Transcript AC Machines
6077SA NUE 046 3 Phase Synchronous Alternators Alternators At the end of this section you will be able to: Identify the basic components of a Alternator List the types of rotors used Test motor windings for suitability to connect to the supply Connect in both Clockwise and counter clockwise rotation List the steps for dismantling it Types Governed By: • Load Current Requirements • Single or Three Phase • Prime Mover Speed Prime Mover Determines Speed of Alternator Slow Speed • Windmill • Diesel Motor • Water turbine High Speed • Steam turbine Number of Poles Speed Determines Number of Poles 50 Hz Required 120 f n p OR 120 f p n Number of Poles 120 f p n 375 RPM = 16 Poles 750 RPM = 8 Poles 1500 RPM = 4 Poles 3000 RPM = 2 Poles Number of Poles Determines Shape of Alternator 16 Poles •Large Diameter • Short length Salient Pole Number of Poles Determines Shape of Alternator 2 Poles •Small Diameter • Long Cylindrical Generated Voltage Dependant on • Flux density • Flux strength • Speed of rotation • Number of turns per pole • Length of pole • Area of pole face Generated Voltage E 4.44 m fN Φm f N = Maximum flux = Frequency = Number of poles Generated Voltage E 4.44 m fNk p k d Φm f = Maximum flux = Frequency N = Number of poles kp = Pitch factor kd =Distribution or Breadth factor Voltage Regulation Coils have both • • Resistance Inductance I E V Voltage Drop Due to R Voltage Drop Due to XL Voltage Regulation Terminal Voltage Vg Unity PF Line Current Voltage Regulation V less than E I V Lagging PF of 45 E Voltage Regulation Terminal Voltage Vg Unity PF Lagging PF Line Current Voltage Regulation V More than than E I E V Leading PF of 45 Voltage Regulation Leading PF Terminal Voltage Vg Unity PF Lagging PF Line Current Voltage Regulation R% = 100 x VNo Load – V Full Load VFull Load If PF = Unity R% = 100 x I x (R x cos + XL x sin) VFull Load Excitation With Brushes DC Generator Brushes Rotor Stator Excitation Without Brushes Excitation Stator Rotating Components Sensor & Regulator Synchronising Generators Synchronized when all lamps dark Synchronising Generators Synchronized when 1 lamp dark 2 lamps light END