3 Phase Power Basics Thomas Greer Executive Director Engineering Services TLG Services
Agenda Terminology Basic Electrical Circuits Basic Power Calculations
Why This Electricity Stuff? To Become an Electrical Engineer? So We Won t Have to Call Our AE? To Moonlight Teaching at the University? I Don t Think So!
Why This Electricity Stuff? Able to talk the talk Fundamental language with customers, consultants, and contractors in this industry Improved technical skills help you to meet and exceed the expectations of your customers
What You Will Take Home Understand basic terminology in electrical circuits and power systems Able to perform basic power calculations
Current The movement of electrons in a circuit. It is the flow of electricity. Unit of measure is the ampere abbreviated AMP or A. Represented in equations by the letter I.
Direct Current Direct Current (DC) - Current flows in one direction Common DC source - battery Current DC Current Time
Alternating Current Alternating Current (AC) - Current flows first in one direction and then the other, reversing direction periodically Common AC source - Commercial Power (AC Generator) + Current AC Current Time -
Voltage Is the electrical potential or force that causes current to flow in a circuit. Unit measure is the volt, abbreviated V.
Impedance Impedance is the total opposition a circuit offers to the flow of electric current DC circuit impedance include resistance only AC circuit impedance includes resistance and reactance Reactance comes from inductors and capacitors Measured in ohms (Ω) Represented in equations by the letter Z
Electric Circuit Route in which current flows from a power source to a load and back to the power source. Switch AC Power Source V Z Load
Hydraulic and Electric Circuit Analogy Battery developing electrical pressure Pump generating mechanical pressure - + Direction of current flow Wire conducting current flow Resistance (electrical load) Electric Circuit Pipe conducting water flow Mechanical Load
Ohm s Law Ohm s Law - The current in an electric circuit is directly proportional to the applied voltage and inversely proportional to the circuit impedance. I = Current (Amps) I = V Z V = Voltage (Volts) Z = Impedance (Ohms) Solving for Voltage or Impedance V = IZ or Z = V I
Applying Ohm s Law I =? V = 120VAC Z=10Ω Example: AC circuit with resistive electric heater load of 10 ohms. I = V/Z I = 120/10 I = 12A
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AC Waveform - 3 Phase C Frequency # Cycles Per Second Hertz 90 150 210 120 180 240 300 360 A 270 330 B One Cycle
Peak and RMS Values 1.0 Peak 1.0 (170V) 0.9 0.8 0.7 RMS 0.707 (120V) 0.6 0.5 0.4 0.3 0.2 0.1 0-0.1-0.2-0.3-0.4-0.5-0.6-0.7-0.8-0.9-1.0 RMS value of an AC current is equal to the DC current which will produce the same average heating effect in a given resistance For Sinewave Irms =.707 Ipeak Ip = 2 Irms
Distorted Sinewave Voltage Waveform with distortion caused by load with switching SCR s
Harmonics Used as Building Blocks to Define a non Sinusoidal Waveform. Periodic Sinusoidal Components Multiples of Fundamental 3rd Harmonic of 60Hz Sinewave is 180Hz Harmonic Distortion - A current or voltage waveform includes includes non 60Hz components. Therefore, it is a distorted sinewave. Most real world 3 phase loads include harmonic distortion.
Power Rate of Doing Work P=V * I P = Power (Volt Amperes or Watts) V = Voltage (Volts) I = Current (Amperes) Z = Impedance (Ohms) Since, V = I * Z, Power can also be expressed as follows: P = V 2 /Z and P = I 2 Z
AC Power Apparent Power Total power measured in Volt-Amperes or VA. Obtained from the measured current and voltage. KVA (Single Phase) = (V * A) / 1000 KVA (Three Phase) = (V LN * A * 3) / 1000 or KVA (Three Phase) = (V LL * A * 3) / 1000 Where 3 = 1.732
AC Power Real Power Power which is actually available to do work. Total power (KVA) includes reactive components due to inductance and capacitance. Power useful for work is resistive component only. Measured in KW (kilowatts) Must be obtained by measurement with a Wattmeter or calculated.
Power Factor Ratio of Real Power to Apparent Power PF = KW / KVA Power Factor is described as leading or lagging based on whether the current leads or lags the voltage For a sinusoidal current and voltage the power factor equals the cosine of the phase angle between the current and voltage
Capacitor Electrical device that stores electrical energy. Does not allow instantaneous voltage change Capacitance - storage capability of capacitor Measured in farads
Capacitor + Capacitor voltage and current Voltage 0 Current - 0 90 180 270 360 Time The capacitor current is out of phase with the generated voltage, and leads the voltage by 90 degrees.
Inductor Device which stores electrical energy. Impedes instantaneous change in current. Inductance - measure of the amount of interaction between alternating current and resultant changing electromagnetic fields in a device. Unit of measure is henry
+ Inductor Inductor voltage and current 0 Voltage Current - 0 90 180 270 360 Time The inductor current is out of phase with the generated voltage, and lags the voltage by 90 degrees.
Lead and Lag Power Factor Components Lagging Power Factor Single - Phase Transformer Three - Phase Transformer Choke Induction Motor Leading Power Factor Filter Unity Power Factor Incandescent Lamps Heaters PFC Power Supplies Synchronous Motors Capacitor
Efficiency Ratio of useful output energy to total useful input energy Power out Kw out Efficiency = = Power in Kw in 110 kva 100 kva load Input and output PF must be known as efficiency is a ratio of Kw s EX: PF in = PF out (this case only) = 0.8 Find efficiency. 100 (.8) Efficiency = 110 (.8) =.91 (100) = 91%
System Efficiencies Overall system efficiency is obtained by multiplying efficiencies of series components Sample System Building Xformer 99% Stepdown Xformer 98% UPS 90% Load PS 80% Overall Efficiency = (.99 *.98 *.9 *.8) = 70%
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Single Phase Systems 220/230/240V - 50 Hz 110/115/120V - 60 Hz load voltages may be obtained from these systems
Single Phase Systems Neutral 240V 120V Three load voltages may be obtained from this system 1. 120 volt single phase, two wire 2. 240 volt single phase, two wire 3. 120/240 volt sing;e phase, three wire
Three Phase Systems 480V N 220/ 480V 480V 380/400/415 (Line-to-Line) Delta Connected System No Neutral Line-To-Line Voltages Only
Three Phase Systems 480V N 277V 380/400/415 220/230/240 277V (Line-to-Neutral) 480V (Line-to-Line) Wye Connected System Load voltages obtained from 480V systems 1. 277 volt single phase, two wire (L-N) 2. 480 volt single phase, two wire 3, 480 volt three phase, three wire 4. 480/277 volt three phase, four wire
Three Phase Systems 208V N 120V 380/400/415 220/230/240 120V (Line-to-Neutral) 208V (Line-to-Line) To find the line-to-neutral voltage if the line-to-line voltage is 208V V 208 1.73 1.73 120V
Three Phase Systems Worldwide Voltages available 60Hz 600/346V (Canada) 480/277V 208/120V 220/127V (Mexico) 50Hz 380/220V 400/230V 415/240V
POWER CALCULATIONS Putting it All Together 38
Determining kva of Power Feeder Service (Single Phase) KVA = V A 1000 Assume a single phase 120 entrance service specified at 20 A. 120 20 KVA = = 2.4 1000
Determining kva of Power Feeder Service (Three Phase) KVA = V A 3 1000 EXAMPLE 2: Assume a 3 phase 208/120 entrance service specified at 200A. 208 200 1.732 KVA = = 72 1000 75kVA UPS should be selected.
Determining kva From Power Profile of Equipment Simple Addition of KVA Values EQUIPMENT VOLTAGE / PHASE LOAD 1 CPU 208 / 3 Phase.11 KVA 1 Controller 208 / 3 Phase 12 Amps 4 Disc 208 / 1 Phase 6 Amps Each 1 Printer 208 / 1 Phase 5 Amps 6 Terminal 120 / 1 Phase 4 Amps Each
P Determining kva From Power Profile of Equipment EXAMPLE (cont) EQUIPMENT CALCULATION INDIVIDUAL CPU None Required KVA =.11 V A 3 Controller KVA = KVA = 4.3 1000 V A Disc KVA = KVA = 1.25 1000 V A Printer KVA = KVA = 1.0 1000 Terminal KVA = V A KVA = 0.48 1000
Determining kva From Power Profile of Equipment EXAMPLE (cont) EQUIPMENT KVA EACH TOTAL KVA LOAD 1 CPU @.11 0.11 1 Controller @ 4.3 4.3 4 Disc @ 1.25 5.0 1 Printer @ 1.0 1.0 6 Terminal @ 0.48 2.9 Total KVA 24.20
Determining kva from Power Profile of Equipment A 30kVA UPS could be selected as a minimum To allow for growth a larger unit should be selected. This should be discussed with your customer to determine what size is needed. Rule of thumb is 20% - 30%
Determining kva from Power Profile of Equipment Load Calculations by Phase Equipment Voltage Load Phase A Phase B Phase C CPU 208v / 3 Phase 30.5 30.5 30.5 30.5 Controller 208v / 3 Phase 12.0A 12.0 12.0 12.0 Disc #1 208v / 1 Phase 6.0A 6.0 6.0 Disc#2 208v / 1 Phase 6.0A 6.0 6.0 Disc #3 208v / 1 Phase 6.0A 6.0 6.0 Disc #4 208v / 1 Phase 6.0A 6.0 6.0 Printer 208v / 1 Phase 5.0A 5.0 5.0 Terminal #1 120v / 1 Phase 4.0A 4.0
Determining kva from Power Profile of Equipment Load Calculations by Phase (continue) Equipment Voltage Load Phase A Phase B Phase C Terminal #2 120v / 1 Phase 4.0A 4.0 Terminal #3 120v / 1 Phase 4.0A 4.0 Terminal #4 120v / 1 Phase 4.0A 4.0 Terminal #5 120v / 1 Phase 4.0A 4.0 Terminal #6 120v / 1 Phase 4.0A 4.0 Total Phase Load 68.5 69.5 71.5
Determining kva from Power Profile of Equipment Load Calculations by Phase (continued) Calculating the kva from the most heavily-loaded phase (phase C): kva = 208V 71.5A 3 kva = 25.8 1000 A 30kVA UPS could be selected as a minimum
Something to take home Single phase capacity V x A = VA 120 x 100 = 12 Kva Three phase capacity V x A x 1.73 = VA 208 x 100 x 1.73 = 36 Kva
Something more to take home Power factor = Kw / Kva Kva = Kw / Pf Must know kva and kw to properly select UPS size kw can be determined from PF and kva Maximum UPS output at rated power factor 100Kva/80kW unit can be fully loaded at 80Kva if load PF is 1.0
The End