Electric Power Systems An Overview. Y. Baghzouz Professor of Electrical Engineering University of Nevada, Las Vegas

Electric Power Systems
– An Overview
Y. Baghzouz
Professor of Electrical Engineering
University of Nevada, Las Vegas
Overview
 Power Generation
 Conventional power generation
 Power generation from renewables
 Power transmission
 Cables and other transmission system equipment
 Power Distribution
 Distribution system equipment
 Power Utilization
 Demand curves
 Power System Analysis

 Power flow, fault currents, economic dispatch.
Basic Conventional Power System Layout
Conventional (non-renewable)
primary energy source
US Electricity Generation by Fuel
Coal Fired Power Plants:
Number of Generators ≈ 1,450
Total Capacity ≈ 350 GW
(Source: http://www.npr.org)
Diagram of a modern coal power plant
(Source: Masters, Renewable and Efficient Electric Power Systems, 2004)
Steam Turbines and their Governors
 Steam turbines can have non-reheat, single-reheat or double-

reheat.
 The steam flow is controlled by the governor. The main amplifier of
the governing system and valve mover is an oil servomotor that is
controlled by a pilot valve.
 Main and reheat stop valves are normally fully open - they are
used only during generator start-up and shut down.
The electric generator
Governor controls turbine torque and power

Exciter controls voltage and reactive power
Violent Failure of a steam-driven generator!
 The explosion below was caused by a faulty valve that prevented the
cutoff of steam into the turbine when the generator went off line,
leading the generator to accelerate to over 6,000 rpm.
 The High speed caused parts of the generator to tear apart.
 Hydrogen escaped from the cooling system, causing the explosion.
Nuclear Power Plants:
Number of Generators ≈ 100
Diagram of a nuclear power plant
 Types of nuclear reactors: Nuclear Fission

 Pressurized Water Reactor (PWR)
 Boiling Water Reactor (BWR)
Natural Gas Power Plants:
Open cycle gas turbine:
Typical efficiency: 30-35%
Air-breathing jet engines are gas

turbines optimized to produce thrust
from the exhaust gases. In our
case, the system is optimized to
produce maximum shaft power.
Combined cycle power plant:
Typical efficiency: 60-65%
Efficiencies are even higher when the steam is used for district heating
or industrial processes.
Hydro Power Plants:
Hydro Power plants
 Low and medium head plants

use Francis turbines
 High head plants use Pelton
wheel turbines
Electricity production from renewables
HYDRO
Hydropower
 Hydropower relies on the water

cycle. Herein:
 Solar energy heats water on
the surface, causing it to
evaporate.
 This water vapor condenses
into clouds and falls back onto
the surface as precipitation
(rain, snow, etc.).
 The water flows through rivers
back into the oceans, where it
can evaporate and begin the
cycle over again
Renewable Power Plants: Large plants are
connected to the sub-transmission or transmission system
Renewable Power Plants: Small plants are
connected to the distribution system (often on the load side)
Electricity production from renewables:
Photovoltaics
Growth in Solar Photovoltaic
 The past decade has seen

explosive growth in global solar
photovoltaic installations.
 Countries with the most PV
capacity in 2010-2011 (MWp) →
PV Plants in Nevada:
 250+ MW (Eldorado Valley), 50 MW (Prim)
 15 MW (1-axis) tracking @ NAFB
 Numerous distributed PV systems (few kW – 350 kW)
concentrating Solar power
Concentrating Solar Power (CSP)
 CSP technologies use mirrors to reflect and

concentrate sunlight onto receivers that collect the solar
energy and convert it into heat.
 This thermal energy can then be used to produce
electricity via a steam turbine or heat engine driving a
generator.
 CSP systems are typically classified by how the various
systems collect solar energy. The three main systems
are
 The linear system
 The tower system
 The dish system.
Linear CSP
Nevada Solar 1 (65 MW)

Power tower CSP
110 MW CSP near Tonopah, NV

(under construction)
Dish/Engine CSP Systems
Biomass
Biomass Energy
Landfill Energy near Las Vegas, NV (12 MW)

Ocean power
Ocean Power
 Energy can be extracted from the power of the waves, from

the tide, or from ocean currents
Capturing Ocean Power
Attenuator
Point Absorber
Tidal Power Oscillating Water Column Ocean Current

Wind
Wind Power … inland and offshore
Installed Wind Capacity by Country (MW)
US Wind Resource Map
Largest wind turbine generator
 Manufacturer: Enercon
 Rated power: 6 MW,
 Rotor diameter: 126 m,
 Total height; 198 m.
Wind Power in Nevada:
Spring Valley Wind (Pine County): 152 MW
geothermal
GEO-
THERMAL
Geothermal
 Dry steam plants use steam

piped directly from a
geothermal reservoir to turn the
generator turbines. The first
geothermal power plant was
built in 1904 in Tuscany, Italy.
 Flash steam plants take high-

pressure hot water from deep
inside the Earth and convert it
to steam to drive the generator
turbines. When the steam
cools, it condenses to water
and is injected back into the
ground to be used over and
over again.
Geothermal in Nevada:
Current Capacity: 385 MW
(+ 150 MW in construction or development stage).
Source: NV Energy Website

Step-up (Station) transformers:
 Size to 1000 MVA

 generator voltage up to 25 kV
 Transmission voltage up to 765 kV
 Forced Air and Forced Oil Cooling.
US Power Transmission Grid
High Voltage Power Lines (overhead)
 Common voltages in north America: 138, 230, 345, 500, 765 kV

 Bundled conductors are used in extra-high voltage lines
 Stranded instead of solid conductors are used.
High Voltage Power Cables (underground)
 Cable lines are designed to be placed underground in

urban areas or under water. The conductors are insulated
from one another and surrounded by protective sheath.
 Cable lines are more expensive and harder to maintain.
They also have a large capacitance – not suitable for long
distance.
Tree Trimming underneath power lines
Before
After
Transmission System Protection
 Protective equipment needs to

protect the system from over-
voltages (surge arrestors) and
over-currents (circuit breakers).
Long line series and shunt compensation
 Shunt reactors are used to compensate the line shunt

capacitance under light load or no load.
 Series capacitors are often used to compensate the
line inductive reactance in order to transfer more power.
Substation Transformers
 Typical size; 20 MVA

 Primary voltage down to 69 kV
 Secondary voltage down to 4.16kV
Distribution Substation Layout
Power distribution lines
(placed underground in new urban areas)
 Primary Distribution voltages: 4.16, 12.47, 13.2, 13.8, 25, 34.5 kV
Power distribution transformers
 The distribution circuits may be overhead or underground.

This will depend on the load density and the physical
conditions of the particular area to be served.
Switched Capacitors
Electrical Power Utilization (electric load)
 Utilization voltage: 120V, 208V*,

240V, 277V, 480V*, 600V*
2/3 –3/4 of electricity is consumed by motors

Demand
 Changes in demand of individual customers is fast and

frequent due to load switching.
Substation Load: 48 hours
 The aggregated demand at the substation is smoother,

and total load fluctuations are usually small.
MW and MVAR loading on a feeder – 4 months
System load: 24-hours
 The aggregated demand on the system is even smoother, and total load
fluctuations are very small.
 The overall daily profile of load can be predicted reasonably well using
forecasting tools.
6000
5000
System Load (MW)
4000
3000
2000
1000
0
1
2
3
5
6
7
8
9
4
10
11
12
13
14
15
17
18
19
20
22
23
24
16
21
Hour of Day
Seasonal Load Patterns
The local load is dominated by winter and summer patterns, with May
and October as shoulder months.
North American Electrical Interconnections
The power system of North America is divided into four major Interconnections
which can be thought of as independent islands.
• Western – Generally everything west of the Rockies.
• Texas - Also known as Electric Reliability Council of Texas (ERCOT).
• Eastern – Generally everything east of the Rockies except Texas and Quebec.
• Quebec.
Western Interconnection
System monitoring. Analysis, Operation and Control
Important Studies:
• Economic generation scheduling and unit commitment
• Power flow analysis
• Short-circuit analysis
• System stability and dynamic analysis
• Load forecasting
• System planning
• Etc …
Generation-load balance
• As electricity itself cannot presently be stored on a large scale,
changes in customer demand are met by controlling conventional
generation, using stored fuels.
• Frequency is maintained as long as there is a balance between
resources and customer demand (plus losses). An imbalance causes
a frequency deviation.
Generator Scheduling (economic Dispatch)
 Given a power system with n generators, and a load forecast, determine the
optimal schedule of each generator while recognizing generating unit limits
and output capability.
6000
5000
System Load (MW)
4000
3000
2000
1000
Base Load
0
1
2
3
5
6
7
8
9
4
10
11
12
13
14
15
17
18
19
20
22
23
24
16
21
Hour of Day
Unit # x
Unit # y
Unit # z
Power Flow Analysis
Red indicates under-

voltage at Bus 3
END!

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Electric Power Systems

 Power System Analysis

 Steam turbines can have non-reheat, single-reheat or double-

Governor controls turbine torque and power

 Types of nuclear reactors: Nuclear Fission

Air-breathing jet engines are gas

 Low and medium head plants

 Hydropower relies on the water

 The past decade has seen

 CSP technologies use mirrors to reflect and

Nevada Solar 1 (65 MW)

110 MW CSP near Tonopah, NV

Landfill Energy near Las Vegas, NV (12 MW)

 Energy can be extracted from the power of the waves, from

Tidal Power Oscillating Water Column Ocean Current

 Dry steam plants use steam

 Flash steam plants take high-

Source: NV Energy Website

 Size to 1000 MVA

 Common voltages in north America: 138, 230, 345, 500, 765 kV

 Cable lines are designed to be placed underground in

 Protective equipment needs to

 Shunt reactors are used to compensate the line shunt

 Typical size; 20 MVA

 The distribution circuits may be overhead or underground.

 Utilization voltage: 120V, 208V*,

2/3 –3/4 of electricity is consumed by motors

 Changes in demand of individual customers is fast and

 The aggregated demand at the substation is smoother,

Red indicates under-

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