Post on 05-Sep-2014
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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.
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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.