Ia X

51 X N 0 I a N vs Ia N vs T Ta

52 X η η vs O/P O/P RESULT:

53 12. Parallel Operation of Two DC Shunt Generators 230 V DPST 3 point starter L F F M F 400Ω/ 1.7 F F G1 (0-20)MC (0-250V)MC V S DPD OFF (0-20)MC G2 400Ω/ 1.7 F F M F F F 230 V DC Suppl Fus Machine Field REV Switch (0-250V)MC (0-20)MC Machine V Fuse Resistive load

54 12. Parallel Operation of Two DC Shunt Generators IM: To run two DC shunts generators in parallel and study the load sharing. pparatus: S.no Equipment Range Type Qty 1 Volt meter 0-250V M.C. 2 2 mmeter 0-20 M.C 3 3 Rheostat 400 /1.7 Wire wound 2 4 Resistive Load 5 KW 1 5 DPDT Switch 2 6 SPST Switch 1 4 Connecting wires 5 Tachometer digital 1 PROCEDURE: 1. Ensure that the paralleling switch S1 is OFF positions.open and the change over switch S IS IN 2. Start machine NO1 and adjust the field excitation so that it generates the rated voltage and record the reading. 3. Put switch S in the positon-1 and the gradually increase in the load in the steps. 4. Note the load current of machine-1 and its terminal voltage. 5. Repeat the step [d] till the machine one is fully loaded. 6. Bring the load to zero and the stop the machine Put change over switch in OFF position. Now start machine-2 and adjust the voltage to rated value and repeat the steps done for machine Stop the machine and put the change over switch in OFF position. 9. Run both machine keeping parallel switches S1 open. 10. djust the voltage each machine to its rated value and if the polarity is correct the parallel volt meter V2 will read zero if not reverse the polarity of any one machine. when parallel volt meter reads zero, close the parallel switch S1 by keeping the

55 change over switch in either voltmeter reads zero, close the parallel switch S1 by keeping the change over switch in either position 1or 2. Load the machine and note down the individual machine load current, the total load current and the busbar voltage. 11. Change the excitation of one of machine and observe the changes in ammeter readings of each machine. Observation Table: S.no Generator 1 Generator 2 Gen1 & Gen 2 Parallel Total Current C, Bus Bar vol Voltage Current Voltage Current Load Current Gen 1 Load Current Gen 2 Result: