Electrical Machines and Energy Systems: Overview SYED A RIZVI

Electrical Machines and Energy Systems: Overview SYED A RIZVI

Electrical Machines and Energy Systems Deal with the generation, transmission & distribution, and utilization of electric power. This course covers the fundamental theory/concepts of the key components of the Electrical Energy System: Generators Transformers Motors It is a lecture/laboratory course; accordingly, theoretical concepts learned in this courses will be reinforced through the laboratory experiments as appropriate. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 2

Generator It is an electrical machine that changes mechanical energy into electrical energy. Electrical voltage is induced (generated) in conductors placed in a magnetic field as the magnetic flux linkage through the conductors changes with time (Faraday s Law of electromagnetic induction). The magnetic flux linkage can be changed either by: Rotating the magnetic field through stationary conductors; or Rotating the conductors in a stationary magnetic field The rotary motion is provided by a Prime Mover, which in turn, could be power by a number of methods such as steam/hydel/wind turbines or a diesel engine etc. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 3

https://www.siemens.com/global/en/home/products/energy/power-generation/generators/sgen-2000p.html#!/ Syed A Rizvi ENS 436, Department of Engineering and Environment Science 4

Transformer A transformer is an electrical device that is used to raise or lower the voltage (or current) level. A single-phase transformer has two electrically isolated windings, which are magnetically coupled through a common ferromagnetic core. The winding that is connected to the electrical power source is called the primary winding. The winding that is used to draw electrical power is called the secondary winding. AC power from the primary winding to the secondary winding is transferred through the shared magnetic field (Faraday s Law of EMI). Syed A Rizvi ENS 436, Department of Engineering and Environment Science 5

Syed A Rizvi ENS 436, Department of Engineering and Environment Science 6

Motor It transfers electrical energy into mechanical energy. The energy transfer happens through interacting magnetic fields. Motors and generators perform similar functions (transforming one form of energy to another) with the role of inputs/outputs interchanged. Therefore, some motors can be used as generators or vice versa (synchronous motors/generators-synchronous machines). There are several kinds of motors based on the input power (AC or DC) as well as the specific methodology used for energy transfer. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 7

Syed A Rizvi ENS 436, Department of Engineering and Environment Science 8

Motor/Generator Key Components Stator Rotor Syed A Rizvi ENS 436, Department of Engineering and Environment Science 9

Motor/Generator Key Components Slip rings Brushes Syed A Rizvi ENS 436, Department of Engineering and Environment Science 10

AC Motors All AC motors are based on a rotating magnetic field generated in the stator of the motor through standard three phase windings or split phase winding in case of single phase motors. A second magnetic field is created through the rotor windings either: Explicitly supplying a DC current or By induced voltage (current) through the transformer action when the stator windings are powered up by an AC source. A torque is then produced causing the rotor to rotate when the poles of the rotor s magnetic field attempt to align with the rotating opposite poles of the stator s magnetic field. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 11

AC Motors (Continued) Synchronous (three phase) The magnetic field in the rotor is established by a separate DC source (external or on-board). External DC source for field current requires slip rings and brusheshigher maintenance costs. Speed in synch with the frequency of the AC supply Provides constant speed for varying load conditions Low starting torque Two types: Salient pole Non-salient pole Syed A Rizvi ENS 436, Department of Engineering and Environment Science 12

AC Motors (Continued) Induction (single or three-phase) The magnetic field in the rotor is established by the induced voltage (current) in the rotor conductors due to the time varying magnetic field of the stator windings. Maximum speed could approach synchronous speed Speed regulation under varying load condition is not trivial Emerging application: Electric cars Two types Squirrel-cage Wound rotor Syed A Rizvi ENS 436, Department of Engineering and Environment Science 13

DC Motors Conventional (Brushed) Stator is wound to provide an electromagnet. Conductors are placed in the rotor s slots. Current is supplied to the rotor conductors through slip rings and brushes. The stator s magnetic field exerts a force on the current carrying conductors (governed by Faraday s Law of EMI) causing the rotor to rotate. The direction of the current through the rotor conductors is maintained during the rotation through a mechanism called commutation. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 14

DC Motors-Conventional (Continued) Wear and tear in slip ring/brushes reduces efficiency and increases maintenance costs. Very high starting torque and relatively simple speed regulation still keeps it among the top candidates for very heavy loads (locomotive, ship propellers etc.). Three types Shunt Series Compound Syed A Rizvi ENS 436, Department of Engineering and Environment Science 15

DC Motors-Conventional (Continued) Reduced efficiency and increased maintenance costs due to wear and tear in slip ring/brushes make them a less attractive choice for electric cars. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 16

DC Motors-Brushless Brushless DC motors use permanent magnets in the rotors to eliminate slip ring/brushes mechanism entirely; however it require a more complex way to power up the stator winding for creating a rotary motion in the rotor. Brushless DC motor can be considered a synchronous motor with permanent magnets in the rotor. Currently, brushless DC motors are the top choice for the electric cars. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 17

Why Study Electrical Machines Now? Need to bring the outdated power infrastructure to 21rst century. Electric vehicles (EV)-the future of transportation Automotive industry has been using IC engines for 140 years. But the planet will run out of oil reserves in about 53 year. EV is the future. Projection: by 2050, 65-75% of light duty trucks will be EVs. Currently, automotive industry is using brushless DC (BLDC) and AC induction motors in EVs. Broad range of EVs will push the need for improved efficiency and speed control under varying load conditions of the electric motors to new limits. Competition spurs innovation. Syed A Rizvi ENS 436, Department of Engineering and Environment Science 18