Lecture 5 - Electrical Power & You PDF

Electrical Power & You IM 115 – Basic Electricity for the Industrial Technician Energy ◼ Definition – Energy (w) is the fundamental ability to do work  energy is measured in joules (J)  the joule is a very small unit of energy Power ◼ Definition – Power (P) is...

Electrical Power & You IM 115 – Basic Electricity for the Industrial Technician Energy ◼ Definition – Energy (w) is the fundamental ability to do work  energy is measured in joules (J)  the joule is a very small unit of energy Power ◼ Definition – Power (P) is the rate at which energy is used  power is energy per time  P= t  Watts ◼ Electrical power is measured in watts (W)  one watt is the amount of power when one joule of energy is used in one second  a watt is a fairly small unit of power ◼ a “standard” light bulb is 60W  in other applications the watt may be a very large (relatively) unit of power and we may see ◼ kilo watts – kW or mega watts - mW Power ◼ With electrical utilities, kilowatts (kW) or megawatts (MW) are common  these units are common measuring units for the power levels being used by large manufacturing facilities or cities. ◼ If we use power in large quantities we need a unit for energy that is much larger than the joule Energy ◼ Since power is energy per time – we can define energy as power  time  P=   = Pt t  the power utility sells energy in kilowatt-hours  Using Voltage and Current I=2A + 20 V - P = V  I = 20V  2 A = 40W This is the power formula we will use for IM 115 Solving the Power Equation ◼ A heater is plugged into a 120V outlet and draws 8.33 amps of current – how much power does the heater consume? P =V x I P = 120 x 8.33 = 1000 watts Solving the Power Equation ◼ A 10W light bulb in a flashlight is run by a 9V battery–how much current does it draw? P P =V I  I = V 10W I= = 1.11A 9V kilo Watt hours ◼ The power company sells power by the kilo Watt hour – kWh ◼ 1 kWh = 1000 Wh A combination of power over a period of time. A load uses a given power (watts) for a certain amount of time. 40 watts x 200 hours = 8000 Wh 8000 Wh ÷1000 = 8 kWh Wattmeter ◼ Measures in kilowatt hours ◼ One kilowatt hour  100 W light bulb for 10 hours  5000 W dryer for 12 minutes ◼ On a house meter, separate dials read the 10k, 1k, 100, 10 and 1 kW  Wattmeter ◼ The voltage and current cause the disc to turn as if it were a small motor  Wattmeter ◼ 1st is 17,650 ◼ 2nd is 18,349 ◼ Difference is 18349 – 17650 = 699 k Wh Digital kWh meter The kilowatt-hour ◼ 60 W light bulb on for 8 hours ◼ How many kWh’s will be consumed? W = P  t = 60W  8 h = 480Wh = 0.480 kWh ◼ To go from Wh to kWh, divide by 1000  The kilowatt-hour ◼ A water pump motor uses 800 W of power. It runs 1/2 minute each time it charges the water tank and runs about 40 times a day. How much will it cost to run this pump monthly if power is purchased at $0.22 per kWH (22 cents per kWh)?.5 𝑚𝑖𝑛𝑢𝑡𝑒 𝑥 40 = 20 𝑚𝑖𝑛𝑢𝑡𝑒𝑠 𝑎 𝑑𝑎𝑦 𝑜𝑟.33 ℎ𝑜𝑢𝑟𝑠 800𝑊 𝑥.33 ℎ𝑜𝑢𝑟𝑠 = 264 𝑊ℎ 𝑥 30 𝑑𝑎𝑦𝑠 = 7920 𝑊ℎ 7920 𝑊ℎ ÷ 1000 = 7.92 𝑘𝑊ℎ 7.92 𝑘𝑊ℎ 𝑥.22 𝑐𝑒𝑛𝑡𝑠 = $1.74 Batteries ◼ Unlike power supplies from the grid, the energy available from a battery is not unlimited ◼ The battery is also not able to produce a variety of voltages – the voltage is fixed by the number of cells and cell make-up ◼ Therefore, a “simpler” energy capacity measurement is used for batteries Ampere-hour Ratings ◼ The ampere-hour rating is a measure of how much current the battery can provide for how long  i.e. 2A for 5 hours => 10 Ah ◼ The battery should also have a rated current level – if you exceed the current level, you may not be able to extract as much energy Ampere-hour Ratings ◼ A battery is rated at 20 Ah @ 5 A  it should produce: ◼ 5A for 4 hours ◼ 1A for 20 hours ◼ ¼ A for 80 hours  it will probably not produce: ◼ 6A for 3.33 hours ◼ 10A for 2 hours Ampere-hour Ratings ◼ If a battery is rated at 300 AH @.5 A, how long can it provide.35 A of current flow? ◼ 300 AH =.35 A * (X hours) ◼ X hours = 300 AH /.35 A = 857 hours Energy ◼ Why do we need electrical energy?  Lighting  Cooking  Heating  Cooling  Pumping  Miscellaneous ◼ These are all “loads” An Average Household Energy Usage ◼ 500 kWh per month ◼ 500 kWh × $.16 /kWh = $80 month ◼ 500 kWh ÷ 30 ÷ 24) = 69 W per hour ◼ Cheap energy is easy to waste ◼ Expensive energy requires more thought and consideration about consumption Load Shifting ◼ Power some loads with systems other than electricity  Electric range ◼ Gas or wood  Electric refrigerator ◼ gas  Electric heat ◼ Gas, wood, solar thermal or geothermal  Electric Clothes Dryer ◼ Gas, fresh air  Dishwasher ◼ Elbow grease Wattage ◼ Operating Watts ◼ P=V×I ◼ Understand operating times of loads that have a duty cycle  Duty cycle = time on ÷ given time increment  20 minutes ÷ 60 minutes =.333 × 100 = 33% Phantom Loads ◼ “unseen loads”  Clock radios  DVD players  Television sets  Bunn coffee makers  Cable boxes  Cordless phones ◼ Any small charger In-rush Wattage ◼ Most inductive loads (motors or coils) have large currents associated with start-up  Usually from 3 to 10 times “run-current”  The same increase to current will increase the required startup wattage  This spike is usually very short (seconds)  The system must be able to deliver the required current level