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The Electric System

• Generation– Production

• Transmission– Bulk Transport– Wholesale

• Distribution– Delivery– Retail Distribution

AC Generators

• Magnetic Induction– When a magnetic

field is moved in close proximity to a conductor, an emf is produced which forces some electrons to move.

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1 Phase AC• Peak Voltage vs RMS Voltage• Frequency (Hertz or Cycles/Second)

-200

-150

-100

-50

0

50

100

150

200 Vo

ltage

0.0000 0.0083 0.0167 0.0250 Time (Seconds)

60 Cycle Sine Wave

3 Phase AC

-200

-100

0

100

200

Volta

ge

0 0.005 0.01 0.015 0.02 0.025 0.03 Time (seconds)

3 Phase - 60 Cycle Sine Waves

Phase A Phase B Phase C

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What Happens Once it’s Generated?

• Delivery!!!!!!– Station Transformers– Transmission System

• Lines & Substations

– Distribution System• Lines & Substations

– Electrical Services• Transformers, Metering, Circuits, and Loads

Station Transformers

• Step-Up Transformers• Raise voltage from

generator to transmission level.

• Reduce amperage from generator to a lower level.

4

Station Transformers

• Magnetic Induction– Primary Coils– Secondary Coils– Iron Core

• Ratio of Secondary to Primary Coils determines voltage output.

Switchyard

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Transmission Lines• Any line with voltage higher than 39 kV.• Carry large amounts of bulk power long distances.• Common Industry Voltages:

– 60, 69, 115, 138, 230, 345, 500 kV• The higher the voltage, the more power the line can generally carry

a longer distance.

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Transmission Characteristics

• Bigger capacity is cheaper per unit.• Underground 10 times more expensive than

overhead• Siting is difficult (no federal right of

eminent domain)

Transmission Substations

• Interconnect/tie the transmission lines together or to transmission lines owned by other entities.– Buy & Sell Power– Emergency Power– Backup Feeds for Reliability

• Some large industrial customers may own their own transmission subs.

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North American Electric Grids

• East• West• Mexico• Quebec• Texas

Distribution System• Lower transmission voltage

to distribution voltage for delivery up and down streets, alleys and roads.

• Distribution voltage is less than 39 kV.

• More economical to build than transmission lines.

• Relatively easy to site.• Large exposure creates

reliability and power quality issues.

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Distribution Lines

• Fan out from the substation to “distribute” power to the users.

• Overhead vs Underground

• Three Phase Distribution– Wye Distribution– Delta Distribution

• Single Phase Feeders/Taps

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3Phase vs Single Phase

Services• Most customers

generally don’t want distribution voltage in their facilities.

• Distribution voltage is lowered to service voltage at the “Service”

• Transformers are used to step-down voltage from distribution levels to lower service voltages.