Power System Analysis
Lecture slides for Chapter 1
The Power System: An Overview
Personal Introduction
• Academic
• PhD electrical engineering, 2013, Norwegian University of Science & Technology
• MSc electrical engineering, 2008, UET Taxila
• BSc electrical engineering, 1998, NWFP UET Peshawar
• Experience
• 2012 – 2018, DNV GL, A Norwegian multinational testing, inspection, certification, and
advisory company
• 2004 – 2008, CIIT Wah Cantt., Educational institution
• 1999 – 2004, Siemens Islamabad, A German multinational working in the electric power
products and projects business
• Specialization
• Electrical power engineering
• Power electronics
• HVDC, FACTS, renewable energy, microgrids
Expectations
• What is a teacher meant for
• Motivation
• Highlighting the relevance of course content out in the field
• Examples from the field
• What is expected of the students
• Discipline
• Feedback
• Participation in the class
Course CLOs
1. APPLY circuit analysis and network analysis techniques on power system
problems such as determination of voltage, current, and powers at various
nodes and across transformer windings.
2. APPLY modelling techniques to synchronous generators, transformers, and
transmission lines for power system analysis.
3. APPLY load flow analysis techniques and concepts of transient stability in power
systems.
4. APPLY short-circuit analysis techniques for balanced and unbalanced faults in
power systems.
Evaluation
• Grading scheme
• Absolute grading (less than 50 = fail)
• Assessments
• Minimum 8 Quizzes (20)
• 2 sessionals (30)
• final (50)
• OBE system
• All CLOs to be passed to pass the course
Introduction to Power System Analysis
• What is power system analysis
• Why do we need analysis of power systems
• When do we perform power system analysis
• How to perform power system analysis
• Job types that require expertise in power system analysis
Power engineering careers
Time/space
Designer
Supplier
User
Pre-feasibility
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Feasibility
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Engineering
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Construction
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Operation
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De-commissioning
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What
• Basically, application of mathematics to power systems much like circuit analysis
• To determine the state of the power system components
• Power system components
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Generators
Lines
Transformers
Loads
• State
• Voltage
• Current
• Power
Why
• To check if the system components operate or will operate within certain limits
• Limits
• Voltage limits
• Current limits
• Power limits
When
• Before building a new power system
• Addition of new generators
• Addition of new transformers
• Addition of transmission corridors
• Upgradation of existing transmission lines
• While analyzing contingencies in a power system
• Analysis of transient phenomena
How
• Perform calculations for power system variables in
• Steady state
• Transient state
• Tools
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Based on time scales of interest
Power Factory
PSSE
PSCAD
Simscape Power Systems (MATLAB/Simulink)
History of electric power systems
• 1882: First power station in New York employing
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DC generator driven by steam engines
Total load 30 kW at 110 V
Load type: lighting
DC motor invented and increased attractiveness of the DC system
DC voltage level transformation is not easy (obstacle to longer transmission distances)
• 1885: Invention of the AC transformer
• Solution to distance problem and capability to serve more loads
History of electric power systems
• 1888: AC motor invented by Nikola Tesla
• 1889: First AC power line in Oregon
History of electric power systems
Types of power generation
• Steam
• Fossil fuel sources (coal, gas, oil)
• Nuclear fuel (Uranium)
• Water (flow of water converted to electrical energy)
• Gas turbines use the energy of the expanding exhaust gases from combustion
• Combustion engine (mostly diesel)
• Renewables (wind, solar, biomass, waste, fuel cells)
Total energy consumption of the world
1973
4674 Mtoe
2009
8353 Mtoe
Sources of electricity
1973
2009
Future trends for electricity
Important variables – power quality
• Voltage magnitude
• Frequency
• Harmonic content
Voltage magnitude
• 1 per unit – supposed to be what is the ‘nominal voltage’ at the connection point
• Examples of nominal voltages
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13.8 kV
765 kV
500 kV
220 kV
132 kV
66 kV
33 kV
11 kV
6.6 kV
3.3 kV
690 V
415 V
Frequency – 50 or 60 Hz
Why
sunsoid??
Frequency – harmonic free
Frequency – harmonic free
Electric industry structure
• Generators (voltage step up)
• Transmission system operators (various transmission level voltages)
• Distribution network operators (medium and low voltage levels)
• Consumers (low voltage)
• Modern trends
• Wind generation to distribution networks at medium voltage
• Solar generation to distribution networks at low voltage
Modern power systems
• Complex interconnection of PS component
• Generation
• Transmission and sub-transmission
• Distribution
• Loads
Generation
• Electromagnetic induction
• Caused by change of magnetic flux
passing through a coil
• Change caused by rotation of magnets
forced by a prime mover
• Magnetic flux produced by DC current or
permanent magnets
Transformer
• Changes voltage levels for efficient
transmission of electricity
• Provides galvanic isolation
• Generation voltage limited to
below 30 kV
Transmission and sub-transmission
• Purpose to carry electric power over long distances close to load centers
• Various voltage levels depending upon transmission distance
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765 kV
500 kV
220 kV
132 kV
66 kV
33 kV
Substations (grid stations)
• Part of the transmission system
• Various types
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High-voltage substations
Receiving substations
Primary substations
Distribution substations
• Functions
• Switching of lines (switching substations)
• Voltage change
• Voltage change for load consumption
Distribution
• Connects distribution substations to consumer premises
• Primary distribution lines at voltages between 3 kV and 33 kV
• Industrial customers get direct MV connection
• Secondary distribution at low voltage 415 V in Pakistan
• Serve commercial and residential customers
• Overhead and underground both
Loads
• Categories
• Industrial
• Commercial
• Residential
• Industrial loads
• Dominated by induction machines
• Loads change with voltage and frequency
• Commercial and residential
• Mostly lighting, heating, and cooling
• Independent of frequency
• Consume very little reactive power
Power definitions
• Real power or active power (kW or MW)
• Reactive power (kVAr or MVAr)
• Complex power or apparent power (kVA or MVA)
Power system load and some definitions
• Total demand: composite of all the load classes plotted as a ‘daily-load curve’
• ‘Peak demand’ or ‘Maximum demand’ = max instantaneous load. Met by small peaking
generators
average daily load
• load factor=
peak load for the day
• daily load
average daily load
average daily load ×24 h
daily energy consumed
factor=
=
=
peak load for the day peak load for the day×24 h peak load for the day×24 h
• annual load factor=
total annual energy
peak load ×8760 h
Power system load and some definitions
• Loads in different classes peak at different times (diversity)
• helps the power system cope
• Power plants economical when operating at high LF
Other definitions
Maximum demand
• Utilization factor=
Installed capacity
Annual energy generation
• Plant factor=
Plant capacity ×8760
System protection
• Obviously, the function is protection against failures
• Protection includes
• Switchgear connected directly to system components
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Instrument transformers
Circuit breakers
Disconnect switches
Fuses
Lightning arrestors
• Controls located in control rooms
• Relays
• Communication cables
• software
Energy control center
• Central control center ensures
• Reliability
• Economical operation
• Components
• Online computers reading in data from the power system SCADA
• Signal processing
• Control console
Computer analysis
• Repetitive analyses for reliable operation of power systems
• Beyond human capacity in reasonable time
• Computers come in
• However, analysis needs modeling first
• Modelling
• All components
• controls
Various types of power system analyses
• Power flow
• Short circuit analysis
• Stability analysis
• Economic scheduling
• Machine transients