Electrical Concepts for Non‐Engineers
2015 Islanded Grid Wind Power March 4, 2015
Richard WiesAssociate Professor
University of Alaska Fairbanks (UAF) Electrical and Computer Engineering (EE)&
Institute of Northern Engineering (INE)
Electrical Concepts for Non‐Engineers► Basic Electric System
► Generation► Transmission► Distribution/Load
► Basic Electrical Concepts► Voltage, Current, & Resistance: Water Tank
Analogy & Ohm’s Law► Parallel & Series Connections► Power & Energy► Types of Loads► Direct Current (DC) vs. Alternating Current (AC)► Frequency & AC Power
► Power Quality► Power Factor: Musher’s Analogy► Efficiency► Voltage & Frequency Variations► Harmonics: Music Analogy
V I · R
P V · I
Energy P · Time
Generation► Generate Power @ Low &
Medium Voltage► Transform to High Voltage
Basic Electric SystemTransmission
► Transmit Power @ High Voltage
Distribution► Transform to Medium &
Low Voltage► Distribute Power to
Customers
► Generation Sources (Low Voltage)► Diesel Electric Generator► Wind Turbine Generators► Solar Photovoltaic (PV) Panels► Battery Bank
► Distribution (Medium Voltage)► Transform to Medium Voltage► Distribute Power to Load► Transform to Low Voltage
► AC Load & Energy Storage► Distribute Power to Customers► Battery Bank
Basic Islanded Electric System
Voltage [V]► Potential Difference► Measured in Volts, V► Unit named for Physicist
Alessandro Volta► Pressure Difference in
Water Tank
Basic Electrical Concepts: Water Tank Analogy
Current [I]► Flow of Electricity in a Wire► Measured in Amperes, A► Unit named for Physicist
André‐Marie Ampère► Difference in Flow Rate
Between Two Water Tanks
Resistance [R]► Impedance to Current Flow► Measured in Ohms, ► Unit named for Physicist
Georg Ohm► Difference in Flow Rate
Between Two Water Tanks
Voltage Current Resistance
Basic Electrical Concepts: Water Tank Analogy (Ohm’s Law)
Parallel Circuits► Multiple Lamps Connected Across the
Source► Same Voltage Across Lamps► Current Path Divides Through Lamps
Basic Electrical Concepts: Parallel & Series Connections
Series Circuits► Multiple Lamps Connected in Line with
the Source► Same Current Path► Voltage Divides Across Lamps
Parallel Series
/
/
+
‐
+
‐
+ ‐/ + ‐/
Basic Electrical Concepts: Power & Energy
Electric Power [P] ► Product of Voltage & Current► Real Work over Time► Measured in Watts, W► Unit named for Mech. Engineer James Watt
Energy ► Product of Electric Power & Time► Measured in Watt‐hours, W‐h► Residential Customers: kW‐h = 1,000 W‐h► Industrial Customers: MW‐h = 1,000,000 W‐h
Basic Electrical Concepts: Direct (DC) vs. Alternating (AC) Current
Direct Current (DC)► Voltage & Current are Constant over Time► One‐Direction (positive or negative)► Sources: Battery, Solar PV Panel
AC Current (AC)► Voltage & Current alternate between
Positive & Negative over Time (Sine Wave)► Period: Time of One Complete Cycle► Sources: Alternator, AC Power Generators
Resistive [R]► Resists Current Flow► Measured in Ohms, ► Demand Real Power, P► Examples: Light Bulbs,
Toasters, Electric Hot Water Heaters, Ovens, Dryers
Basic Electrical Concepts: Types of Loads
Inductive [L]► Chokes AC Current Flow &
Requires a Magnetic Field► Measured in Henries, H► Demand Reactive Power, +Q► Examples: Electric Motors in
Appliances & Industry
Capacitive [C]► Blocks DC Current Flow &
Charge if Voltage Applied► Measured in Farads, F► Provide Reactive Power, ‐Q► Examples: Electronics &
Power Factor Correction
Resistor Inductor Capacitor
Basic Electrical Concepts: Frequency & AC Power
Frequency [f]► Number of AC Cycles per Second► Measured in Hertz, Hz► Named for Physicist Heinrich Hertz► US Standard for Power Systems: 60 Hz
AC Power► P: Real Power (Useful) in Watts, W► Q: Reactive Power (Magnetic) in Volt‐Amps
Reactive, VARS► S: Apparent Power (Utility) in Volt‐Amps, VA
120 ·
http://www.animations.physics.unsw.edu.au//jw/electricmotors.html
Link to AC Generation Animations
Power Quality: Power FactorPower Factor [pf]
► Ratio of Useable Real Power, P to the Utility Apparent Power, S► : Power Factor Angle
S [VA]Q [VARS]
P [W]
θcosSP
pf Power Factor for Resistive & Inductive Load
Dog Mushing Power Factor Explanation
Working Real Power, PNon‐Working
Reactive Power, Q
22 QPS
Power Quality: EfficiencyEfficiency []
► Ratio of Real Output Power, Pout to the Real Input Power, Pin► Ploss: Real Power Loss
in
lossin
in
out
PPP
PP
Efficiency
Plant Efficiency
Power Quality: Voltage & Frequency Variations
Causes of Power Quality Problems
► Voltage Variations► Sags & Swells (Short Term)► Under & Over‐Voltage (Long Term)► Voltage Fluctuations (Flicker)► Voltage Imbalance
► Frequency Variations
Voltage Flicker
Voltage Sag, Swell, & Interruption
Voltage Imbalance
Power Quality: Harmonics (Impure Sine Waves)
Causes of Harmonics► Switching Power Supplies► Examples:
► Electronic Ballasts► Computer Power Supplies► Electric Motor Drives
Laptop Power Supply Current Harmonics 3‐Phase Voltage Distortion
Harmonic Principle: Vibrating String
Modern Electric Power Grid Terminology: Smart Grid
► Smart Grid (opposite of a dumb grid)► Modernized utility electricity delivery systems with
computer‐based remote control and automation.
Modern Electric Power Grid Terminology: MicroGrid
► MicroGrid Institute Definition► Small energy system capable of balancing captive
supply and demand resources to maintain stable service within a defined boundary.
Questions?Contact Info:Richard Wies, Ph.D., P.E.Electrical and Computer EngineeringEmail: [email protected]: (907) 474‐7071
