Transcript CB077-2.15_NorthShore_Intro to Elect Util Industy

Section 3
TRANSMISSION & DISTRIBUTION
• US Bulk Power Transmission System
• Transmission & Distribution (T&D) Components
• New T& D Technologies
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T & D – Transmission
• Net Utility Investment (USA)
Generation 55%
Transmission 12%
Distribution 29%
Other
4%
• Bulk Power Transmission systems route power
from Generating Plants to Distribution Systems
T & D – Transmission Grid
• USA Bulk Transmission divided into three main
power grids
Eastern Interconnect
Western Interconnect
Texas Interconnect
• Connections between interconnects
East/West-limited, Texas/others- DC only
Mexico linked to West & Texas
Canada linked to East % West
T & D – Transmission Grid (cont)
• Interconnects subdivided into ten NERC
(North American Electric Reliability Council)
regions
• New England region served by NPCC
(Northeast Power Coordinating Council)
• Interconnects also divided into 152
RTO’s (Regional Transmission Operators) and
ISO’s (Independent Switching Operators)
T & D – Transmission Systems
• The transmission system is the “trunk” of
power delivery
• Power from many generators is pooled in the
transmission system and each distribution
system draws from this pool
• Transmission lines run not only from power
plants to distribution systems but also they
run between other transmission lines to
provide redundancy of supplies and allow
rerouting of power to avoid outages
T & D – Transmission System (cont)
• Transmission System power transmitted usually
with “three phase” AC (69kv -765 kv)
• DC transmission gaining greater use
(+/- 250kV - +/-500kV)
• DC used between “asynchronous” grids
• AC power needs power sources and lines to be
synchronized to facilitate safe and controlled
switching to control flows
• Transmission lines also can carry data (PLCPower Line Carrier and BPL- Broadband over
Power Lines
T & D – Transmission System Problem Issues
– Overloaded – increasing demand on grid
– Power Quality issues
#1 –Surges caused by lightning strikes
OthersVoltage sags and swells, Impulse events, Decaying
oscillating voltages, commutation notches, harmonic
voltage
– System overloads results in brownouts, blackouts
and rolling blackouts
T & D –Transmission Components
•
•
•
•
Transmission lines – OH (overhead)
Transmission lines- UG (underground)
Subtransmission lines
Substations
– Change voltage (step-up or step-down)
– Regulate voltage (keep within acceptable limits)
– Switch T&D circuits into and out of grid system
– Measure and meter
– Connect generation plants to system
– Make intersystem connections and switching
– Connect to Distribution systems
T & D – Substations
• Four common types of Substation
Step-up transmission
Step-down transmission
Distribution
UG Distribution
• Substations usually built with a “bus” , high
voltage switches and ”circuit breakers”
– usually multiples of both
T & D – Distribution Systems
• Distribution System
– originates at a distribution substation
– includes the lines, poles, transformers, and all
other equipment needed to deliver electric
service to consumers at the required voltages
(voltages vary by customer types)
• Classification of customers
Industrial, Commercial, Residential, Transportation
T & D – Distribution Components
– Substations
– Distribution Feeder circuits
– Switches
– Protective equipment (circuit breakers, reclosers,
sectionalizers, fuses etc.)
– Primary circuits (5kv -23kv AC)
– Distribution transformers (OH &UG)
– Secondary Lines ( 120-600v AC)
– Services (120/240, 120/208, 277/480 volts AC)
T & D – New Technology
• Power Electronics (replace traditional devices
such as switches, controllers, capacitors, and
condensers
– Often functions can be combined into one device
• DOE (Dept of Energy –federal) GridWorks
Program to support improving electric reliability by
Modernization of key grid components –cables,
conductors, substations, protective systems and
power electronics
T & D – New Technology(cont)
• New Grid concepts
– Minigrids
– Power parks
– DC microgrids
– Flexible AC Transmission Systems
– Electric load as a reliable resource
• Price responsive load
• Emergency responsive load
– EPRI (Electric Power Research Institute)says
Greatest challenge facing T&D
“enhancing system reliability and performance while
maximizing the utilization of power delivery assets”