Download - 3 GenTranDist Lecture.325
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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
Voltage
0.0000 0.0083 0.0167 0.0250
Time (Seconds)
60 Cycle Sine Wave
3 Phase AC
-200
-100
0
100
200
Voltage
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 its
Generated? Delivery!!!!!!
Station Transformers
Transmission System
Lines & Substations
Distribution System
Lines & Substations
Electrical Services Transformers, Metering, Circuits, and Loads
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 Substations Interconnect/tie the transmission lines
together or to transmission lines owned byother entities.
Buy & Sell Power
Emergency Power
Backup Feeds for Reliability
Some large industrial customers may owntheir own transmission subs.
North American Electric Grids
East
West
Mexico
Quebec
Texas
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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 thesubstation todistribute power tothe users.
Overhead vsUnderground
Three PhaseDistribution Wye Distribution
Delta Distribution Single Phase
Feeders/Taps
3Phase vs Single Phase
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Services
Most customersgenerally dontwant distributionvoltage in theirfacilities.
Distributionvoltage is loweredto service voltageat the Service
Transformers areused to step-down
voltage fromdistribution levelsto lower servicevoltages.
Transformers
Magnetic Induction
Primary Coils
Secondary Coils
Iron Core
Ratio of Secondary
to Primary Coilsdetermines voltage
output.
Watts=Volts*Amps
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Transformers
Step-Up Transformers
Raise voltage from line
to load side.
Reduce amperage from
line to load side.
Step-Down
Transformers
Do the opposite.
Services
Primary Service vsSecondary Service
Overhead vs Underground
Common Service Types Three Phase
Wye
Closed
Open
Delta
Corner Grounded
Center Tapped
Open
Single Phase
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Three Phase Service
Wye
Delta
Corner Grounded
Center Tapped
Open
Wye Service Customers needing three
phase for some equipment
and also having large
amounts of single phase load
Many small commercial &
industrial buildings
208/120 Wye
208 3 phase
120 single phase
480/277 Wye
480 three phase
277 single phase
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3 Phase Wye System
3 wires connect all at a
common point which
is grounded.
End points become the
connection points for
the 3 phases.
Y system wye
2 separate voltages Phase to Phase
Phase to Ground
208/120 Wye
Smaller customers
requiring mostly
single phase and
some 3 phase.
480 volt services
are more
economical forlarger motor loads.
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480/277 Wye
Voltages
480 volts phase to phase
277 volts phase to ground
Requires step down
transformer to produce
120 volts for receptacles
277 volt lighting fixtures
are available
3 Phase Delta Systems Generally built to areas with
mostly 3 phase load and notmuch single phase load. (oilpumping, irrigation, etc.)
Advantages: Expense of one lesswire to build and maintain.
Disadvantage: Unbalancedvoltages from amounts of singlephase load.
Phases connected end to end
Each phase relies on the sharingof one wire as a supply and returnpath for the others.
Voltage the same between any 2wires
Popular for ungroundedsystems
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Center-Tapped Delta
Customers with mostlythree phase equipment andvery little single phaseequipment. Manufacturing &
processing facilities
240/120 CT Delta Smaller 3 Phase Services
with mostly 3 phase load.
240 three phase
120 single phase
480/240 CT Delta
Larger 3 Phase Serviceswith mostly 3 phase load.
480 three phase 240 single phase
High or Wild Leg
A
BC
G
Neutral Wire
Corner Grounded Delta
240 or 480 volts.
Usually only for 3
Phase Motor/Pumping
Load.
Oil Pumps
Irrigation Pumps Municipal Water
A
B
C
G
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Open Delta
Uses only 2transformers
Often from a V-Phase DistributionLine.
Wye with 2Phases and aNeutral.
Less Expensive
Light 3 Phase
Open Wye Primary to Open Delta Secondary
ACN
abc
n
H2H1H1 H2
X1
X2
X3 X1X2
X3
3 Phase 4 Wire Open Delta Secondary: 120/240, 240/480, etc for lights and power
Open Wye (V Phase) Primary
Single Phase Service
120/240 volt service.
Neutral attached to
center bushing in
transformer.
120 volts Hot to
Neutral
240 volts Hot to Hot
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Single Phase from
3 Phase Systems
Individual single phase
loads can be connected and
balanced to resemble a 3
phase load.
Voltages will be different
in Wye & Delta systems
If not balanced, voltageunbalances will result.
Secondary System
Transformer
Service Drop
Meter Loop
Meter
Ground Rod
Main Breaker Box
Circuits
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Service Drop
Overhead:
Service Drop
Underground:
Service Lateral
Three Phase:
3 or 4 wires
Single Phase:
2 or 3 wires
Triplex Quadraplex
Meter Loop
A Meter Loop is
comprised of:
Weatherhead
Service Mast/Riser
Meter Base/Can
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Meter
The Cash Register
Owned by Utility
Installed in customers
equipment.
Main Disconnect Today, electrical
codes require sometype of disconnectdevice (switch) to shutoff all the circuitssupplied by thedisconnect.
Usually a MainBreaker in the
breaker box. Older or larger
facilities may haveMain Disconnectsrather than mainbreakers.
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Ground Wire/Rod
Most electrical systems in North
America are grounded for safety
and lightning protection.
Their is generally a ground
wire/rod at the:
Service transformers.
Meter Base
Breaker Box
Formal Names: Grounding System Conductor (wire)
Grounding System Electrode (rod)
Breaker/Fuse Box
Formally called the
Service Entrance Panel
Provides a location for
breakers or fuses to
protect the individual
circuits in the facility.
Some larger customers
have Sub-panels which
contain breakers and
fuses.
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Circuits Feeders
circuits supplying servicesor sub-panels.
the service drop is afeeder.
Branch Circuits Individual Branch Circuit
Circuit to one piece ofequipment
Appliance Branch Circuit.
Circuit to several fixedappliances
Lighting Branch Circuit
Circuit supplying onlylighting fixtures.
General Purpose BranchCircuit
Circuit to receptacles andlights.