**Electric Power Distribution, Generators and Motors ** Benchmark Companies Inc PO Box 473768 Aurora CO 80047

**Electric Power Distribution, **

**New ideas for today** • Magnetic induction • Lenz’s law • Transformers and power transmission • Motors and Generators

**Observations about Power Distribution** Household power is AC (alternating current) Power comes in voltages like 120V & 240V

**Observations about Power Distribution** Power is transmitted at “high voltage” like 500KV

**Observations about Power Distribution** Power transformers are visible everywhere

**Observations about Power Distribution** Power substations are visible on occasion

**Power Consumption in wires** • Reminder: power consumption = current x voltage dropIxV voltage drop = resistance x current IxR power consumption= resistance x current2 I2xR • Impact of the calculation: Wires waste power as heat Doubling current quadruples wasted power

**Power Consumption in wires** • Example: Resistance of 1 mile of power line is 10 Ohms. • Determine the voltage drop across the power line if 200 Amps is transmitted at 240 Volts to power one typical house. The Power consumed across 1 mile is I2xR = 200A2x10 = 400KW is needed before we can begin to deliver power to a typical house.

**DC** AC Edison Tesla Westinghouse

**DC= “direct current”** AC=“alternating current” DC vs AC a visual approach DC can supply power . So can AC For transmission AC is superior

**DC= “direct current”** AC = alternating current Let’s explore why…… AC=“alternating current” Rotation Amplitude Amplitude/Time

**AC = alternating current** As a conductor is rotated within a magnetic field alternating current is produced in that conductor Rotation within a magnetic field Amplitude Current Amplitude vs. time 0o 90o 180o 270o 360o 90o 0o 180o Positive Amplitude P N Negative Amplitude 360o 270o Time

**Power Transmission** • For efficient power transmission: • Use low-resistance wires (thick, short copper) • Use low current and high voltage drop • Can accomplish this with AC (alternating current) power transmission.

**Click for Bar Magnet ** And Pick-up coil example

**Electromagnetic Induction** Changing magnetic field produces an electric field

**Electromagnetic Induction** Current in a conductor produces a magnetic field

**Electromagnetic Induction** An Induced magnetic field opposes the original magnetic field change (Lenz’s law)

**Lenz’s Law**

**Electromagnet ** Transformer Example

**Transformer** • Alternating current in one circuit induces an alternating current in a second circuit • Transfers power between the two circuits • Doesn’t transfer charge between the two circuits

**Transformer on fire**

**Transformers** • Power arriving in the primary circuit must equal power leaving the secondary circuit • Power = current x voltage • A transformer can change the voltage and current while keeping the power unchanged!

**Step Down Transformer** • Fewer turns in secondary circuit so charge is pushed a shorter distance • Smaller voltage rise • A larger current at low voltage flows in thesecondary circuit

**Step Up Transformer** • More turns in secondary circuit so charge is pushed a longer distance • Larger voltage rise • A smaller current at high voltage flows in the secondary circuit

**Observations about Electric Generators and Motors** • A generator provides electric power • A generator requires a mechanical power • A motor provides mechanical power • A motor requires electric power Alternator

**Click me**

**Electric Generator** Rotating magnet • makes changing magnetic field • induces AC current in the loop Converts mechanical power into electrical power

**Electric Motor** Input AC power • AC current makes changing magnetic field • causes magnet to turn Converts electrical power into mechanical power A motor is a generator run backwards !

**End of Presentation**