Tutorial onPower Distribution

Circuits

G. Heydt

Arizona State University

March, 2003

What is power distribution?Power systems are made up of:• Generation• Transmission• Distribution

Generation systems are the large generating units that produce AC voltages at high power levels. Transmission systems are long distance, very high power level systems to transmit power from city to city. Distribution systems are local, lower power systems that take power from the intercity grid and bring this to residences, commercial customers, and industrials

Typical numbers

Generation Transmis-sion

Distribution

Typicalvoltages

35 kV 345 kV 15 kV

Typicalpower

800 MW 800 MW 1 MW

Typical size In a powerplant

Inter-city,200 km

Local inneighbor-

hood, 5 km

Typical configurations

Transmission systems are NETWORKED usually. That is there are many loads and many sources, and many lines that join these points in a mesh, networked fashion.

FLAGSTAFF

PRESCOTT

PHOENIX

TEMPE

NOGALES

WINSLOW

HOLBROOK

Typical configurationsTransmission systems are networked so that power can be delivered between load centers by several routes. If a line is removed from service, power can be rerouted. Like power delivered to Nogales from Flagstaff by two different routes.

FLAGSTAFF

PRESCOTT

PHOENIX

TEMPE

NOGALES

WINSLOW

HOLBROOK

Distribution systems

Distribution system configuration is usually different -- rather than being networked, distributuin systems are usually RADIAL. That means lines go from A to B to C to D to ...

RURAL RD PRICE RD MESA-W MESA-C MAIN ST

Distribution systems

Power can only flow in one direction in the radial system

RURAL RD PRICE RD MESA-W MESA-C MAIN ST

Distribution systems

Why is this configuration used?• Safety (only one source direction - when it

is interrupted, the line is dead)• Cost -- it is cheaper• Easy to locate problems

RURAL RD PRICE RD MESA-W MESA-C MAIN ST

But there are advantages of reliability of networked systems - provided cost, safety, control, and maintenance issues can be resolved.

A TYPICAL RADIAL

DISTRIBUTION SYSTEM

Research and study areas• The reliability vs cost of networked

systems versus radial systems

• Use of networked systems (they do this in big cities like Chicago and New York)

• Control of power in a networked distribution system

Deployment of distribution components,multiple feeds, and over-capacity

Cost

INVESTMENT COST

COST OF SERVICEINTERRUPTIONS ANDLOSS OF PRODUCTIVITY

TOTAL COST

Directed reading

Some easy to read texts on distribution engineering:

Acknowledgements

• To my colleagues and students who are working on the project

• To Dr. Momoh at the NSF

• To the staff at ONR for their input