3 Phase Power Basics
Thomas Greer
Executive Director – Engineering
Services
TLG Services
Agenda
z
z
z
Terminology
Basic Electrical Circuits
Basic Power Calculations
Emerson Confidential
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!
Emerson Confidential
Why This Electricity Stuff?
z
z
z
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
Emerson Confidential
What You Will Take Home
z
z
Understand basic terminology in electrical
circuits and power systems
Able to perform basic power calculations
Emerson Confidential
Current
z
z
z
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”.
Emerson Confidential
Direct Current
z
z
Direct Current (DC) - Current flows in one direction
Common DC source - battery
DC Current
Current
Time
Emerson Confidential
Alternating Current
z
z
Alternating Current (AC) - Current flows first in one
direction and then the other, reversing direction
periodically
Common AC source - Commercial Power (AC Generator)
+
AC Current
Current
Time
-
Emerson Confidential
Voltage
z
z
Is the electrical potential or force that causes
current to flow in a circuit.
Unit measure is the volt, abbreviated “V”.
Emerson Confidential
Impedance
z
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
z
z
Measured in ohms (Ω)
Represented in equations by the letter “Z”
Emerson Confidential
Electric Circuit
z
Route in which current flows from a power
source to a load and back to the power source.
Switch
AC Power Source
Emerson Confidential
V
Z
Load
Hydraulic and Electric Circuit Analogy
Pump generating mechanical pressure
Battery developing
electrical pressure
-
Wire conducting
current flow
+
Direction of current
flow
Resistance
(electrical load)
Electric Circuit
Emerson Confidential
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 = V
Z
I = Current (Amps)
V = Voltage (Volts)
Z = Impedance (Ohms)
V = IZ
Solving for Voltage or
Impedance
or
Z=
Emerson Confidential
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
Emerson Confidential
Are You Still There?
Any Questions?
Emerson Confidential
AC Waveform - 3 Phase
C
B
One Cycle
Emerson Confidential
360
330
300
270
240
210
150
A
90
120
180
Frequency
# Cycles Per Second
Hertz
Peak and RMS Values
1.0
0.9
0.8
0.7
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
Emerson Confidential
Peak 1.0 (170V)
z
RMS 0.707 (120V)
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
Emerson Confidential
Harmonics
z
Used as Building Blocks to Define a non
Sinusoidal Waveform.
– Periodic Sinusoidal Components
– Multiples of Fundamental
• 3rd Harmonic of 60Hz Sinewave is 180Hz
z
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.
Emerson Confidential
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 = V2/Z
and P = I2Z
Emerson Confidential
AC Power
z
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) = (VLN * A * 3) / 1000 or
– KVA (Three Phase) = (VLL * A * √3) / 1000
Where √3 = 1.732
Emerson Confidential
AC Power
z
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.
Emerson Confidential
Power Factor
z
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
Emerson Confidential
Capacitor
z
z
z
Electrical device that stores electrical energy.
Does not allow instantaneous voltage change
Capacitance - storage capability of capacitor
– Measured in “farads”
Emerson Confidential
Capacitor
Capacitor voltage and current
+
Voltage
Current
0
0°
90°
180°
Time
270°
360°
The capacitor current is out of phase with the generated voltage,
and leads the voltage by 90 degrees.
Emerson Confidential
Inductor
z
z
z
z
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”
Emerson Confidential
Inductor
Inductor voltage and current
+
Voltage
Current
0
0°
90°
180°
Time
270°
360°
The inductor current is out of phase with the generated voltage, and
lags the voltage by 90 degrees.
Emerson Confidential
Lead and Lag Power
Factor Components
Lagging Power Factor
Leading Power Factor
Single - Phase
Transformer
Filter
Three - Phase
Transformer
Capacitor
Choke
Unity Power Factor
Induction Motor
•
•
•
•
Emerson Confidential
Incandescent Lamps
Heaters
PFC Power Supplies
Synchronous Motors
Efficiency
Ratio of useful output energy to total useful input energy
Power out
Kw out
Kw in
Power in
100 kva load
110 kVA
Efficiency =
=
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%
Emerson Confidential
System Efficiencies
Overall system efficiency is obtained by multiplying
efficiencies of series components
Sample System
Building
Xformer
99%
Stepdown
Xformer
98%
UPS
90%
Overall Efficiency = (.99 * .98 * .9 * .8) = 70%
Emerson Confidential
Load PS
80%
Still With Me?
Any Questions?
Emerson Confidential
Single Phase Systems
220/230/240V - 50 Hz
110/115/120V - 60 Hz
load voltages may be obtained from these systems
Emerson Confidential
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
Emerson Confidential
Three Phase Systems
480V
N
380/400/415
480V
(Line-to-Line)
220/
480V
¾Delta Connected System
¾No Neutral
¾Line-To-Line Voltages Only
Emerson Confidential
Three Phase Systems
480V
277V
N
380/400/415
480V (Line-to-Line)
220/230/240
277V (Line-to-Neutral)
Wye Connected System
Load voltages obtained from 480V systems
1.
2.
3,
4.
277 volt single phase, two wire (L-N)
480 volt single phase, two wire
480 volt three phase, three wire
480/277 volt three phase, four wire
Emerson Confidential
Three Phase Systems
208V
120V
N
380/400/415
208V (Line-to-Line)
220/230/240
120V (Line-to-Neutral)
To find the line-to-neutral voltage if the line-to-line
voltage is 208V
V
1.73
Emerson Confidential
208
1.73
120V
Three Phase Systems
z
Worldwide Voltages available
– 60Hz
• 600/346V (Canada)
• 480/277V
• 208/120V
• 220/127V (Mexico)
– 50Hz
• 380/220V
• 400/230V
• 415/240V
Emerson Confidential
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.
KVA =
120 • 20
1000
Emerson Confidential
= 2.4
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.
KVA =
208 • 200 • 1.732
1000
75kVA UPS should be selected.
Emerson Confidential
= 72
Determining kVA From Power Profile
of Equipment
Simple Addition of KVA Values
EQUIPMENT
1 CPU
VOLTAGE /
PHASE
208 / 3 Phase
LOAD
.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
Emerson Confidential
Determining kVA From Power Profile
of Equipment
EXAMPLE (cont)
EQUIPMENT
CPU
Controller
INDIVIDUAL
None Required
V •A• √3
KVA =
1000
KVA = .11
KVA = 4.3
Disc
KVA =
V•A
1000
KVA = 1.25
Printer
KVA =
V•A
1000
KVA = 1.0
Terminal
KVA = V • A
1000
Emerson Confidential
P
CALCULATION
KVA = 0.48
Determining kVA From Power Profile
of Equipment
EXAMPLE (cont)
EQUIPMENT
1 CPU
1 Controller
4 Disc
1 Printer
6 Terminal
Emerson Confidential
KVA EACH
@ .11
@ 4.3
@ 1.25
@ 1.0
@ 0.48
Total KVA
TOTAL
KVA LOAD
0.11
4.3
5.0
1.0
2.9
24.20
Determining kVA from Power
Profile of Equipment
z
A 30kVA UPS could be selected as a minimum
z
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%
Emerson Confidential
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
Disc #3
208v / 1 Phase
6.0A
6.0
Disc #4
208v / 1 Phase
6.0A
6.0
Printer
208v / 1 Phase
5.0A
Terminal #1 120v / 1 Phase
4.0A
Emerson Confidential
6.0
6.0
6.0
6.0
5.0
5.0
4.0
Determining kVA from Power
Profile of Equipment
Load Calculations by Phase (continue)
Equipment
Voltage
Load
Phase “A”
Terminal #2 120v / 1 Phase
4.0A
4.0
Terminal #3 120v / 1 Phase
4.0A
Terminal #4 120v / 1 Phase
4.0A
Terminal #5 120v / 1 Phase
4.0A
Terminal #6 120v / 1 Phase
4.0A
Total Phase Load
Emerson Confidential
Phase “B”
Phase “C”
4.0
4.0
4.0
4.0
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):
208V • 71.5A • √ 3
kVA =
1000
kVA = 25.8
A 30kVA UPS could be selected as a minimum
Emerson Confidential
Something to take home
z
Single phase capacity
– V x A = VA
– 120 x 100 = 12 Kva
z
Three phase capacity
– V x A x 1.73 = VA
– 208 x 100 x 1.73 = 36 Kva
Emerson Confidential
Something more to take home
z
Power factor = Kw / Kva
– Kva = Kw / Pf
z
Must know kVA and kW to properly select UPS size
– kW can be determined from PF and kVA
z
Maximum UPS output at rated power factor
– 100Kva/80kW unit can be fully loaded at 80Kva if load PF is 1.0
Emerson Confidential
The End