AC Machines 6077SA NUE 046

3 Phase Synchronous Alternators

At the end of this section you will be able to: 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

Determines Speed of Alternator Prime Mover Determines Speed of Alternator High Speed Slow Speed Windmill Diesel Motor Water turbine Steam turbine

Speed Determines Number of Poles 50 Hz Required OR

Number of Poles 375 RPM = 16 Poles 750 RPM = 8 Poles 1500 RPM =

Determines Shape of Alternator Number of Poles Determines Shape of Alternator 16 Poles Large Diameter Short length Salient Pole

Determines Shape of Alternator Number of Poles Determines Shape of Alternator Small Diameter Long 2 Poles 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 Φm f N = Maximum flux = Frequency = Number of poles

Generated Voltage Φm f N kp kd = Maximum flux = Frequency = Number of poles = Pitch factor =Distribution or Breadth factor

Voltage Regulation Resistance Inductance Coils have both I E V Voltage Drop Due to R Voltage Drop Due to XL

Voltage Regulation Vg Unity PF Terminal Voltage Line Current

Voltage Regulation V less than E I V E Lagging PF of 45

Voltage Regulation Vg Terminal Voltage Unity PF Lagging PF Line Current

Voltage Regulation V More than than E I E V Leading PF of 45

Voltage Regulation Leading PF Vg Terminal Voltage Unity PF Lagging PF Line Current

Voltage Regulation If PF = Unity 100 x VNo Load – V Full Load R% = 100 x I x (R x cos + XL x sin) R% = VFull Load

Excitation With Brushes DC Generator Brushes Rotor Stator

Excitation Without Brushes Rotating Components Excitation Stator Sensor & Regulator

Synchronising Generators Synchronized when all lamps dark

Synchronising Generators Synchronized when 1 lamp dark 2 lamps light

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