January 21, 2016
ECE 498HZ: Power Distribution
System Analysis
Lecture 2: Introduction to Distribution Systems
Hao Zhu
Dept. of Electrical & Computer Engineering
University of Illinois, Urbana-Champaign
haozhu@illinois.edu
Announcements / Re-cap
 Lecture notes will be uploaded, but I will also use the board
 Midterm tentatively scheduled on Thursday, March 31 (in class)
 Course tour: Ameren TAC
 Anatomy of a distribution system https://youtu.be/fQNQKkvGQL0
 Why multiple regions or markets for the power grid?
2
Growth of electricity generation
 Growth of fuels used to produce electricity in US reflects growth of
loads from 1950 to 2015 (units: Billion Kilowatthours)
– Footnote a: Conventional hydroelectric power, wood, waste,
geothermal, solar/PV, and wind
[Source: EIA, Monthly Energy Review, Dec. 2015, Fig. 7.2]
3
Illinois utility companies
 Ameren Illinois
– Serving central and south Illinois
– Part of the Mid-continent Independent System Operator (MISO)
 Comed
– Serving Chicago and Northern Illinois
– Part of PJM Interconnection (since May 2004), interconnected with
American Electric Power (AEP) at Ohio
 Also municipal and co-ops
4
Illinois electricity profile
5
Substations
 It can be fed by multiple subtransmission lines or directly from
HV line
 Serve one or more primary feeders
 Components
– switching
– voltage transformation
– voltage regulation
– protection
– metering
[Kersting’s, Fig. 1.2]
6
Switches
 Manual switches at substations & feeders
– Usually no controls/communication
– Not designed to isolate a fault current
– Use to isolate equipment for maintenance,
or change topology of network
 Remote controlled switches
– Controlled through signals sent by SCADA
system
Photo courtesy of Kevin
Schneider (PNNL)
7
Disconnect switches
Photo courtesy of Ian Dobson (Iowa State Univ.)
8
Protection devices
 Circuit breakers: like switches
 Fuses: low-cost thermal device
 Relays: measure current & voltage
and generate control signals for
circuit breakers
 Reclosers: “advanced” circuit
breakers designed to minimize the
number of customers affected by
temporary faults
 Sectionalizers: used in conjunction
with a rescloser to “sectionalize” the
feeder.
Photo courtesy of
Ian Dobson (Iowa
State Univ.)
9
Breaker-and-a-half scheme
[Kersting’s, Fig. 1.3]
10
Voltage transformers
 Steps voltage down to the
distribution voltage level,
household level
 3-phase, or single-phase
 Voltage issues are much more
important than frequency issues in
distribution systems!!
11
Load tap changer (LTC)
 A selector switch device attached to
transformers
 To maintain a constant low-side or
secondary voltage with a variable
primary voltage supply
 Or to hold a constant voltage out
along the feeders on the low-voltage
side for varying load conditions
 Also termed as tap changing under
load (TCUL) transformers
"Tap changing switch" by
BillC at English Wikipedia
12
[Gonen’s book, 2014]
Voltage regulators and capacitors
 Voltage regulators: induction devices in shunt or series with
regulated circuit for the control of its voltage
 Capacitors: perform power factor correction with additional
switching and protective elements
13
[Gonen’s book, 2014]
Radial feeders











[Kersting’s, Fig. 1.4]
Primary “main” feeder
Laterals
a, b, c phases
3, V, 1-phase connections
Voltage regulators
Delta-Wye transformers
Shunt capacitor banks
Transformers
Secondaries
Protection devices
Loads
14
Distribution feeder map
 Lines (overhead and underground)
– Distances, conductor sizes, phasing
 Distribution and in-line transformers
– kVA rating, phase connection
 Shunt capacitors
– kVAR rating, phase connection
 Voltage regulators
– Phase connection, type (3-, 1-phase)
 Switches
– normal open/close status
123-bus feeder
[Kersting’s Fig. 1.5]
15
Electrical characteristics
 Overhead and underground spacing
 Conductor tables
– Radius, diameter, resistance
 Voltage regulators
– Ratios, compensator settings
 Transformers
– Voltage ratings, impedance (R+jX)
– No-load power loss
 Use all the information to obtain the
feeder representation (the “one-line”
diagram)
123-bus feeder
[Kersting’s Fig. 1.5]
16