2 Marks | Electric Motor

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  ROEVER ENGINEERING COLLEGE DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERINGSolid State DrivesTwo Marks Questios ad Aswers!NIT I# F!NDAMENTALS OF ELECTRIC DRIVES $% &'at are t'e ('oi(es o) ele(tri(al drives* or &'at are t'e )a(tors to +e (osidered duri, sele(tio o) ele(tri( drives* a.Steady state operation requirementsb.Transient operation requirementsc.Requirements related to the sourced.Capital, running and maintenance needs, lifee.Space and weight restrictions if anyf.Environment and locationg.Reliability -% &'at is .eat +/ re,eerative +reaki,* Regenerative Braing is the operation of the motor as a generator, while it is still connected to the supply networ. !echanical energy is converted into electrical energy, part of which is returned to the supply. Rest of the energy is lost as heat in the windings and the bearings of the electrical machine. 0% &'at are t'e (o.1oets o) load tor2ues* a. riction torque, #T f  $ results from relative motion between surfacesb.%indage torque,#T w $ is caused by the rotating components setting up air #or other fluid$ movement.c.&oad torque,#T l $ required by the application. 3% Draw t'e .ulti2uadrat o1eratio o) drives%4% De)ie e2uili+riu. o1erati, 1oit% Equilibrium operating point is instant in which motor torque equals to the load torque.  5% De)ie stead/ state sta+ilit/% The steady state stability is the ability of the drive to restore to its equilibrium point after a small departure from it due to a disturbance in the motor or load. 6% &'at are t'e advata,es o) ele(tri(al drives* i.They have fle'ible control characteristics.ii.They are available in wide range of torque, speed and power.iii.Electric motors have high efficiency, low no load losses and considerable short time overloading capacity.iv.They are adoptable to almost any operating conditions such as e'plosive environment, submerged, vertical mountings and so on.v.They do not pollute the environment.vi.Can operate in all the four quadrants of speed torque plane.vii.They can be started instantly and can immediately be fully loaded. 7% &'at is .eat +/ a((eleratio* (rive operates in acceleration whenever an increase in its speed is required. or this speed)torque curve is changed so that the motor torque e'ceeds the load torque #T m *T & $. 8% &'at is .eat +/ de(eleratio* !otor operation in deceleration mode is required when a decrease in its speed is required. (eceleration occurs when load torque e'ceeds the motor torque #i.e, T m +T & $. %henever the reducing the motor torque to ero does not provide enough deceleration, mechanical braes may be provided. -lternatively, electrical braing may be employed. $9% &'at are t'e t'ree .odes o) o1eratio o) ele(tri(al drive* i.Steady stateii.-cceleration including startingiii.(eceleration including stopping $$% &rite dow t'e )uda.etal tor2ue e2uatio% l m T dt d  J T   += ω  The torque developed by the motor #T$ is counter balanced by the load torque #T l  $ and a dynamic torque, #d/ m  0dt$. $-% &'at do /ou .ea +/ )our 2uadrat o1eratio* 1uadrant 2 3 orward !otoring1uadrant 22 3 orward Braing1uadrant 222 3 Reverse !otoring1uadrant 243 Reverse Braing $0% &'at are t'e di))eret t/1es o) drives* i.5roup (rive ii. 2ndividual driveiii.!ultimotor (rive $3% Metio so.e o) t'e a11li(atios o) ele(tri(al drives* i.Transportation Systemsii.Rolling !illsiii.6aper !illsiv.Te'tile !ills  v.!achine Toolsvi. ans and 6umpsvii.Robotsviii.%ashing !achines etc. !NIT II# CONVERTER:C;OPPER FED DC MOTOR DRIVE 7. Draw t'e s1eed < tor2ue ('ara(teristi(s o) a D%C%S'ut .otor%-%Metio t'e .et'ods to (otrol t'e s1eed o) a DC s'ut .otor% i.-rmature 4oltage Controlii. ield lu' Controliii.-rmature Resistance Control8. &'at is .eat +/ dut/ (/(le i a ('o11er (ir(uit* 2t is the ratio of the 9: time period to the total time period of the chopper circuit. T t Cycle Duty  on = δ  , ;. Draw t'e dia,ra. o) re,eerative )ed se1aratel/ e=(ited D%C% .otor drive* BCE EL a R  a D 2 CVT r1 <. Metio t'e a11li(atios o) ('o11er )ed d( drives% i.Te'tile !illsii.Cranesiii.!achine Toolsiv.Electric Tractionv.Electric 4ehicles          S     e     e       d Torue  =. &'/ t'/ristors are ot 1re)erred ow<a<da/s )or ('o11er )ed DC drives* Thyristors are not preferred for chopper fed (C drives because they need high power control signals and a separate commutation circuit for triggering. >. &'at is dis(otiuous (odu(tio .ode* %hen the armature current does not flow continuously, the motor is said to operate in discontinuous conduction mode.?. Draw t'e re,eerative +raki, ('ara(teristi(s o) a se1aratel/ e=(ited .otor% @. &'at is .eat +/ (riti(al s1eed i 1'ase (otrolled DC drives* The speed which separates the continuous conduction from discontinuous conduction for a given A is nown as critical speed. $9%&'at is TRC (otrol s('e.e* 2t is a strategy to control the average output voltage by varying #t on  0T$. This is implemented in two ways such as,a.Constant requency Systemb.4ariable requency System77. &'at are t'e )our 2uadrats o) d( drives* 1uadrant 2 3 Rectifier1uadrant 22 3 2nverter1uadrant 222 3 Rectifier1uadrant 24 3 2nverter7. &'at are t'e advata,es o) t'ree 1'ase drives over si,le 1'ase drives* a.Reduced ripple in armature currentb.Requires less filtering arrangementc.-rmature current is mostly continuousd.2mprove performancee.2ncrease power rating78. &'at is a lie (o..utated iverter* ull converter with the firing angle delay greater than @o is called line commutated inverter. Such operation is used in regerative braing mode of a (C !otor.7;. State t'e advata,es o) d( ('o11er drives% i.Reduced current rippleii.Reduced !achine lossesiii.Elimination of discontinuous conductioni a i a7 i a ω tTt on v a 
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