Bsic Components O An Electric Dries System A modern electric dries system hs ie unctionl bsic component : 1. Mechnicl Lods 2. Electricl Motors 3. Sttic Conerters (Power Electronic) 4. Power Sources 5. Controller Power Sources Power Electronic Conerters Electric Motor Mechnicl Lods EE467(Mchines & Electricl Dries Controller
The bsic criterion in selecting n electric motor or gien dries ppliction : 1. Power leel nd perormnce required by the lods during stedy-stte stte nd dynmic opertion. Ex: n ppliction or which high strting torque is needed dc series motor might be better choice thn n c induction motor. n Constnt speed pplictions, synchronous motor be more suitble thn induction or dc motors 2. Enironmentl ctors (determine the motor type) Ex: n ood processing, chemicl industries, ition, where the enironment must be clen nd ree rom rcs, dc motor cn not be used unless they re encpsulted. 3. The cost o the electric motors. n generl, brushless dc motors re more expensie, wheres squirrel cge induction motors re the choppers 4. The unction o conerters (we orms) Ex: the power source is n c type nd the motor is dc mchine. The conerter trnsorms the c weorm to dc. (stbility, eiciency nd perormnce o motor tht using this conerter.
1. Mechnicl Lods Mechnicl lods exhibit wide ritions o speed-torque chrcteristics, Generlly cn be expressed s : T = CTr n n r k.1 Where : C is proportionlity constnt T r is the lods torque n r is speed o lod n is operting speed P = Tω The mechnicl power P o the lod torque T is gien by : P =Tω 2π n ω = 2π = 60
Type o the Mechnicl Lods: 1. Torque ndependent o Speed (torque constnt) The power liner dependent o speed, Ex: Hoist or the pumping o wter or gs ginst constnt pressure. 2. Torque Linerly Dependent on Speed Ex: Motor driing dc genertor connected to ixed-resistnce lod, nd the ield o the genertor is constnt. 3. Torque Proportionl to the Squre o Speed Ex: ns, centriugl pumps, nd propeller. 4. Torque nersely Proportionl to Speed Ex: Milling nd boring mchines. The lod usully requires lrge torque t strting speed nd t low speeds.
2. Electric Motors Speed-Torque Chrcteristics Electric motors he wide rition o speed-torque chrcteristics Cure : Synchronous or reluctnce motor (Constnt speed) Cure : Shunt or seprtely excited dc motor (speed slightly reduced when the lod torque increse) Cure : Series dc motor (speed is high t light loding condition nd low t hey loding) Cure V : nduction motor (during stedy stte, they opertion t the liner portion o speed-torque chrcteristic speed is high t light loding, the mximum deeloped torque is limited to T mx n electric drie ppliction, electric motors should be selected to mtch the intended perormnce o lods. Ex: n constnt speed ppliction, the synchronous motor is probbly the best option.
3. Power Sources Two mjor type o power sources re used in industril pplictions: 1. Alternting Current (c), single phse or three-phse, 60Hz or 60 Hz, 240V/415V, 220V/380V, 120V/90V, 11kV/415V, etc. 2. Direct Current (dc) Extensie industril instlltion usully he more thn one type o power sources t dierent oltges nd requencies, Commercil irplnes, or exmples, my he 400Hz c sources in dditionl 270 olt sources.
4. Conerters The min unction o conerters is to trnsorm the weorm o power sources to tht the required by n electric motor in order to chiee the desired perormnce. Type o Conerters : 1. dc to c conerter (inerter). The output o this conerter is requency, current/oltge cn be djusted ccording to the ppliction 2. dc to dc conerter (dc chopper). The output o this conerter is rible mgnitude o oltge. 3. c to dc conerter (rectiier). The output o this conerter is rible mgnitude o dc oltge, input is single or three-phse c oltge. 4. c to c conerter (c chopper). The output o this conerter is requency nd c rible oltge, the input is constnt requency nd c oltge.
Motor DC dries System by Using Two Sttic Conerters (ectiiers)
Motor DC dries System by Using Three Sttic Conerters (Two ectiiers nd one DC Chopper)
Equilent Circuit o Seprtely DC Motor Equilent Circuit o Seprtely DC Motor V = g E V + = ω + = d T = B +T L = ω ω P =T d ) / ( V V V = ω =
Chrcteristic o Seprtely Excited DC Motor
Equilent Circuit o Series DC Motor Equilent Circuit o Series DC Motor g E ω ω = = g E V + + = ) ( ω + + = ) ( 2 d T = = B +T L = ω ω P =T d (14) V V ) ( ) ( + = + ω =
Chrcteristic o Series Excited DC Motor
Mode : Motoring Seprtely DC Motor Series DC Motor
Mode : egenertie Brking Seprtely DC Motor Series DC Motor
Mode : Dynmic Brking Seprtely DC Motor Series DC Motor
Mode : Plugging Brking Seprtely DC Motor Series DC Motor