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Download Power Delivery Basics Presentation, December 3, 2009
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Salt Lake Electrical Plan Task Force December, 2009 Power Delivery Basics 1 Voltage & Current V=IxR Voltage (volts) = Current (amps) x Resistance (ohms) – Voltage is a measure of electrical “pressure.” Think of voltage (V) as water pressure in a hose. The pressure at the source is greater than the pressure at the outlet. The pressure at the end of a 500’ hose is less than the pressure at the end of a 50’ hose. – Think of resistance (R) as being like the friction inside the hose 2 Voltage & Current – Current (I) is the movement of electrons through a conductor, measured in amperes or amps. Current is analogous to flow in a hose (gallons) A 1” diameter hose can provide more flow than a 5/8” diameter hose 3 Power P=VxI Power (volt-amperes) = Voltage (volts) x Current (amps) Power has two components: Watts, Vars For our discussion we will only use Watts Power (watts) = Current (amps) x Voltage (volts) 4 Power – The basic unit of measure for power is the watt (W) 1,000 watts = 1 kilowatt = 1 kW 1,000,000 watts = 1 megawatt = 1 MW – The maximum amount of power a transmission line can carry is referred to as capacity. Capacity is a function of the voltage and the wire size. P=VxI The higher the voltage, the more power a line can carry. The higher the current (the larger the wire – or conductor), the more power a line can carry. 5 Quick Quiz 1. Which conductor can carry the most power? A. B. 2. For the conductor in figure B above, which voltage can provide the most power? A. 46,000 volts (46 kV) B. 138,000 volts (138 kV) P (power) = V (volts) x I (amps) 6 Energy Energy is the measure of power used over time. The basic unit of measure for electrical energy is the watt-hour. 1,000 watt-hours = 1 kilowatt-hour = 1 kWh 1,000,000 watt-hours = 1 megawatt-hour = 1 MWh Your power bill at home shows energy usage in kilowatt-hours (kWh). A 100 watt light bulb operated for 10 hours uses 1,000 watthours or 1 kWh. That would cost about 8 cents. Average Utah residential customer uses 800 kWh per month 7 Capacity versus Energy – An electrical system is designed to provide: Capacity (kW) Energy (kWh) – Capacity is the maximum amount of electricity a line (or other electrical equipment) can carry at any instant. The electrical system must have the capacity to serve the demand placed on it by the customer(s) at any given time. Typically the peak demand for Wasatch and Summit counties occurs in the winter. – Energy describes the flow of power over a period of time. 8 Highway Analogy – Draw a line across a highway. – In one direction, only one car can cross this line at a time. So the capacity of the highway at any instant is one car. – This is like the capacity of a wire measured in kilowatts. 9 Highway Analogy – If we add time to the equation and a total of 500 cars that cross the line in one hour, we can say we have accommodated 500 carhours. – If 500 cars per hour cross the line for two hours we have 1,000 car-hours. – This is analogous to kilowatt-hours of energy. – When more people need to travel the highway we must increase the number of lanes to accommodate additional traffic = $$$. 10 Load Growth – As customer demand grows, Rocky Mountain Power can: 1. Increase system capacity to provide more power New lines and substations Increase capacity of existing facilities where possible 2. Decrease load during peak hours so less capacity is needed. This is called demand response/control. 3. Decrease load via energy efficiency. – Rocky Mountain Power uses all three options 11 Power Delivery and Utility Components 12 Power Delivery and Utility Components Substations – A substation transforms or changes voltage levels and contains equipment to protect utility components. – Substations can contain the following: Transformers – cell phone chargers contain transformers Switches – think of light switches in your house Circuit breakers – think of the circuit breakers in your house – Substations do not generate power 13 Power Delivery and Utility Components Substations – Major substations: Convert power from high voltage transmission lines (230 kV, 345 kV) to sub-transmission voltages (46 kV, 138 kV) – Regional substations: Convert power from sub-transmission lines (46 kV, 138 kV) to other sub-transmission voltages and distribution voltages (12.5 kV, 25 kV) – Local substations: Convert power from sub-transmission lines (46 kV, 138 kV) to distribution voltages (12.5 kV, 25 kV) When local substations are added, we must ensure there is capacity at regional and major substations as well. 14 Major substation Legend Regional substation 345 kV 138 kV 46 kV 12.5 kV Local substation Local substation Power Delivery and Utility Components Transmission Lines (Main Grid) Energy is transmitted via high voltage lines (230kV, 345kV) from the power generators to major substations High voltage is used for long distance, bulk energy transmission. High voltage transmission lines are to electricity as an interstate freeway is to transportation. There are few off-ramps or exits (substations). 16 Legend 345 kV 138 kV 46 kV 12.5 kV Main Grid Transmission Lines = Freeways Power Delivery and Utility Components Sub-transmission Lines (Local Transmission) – Sub-transmission voltages – 46 kV and 138 kV. – Used to transmit energy from major substations to regional and local substations. – Sub-transmission = state highway or arterial road 18 Local Transmission = 4 Lane Hwy Legend 345 kV 138 kV 46 kV 12.5 kV Lower Voltage Local Transmission = 2 Lane Hwy Main Grid = Freeway Power Delivery and Utility Components Distribution Lines (Feeders or Circuits) – Distribution voltages range from 7.2 kV to 25 kV. – These lines deliver electricity to your neighborhood. – Distribution line = residential street – Delivery (residential, commercial) voltages range from 120 V to 480 V. – Transformed to residential voltage by transformers in the neighborhood – Service drop = driveway 20 Local Transmission = 4 Lane Hwy Legend 345 kV 138 kV 46 kV 12.5 kV Local Transmission = 2 Lane Hwy Main Grid = Freeway Distribution = Surface Streets