Lecture 11 Electrical Networks 1

Lecture 12 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 13 ELECTRIC CIRCUIT IS AN INTERCONNECTION OF ELECTRICAL COMPONENTS TYPICAL LINEAR IRCUIT

Lecture 14 Objectives To analysis, design and measurement of linear analog electrical network systems across engineering disciplines and within subdisciplines of Electrical Engineering.

5 Lecture 1 EE Subdisciplines

Lecture 16 EE Subdisciplines Power Electromagnetics Communication/Signal Processing Digital Controls Solid State

Lecture 17 Power Generation of electrical energy Storage of electrical energy Distribution of electrical energy Rotating machinery-generators, motors

Lecture 18 Electromagnetics Propagation of electromagnetic energy Antennas Very high frequency signals ~ 10 8 Hz Fiber optics ~ 1G b/s

Lecture 19 Communications/Signal Proc. Transmission of information electrically and optically Modification of signals –enhancement –compression –noise reduction –filtering

Lecture 110 Digital Digital (ones and zeros) signals and hardware Computer architectures Embedded computer systems –Microprocessors –Microcontrollers –DSP chips

Lecture 111 Controls Changing system inputs to obtain desired outputs Feedback Stability

Lecture 112 Solid State Devices –Transistors –Diodes (LED’s, Laser diodes) –Photodetectors Miniaturization of electrical devices Integration of many devices on a single chip (VLSI)

13 Lecture 1 Electric Power

Lecture 114 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 115 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 116 Electric Load 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 Intermediate load Peak load P_max Base load (large thermal and nuclear plants) Intermediate loads (medium steam and hydro) Peak load (gas turbine and combined cycle plants) Typical Daily Load Curve

Lecture 117 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 118

Lecture 119 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 kV 2) The main transformer increases the voltage to 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 120 Electrical Power Transmission 4) The high voltage substation reduces the voltage to 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 ( 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 121 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 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 122 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 123 Motion to Electricity When magnets are moved near a wire, an electric current is generated in that wire.

Lecture 124 Steam Turbine

Lecture 125 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 126 Generating Station

Lecture 127 Transmission Lines 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)

Lecture 128 AC versus DC 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.

Lecture 129 Why do we use AC for power transmission? Power levels correspond to V 2. 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 130 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 131 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.