ROEVER COLLEGE OF ENGINEERING & TECHNOLOGY Elambalur- Perambalur DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

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1 ROEER COLLEGE OF ENGINEERING & TECHNOLOGY Elambalur- Perambalur DEPRTMENT OF ELECTRICL ND ELECTRONIC ENGINEERING ELECTRICL MCHINE LBORTORY 1 Laboratory Observation Book ersion - 01 Name: Register Number: III emester, II Year cademic Year CONTENT N Date Experiment Name Remarks 1. Open circuit and load characteristics of separately excited DC shunt generators. 2. Open circuit and load characteristics of self excited DC shunt generators. 3. Load characteristics of DC compound generator with differential and cumulative connection. 4. Load characteristics of DC shunt motor. 5. Load characteristics of DC compound motor. 6. Load characteristics of DC series motor. 7. winburne s test of DC shunt motor. 8. peed control of DC shunt motor 9. Hopkinson s test on DC motor-generator set. 10. Load test on single-phase transformer and three phase 11. transformer connections. Open circuit and short circuit tests on single phase transformer. 12. umpner s test on transformers. 13. eparation of no-load losses in single phase transformer. Page 1 of 48

2 FETY 1. ome of the experiments involve voltages that could conceivably lead to serious injury or death. Therefore strict adherence to the following rules will greatly decrease the probability that accidents will occur. However, no set of rules can replace basic common sense, and all persons using the laboratory are encouraged to constantly THINK FETY! 2. lways assume all circuits are energized unless you know with certainty that they are not. 3. Use one hand to make connections. 4. Never work on electrical circuits with wet or moist hands. 5. Do not play with equipment not directly involved in your experiment. 6. When in the lab do not wear clothing or jewelry which could constitute a health hazard. hoes, preferably rubber soled ones, must be worn in the lab. Long hair presents a hazard near moving parts of machinery. 7. It is important for safety reasons for anyone to easily trace out your test circuit and, therefore do not work on a cluttered bench. 8. Never touch moving parts of machinery. 9. Think out ahead of time the consequences of closing or opening a switch. 10. Never alter an energized circuit unless you are certain of the outcome. 11. If you know or suspect that an accident is about to occur, take immediate steps to prevent it but do not jeopardize your own safety in so doing. THINK FETY Roever College of Engineering & Technology / Department of EEE Page 2 of 48

3 EXP.NO. DTE: OPEN CIRCUIT ND LOD CHRCTERITIC OF EPRTELY EXCITED DC HUNT GENERTOR IM: To obtain the OCC and load test of the given separately excited DC generator and hence to determine 1. Critical field resistance 2. Critical speed 3. OCC at the specified speed PPRTU REQUIRRED NME PLTE DETIL: l.n pparatus Type Range Quantity o. 1. oltmeter Digital (0-300) 2 2. mmeter Digital (0-20) 1 3. mmeter Digital (0-2) 1 4 Rheostat 1200 ohm/ Rheostat 250 ohm/ Tachometer Digital 1 rmature Field Rated oltage:220olts Rated oltage:220olts Rated Current: 17mps Rated Current:1mps Rated oltage:220olts Rated oltage:220olts Rated Current: 13mps Rated Current:0.8mps Rated peed:1500 RPM (Revolution Per Minutes ) Make: Omega hunt Motor 5hp Generator 3hp Rating: 125% of rated current 125*17/100= THEORY: DC generator requires an excitation circuit to generate an induce voltage depending on whether excitation circuit consumes power for the armature of the machine or from separately require power supply. Generators may be classified as self excited or separately excited generators respectively. The induced emf in DC generators is given by the equation PфZN/60 volts. tate P,Z, are constants the above equation are written as Eg= KфN. I f the speed of the generator also maintained constant then Eg = Kф but the flux is directly proportional to the current Hence Eg =K2If.From the above equation it is clear that the induced emf is directly propositional to the field current when speed maintained constant,. The plot between the induced emf and the field current is known as open circuit characteristics of the DC generator. The typical shape of the characteristics is shown in fig. The induced emf when the field current is zero is known as residual voltage. This emf is due to the presence of a small amount of flux detained. In the field poles of the generator called residual flux. Once the OCC is obtained parameters such as critical field resistance, critical speed and the maximum voltage to which the machine can build up can be determined. If required the OCC at a different speeds can also be obtained..critical speed is minimum speed below which the generator shunt fails to excite. PRECUTION: 1. Remove the fuse carriers before wiring and start wiring as per the circuit diagram. 2. Keep the motor field rheostat at minimum resistance position and generator field rheostat at maximum position 3. The PT switch is kept open at the time of starting the experiment. 4. calculations. s the test is a no-load test the required fuse ratings are 20% of motor rated current. 5. Replace the fuse carriers with appropriate fuse wires after the circuit connections are checked by the staff-in-charge. Roever College of Engineering & Technology / Department of EEE Page 3 of 48

4 (300, 2) CIRCUIT DIGRM FOR OPEN CIRCUIT ON EPRTELY EXCITED DC HUNT GENERTOR 220, DC upply 220, DC upply D P T w i Tc h 1 D P T Three point starter L F F1 F2 M (500, 1.2) 1 I (0 20 ) G (0-2 ) IF F1 F2 (0 300) L PROCEDURE 1. The circuit connections are made as per the circuit diagram in the shown figure. 2. Keeping the motor field rheostat in its minimum position generator field maximum position; and the starter in its OFF position, the main supply is switched ON to the circuit. 3. The motor is started using the three point starter by slowly and carefully moving the starter handle from its OFF to ON position. 4. The motor to brought to its rated speed by adjusting its rheostat and checked with the help of a tachometer. 5. With the PT switch open, the residual voltage is noted. 6. Now the PT switch is closed and the Generator field Rheostat is varied in step and at each step the field current (If) and the corresponding induced EMF (Eg) are recorded in the tabular column. This procedure is continued unit generator voltage reaches 120% of its rated value the machine is maintained constant. 7. fter the experiment is completed the various rheostats are brought back to their original position in sequence and then main supply is switched off. LOD TET ON ELF EXCITED DC GENERTOR IM: To conduct the direct load test on the given self excited DC generator to plot. 1. External characteristics(or load characteristics) 2. Internal characteristics(or total characteristics) THEORY: DC generator works on the principle of Faraday s Law of Electromagnetic induction, which says that, Whenever a conductor is moved in magnetic field, an EMF is generated in it. The magnitude of induction EMF is directly proportional to the rate of change of flux. The voltage equation for a DC shunt generator is given; by L=Eg-IaRa; Under No Load Condition; ince Ia,Is negligibly small, From the above equation, the terminal voltage(l),is the no; load induced EMF(Eg), as the load on the generator increases, Roever College of Engineering & Technology / Department of EEE Page 4 of 48

5 (300, 2) ariable Resistive load 5 KW the load current and hence the armature current increases due to armature reaction the induced EMF in the armature decreases. lso increased armature current causes increase in IaR a drop. Hence the terminal voltage decreases with increase load. The plot between the terminal voltage (L) and load current (IL) is known as the external of load characteristics. The plot between the induced EMF (Eg) and the armature current (Ia) is known as the internal or total characteristics. The type of graph of internal and external characteristics is shown in model graph. PRECUTION: (Not to be included in the record) 1. Remove the fuse carriers before wiring and start wiring as per the circuit diagram. 2. Check the positions of the various rheostats as specified below; *Motor field rheostat is kept at minimum resistance position *Generator field rheostat is kept at maximum resistance position 3. The DPT switch on the load side is kept open at the time of starting the experiment. 4. calculation. s this is a load test, the required fuse ratings are 120% of the motor rated current for supply side DPT. 120% of the generator rated current for load side DPT. 5. Replace the fuse carriers with appropriate fuse wires after the circuit connections are checked by the staff-in-charge. CIRCUIT DIGRM FOR LOD TET ON EPRTELY EXCITED DC HUNT GENERTOR 220, DC upply 220, DC upply D P T wi Tc h 1 D P T Three point starter L F F1 F2 M (500, 1.2) 1 G (0 20 ) Ia (0-2 ) I F F1 F2 (0 300) L D P T wi Tc h 2 (0 20 ) I L L o a d Tabulation for Load Test: l.no field current [If] in mps Load voltage [ L ] in olts Load current [I L ] in mps rmature Current Ia = I L If mps rmature drop Ia Ra In volts Generated emf [Eg = L IaRa] In volts Roever College of Engineering & Technology / Department of EEE Page 5 of 48

6 PROCEDURE: 1. The circuit connections are made as per the circuit diagram. 2. Keeping the motor field rheostat in which minimum position, generator field rheostats in maximum position and the starter in its off position, the main supply is switched ON to the circuit. 3. The motor is started using the 3-point starter by slowly and carefully moving the starter handle from its OFF to ON position. 4. The motor is brought to its rated speed by adjusting its field rheostat and checked with the help of the tachometer. 5. With the DPT switch open, the potential divider is slowly varying until generator voltage is equal to its rated value (220). The terminal voltage and the field current are noted in the tabular column. 6. The DPT switch on the load side is now closed and the load on the generator is gradually increased in steps. t each step the speed of the generator is checked and maintained constant at its rated value by adjusting the field rheostat of the motor. fter satisfying this condition of each of loading, the terminal voltage(l), field current(if) and the load current (IL) are noted down in the tabular column. 7. This procedure is continued until the generator is loaded to 120%of its rated value. 8. Once the experiment is completed the load on the generator is gradually decreased, the various rheostats are brought back to their original position in sequence and the main supply is switched OFF. PROCEDURE FOR MEUREMENT OF RMTURE REITNCE: 1. The circuit connections are made as per the circuit diagram. 2. Keeping the lamp load at the OFF position the main supply is switched ON. 3. The load is increased such that the current in the circuit is approximately adjusted to 25%,50% and 75% of rated current of the generator and at these load conditions the armature voltage () and current(i) are noted in the tabular column. CLCULTION: 1. Determinations of armature resistance(ra); The armature winding resistance is calculated using ohms law Ra=a/Ia for each set of readings and the average of them is calculated. The effective resistance of the armature winding after taking into account the effect of temperature rise and skin effect is 1.2 times the average resistance Ra i.e. Ra(effective)=1.2 Ra(average). 2. To plot the internal characteristics, the armature current and the induced EMF are calculated using the expression, Ia=ILIF and Eg=LIaRa(eff) 3. The plots of L s IL and Eg s Ia are drawn to scale in the same graph sheet. Circuit diagram for find the generator armature resistance [Ra] (0 10 ) I 220, DC upply DPT (50, 5) MC (0 300) L MC 1 G 2 Roever College of Engineering & Technology / Department of EEE Page 6 of 48

7 Open circuit voltage in olts [Eo] Generated emf in olts [Eg] Load voltage in olts [L] Procedure for find armature resistance Ra: 1. Connections are given as per circuit diagram 2. Check loading rheostat must be at maximum resistance position. 3. Close the DPT switch and vary the loading rheostat for various values in steps and noted the corresponding voltmeter and ammeter reading. 4. Open the DPT switch after loading rheostat begins its initial position. Tabulation for Finding rmature Resistance: l.no rmature voltage a rmature current I Ra = a/ Ia Model graph Open circuit characteristics Internal (Eg s Ia) and External ( L s I L ) characteristics Eo s If Eg s Ia If Eo L s I L Field current [If] in amps MODEL CLCULTION: Ia = I L I F Eg= L IaRa(eff) Load current [I L ] in amps REULT: The direct load test on the given self-excited DC generator has been conducted and the internal & external characteristics are plotted. Review questions: 1. What is the difference between a separately excited dc generator and shunt generator? 2. If a DC shunt generator fails to build up voltage, what may be the probable reasons? 3. What is PT? What is its use in this experiment? 4. What is the reason the presence of residual magnetism in the field poles? 5. Why does the terminal voltage decrease as the load current increases? Roever College of Engineering & Technology / Department of EEE Page 7 of 48

8 EXP.NO. DTE: OPEN CIRCUIT ND LOD CHRCTERITIC OF ELF EXCITED DC HUNT GENERTOR IM: To conduct OCC and load test of a separately excited DC generator and to plot the internal and external characteristics. PPRTU REQUIRRED: l.no pparatus Type Range Quantity 1. oltmeter Digital (0-300) 1 2. mmeter Digital (0-5) 1 3. mmeter Digital (0-2) 1 4. Rheostat 250 ohm/ Rheostat 1200ohm/ Tachometer 1 Name plate details Rating: 125% of rated current 125*17/100= THEORY: Due to residual magnetism in the poles some EMF is generated even when If = 0. Hence the curve starts a little way up. The slight curvature at the lower end is due to magnetic inertia. It is seen that in the first part of the curve is practically straight. Hence the flux and the consequently the generated EMF is directly proportional to the exciting current. However at the higher flux densities where it is small iron path reluctance becomes appreciable and straight. Field windings are connected parallel to the armature and it is called dc shunt generator. Due to residual magnetism some initial emf and hence some current will be generated. This current while passing into the field coils will strengthen the magnetism of poles. This will increase pole flux which will further increase the generated emf. Increased emf and flux proceeds till equilibrium reached. This reinforcement of emf and flux proceeds till equilibrium reached at some point. i) rmature Reaction rmature reaction is the effect of magnetic field set up by the armature current on the distribution of flux under main poles of a generator. Due to demagnetizing effect of armature reaction, pole flux is weakened and so induced e.m.f in the armature is decreased. ii) rmature Resistance s the load current increases, more voltage is consumed in ohmic resistance of armature circuit. Hence the terminal voltage (t=e IaRa) is decreased where E is the e.m.f induced in armature under load condition. iii) Drop In Terminal oltage The drop in terminal voltage (t) due to armature resistance and armature reaction results in decreased field current, which further reduces e.m.f induced. For a shunt generator Ia = IL If E = t IaRa The drop in terminal voltage (t) due to armature resistance and armature reaction results in decreased field current, which further reduces e.m.f induced. For a shunt generator Ia = IL If E = t IaRa PRECUTION: 1. Motor field rheostat should be kept at minimum resistance position. 2. Generator field rheostat should be kept at minimum resistance position. 3. tarter should be in off position before switching on the supply. 4. The DPT switch must be kept open. rmature Field Rated oltage:220olts Rated oltage:220olts Motor Rated Current: 17mps Rated Current:1mps 5hp Rated oltage:220olts Rated oltage:220olts Generator Rated Current: 13mps Rated Current:0.8mps 3hp Rated peed:1500 RPM (Revolution Per Minutes ) Make: Omega Roever College of Engineering & Technology / Department of EEE Page 8 of 48

9 (500, 1.2) CIRCUIT DIGRM FOR OPEN CIRCUIT TET ON ELF EXCITED DC HUNT GENERTOR (300, 1.7) ariable Resistive load 5 KW (500, 1.2) 1 G F1 (0 300) L (300, 1.7) MC 220, DC upply D P T wi Tc h 1 Three point starter L F F1 M 1 I (0 20 ) (0 2 ) F2 2 2 F2 PROCEDURE (OCC TET) 1. Connections are given as per the circuit diagram. 2. Close the DPT switch. 3. The motor is started with the help of THREE POINT starter. 4. djust the motor speed to rated speed by adjusting motor field rheostat when the generator is disconnected from the load by DPT switch By varying the generator field rheostat gradually, the open circuit voltage [Eo] and corresponding field current (If) are tabulated up to 125 % of rated voltage of generator. The motor is switched off by using DPT switch 1 after bringing all the rheostats to initial position. CIRCUIT DIGRM FOR LOD TET ON ELF EXCITED DC HUNT GENERTOR 220, DC upply D P T wi Tc h 1 Three point starter L F F1 F2 M I (0 20 ) G I F (0 2 ) F1 F2 (0 300) L D P T wi Tc h 2 (0 20 ) I L L o a d PROCEDURE (LOD TET) 1. Connections are given as per the circuit diagram 2. The prime mover is started with the help of three point starter and it is made to run at rated speed when the generator is disconnected from the load by DPT switch By varying the generator field rheostat gradually, the rated voltage [Eg] is obtained. 4. The ammeter and voltmeter readings are observed at no load condition. 5. The ammeter and voltmeter readings are observed for different loads up to the rated current by closing the DPT switch 2. Roever College of Engineering & Technology / Department of EEE Page 9 of 48

10 6. fter tabulating all the readings the load is brought to its initial position. 7. The motor is switched off by using DPT switch 1 after bringing all the rheostats to initial position. GRPH: 1. Field current s Generated voltage 2. Load current s Load voltage Tabulation for Open Circuit Test on eparately Tabulation for Load Test: Excited D.C hunt Generator: l.no Open circuit voltage in olts [E o ] Field current in mps [I f ] l.no rmature current [Ia] in mps Load voltage [ L ] in olts Load current [I L ] in mps rmature drop Ia Ra In volts Generated emf [Eg = L IaRa] In volts Circuit diagram for find the generator armature resistance [Ra] 220, DC upply DPT (50, 5) (0 10 ) I (0 300) L 1 G 2 Procedure for find armature resistance Ra: 1. Connections are given as per circuit diagram 2. Check loading rheostat must be at maximum resistance position. 3. Close the DPT switch and vary the loading rheostat for various values in steps and noted the corresponding voltmeter and ammeter reading. 4. Open the DPT switch after loading rheostat begins its initial position. To find rmature Resistance Ra: L.NO rmature Current Ia (mps) rmature oltage a (olts) verage Ra rmature Resistance Ra = a/ia (Ohms) Roever College of Engineering & Technology / Department of EEE Page 10 of 48

11 Open circuit voltage in olts [Eo] Generated emf in olts [Eg] Load voltage in olts [L] Model graph Open circuit characteristics Internal (Eg s Ia) and External ( L s I L ) characteristics Eo s If If Eg s Ia Field current [If] in amps L s I L Load current [I L ] in amps MODEL CLCULTION: Ia = I L Eg = L Ia Ra REULT: Thus an OCC and LOD characteristics of a separately excited generator was performed and the respective graphs were drawn. Review questions: 1. What is the principle of generator? 2. What is meant by residual magnetism? 3. What is critical field resistance? 4. What is meant by saturation? 5. What are the reasons for the drooping load characteristics? Roever College of Engineering & Technology / Department of EEE Page 11 of 48

12 MC (300, 1.7) ariable Resistive load 5 KW (500, 1.2) EXP.NO. DTE: LOD CHRCTERITIC OF DC COMPOUND GENERTOR WITH DIFFERENTIL ND CUMULTIE CONNECTION im: To conduct load test on DC compound generator and obtain the load characteristic curves Exercise Obtain the following curves for cumulative, differential and shunt generator a. I L s for DC cumulative compound generator b. I L s for DC differential compound generator ll graphs should be drawn on the same graph sheet pparatus Required: l.no Name of the component type Range Quantity mmeter oltmeter Rheostat Rheostat Tachometer ariable resistive load Digital Digital Wire wound Wire wound Digital / nalog tar connected Ω, Ω, KW Name plate details: Field Motor peed Type HP rmature Generator peed Type Field KW rmature rating: No Load: 10 % of rated current (full load current) = Load test: 125 % of rated current (full load current) = CIRCUIT DIGRM OF LOD TET ON COMPOUND GENERTOR 220, DC upply D P T wi Tc h 1 Three point starter L F F1 F2 M 1 2 I 1 2 G Y2 Y1 F1 F2 (0 300) L D P T wi Tc h 2 (0 20 ) I L I L L o a d Precautions: 1. Motor field rheostat should be kept at minimum resistance position 2. Generator side field rheostat should be kept at maximum resistance position 3. Before starting the motor starter should be in off position 4. Initially the generator should be no load. 5. The machine should be run at its rated speed throughout the experiment. Page 12 of 48

13 Load voltage ( L ) in olts Procedure: 1. Connections are given as per the circuit diagram. 2. The motor is started with the help of a starter. 3. djust the motor speed to rated speed using rheostat. 4. oltage generated due to residual magnetism is noted. 5. The field excitation to the generator is increased in steps and the corresponding generated voltage is noted. 6. This procedure is continued until the built up voltage is 10 % greater than the rated voltage. 7. Now close the switch and vary the load rheostat note down the current drawn by the load. 8. gain get the motor speed to rated speed by adjusting the field rheostat. 9. Next vary the load and note the armature readings. 10. This procedure is continued until the load draws the rated current of the generator. 11. Now reverse the series field winding connection and repeat the procedure for doing load test and note down the armature reading. Note: If generating voltage of generator is increases with increasing of load current, it means generator is running under cumulative mode. If generating voltage of generator is increases with decreasing of load current, it means generator is running under differential mode. Tabulation for Cumulative Mode: l.no Load voltage in olts Load current in mps peed in RPM Tabulation for Differential Mode: l.no Load current in mps Load voltage in olts peed in RPM Cumulative mode ( L s I L ) Differential mode Load current (I L ) in mps Model graph: REULT: Thus an LOD characteristic of a compound generator was performed and the respective graphs were drawn. Review questions: 1. What is called as cumulative compound operation? 2. What is meant by differential compound operation? 3. What are functions of commutator? 4. What are the applications of compound generator? Roever College of Engineering & Technology / Department of EEE Page 13 of 48

14 EXP.NO. LOD CHRCTERITIC OF DC HUNT MOTOR DTE: IM: To conduct load test on D.C motor and to obtain performance characteristics PPRTU REQUIRED l. No. pparatus Type Range Quantit y 1. oltmeter Digital (0-300) 1 2. mmeter Digital (0-20) 1 3. Rheostat 230 ohm/ Tachometer Digital 1 DC HUNT MOTOR NME PLTE DETIL rmature Field Rated oltage:220olts Rated oltage:220olts Rated Current: 12mps Rated Current:0.6mps Rated peed:1500 RPM (Revolution Per Minutes ) Make: BENN Rating: 125% of rated armature current (12 mps) 125*12/100=15 THEORY: The shunt motor has a definite no load speed hence it does not run away when load is suddenly thrown off provided the field circuit remains closed. The drop in speed from no-load to full load is small hence this motor is usual referred to a constant speed motor. The efficiency curve is usually of the same shape for all electric motors and generators. The shape of efficiency curve and the point of maximum efficiency can be very considerable by the designer, though it is advantageous to have an efficiency curve which is fairly flat. o that there is little change in efficiency between load and 25% overload and to have the maximum efficiency as near to the full load as possible. From the curves it is observed that is certain value of current is required even when output is zero. The motor input under no-load conditions goes to meet the various losses, occurring within the machine. s compared to other motors a shunt motor is said to have a lowest starting torque. But this should not be taken off mean that is shunt motor is incapable of starting heavy load. ctually it means that series and compound motor as capable of starting heavy load with les excess of current inputs over normal values then the shunt motor and the consequently the depreciation on the motor will be relatively less. CIRCUIT DIGRM FOR LOD TET ON DC HUNT MOTOR, (0 30 ) I L Digital Three point starter L F 220, DC upply D P T w i tc h (0 300) L Digital (300, 1.7) I Z Z ZZ M I 1 2 BRKE DRUM PRECUTION: 1. The motor field rheostat should be kept at minimum resistance position. 2. The motor should be started at no load condition. 3. The motor should be cooled by circulating water throughout the experiment. 4. tarter should be in off position before switching on the supply. Roever College of Engineering & Technology / Department of EEE Page 14 of 48

15 peed (N) in rpm peed (N) in rpm Torque (T) in N-m l No Efficiency in % 5. The DPT switch must be kept open. 6. Before connecting the meters check the polarity and zero error. PROCEDURE: 1. Connections are given as per the circuit diagram. 2. Observe the precaution and using three-point starter the motor is started to run at the rated speed by adjusting the field rheostat if necessary. 3. The meter readings are noted at no load condition. 4. By using break drum with spring balance arrangement the motor is loaded and the corresponding readings are noted up to the rated current. 5. fter observation of all the readings the load is released gradually 6. The motor is switched off by using DPT switch. TBULR COLUMN FOR LOD TET ON DC HUNT MOTOR Radius of the brake drum (R) = in m Thickness of the belt (t) = in m Load oltage in olts Load current I L in mps peed in rpm pring balance Reading In kg Input Power = L *I L in Watts Torque T = (1~2)*9.81*R in NM Output Power = 2лNT/ 60 in Watts MODEL GRPH () Electrical characteristics in % N I L T % T in N-m peed in rpm I L in mps Output power in watts (B) Mechanical characteristics (C) Torque, peed s Load current T s N I L s N I L s T Torque ( T ) in N-m Load current (I L ) in mps Roever College of Engineering & Technology / Department of EEE Page 15 of 48

16 MODEL CLCULTION: Input power = L *I L Watts Output power = 2лNT/ 60 Watts Torque T= (1~2)*9.81*R N-m, where R is the radius of the brake drum in meter Output power Efficiency η = x 100 Input power GRPH: 1. Output power s efficiency 2. Output power s current 3. Output power s torque 4. Output power s speed 5. peed s torque REULT: Thus the load test on D.C shunt motor was performed and the respective graphs were drawn. Review questions: 1. Why should the field rheostat be kept in the position of minimum resistance? 2. What is the loading arrangement used in a dc motor? 3. How can the direction of rotation of a DC shunt motor be reversed? 4. What are the mechanical and electrical characteristics of a DC shunt motor? 5. What are the applications of a DC shunt motor? Page 16 of 48

17 LOD CHRCTERITIC OF DC COMPOUND MOTOR Exp no: Date : im: To conduct load test on DC compound motor and draw the characteristic curves Exercise Draw the following characteristic curves for DC compound motor a. Output s η% b. Output s T c. Output s N d. Output s I L e. Torque s N pparatus Required: l.no Name of the component type Range Quantity mmeter oltmeter Rheostat Tachometer MC MC Wire wound Digital / nalog Ω, Name plate details: MOTOR rating calculation for field and armature: Load test 125 % of rated current CIRCUIT DIGRM FOR LOD TET ON DC COMPOUND MOTOR 220, DC upply D P T w Four point starter L (300, 1.7) N F F1 F2 (0 15 ) I L Y1 (0 300) L Y2 M BRKE DRUM Formulae Used: t (i) Torque = ( 1 ~ 2 ) 9.81 ( R ) in N-M 1, 2 spring balance readings in Kg 2 R- Break drum radius in m (ii) Input power = x I in Watts (iii) Output power = 2 NT / 60 in Watts N peed of the motor in RPM (iv) Percentage of efficiency = (Output power /Input power) x 100. Roever College of Engineering & Technology / Department of EEE Page 17 of 48

18 Precautions 1. tarter should be in off position before switching on the supply. 2. The DPT switch must be kept open. 3. The motor field rheostat must be kept at minimum resistance position 4. There should be no load on the motor at the time of starting. 5. Before connecting the meters check the polarity and zero error. Procedure for DC Compound motor 1. Connections are given as per the circuit diagram. 2. Observe the precaution and using four-point starter the motor is started to run at the rated speed by adjusting the field rheostat if necessary. 3. The meter readings are noted at no load condition. 4. By using break drum with spring balance arrangement the motor is loaded and the corresponding readings are noted up to the rated current. 5. fter observation of all the readings the load is released gradually 6. The motor is switched off by using DPT switch. TBULTION FOR LOD TET ON DC COMPOUND MOTOR Radius of the brake drum (R) = in m Thickness of the belt (t) = in m l No Load oltage in olts Load current I mps speed in rpm pring balance Reading In kg Input Power in Watts Torque in NM Output Power in Watts Efficiency in % MODEL GRPH () Electrical characteristics N I L T % in % T in N-m peed in rpm I L in mps Output power in watts Roever College of Engineering & Technology / Department of EEE Page 18 of 48

19 peed (N) in rpm peed (N) in rpm Torque (T) in N-m (B) Mechanical characteristics (C) Torque, peed s Load current T s N I L s N I L s T Torque ( T ) in N-m Load current (I L ) in mps Model calculation: Graph: Output s η% Output s T Output s N Output s IL Torque s N Result: Thus the load test on D.C compound motor was performed and the respective graphs were drawn. Review questions: 1. Why 4 point starter used in DC compound motor? 2. What is the loading arrangement used in a dc compound motor? 3. How can the direction of rotation of a DC compound motor be reversed? 4. What are the mechanical and electrical characteristics of a DC compound motor? 5. What are the applications of a DC compound motor? Roever College of Engineering & Technology / Department of EEE Page 19 of 48

20 EXP.NO. LOD CHRCTERITIC OF DC ERIE MOTOR DTE: IM: To conduct load test on D.C series motor and to obtain performance characteristics PPRTU REQUIRRED l.no pparatus Type Range Quantity 1. oltmeter Digital (0-300) 1 2. mmeter Digital (0-20) 1 3. Tachometer Digital 1 Rating: 125% of rated current 125*12/100 =15 THEORY: DC ERIE MOTOR NME PLTE DETIL The drop in speed with increased load is much prominent in series motor than in a shunt motor hence a series motor is not suitable for application requiring a substantially constant speed. For a given current input a starting torque developed by a series motor is greater than that developed by a shunt motor. Hence series motors are used where huge starting torques is necessary that means for cranes and traction purpose. In addition to huge starting torque there is another unique characteristic of series motor which makes this especially desirable for traction work that means when a load comes on a series motor it response by decreasing its speed and supplies the increased torque with a small increase in current. On the other hand a shunt motor under the same condition would hold its speed nearly constant and would supply the required increased torque with a large increase of input current. PRECUTION: 1. tarter should be in off position before switching on the supply. 2. The motor should be started with some load 3. The motor should be stopped with some load. 4. Before connecting the meters check the polarity and zero error. PROCEDURE: 1. Connect as per the circuit diagram 2. Close the DPT switch 3. tart the motor using two point starter 4. Note down the reading of voltmeter, ammeter, speed and spring balance reading. 5. pply load in steps and note down the corresponding reading till the rated current is reached. CIRCUIT DIGRM FOR LOD TET ON DC ERIE MOTOR 220, DC upply Formula used Input power = L *I L Watts Output power = 2лNT/ 60 watts D P T w i tc h, 15 (0 30 ) I L Digital (0 300) L Digital Two point starter L N rmature Field Rated oltage:220olts Rated oltage:220olts Rated Current: 12mps Rated Current: 12mps Rated peed:1500 RPM (Revolution Per Minutes ) Make: BENN M 1 2 BRKE DRUM Roever College of Engineering & Technology / Department of EEE Page 20 of 48

21 peed (N) in rpm l No Torque T= (1~2) *9.81*R N-m, where R is the radius of the brake drum in metre. Efficiency η = (Output power / Input power ) * 100 Tabulation for load test on DC eries motor Radius of the break drum (r) = m, Thickness of the Belt (t) = in m Load oltage L in volts Load Current I L amps peed in RPM pring Balance (Load) reading In Kg 1 2 1~2 Torque (T) (1~2)(rt/2)(9.81) in Nm Input Power L xi L in Watts Output Power 2 NT/60 in Watts Efficiency ( ) O/P / I/P in % Model calculation: Model graph: ) Electrical characteristics B) Mechanical characteristics N I L T % in % T in N-m T s N I L in mps peed in rpm Output power in watts Torque ( T ) in N-m REULT: Thus the load test on D.C series motor was performed and the respective graphs were drawn. Review questions: 1. Why a DC series motor should not be stared without load? 2. Why a DC series motor has a high starting torque? 3. Compare the resistances of the field windings of DC shunt and series motor? 4. What are the applications of DC series motor? 5. Comment on the peed Torque characteristics of a DC series motor. Roever College of Engineering & Technology / Department of EEE Page 21 of 48

22 EXP.NO. WINBURNE TET OF DC HUNT MOTOR IM: To predetermine the efficiency of a DC shunt machine by conducting the winburne s Test 1. as a motor 2. as a generator DTE: NME PLTE DETIL: DC HUNT MOTOR 5 HP Rated oltage: 230 Rated Current: 17 Rated peeds: 1500 RPM Excitation oltage: 230 DC PPRTU REQUIRED: L.NO. PPRTU RNGE TYPE QUNTITY 1 mmeter 0 10 MC 1 No. 2. mmeter 0 1/2 MC 1 No. 3. oltmeter MC 1 No. 4 oltmeter 0 5 MC 1 No. 4. Rheostat 250 Ω, 1.5 MC 1 No. 5. Rheostat 1200 Ω, 0.8 MC 1 No. 6. Tachometer Digital 1 No. FUE RTING: rating = 40 % of rated current = 40/100 * 17 = THEORY: In this method the losses are measured separately and from their knowledge efficiency at any desired load can be predetermined. Hence the only running test needed is the no load test. This test is applicable to the machine in which flux is practically constant i.e shunt wound and compound wound machines. The machine is to run as a motor at its rated voltage. The speed is adjusted to rated speed with help of shunt field regulator. The no load current and field current are measured using ammeters. This test is convenient and economical because power required to test a large machine is small i.e. only input power is required. The efficiency can be predetermined at any load because constant losses are known. In this test we are not taking into account the change in iron loss from no load to full load. In this test it is impossible to know that whether commutation would be satisfactory at full load and whether temperature rise would be within specified limits. PRECUTION: 1. The field rheostat must be kept in minimum resistance position. 2. The starter handle must be kept in OFF position before switching ON the supply. 3. The motor must be started at no load condition. Roever College of Engineering & Technology / Department of EEE Page 22 of 48

23 PROCEDURE: 1. Connections are made as per the circuit diagram. 2. The supply is switched ON by closing the DPT switch. 3. The field rheostat is adjusted till the motor attains its rated speed. 4. The readings of the ammeters and voltmeter are noted under no load conditions. 5. The rheostat is brought back to the minimum position and the supply is switched OFF. 6. The DC resistance of the armature is determined using a voltmeter and an ammeter. (0 10 ) I Three point L F MC 220, DC upply D P T w i (300, 1.7) (0 300) L MC (0 2 ) I F MC F1 F2 M 1 2 FORMUL: Constant Losses Wc = Io (Io Ish) 2 Ra Watts s a Motor: Input power = L I L Watts Ia =I L If mps rmature Cu loss = Ia 2 Ra Watts Total Loss = Wc Cu loss Watts Output power = Input Total loss Watts % Efficiency = Output/Input * 100 s a Generator: Ia =I L If mps rmature Cu loss = Ia 2 Ra Watts Total Loss = Wc Cu loss Watts Output power = L I L Watts Input power = Output Total loss Watts % Efficiency = Output/Input * 100 Formulae Used: rmature resistance [Ra] = 1.6x R DC in ohms Constant loss [W CO ] = I O I 2 ao R a in watts rmature current [I a ] = I L I f in mps Copper loss [W CU ] = I 2 a R a in watts Roever College of Engineering & Technology / Department of EEE Page 23 of 48

24 Total loss [W total ] = constant loss copper loss in watts Input power for motor [W i ] / output power of generator [W o ] = I L in watts Output power of motor [W o ] = input power Total loss in watts Input power for generator [W i ] = output power total losses in watts Percentage of efficiency = [output power / input power] x 100 Where, 1.6 adds the skin effect R DC resistance of the armature coil when it is energized by DC supply Power input to the machine at no load = Io watts Constant loss of D.C machine = Io - Iao 2 Ra Predetermination of as Motor Pi = L x I L Ia = I I F ; Wc = Ia 2 Ra P L = Wc Wo P o = P i P L % = Po/ Pi x 100 Predetermination Of s Generator Po= x I Ia = I I F ; Wc = Ia 2 Ra P L = Wc Wo Po = Pi Pl % = Po/ Pi x 100 Tabulation (For No Load Test): in in volts I ao in amps I F in amps peed in RPM Tabulation for Finding rmature Resistance: rmature rmature rmature l.no resistance voltage a current Ia Ra Predetermination of as Motor: Pi = I L.NO L in olts L in L x I mps L Ia = I L - I F Wc = Ia 2 Ra Pl = Wc Wo Po = Pi Pl % = Po/ Pi x 100 Roever College of Engineering & Technology / Department of EEE Page 24 of 48

25 Predetermination of as Generator: L.NO in olts I in mps Po = x I Ia = I If Wc = Ia 2 Ra Pl = Wc Wo Pi = Po Pl % = Po/ Pi x 100 Circuit diagram for find the generator armature resistance [Ra] (0 10 ) I 220, DC upply DPT (50, 5) MC (0 300) L MC 1 G 2 Procedure for find armature resistance Ra: 1. Connections arte given as per circuit diagram 2. Check loading rheostat must be at maximum resistance position. 3. Close the DPT switch and vary the loading rheostat for various values in steps and noted the corresponding voltmeter and ammeter reading. 4. Open the DPT switch after loading rheostat begins its initial position. Tabulation for Finding rmature Resistance: l.no rmature voltage a rmature current I Ra = a/ Ia Roever College of Engineering & Technology / Department of EEE Page 25 of 48

26 Model calculation: GRPH: 1. Output power s efficiency ( as a motor) 2. Output power s efficiency ( as a generator) in % N I L T % T in N-m I L in mps peed in rpm REULT: Output power in watts Thus the winburne s test ( no load test) was conducted and the following efficiency were predetermined at different loads: 1. Efficiency as motor 2. Efficiency as generator. Review questions: 1. What is the purpose of winburne s test? 2. What are the constant losses in a DC machine? 3. What are the assumptions made in winburne s test? 4. Why is the indirect method preferred to the direct loading test? 5. The efficiency of DC machine is generally higher when it works as a generator than when it works as a motor. Is this statement true or false? Justify your answer with proper reasons. 6. How the motor speed increases when field current reduces? 7. What speed control is suitable for below rated speed? 8. What speed control is suitable for above rated speed? Roever College of Engineering & Technology / Department of EEE Page 26 of 48

27 EXP.NO. PEED CONTROL OF DC HUNT MOTOR DTE: IM: To control the speed of DC shunt motor by 1. rmature control method 2. Field control method PPRTU REQUIRRED DC HUNT MOTOR NME PLTE DETIL l.no pparatus Type Range Quantity 1. oltmeter Digital (0-300) 1 2. mmeter Digital (0-5) 1 3. mmeter Digital (0-2) 1 4. Rheostat 250 ohm/ Tachometer Digital 1 rmature Field Rated oltage:220olts Rated oltage:220olts Rated Current: 11mps Rated Current:0.8mps Rated peed:1500 RPM (Revolution Per Minutes ) Make: Omega Rating: 25% of rated current 25*17/100= THEORY: Flux Control method The speed of the DC motor is inversely propositional to the flux per pole, when the armature voltage is kept constant. By decreasing the flux the speed can be increased and vice versa. Hence the main flux of field control method the flux of a DC motor can be changed by changing field current with help of a shunt field rheostat. ince shunt field current is respectively small shunt field rheostat has to carry only a small amount of current which means I 2 R losses is small so that rheostat is small in size.this method is very efficient. rmature Control method This method is used when speed below the no load speed are required. s the supply voltage is normally constant the voltage across the armature is varied by inserting a variable rheostat in series with the armature circuit. s conductor resistance is increased potential difference across the armature is decreased, herby decreasing the armature speed. F or a load of constant torque speed is approximately propositional to the potential difference across the armature. PRECUTION: 1. rmature rheostat must be kept at maximum resistance position. 2. Field rheostat should be kept at minimum resistance minimum position. PROCEDURE: RMTURE CONTROL METHOD: 1. Connect as per the circuit diagram 2. Close the DPT switch 3. tart the motor using three point starter 4. By keeping the field current (If) as constant value, adjust the armature rheostat and note down the corresponding armature voltage and motor speed. 5. Repeat the step four till the motor reaches the rated speed. FLUX CONTROL METHOD: 1. Connect as per the circuit diagram 2. Close the DPT switch 3. tart the motor using three point starter Roever College of Engineering & Technology / Department of EEE Page 27 of 48

28 4. By keeping the armature voltage as constant value, adjust the field rheostat and note down the corresponding field current and motor speed. Circuit Diagram for peed Control of DC shunt Motor (0 10 ) I L Digital 220, DC upply D P T w i tc h (0 300) L Digital Three point starter L (650, 1) Field rheostat F (0 2 ) I F Digital (50, 5) rmature rheostat I F Z ZZ M I TBULR COLUM for RMTURE CONTROL METHOD & FIELD CONTROL METHOD L.NO Field Current If = 0.6 rmature oltage a in peed N in RPM Field Current If = 0.5 rmature oltage a in peed N in RPM L.NO rmature oltage a = 180 Field peed N Current in I f in RPM rmature oltage a = 170 Field peed Current N in I f in RPM GRPH: 1. Field current s speed 2. rmature voltage s speed REULT: Thus the speed of DC shunt motor was controlled by 1.rmature control method 2. Field control method and the respective graphs were drawn. Review questions: 1. How does the speed of a DC shunt motor vary with armature voltage and field current? 2. Compare the resistance of the armature and field winding. 3. What is the importance of speed control of DC motor in industrial application? 4. Which is of the two method of speed control is better and why? 5. Why is the speed of DC shunt motor practically constant under normal load condition? Roever College of Engineering & Technology / Department of EEE Page 28 of 48

29 250, , 1.5 EXP.NO. HOPKINON TET DTE: IM: To conduct the Hopkinson s test on the given pair of DC machines and to obtain the performance curve. NME PLTE DETIL: Generator: Power : KW Motor: Power : HP oltage : oltage : peed : RPM peed : RPM Current : Current : PPRTU REQUUIRED: L.NO PPRTU RNGE TYPE QTY 1 oltmeter 2 oltmeter 3 mmeter 4 mmeter 5 Tachometer 6 PT knife switch Rating: Rating = 125% of rated current = 125/100 * Circuit diagram for HOPKINON TET 220, DC upply D P T wi Tc h 3 POINT TRTER L (0 300) m, MC F F1 F2 0-20, I M 0-20, I GMF, MC THEORY: In this method full load test can be carried out on two shunt machines without wasting their outputs. The two machines are mechanically coupled and adjusted so that one of them runs as a motor and the other runs as a generator. The mechanical output of the motor drives the generator and the electrical output of the generator drives the motor. Due to losses the generator output is not sufficient to drive the motor and vice versa. The motor is started with no load. Then the field of one is weakened and the other is strengthened so that the former runs as motor and the latter as generator. Initially the PT switch is kept open. The field is adjusted so that the motor runs at rated speed. The voltage is adjusted by the field regulator until the voltmeter reads zero indicating that the voltage is same in polarity and magnitude as that of main supply. Then the switch is closed to parallel the machines. By adjusting the respective field regulators any load can be thrown on the machine. Generator current I 1 can be adjusted to any desired value by increasing the excitation of generator or by reducing the excitation of motor. M PT (0 300) g, MC , I G G , I GF, MC ` F1 F2 (0 300) g, MC Roever College of Engineering & Technology / Department of EEE Page 29 of 48

30 The power required for this test is very small when compared to the full load power of two machines. s machines are tested under full load conditions the temperature rise and commutation quantities are observed. PRECUTION: 1. The starter handle must be kept in OFF position at the time of switching on supply 2. The field rheostat of the motor must be kept in minimum resistance position. 3. The PT switch is closed only when the voltmeter connected across the motor and generator shows zero reading. PROCEDURE: 1. Connections are made as per the circuit diagram. 2. The supply is switched ON by closing the DPT switch. 3. The motor is started using three point starter. 4. The direction of rotation of the motor is checked if it is proper otherwise the field terminals of the motor are interchanged. 5. The field rheostat of the motor is adjusted till the motor attains its rated speed. 6. The field rheostat of the generator of the generator till the voltmeter connected across the PT switch reads zero. 7. The PT switch is closed. 8. The readings of the ammeter and voltmeter are noted and tabulated. FORMULE: 1. rmature Cu loss of generator = (Ifg Ig) 2 Ra Watts 2. rmature Cu loss of motor = (Ig Im Ifm) 2 Ra Watts 3. hunt Cu loss of generator = g Ifg Watts 4. hunt Cu loss of motor = m Ifm Watts 5. Power drawn from supply = m Im Watts 6. tray loss Wc = mim {(Ifg Ig) 2 Ra (Ig Im Ifm) 2 Ra gifg mifm} Watts 7. tray loss of single machine = Wc/2 8. Total loss in generator = Wc/2 (Ifg Ig) 2 Ra g Ifg Watts 9. Total loss in motor = m Ifm (Ig Im Ifm) 2 Ra Wc/2 Watts 10. Output of generator = g Ig Watts 11. Input of generator = Output losses 12. Efficiency of generator = output power/input power * 100 % 13. Input to the motor = m (Ig Im) Wattts 14. Output power of motor = Input losses Watts 15. Efficiency of motor = Output power/input power *100% HOPKINON TET- TBULR COLUMN m olts Motor Im mps Ifm mps g olts Generator Ig mps Ifg mps rmature Cu Loss of Generator (Ig Ifg) 2 Ra Watts rmature Cu Loss of Motor (IgIm- Ifg) 2 Ra Watts hunt Cu loss of generator gifg Watts Roever College of Engineering & Technology / Department of EEE Page 30 of 48

31 GRPH: 1. Output Efficiency (of generator) 2. Output Efficiency (of motor) % In % of Generator In % of motor Output power in watts Model calculation REULT: Thus the Hopkinson s test was conducted and the performance curve drawn. I QUETION: 1. What is the purpose of Hopkinson s test? 2. What are the advantages of Hopkinson s test? 3. What are the conditions for conducting the test? 4. Why the adjustments are done in the field rheostat of generator and motor? 5. If the voltmeter across the PT switch reads zero what does it indicate? Roever College of Engineering & Technology / Department of EEE Page 31 of 48

32 EXP.NO. DTE: LOD TET ON INGLE-PHE TRNFORMER ND THREE PHE TRNFORMER CONNECTION IM: To conduct load test on single phase transformer and to obtain percentage efficiency & regulation. PPRTU REQUIRRED: l.no pparatus Type Range Quantity 1. oltmeter MI (0-300) 2 2.` mmeter MI (0-5) 2 3. Lamp load 3KW/ ф Transformer 1 K, 230/ Wattmeter UPF 0-300/ uto Transformer 230/ NME PLTE DETIL ingle Phase Transformer Primary oltage: 230 econdary oltage: 115 Capacity: 1 K Frequency: 50 Hz Rating: 125% of rated current 125*4.34 /100 5 THEORY: When the secondary is loaded the secondary current I2 is setup. The magnitude and phase of I2 with respect to 2 is determined by the characteristics of the load. The secondary current sets up its own mmf and hence its own flux ф2 which is in opposition to main primary flux ф which is due to I0 the secondary ampere turns N2*I2 are known as demagnetizing ampere turns.the opposing secondary flux I2 weakens the primary flux ф momentary. Hence primary back Emf E1 tends to be reduced. For a moment 1 gain the upper hand over E1 and hence causes more current to flow in primary. Let the additional primary current be I2 1.It is known as load component of primary current. This current is antiphase with I2 1 the additional primary mmf N1*I2 sets up its own flux ф2 1 which is in opposite to ф2 and is equal to its magnitude. Hence the two cancel each other out. o the magnetic effects of secondary current I2 are immediately neutralized by the additional primary current I2 1.Hence whatever the load conditions be, the net flux passing through core is approximately the same as no-load. PRECUTION: 1. The autotransformer should be kept at minimum voltage position. 2. Before switching off the supply the variac should be brought back to0 minimum voltage position. PROCEDURE: 1. Connect as per the circuit diagram 2. Close the DPT switch 3. djust the uto transformer till the rated voltage is reached 5. Note down the readings of primary voltmeter, ammeter and wattmeter& secondary voltmeter, ammeter and wattmeter 6. pply load in steps and note down the corresponding reading till the rated current is reached. Roever College of Engineering & Technology / Department of EEE Page 32 of 48