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Electric Machines & Drives. Topics covered – DC Motors DC Generators AC 3 phase Induction Motors AC 3 phase Synchronous Machines Fundamentals of Power Controls USF Course Material available at; thomasblairpe.com/EMD. IEEE EMD Seminar Tom Blair, P.E. 1.

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## Electric Machines & Drives

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**Electric Machines & Drives**• Topics covered – • DC Motors • DC Generators • AC 3 phase Induction Motors • AC 3 phase Synchronous Machines • Fundamentals of Power Controls • USF Course Material available at; • thomasblairpe.com/EMD IEEE EMD Seminar Tom Blair, P.E. 1**Chapter 4 - DC Generators**AC generator E = B*L*V Slip Ring Component of V perpendicular to B IEEE EMD Seminar Tom Blair, P.E. 2**Chapter 4 - DC Generators**Commutator IEEE EMD Seminar Tom Blair, P.E. 3**Chapter 4 - DC Generators**Which unit below is AC machine and which is DC machine? IEEE EMD Seminar Tom Blair, P.E. 4**Chapter 4 - DC Generators**Slot construction Lap Winding 4 coils = 4 slots = 4 commutator bars 2 poles = 2 brushes eA+eB+eC+eD = 0 (no circ current) Brush Volt = eB+eC or eA+eD IEEE EMD Seminar Tom Blair, P.E. 5**Chapter 4 - DC Generators**Magnitude -> angle between V and B IEEE EMD Seminar Tom Blair, P.E. 6**Chapter 4 - DC Generators**Voltage in slot 4/10 max Voltage in slot 1/7 min IEEE EMD Seminar Tom Blair, P.E. 7**Chapter 4 - DC Generators**Proportional to flux and speed Off neutral brush effectively reduces Z IEEE EMD Seminar Tom Blair, P.E. 8**Chapter 4 - DC Generators**Armature reaction Current produces Magnetic Field IEEE EMD Seminar Tom Blair, P.E. 9**Chapter 4 - DC Generators**Armature induced field adds to pole induced field. Resultant field shifts neutral point. Also, saturation of points 2 ,3 (Pole Tip Saturation) causes reduced EO IEEE EMD Seminar Tom Blair, P.E. 10**Chapter 4 - DC Generators**Commutating Pole Field proportional to load Compensate neutral shift Due to armature reaction (Slightly greater than Armature reaction flux) Note, does not change Saturation at main poles -> EO still effected. IEEE EMD Seminar Tom Blair, P.E. 11**Chapter 4 - DC Generators**No Load operation Saturation Curve Field Flux vs Exciting amps (similar to B-H Curve) Designed to operate at “knee” of point a & b. IEEE EMD Seminar Tom Blair, P.E. 12**Chapter 4 - DC Generators**Shunt Generator – no external field source needed IEEE EMD Seminar Tom Blair, P.E. 13**Chapter 4 - DC Generators**Voltage Control Nonlinear Moving P to N, reduced EO Moving P to M, increases EO IEEE EMD Seminar Tom Blair, P.E. 14**Chapter 4 - DC Generators**EO noload – intersection of Saturation curve & RF For this example: RF > 200 W E0=0 Critical Value (When starting, where should rheostat position be??) IEEE EMD Seminar Tom Blair, P.E. 15**Chapter 4 - DC Generators**Exciting current constant, speed constant, EO constant E12 depend on drop across RO Load Curve Shown – typical drop less than 10% (Pole Tip Saturation also leads to E12 drop) Shunt Generator – typical drop about 15% due to EO drop IEEE EMD Seminar Tom Blair, P.E. 16**Chapter 4 - DC Generators**Compound Generator – Series & Shunt Coils Series coil same direction as Shunt – mmf adds E0 raises as load increases maintaining E12 IEEE EMD Seminar Tom Blair, P.E. 17**Chapter 4 - DC Generators**Over-compound generator E12 increases. Differential-compounded – Series coil opposite direction – mmf subtracts, EO drops as load increases. IEEE EMD Seminar Tom Blair, P.E. 18**Chapter 4 - DC Generators**# Poles = # Brush sets Larger Machine -> More poles -> More brush sets Control amps per brush (current density) Also more Brush per Brush set -> reduce current density. Generator construction Field Stationary Electromagnet – Salient Poles Air Gap 1mm - 5mm IEEE EMD Seminar Tom Blair, P.E. 19**Chapter 4 - DC Generators**IEEE EMD Seminar Tom Blair, P.E. 20**Chapter 4 - DC Generators**Armature Construction Rotating Commutator, Iron Core, & Coils IEEE EMD Seminar Tom Blair, P.E. 21**Chapter 4 - DC Generators**# slots = # coils = # commutator sections Mica insulator between commutator sections Coils connected to commutating element Eccentricity causes brush bounce -> arcing IEEE EMD Seminar Tom Blair, P.E. 22**Chapter 4 - DC Generators**Brush set connection – alternating + and - IEEE EMD Seminar Tom Blair, P.E. 23**Chapter 5 – DC Motors**Constructed same as DC generator Torque & Speed control with high efficiency Starting methods IEEE EMD Seminar Tom Blair, P.E. 24**Chapter 5 – DC Motors**EO proportional to speed At rest EO = 0 At steady state EO = ES – I*R EO = counter-electromotive force (CEMF) IEEE EMD Seminar Tom Blair, P.E. 25**Chapter 5 – DC Motors**Mechanical Power & Torque - IEEE EMD Seminar Tom Blair, P.E. 26**Chapter 5 – DC Motors**Mechanical Torque – proportional to flux and armature current IEEE EMD Seminar Tom Blair, P.E. 27**Chapter 5 – DC Motors**Speed of Rotation – Proportional to Es and inversely proportional to flux (field current) Bonus Question, what happens to DC motor on Loss of Field Current? IEEE EMD Seminar Tom Blair, P.E. 28**Chapter 5 – DC Motors**Rheostat allows control of EO -> speed control Efficiency very poor Small motors only. IEEE EMD Seminar Tom Blair, P.E. 29**Chapter 5 – DC Motors**Speed control via field control Flux increase -> speed decrease Operate above base speed IEEE EMD Seminar Tom Blair, P.E. 30**Chapter 5 – DC Motors**As load increases, Tload increases, causing armature current to increase causing speed to drop Speed regulation good (10%-20%) IEEE EMD Seminar Tom Blair, P.E. 31**Chapter 5 – DC Motors**Series Motor – Different torque speed characteristic Starting torque higher Reduction in load = reduced flux = higher speed Bonus Question – what happens if load removed? IEEE EMD Seminar Tom Blair, P.E. 32**Chapter 5 – DC Motors**As load decreases, Tload decreases, causing armature current to decrease causing flux to drop causing speed to increase rapidly Speed regulation poor IEEE EMD Seminar Tom Blair, P.E. 33**Chapter 5 – DC Motors**Compound DC Motor – Both series & shunt field No load, shunt field controls max speed Full load, series field adds to mmf -> increased flux -> speed decreases Regulation 10% - 30% Differential Compound – series field mmf subtracts from shunt field mmf IEEE EMD Seminar Tom Blair, P.E. 34**Chapter 5 – DC Motors**IEEE EMD Seminar Tom Blair, P.E. 35**Chapter 5 – DC Motors**Direction of Rotation – Reverse Armature or Field Commutation polarity associated with Armature polarity IEEE EMD Seminar Tom Blair, P.E. 36**Chapter 13 – Three Phase Induction Machines**Stator – laminated core, slots, 3phase winding Rotor – laminated core, slots, 3phase winding or squirrel cage winding Squirrel cage induction motor Bare copper (aluminum) bars welded to copper (aluminum) end rings Wound rotor induction motor Three phase insulated winding – three slip rings – external resistor IEEE EMD Seminar Tom Blair, P.E. 37**Chapter 13 – Three Phase Induction Machines**IEEE EMD Seminar Tom Blair, P.E. 38**Chapter 13 – Three Phase Induction Machines**Faraday’s Law Lorentz Force IEEE EMD Seminar Tom Blair, P.E. 39**Chapter 13 – Three Phase Induction Machines**Field speed = 120 * f / p Salient Pole Stator -> Smooth Stator Phase group -> group = #phase * #poles(*#winding) Group = 3*2=6 #slot = #coils Lap wound coil construction IEEE EMD Seminar Tom Blair, P.E. 40**Chapter 13 – Three Phase Induction Machines**stator IEEE EMD Seminar Tom Blair, P.E. 41**Chapter 13 – Three Phase Induction Machines**IEEE EMD Seminar Tom Blair, P.E. 42**Chapter 13 – Three Phase Induction Machines**Motor enclosures TENV – totally enclosed, non ventilated TEFC – totally enclosed, fan cooled TEBC – totally enclosed, blower cooled TEWAC – totally enclosed, water to air cooled TEAAC – totally enclosed, air to air cooled WPII – Weather protected (two 90 degree turns in air path) ODP – Open drip proof IEEE EMD Seminar Tom Blair, P.E. 43**Chapter 13 – Three Phase Induction Machines**Synchronous speed vs. asynchronous speed IEEE EMD Seminar Tom Blair, P.E. 44**Chapter 13 – Three Phase Induction Machines**• Starting Characteristics – • Revolving field set up by applied stator voltage • Field induced voltage (E2) in rotor bars. • Induced voltage induces current in rotor bars. • Induced current in magnetic field induces force on conductors in direction of rotating magnetic field. • As rotor speed increases – rate at which rotor bars cut field reduces (reducing E2) • Reduced E2 -> reduced rotor current ->reduced force • When load torque = motor torque, steady state IEEE EMD Seminar Tom Blair, P.E. 45**Chapter 13 – Three Phase Induction Machines**Power & PF vs loading while motor at speed. IEEE EMD Seminar Tom Blair, P.E. 46**Chapter 13 – Three Phase Induction Machines**Percent difference between synch speed and actual speed = slip IEEE EMD Seminar Tom Blair, P.E. 47**Chapter 13 – Three Phase Induction Machines**Rotor Voltage (E2) and frequency (f2) IEEE EMD Seminar Tom Blair, P.E. 48**Chapter 13 – Three Phase Induction Machines**Induction motors are designed to operate successfully with voltage variations of ±10%. Effects of a 10% variation on a typical design B induction motor at full load shown below. IEEE EMD Seminar Tom Blair, P.E. 50

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