www.jntuworld.comwww.jntuworld.comBRAKE TEST ON DC COMPOUND MOTOR AIM: To conduct the break test on dc compound motor and draw performance curves. APPARATUS: S.NOAPPARATUSRANGETYPEQUANTITY 1VOLTMETER(0-300)VMC1 2AMMETER(0-20)AMC1 3RHEOSTAT570/1.2A_1 4TACHOMETER(0-1000)RPMDIGITAL1 5CONNECTING WIRES __AS PER REQUIRED THEORY: Another method of testing a dc motor is brake test method.This is direct method of testing the motor.In this method the motor is putting on the direct load by means ofa belt and water cooled pulley arrangement..By adjusting the tension ofbelt.The load is adjust the various values of currents.The load isfinally adjusted to get full loadcurrent the power development gets wasted against the friction b/w belt and shaft.due to the www.jntuworld.comwww.jntuworld.combraking action of belt the test is called brake test.In the brake test compound motor we are mainly used in long shunt compound motor .In this type the shunt field winding is connected across the combination of armature and series of field winding.The resistance of field winding in series Rse and shunt field winding Rsh.The total current dfrawn from supply is I L I L=Ise+Ish, Ise=Ia Long shunt compound motor is compared to shunt mot so the torque produce in the motor is Ia. PROCEDURE: 1. Connections are made as per the circuit diagram.. 2. Make sure that noload is applied onthe motors and the motor field rheostat should be in minimum position . 3.Start the motorby using 3-point starter and adjust the speed of the motor in the rated value by using rheostat of motor 4.take the readinrs of ammeter,voltmeter and speed of motor on noload. 5.By gradually applying load and take reading of ammeter, voltmeter,spring balance and speed of motor for each and every load. www.jntuworld.comwww.jntuworld.com 6.Increase the load up to full load that means up to reading of ammeter read as rated value. 7.By slowly varying the load on the motar to zero and stop the motor. 8.Calculate the torque and efficiency using the formulae. 9.Draw the performance charecterstics curves. MODEL CALCULATIONS:

Radius(r)= Speed(N)=

Spring balance reading S1=S2= Torque(T)=9.81(S1-S2)r N-M

Inputpower=V IL

Outputpower=2NT/60 Efficiency=output/input100 www.jntuworld.comwww.jntuworld.com TABULAR FORM: S.NO LOAD CURRRENT (IL) VOLTAGE () SPEEDSPRING BALANCE S1S2 KGS TORQUE 9.81(S1-S2)r INPUT (VIL) OUTput 2NT/60 =o/p/i/p100 PRECAUTIONS: 1.Avoid loose connections. 2.Readings are taken without parellox error. 3.check the position of rheostat before startinr the experiment. www.jntuworld.comwww.jntuworld.com APPLICATIONS: 1.Stamping Processes. 2.Rolling mills. 3.Conveyers. 4.Elevators. 5.Punches. 6.Hoists. RESULT: www.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.comLOAD TEST ON DC SERIES GENERATOR AIM: To conductload test on Dc series generator and to draw the characteristics of series generator. APPARATUS: S.NOAPPARATUSRANGETYPEQUANTITY 1AMMETER0-20AMC2 2VOLTMETRE 0-300VMC1 3RHEOSTAT18/1.2AWIREWOUD2 4TACHOMETER (0-10000)RPM DIGITAL1 THEORY: Incaseofseriesgeneratorarmaturecurrent,seriesfieldcrrent,loadcurrent are equal, Ia=Ise=I L As load current increases,Ise increases.the flux is directly proportional to Ise sofluxisalsoincrease.Theinducedemfisproportionaltofluxhence inducedemfalsoincreases.ThusthecharactrsticsofEagainsti..einternal charactersticsisofincreasingbutitseffectisnegligiblecomparedto increaseinE.Butforhighloadcurrent,saturationoccursandfluxremains constant.In such a case,due to the drop Ia(Ra+Rse) increases. Now as I L=Ia increases thus the drop Ia(Ra+Rse)increases. V t =E-Ia(Ra+Rse) Thus the external characterstics is also of rising nature asE Increasesbut it will be below internal characterstic due to drop Ia(Ra+Rse) www.jntuworld.comwww.jntuworld.comPROCEDURE: 1.connections are made as per circuit diagram. 2.Before starting the experiment maintain rheostat at maximum position. 3.Switch on the power supply,start the motor using 2-point starter without applying load . 4.By varying the rheostats made the speed to rated speed i..e 1500 rpm. 5.Now apply load ,one by one each and every time maintain the speed to rated speed i..e 1500rpm by using rheostat take voltmeter and ammeter readings. 6.Increase the load up to rated current. 7.Before stop the motor the rheostats are comes back to original position. 8.Draw the internal&external characterstics of generator. MODEL CALCULATIONS: Ia= Ra= V= Rse= Drop=Ia(Ra+Rse) E=V+Ia(Ra+Rse) www.jntuworld.comwww.jntuworld.com TABULAR FORM: S.NO CURRENT Ia VOLTAGE (V) Drop Ia(Ra+Rse) Eg=V+Ia(Ra+Rse) PRECAUTIONS: 1.Avoid loose connections. 2.Readings are taken without parllox error. 3.For this first starting at no-load. www.jntuworld.comwww.jntuworld.comAPPLICATIONS: The series generators have raising external charecterstics .Due to this raising charecterterstics it is used as booster to compensate for the resistance voltage drop in the feeders of the d.c distribution system. RESUL www.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.comBRAKE TEST ON DC SHUNT MOTOR AIM: To conduct Brake test on dc shunt motor and draw the performance characterstics. APPARATUS: S.NO APPARATUS RANGE TYPE QUANTITY 1 2 3 4 5 .

Voltmeter Ammeter Tachometer Rheostat Connecting wires (0-300v) (0-20A) (0-10000) 570/1.2A - MC MC Digital Wire wound - 1 1 1 - - THEORY: In this direct method and consisting of applying a brake to a water cooled pulley mounted on the motor. The brake band is fixed with the help of wooden blocks gripping the pulley. One end of the band is fixed to earth via a spring balance s and the other is connected to a suspended weight W1. The motor is running and the load on the motor is adjusted till it carries its full load current. The simple brake test descrided abovecan be used for small motors only. Becauseinthecaseoflargemotoritisdifferenttodissipatethelarge amount of heat generated at the brake. Another simpledmethod ofmeasuringmotoroutput isbythe use of poney brake one form of the diagram. The tension of rope can be adjusted with the help of swivels obviously. www.jntuworld.comwww.jntuworld.com PROCEDURE: 1.Connectios are made as per circuit diagram. 2,Make sure that no-load is applied to moto and motor field rheostst should be in minimum position. 3.Start the motor by using 3-point starter and adjust the speed of the motor to its rated speed by using field rheostat of motor. 4.Take readings of the ammeter and voltmeter and speed of the motor for each and every load. 5.By gradually increasing the load take readings of ammeter,voltmeter,spring balance measure up toits full load. 6.By slowly varying the load on the motor to zero and switch off the supply . 7.Calculate the torque and efficiency and draw the performance characteristics curve. www.jntuworld.comwww.jntuworld.com MODEL CALCULATIONS: Speed(N)= Spring balances S1= S2=Radius r= Torque T=9.81(S1-S2)r N-M Inputpower=VIwatts Outputpower=2NT/60watts Efficiency() =o/p/i/p100 www.jntuworld.comwww.jntuworld.com PRECAUTIONS: 1.Avoid loose connections. 2.Readings are taken without parallox error. 3.Do not touch wire terminals. APPLICATIONS: 1.For driving constant speed line shafting lathes. 2.Centrifugal pumps. 3.Machine tools. 4.Blowers and fans. 5.Reciprocating pumps. RESULT: www.jntuworld.comwww.jntuworld.com www.jntuworld.comwww.jntuworld.com www.jntuworld.comwww.jntuworld.com LOAD TEST ON DC SHUNT GENERATOR AIM: To conduct load test on dc shunt generator and to draw performance characteristics curves at the given motor. APPARATUS: S.NO APPARATUS RANGE TYPE QUANTITY 1 2 3 4 5 .

Voltmeter Ammeter Tachometer Rheostat Connecting wires (0-300v) (0-20A) (0-2A) (0-10000) 570/1.2A 18/12A - MC MC MC Digital Wire wound Wire wound - 1 1 1 1 2 1 - THEORY: Load test on dc shunt generator consist of two charactersticsthey are 1.Internal characterstics 2.External characterstics Internal characterstics: www.jntuworld.comwww.jntuworld.comIdeally the induced emf is not dependent on the load currents IL (or) armaturecurrentIabutasloadcurrentincreases,armaturefluxIa increases to supply the load demand.As Ia increases,armature flux increases. Due to the armature reaction , main flux pattern gets distorted. Hence lesserfluxgetslinkedwiththearmatureconductors.Thisreducesthe induced emf. External Characteristics: For dc shunt motor E= Vt+IaRa neglecting the other drops. So as load currentincreasesIaincreases.ThusthedropIaRaincreasesandterminal voltages. Vt= E- IaRa decreses. But the value of armature resistance is very small, the drop in terminal voltages as load current changes from no load to fullloadisverysmall.Hencedcshuntgeneratoriscalledconstantvoltage generator . PROCEDURE: 1.Connect the circuit as shown in the circuit. 2.Before starting the experiment the motor field rheostat must be at minimum position and generator field rheostat must be at maximum position. 3.Give the supply and start the motor by using 3-point starter. 4.Adjust motor speed by varying the motor field rheostat upto rated speed. 5.By varying generator field rheostat obtained rated voltage i.e 230v. 6.By gradually applying load one by one, every time by changing the rheostat of motor to its rated speed take the readings of ammeter,voltmeter at each load. 7.Apply the load upto rated current . 8.Before stop the motor ,remove the load and bring back the rheostat to its original position. 9.Stop the power supply. www.jntuworld.comwww.jntuworld.com 10.Draw the internal and external characteristics of shunt generator. MODEL CALCULATIONS: Ra = Voltage (V) = Load current (IL ) = Field current (Ish) = I =IL+Ish Drop =IaRa Eg =V+IaRa www.jntuworld.comwww.jntuworld.comTABULAR FORM: Terminal voltage (v) Load current (IL) Field current (Ish) Ia=IL+Ish Drop IaRa Eg=V+IaRa PRECAUTIONS: 1.Avoid loose connections. 2.Readings are taken without parallox error. 3.Before starting the experiment the motor rheostat must be in minimum position and generator rheostat in maximum position. APPLICATIONS: 1.Shunt generators with field regulators are used for ordinary lighting and power supply purposes. 2.They are also used for charging batteries because their terminal voltages are almost constant. RESULT: www.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.comLOAD TEST ON DC COMPOUND GENERATOR AIM:To conduct load test on dc compound generator and to draw performance characterstics. APPARATUS: S.NO APPARATUS RANGE TYPE QUANTITY 1 2 3 4 5 .

Voltmeter Ammeter Tachometer Rheostat LOad (0-300v) (0-20A) (0-1500rpm) 570/1.2A 3kw/230v MC MC Digital Wire wound Resistance 1 1 1 1 2 THEORY: It is a combination of a few series and a few shunt windings and can be either short shunt or long shunt in a compound generator the shunt field isstrongerthantheseriesfield.Whenseriesfieldaidstheshuntfield generator is said to be cumulative compound on the other hand if series field opposes the shunt field the generator is said to be differentially compounded. Loadcharactersticsdepandsonwhethergeneratoriscummultively compoundedordifferentiallycompoundgenerator.Incumulatively compoundt=sh+se.AsloadcurrentincreasesIaincreaseshenceIse www.jntuworld.comwww.jntuworld.comalsoincreasesproducingmoreflux.Thustheinducedemfincreasesand terminal voltage also increases ,But as Ia increases the various voltage drops andthearmaturereactiondropsalsoincreases.Hencethereisdropinthe terminal voltage. If drop in terminal voltage (Vt) due to increasing I1 is more dominated thanincreasinginV1duetoincreaseinfluxthengeneratoriscalledunder compounded and its characterstics is dropping in nature. IndropinV1duetoarmaturereactionandotherdropsismuchless than increases in V1 due to increases in the flux then generatoris called over compoundanditscharactersticrisinginnatureif theeffectsofthe twoare suchthatonfullloadcurrentV1 issameasnoloadinducedemfi.ethe effectsareneutralingeachotheronfullloadthengeneratoriscalledflat compoundedorlevelcompounded.Indifferentialcompoundt=sh~se.The net flux in difference between the two as I1 increases sh isalmostconstantbutseincreasesrapidly.Hencetheresultantfluxdrasticallythereisdropduetoarmatureresistanceseriesfieldresistance reaction due to which terminal voltage drops further. PROCEDURE: (For cumlative compound generator): 1.Connections are made as shown in circuit diagram. 2.Before starting experiment generator rheostat shoud be in maximum position and motor rheostat should be in minimum position and must be in no load condition. 3.Fora given power supply the motor speedis set at rated speedby varying the motor rheostat and by changing the generator rheostat voltage is obtained. 4.Now by applying the load one by one and every time by changing the rheostat of motor the speed is maintained constant. 5.Before stopping the machine load is removed one by one alsoset the rheostat to its original position. www.jntuworld.comwww.jntuworld.com6.Draw the performance charecterstics by taking load current on x-axis and terminal voltage on y-axis. (For DIFFERENTIAL COMPOUND GENERATOR): 1.Connections are made as per circuit diagram. 2.Before starting the experiment gtr rheostatbe maximum position and motor field rheostat shoud me in minimum position . 3.The motor speed is set at rated speed by changing the rheostat of motor and by generator rheostat to rated is obtained and readings are noted 4.Now by applying the load one by one and every time by changing the rheostat of motor the speed is maintained constant. 5.Before stopping the machine and is removed one by one and also set the rheostat to its original position. And Draw the performance characterstics by taking load current on x-axis and terminal voltage on y-axis. MODEL CALCULATIONS: Ra= Rse= V= Ia=IL+Ish Eg=V+Ia(Ra+Rse) www.jntuworld.comwww.jntuworld.com TABULAR FORM: (For Differential compound generator) (For Cumulatively compound generator ) S.NO Terminal voltage(V) Load current IL(A) Field Current If(A) Ia=IL+Ish Eg=V+Ia(Ra+Rse) S.NO Terminal voltage(V) Load current IL(A) Field Current Ish(A) Ia=IL+Ish Eg=V+Ia(Ra+Rse) www.jntuworld.comwww.jntuworld.com PRECAUTIONS: 1. Avoid loose connections. 2. Readings are taken without parallax error. APPLICATIONS: 1.Differentially compounded generators are used in arc welding. 2.Cumulatively compounded generators are used as boosters in certain types of distribution systems particularly in D.C. railway service. RESULT: www.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.com (A) SWINBURNS TEST AIM:To conduct experiment to predetermine the efficiency of a machine at any load when machine acts as a motor and generator. APPARATUS: APPARATUS RANGE TYPE QUANTITY Voltmeter Ammeter Tachometer Rheostat Connecting wires (0-300v) (0-20A) ,(0-5A) (0-10000)rpm 570/1.2A , 18/12A - MC MC Digital Wire wound - 1 1 1 - - THEORY: It is simple method in which losses are measured separately and from theirknowledge,efficiencyatanydesiredloadcanbepredetermined.The onlyrunningtestneededisno-loadtest.Howeverthistestisapplicableto thosemachinesinwhichfluxispracticallyconstanti.esshuntand compound wound machines. Themachineisrunningasitsratedvoltagestampedonthename plate.The speed is adjusted to the ratedspeed with the help of shunt regulator as shown in ckt .The no- load current Io is measured by the ammeter which is connected in series with the 3-point starter and shuntfield current Ish is givenbytheammeterwhichisconnectedwiththerheostat.Incirculating armature cu losses, hot resistance of armature should be used.A stationary measurement of armature circuit resistanceat the room temperature of say 15 0C ismadebypassingcurrent throughthearmaturefromalowvoltaged.csupply. www.jntuworld.comwww.jntuworld.comIf we substract from the input the no load armature cu loss,then we get constantlossesofthemachine,itsefficiencyatanyotherloadcanbe determined as for both motors as well as generator. PROCEDURE: 1.Connections are made as shown in the circuit diagram. 2 .Give 220v, DC supply and start the motor through 3-point starter. 3. Make the motor to run at the rated speed with the help of fieldrheostat. 4. Note down the readings at no load current I0 , field current Ish and voltage. 5.Bring the motor field rheostat to organized position and switch off the supply. 6.Calculate the efficiency of different loads when acts as both generator and motor. 7.Draw the graph for efficiency verses load and also current. MODEL CALCULATIONS: When the machine acts as a motor: WC= V0I0 -Ia02 RaWhere Ra= = V0I0-(I0-Ish)2 Ra

When the machine acts as a generator: WC= V0I0 Ia02 Ra

= V0I0-(I0+Ish)2 Ra www.jntuworld.comwww.jntuworld.com TABULAR FORM:

Shunt current (Ish)A No load current (I0)A No load voltage(V0)V MODEL CALCULATIONS: (When the machine acts as motor) Ra= IL= Ish= Armature current ,Ia=IL-Ish Armature current ,Ia= Armature resistance,Ra= Armature cu losses=Ia 2Ra www.jntuworld.comwww.jntuworld.com Constant losses,W=V oI o-Ia o2Ra i/p power,= VL IL Total constant losses=Wc+ Iao 2Ra O/p power=i/p-Total losses Efficiency = o/p/i/p 100 TABULAR FORM: When the machine is acting as generator: IL Voltage (V) t.cu loss IL 2 (Rag + Rse) Stary lossWs /2 T.loss Wg = Ws /2+ Wcu o/pVIL I/P VIL +T.L =o/p/i/p www.jntuworld.comwww.jntuworld.comWhen the machine is acting as motor: IL Voltage (V) t.cu loss IL 2 (Ram+ Rse) Stary lossWs /2 T.loss Wg = Ws /2+ Wcu o/pVIL I/P VIL -T.L =o/p/i/p PRECAUTIONS: 1. Avoid loose connections. 2.Readings are taken without parallax error. 3.Before starting the motor,maintain the rheostat of motor at minimum position. APPLICATIONS: 1.It is convenient and economical because power requied to tes a large machine is small i.e only no.load input power. 2.The efficiency can be predetermined at any load because constant losses are know. RESULT: www.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.com (b) SPEED CONTROL OF DC SHUNT MOTOR AIM:Toconduct an experiment on speed control of dc shunt motor by 1.Field control method. 2.Armature control method. And draw performance characterstics. APPARATUS: APPARATUS RANGE TYPE QUANTITY Voltmeter Ammeter Tachometer Rheostat Connecting wires (0-200v) (0-2A) (0-10000)rpm 570/1.2A - MC MC Digital Wire wound -

1 1 1 - - THEORY :(flux control method): Generallyweknowthat,bydecreasingtheflux,the speed can be incresesd and by increasing the flux,the speed can be decresed .Hence the name flux (or) field control method the flux of a dc motor can be changed by changing Ish with help of a shunt field rheostat has to carry only asmallcurrent,whichmeansitslossissmallsothatrheostatissmallin size.Thismethodistherefore,veryefficient.Innon-interpolarmachine,the speed can be increased by this method in the ratio 2:1 .Anyfurther weaking offluxadverselyaffectsthecommunicationandheneputsalimittothe www.jntuworld.comwww.jntuworld.commaximumspeedobtainablewiththemethod.Inmachinefittedwith interpoles ,a ratio of maximum to minimum speed of 6:1 is fairly common. Armature control mehods: This method is used when speedsbefore the no-load speed are requird as the supply voltage is normally constant,the voltage across the armature is varied by inserting a variable rheostat or resistance in series with thearmaturecircuitasshowincktascontrollerresistanceisincreased,pd across the armature is decreses,thereby decreasing the armature speed .For a loadconstanttorque,speedisapproximatelyproportionaltothep.dacross thearmature.Fromthespeed/armaturecurrentcharacterstics,itisseenthat greater the resistance in the armature circuit ,grater is the fall in the speed. PROCEDURE: (FIELD CONTROL METHOD) 1.Connect the circuit as shown in fig. 2.Start the motor by using 3-point starter.

3.By slowly varying the field rheostat ,run the motor to the rated speed and note the values of speed and field current. 4.Slowly increase the field rheostatand note the field current I f and speedN. 5.Draw the graph for N and I f . ARMATURE CONTROL METHOD: 1.Connect the circuit as shown in fig. 2.Keep field regulation at its original positions . 3.By slowly varying the armature rheostat ,note the readings across motor terminals. 4.Draw the graph b/w speed and voltage. www.jntuworld.comwww.jntuworld.com www.jntuworld.comwww.jntuworld.com TABULAR FORM (Field control method) Field current(If)ASpeed(N)rpm (Armature control method); Armature voltage(V)vSpeed(N)rpm PRECAUTIONS: 1. Avoid loose connections. 2.Readings are taken without parallax error. www.jntuworld.comwww.jntuworld.com APPLICATION: 1.These tests are simple for drawing their characterstics curves. 2.Inorder to control the speedof certain machines i.e in which maintain the flux constant,these method are best and suitable. RESULT: www.jntuworld.comwww.jntuworld.com www.jntuworld.comwww.jntuworld.comSEPERATION OF LOSSES BY CONDUCTING RETARDATIONTEST AIM:To determine iron losses mechanical losses and of a dc shunt motor by conducting retardation test. APPARATUS: APPARATUS RANGE TYPE QUANTITY Voltmeter Ammeter Tachometer Rheostat Two way switch (0-300v) (0-2A)(0-20A) (0-10A) (0-200)rpm 290/1.2A (0-10A) MC MC Digital Wire wound -

1 1 1 - - 1 THEORY: Retardation is another method for finding the losses of a machine. Thismethodisapplicabletoshuntmotorandgeneratorandisusedfor finding the stray losses. Then knowing the armature and shunt cu losses at a given load current efficiency can be calculated. The machine is run up to speed slightly greater than normal and then thesupplyiswithONandOFF.Thearmatureslowdownanditskinetic www.jntuworld.comwww.jntuworld.comenergyisused,uptosupplythelossesproducedbyrotation.IfZisthe momentofinertiaofarmatureandwisitsangularvelocityatanyinstant .The rotational velocity at any point instant.The rotational losses P=d/dt(kinetic energy) =d/dt(1/2kV 2)=jwdw/dt Two quantities to known are: 1.Moment of inertia 2.dw/dt The motor is brought up to speed such that voltmeter reads,a bit highter than 250v.The supply is cutoff on the taken by the voltage to drop from 250v to 230 v is noted by the stopwatch.The supply is given the motor brought up to speed such that a voltmeter reads a bit higher than the 250v restored and motor speed brought to full value and supply again cut off.The time taken by the voltage drop from 250v to 210v is noted. PROCEDURE: 1.Connectons are made as per ckt diagram. 2.Keep the switch s1 is open and s2 is in position 1 initially. 3.By closing the switch s supply is given to the circuit by using 3-point starterkeep the motor at rated speed 1500rpm. 4.After attaining 1300rpm open the switch s1 and note down the full time t1 of speed from 1800to 1200rpm. 5.Repeat step2,step3,step4&step5. 6.Supply attaining 1800rpm with exicitation the supply is off and note down the time following speed. www.jntuworld.comwww.jntuworld.comMODEL CALCULATIONS: Case(1):without excitation. W in =(2/60)2I N du/dt----1 Case(2):with full excitation. Stray losses W s=(2/60)2IL(v)du/dt-2 Ws=w[

t 2 /t3 t 4] Where w1=V IL From 2,I=ws/wskg/m2 Losses wi=ws-wm TABULAR FORM: S.NONature of excitationTIME 1Without loadT1 2With loadT2 PRECAUTIONS 1. Avoid loose connections. 2.Readings are taken without parallax error. RESULT: www.jntuworld.comwww.jntuworld.com www.jntuworld.comwww.jntuworld.com www.jntuworld.comwww.jntuworld.comOPEN CIRCUIT CHARACTERSTICS OF DC SHUNT GENERATOR AIM: 1.Magnetic characterstics of dc shunt generator. 2.Determination of critical field resistance and critical field, APPARATUS: S.NO APPARATUS RANGE TYPE QUANTITY 1 2 3 4 .

Voltmeter Ammeter Tachometer Rheostat (0-300v) (0-2A) (0-10000rpm) 570/1.2A MC MC Digital Wire wound

1 1 1 1 THEORY: Connectthefieldwindingbacktothearmatureandrunthe machine as a shunt generator. Due to residual magnetism in the poles, some emfandhencecurrent,wouldbegenerated.Thiscurrentwhilepassingthrough the field coils will strengthen the magnetism of the poles .This will increasethepolefluxwhichwillfurtherincreasethegeneratedemf increasedemfmorecurrentwhichfurtherincreasethefluxsoon.This mutual reinforcement of emf and flux proceeds until equilibrium is reached atsomepoinlikep.Thepointliesontheresistancelineoaofthefield www.jntuworld.comwww.jntuworld.comwinding.Let r be the resistance of field windingline OA is drawn such that itsslopeequalsthefieldwindingresistance.Resistancelinejustliesalong theslope.Thenwiththatvalueoftheresistance,themachinewilljust excite.Thevalueoftheresistancebythetangenttothecurve,isknownas critical resistancefor given speed. Critical speed of a shunt generator of a shunt generator is that speed for which the given shunt field resistance represents critical resistance. Critical speed NC =BC/AC full speed N PROCEDURE: 1Connections are made as per ckt diagram. 2.Dc supply is given and start the motor by using 3-point starter. 3.Make sure that field rheostat of motor is to be in minimum positionand field generator should be in maximum position. 4.By slowly varyingthe fieldrheostat of motor adjust its speed to its rated speed. 5.Byslowly varying the field rheostat of generator from maximum to minimum position 6.Take rheostat of generator and motor should be in original position then switch off the supply. 7.Draw the graph for field current (I) and E taking I on x-axis and E on y-axis. 8.From graph fnd critical resistance and critical speed. MODELCALCULATIONS: a)Critical field resistance Rc=OA/OB E=If Rsh b)critical speed Nc=N CD/CFrpm www.jntuworld.comwww.jntuworld.com TABULAR FORM: S.NOGenerated EmfField current(If) PRECAUTIONS 1. Avoid loose connections. 2.Readings are taken without parallax error. RESULT: www.jntuworld.comwww.jntuworld.comwww.jntuworld.comwww.jntuworld.comFIELD TEST ON DC- SERIES MOTYOR AIM:To find the efficiency of Dc series motor by conducting field test on a series motor generator set. APPARATUS: S.NO APPARATUS RANGE TYPE QUANTITY

1. 2. 3. 5. Voltmeter Ammeter Rheostat Tachometer

( 0-300)V (0-20)A 18/12A (0-9999)RPM THEORY: Thisisoneofmethodoftestingthedcseriesmotors.unlikeshunt motors,theseriesmotorcannotbetestedbythemethodswhichare availableforshuntmotorasitisimpossibletorunthemotoratno-load.It may run at dangerously high speed on no-load in case of small series motors brake test may be employed. The series motors are usually tested in pairs .The field test is applied to two similar seriesmotors which are coupled. One machine is made to run as a motor whilethe other as a generator which is separately exicted the fields of the two machines areconnected in seriessothatboththemachinesareequallyexicted.Thiswillmakeiron lossessameforthetwomachines.Thetwomachinesarerunningatthe same speed . The generator output is given to the variable resistance. The resistance is changed until the current taken by motor reaches full load value.This will be indicated by ammeter. The other readings of different meters are then recorded. www.jntuworld.comwww.jntuworld.comPROCEDURE: 1.Make the connections are made as per the circuit diagram. 2.Before starting the experiment make sure that generator is loaded. 3.Switch ON the power supply and start the motor by using 2-point starter. 4.Obtain the rated speed by using varying load. 5.Note down the readings ofcorresponding meters. 6.Measure the ammeters field resistance of both machines immediatelyafter switch OFF the supply7.Calculatethe efficiency of both machines. MODEL CALCULATIONS: Input power Win=VIm Output = VgIg Total losses =VIm- VgIg Total copper losses = Im 2 Ram + Ig 2Rag + Isem 2(Rsem + Rseg) Stray losses = Total losses Total copper loss Stray losses for each machine = Ws /2 MACHINE ACTS AS A GENERATOR: Armature copper losses = IL 2 (Rag + Rse) Stray losses = Ws /2 Total losses = Ws /2 + Armature copper losses. Output = VIL

Input = VIL+ Total losses Efficiency = output / input x 100 www.jntuworld.comwww.jntuworld.com MAVHINE ACTS AS A MOTOR: Armature copper losses = IL 2 (Ram + Rsem) Stray losses = Ws /2 Total losses = Ws /2 + Armature copper losses. Input = VIL Output = VIL-Total losses

Efficiency = output / input x 100 www.jntuworld.comwww.jntuworld.comTABULAR FORM: S.NO Voltage (V) Motor i/p Voltage(Vm) Generator o/p (Vg) Current (Im) Load current (Ig) MACHINE ACTS AS A GENERATOR: IL Voltage (V) t.cu loss IL 2 (Rag + Rse) Stary lossWs /2 T.loss Wg = Ws /2+ Wcu o/pVIL I/P VIL +T.L =o/p/i/p MACHINE ACTS AS A MOTOR: IL Voltage (V) t.cu loss IL 2 (Ram+ Rse) Stary lossWs /2 T.loss Wg = Ws /2+ Wcu o/pVIL I/P VIL -T.L =o/p/i/p www.jntuworld.comwww.jntuworld.com PRECAUTIONS: 1.Avoide loose connections. 2.Take the readings with out parallax error. 3.Double check the circuit before giving the supply. 4.The motor armature rheostat in maximum position and motorfield rheostat in minimum position. RESULT: www.jntuworld.comwww.jntuworld.com