* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electrical Machines
Power over Ethernet wikipedia , lookup
Power inverter wikipedia , lookup
Wireless power transfer wikipedia , lookup
Audio power wikipedia , lookup
Pulse-width modulation wikipedia , lookup
History of electric power transmission wikipedia , lookup
Buck converter wikipedia , lookup
Mains electricity wikipedia , lookup
Utility frequency wikipedia , lookup
Voltage optimisation wikipedia , lookup
Three-phase electric power wikipedia , lookup
Commutator (electric) wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Electric power system wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Power factor wikipedia , lookup
Distribution management system wikipedia , lookup
Alternating current wikipedia , lookup
Dynamometer wikipedia , lookup
Brushless DC electric motor wikipedia , lookup
Power engineering wikipedia , lookup
Rectiverter wikipedia , lookup
Electrification wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Electric motor wikipedia , lookup
Stepper motor wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Electrical Machines LSEGG216A 9080V Synchronous Motors Week 14 Introduction • State the principles of operation of a synchronous motor. • Identify the main parts of a synchronous alternator/motor. • List the methods used to provide the excitation of a synchronous alternator/motor. • List the starting methods of synchronous Motor Types 3 Phase 1 Phase • Reluctance • Hysteresis • Permanent Magnet • Inductor Characteristics • • • • • • High operating efficiency Smooth constant starting & accelerating torque Versatile power factor control Constant speed Considerably more expensive than induction motors Zero starting torque Stator Same as an induction motor’s stator Some books may call this the Armature Rotor • Wound simular to a wound rotor induction motor • When operating DC voltage is placed across this coil to produce an electromagnet Some books may call this the Field Windings Motor Speed • Magnetic force is obtained from an external source (In an induction machine rotor’s magnetism is induced from the stator) • Rotor poles lock onto the RMF Called “Excitation” • Rotor operates at synchronous speed 120 f = Nrotor N sync P Torque Angle No Load Torque Angle Torque Angle Dependant on: • Load torque • Excitation • The magnetic link between the stator & the rotor can be thought of as a connecting spring. Full Load • The excitation can be used to strengthen the spring Torque Angle If the load Torque fluctuates Or Changes rapidly • The magnetic “Spring” will bounce • Causing large fluctuations in supply current • Amortisseur windings are added to the rotor • Also known as hunting Amortisseur Windings Similar to the squirrel cage found in induction machines Also Known as “Damper “ windings • When relative movement between the stator and the rotor poles occurs • Voltage is induced into these windings. • Subsequent induced magnetic field tends to slow movement and act like a “shock absorber” • Can be used to aid starting in a simular way to that of the squirrel cage conductors Starting Zero starting Torque Number of methods: • Pony Motor • Low Frequency Pony Motor Starting An auxiliary smaller motor is used to spin the main motor up to or near Synchronous speed Starting Low Frequency • The rotor’s excitation windings are short circuited • Act like a wound rotor induction motor • Supply is applied at reduced voltage & frequency • Rotor builds up speed • Excitation is then applied to windings and rotor locks in Tumit 3 and the Shoalhaven hydro schemes use this system Motor Uses • Can be used as a standard motor similar to an induction motor As an induction machine is cheaper it is seldom used just as a motor • Main use as a power factor correction device Sometimes called a rotary capacitor Power Factor Correction The stator current will drop And the Power Factor Improves As we increase the excitation The stator current will increase Power Factor Correction And the Power Factor detieriates If we continue to increase the excitation Power Factor Correction Curve A = Stator Current Curve B = Power Factor These curves are known as “Vee Curves” Power Factor Correction These curves are only applicable for a set load torque A different load will produce a different set of curves Power Factor Correction If the bride is over Unityexcited she will lead you to the marriage bed Lagging Under Excited Leading Over Excited Power Factor Correction A motor has full load of 100A and an excitation current of 8A what will be: • The stator current? • PF of the motor? Power Factor Correction PF = 0.9 Lagging Stator Current 38% X 100A = 38A Example • A load of 450 kVA operates at a power factor of 0.65 lagging. • An additional synchronous motor is added having an input power of 90 kW and a maximum power factor of 0.85 leading. • Determine reactive power and the overall power factor 450 x cos 49.5= 292.5kW 49.5 450kVA 450 x sin 49.5= 342kVar Example • A load of 450 kVA operates at a power factor of 0.65 lagging. • An additional synchronous motor is added having an input power of 90 kW and a maximum power factor of 0.85 leading. • Determine reactive power and the overall power factor 292.5 + 90 = 382.5kW tan-1 x 286/382.5 = 36.8 PF = 0.8 Lag 90 x tan 31.8 = 292.5kW 49.5 31.8 55.8kVar 342 – 55.8 = 286kVar 90kW 450kVA 342kVar