3 gentrandist lecture.325

7/29/2019 3 GenTranDist Lecture.325

1/18

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.


2/18

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


3/18

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.


4/18

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


5/18

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.


6/18

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


7/18

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


8/18

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


9/18

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


10/18

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.


11/18

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


12/18

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


13/18

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


14/18

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


15/18

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


16/18

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.


17/18

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.


18/18

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.

3 gentrandist lecture.325

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