Electrical Networks 1

1. Electrical Networks 1 Lecture 1

2. A Question • Can you point out different types of electrical or electronic equipments, devices in this classroom? • What about if we are not able to use them, because of no electrical power? Lecture 1

3. TYPICAL LINEARIRCUIT ELECTRIC CIRCUIT IS AN INTERCONNECTION OF ELECTRICAL COMPONENTS Lecture 1

4. Objectives • To analysis, design and measurement of linear analog electrical network systems across engineering disciplines and within subdisciplines of Electrical Engineering. Lecture 1

5. EE Subdisciplines Lecture 1

6. EE Subdisciplines • Power • Electromagnetics • Communication/Signal Processing • Digital • Controls • Solid State Lecture 1

7. Power • Generation of electrical energy • Storage of electrical energy • Distribution of electrical energy • Rotating machinery-generators, motors Lecture 1

8. Electromagnetics • Propagation of electromagnetic energy • Antennas • Very high frequency signals ~ 108 Hz • Fiber optics ~ 1G b/s Lecture 1

9. Communications/Signal Proc. • Transmission of information electrically and optically • Modification of signals • enhancement • compression • noise reduction • filtering Lecture 1

10. Digital • Digital (ones and zeros) signals and hardware • Computer architectures • Embedded computer systems • Microprocessors • Microcontrollers • DSP chips Lecture 1

11. Controls • Changing system inputs to obtain desired outputs • Feedback • Stability Lecture 1

12. Solid State • Devices • Transistors • Diodes (LED’s, Laser diodes) • Photodetectors • Miniaturization of electrical devices • Integration of many devices on a single chip (VLSI) Lecture 1

13. Electric Power Lecture 1

14. The Electrical Power System • Power is one of the main subdisciplines of EE. • The power generation, transmission and distribution system is something we all use all the time. • It is an excellent example of a case where electrical networks are used to model the flow of energy. Lecture 1

15. Consider what we do here. • We usually generate a huge amount of power in a centralized location. • We ship it to you when you flip the switch • You then decide that you will light a desk lamp located 18 inches above your desk, about 2 feet in on the right. • You can easily change your mind and put the lamp on the left! • This is magic. Lecture 1

16. The load changes continuously Daily Seasonal The daily maximum occurs around 4-6 PM , the minimum at night. The load or demand is defined as the average load (MW) for 15 minutes Seasonal changes: Summer load is higher than the winter load in AZ. Base load (large thermal and nuclear plants) Intermediate loads (medium steam and hydro) Peak load (gas turbine and combined cycle plants) P_max Peak load Intermediate load Base load 0 6 12 18 24 Electric Load Typical Daily Load Curve Lecture 1

17. What to notice about what follows • We do NOT create energy out of nowhere. • Instead, we convert some form of energy. In a fossil power plant, chemical energy is converted to a mechanical motion of a rotating turbine and generator. The result is electric energy. Lecture 1

18. Lecture 1

19. Electrical Power Transmission 1) The generating station converts the energy of gas, oil, coal or nuclear fuel to electric energy. The generator voltage is around 15-25 kV 2) The main transformer increases the voltage to 230-765 kV. This reduces the current and losses. 3) The high voltage transmission line transports the energy from the generating station to the large loads, like towns. Example: Energy generated at Palo Verde is transported by 500 kV lines to Phoenix, San Diego, Los Angeles, Albuquerque and El Paso. Lecture 1

20. Electrical Power Transmission 4) The high voltage substation reduces the voltage to 120-69 kV. The substation serves as a node point for several lines. 5) The sub-transmission lines (69 kV-120 kV) connect the high voltage substation with the local distribution station. 6) Distribution lines (12 -15 kV) distribute the energy along streets or underground. Each line supplies several step down transformers distributed along the line. 7) The distribution transformer reduces the voltage to 230/115V, which supplies the houses, shopping centers etc.. Lecture 1

21. Generating Station Type of Generation stations • Thermal Power Plant. The large (more than 500 MVA) plants carry constant load (base load plant), Smaller plants loads are regulated but they operate continuously. Minimum down time is 20-35 hours. • Nuclear Power Plant. These plants carry constant load and are used as base loads plants. • Hydroelectric Plants. It is economically desirable to load these plants to the maximum capacity, because of the low energy cost. (Water is free). Other factors: flood control, irrigation and salmon migration. • Combined steam and Gas-Turbine Power Plants. High efficiency plants for variable load. • Gas-turbine. Peak load plants, high operating and low investment cost • Solar, Wind. Loaded to the maximum capacity, when sun or wind power available. Lecture 1

22. Hydro Power Plant • The water is stored in the lake, which is at higher ground (Lake Pleasant). • A canal and pipe system transfers the water to the power house. • The potential energy of the water is transformed to mechanical energy in the turbine. • The turbine drives the generator and converts the water mechanical energy to electrical energy. Lecture 1

23. Motion to Electricity When magnets are moved near a wire, an electric current is generated in that wire. Lecture 1

24. Steam Turbine Lecture 1

25. Steam Turbine • The moving blades are attached to the shaft. • The stationary blades are attached to the casing. • The control valves regulate the steam flow. • The turbine often has three stages: high, medium and low pressure (right to left) • The high pressure steam drives the turbine (3600rpm). • The generator is connected directly to the turbine shaft Lecture 1

26. Generating Station Lecture 1

27. Type of transmission lines: Extra high voltage lines 345 kV, 500 kV, 785 kV Interconnection between systems. (National Grid) High Voltage lines 120 kV, 220 kV Inter connection between substations. Sub-transmission lines 45 kV, 69 kV, 120 kV Substation and large customer Distribution Line 2.4 kV- 45 kV , 15 kV Supplies houses High Voltage DC lines 120 kV- 600 kV Interconnection between regions. (Oregon-California) Transmission Lines Lecture 1

28. AC is alternating current AC quantities always vary sinusoidally in time Usually, we will know the frequency and solve for the amplitude and phase. DC is direct current DC quantities are always constant in time. DC can not be directly transformed to lower or higher voltages. AC versus DC Lecture 1

29. Why do we use AC for power transmission? • Power levels correspond to V2. Therefore, to get a huge power out of Palo Verde, we need huge V’s. We need to step the voltage down before it reaches our classroom. The power company wants to do this in a lossless fashion. AC allows them to do this by using transformers. Lecture 1

30. Why Are There Three Conductors in Power Transmissions Lines? • Most AC power transmission systems have three conductors. • The voltage on each phase (referenced with respect to earth ground) is a sinusoid with a phase difference of 120 from the voltages in the other two phases. Lecture 1

31. Three Phase • A three conductor transmission system is called a three-phase system. • The power delivered by a three phase system (assuming a balanced load) is constant, even though the voltages in each phase vary sinusoidally. • Three phase systems are more efficient than single systems due to reduced power losses. Lecture 1