Impact of Non-Linear Loads on
Wiring Requirements
Jens Schoene
December 06, 2011
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Who we are
 EnerNex is a consulting company with headquarter in Knoxville, TN
 Power System Studies
–
–
–
–
Power Quality
Wind and Solar (design, generator modeling,…)
T&D (bulk system analysis, SSR, CSS)
Safety (arc flash, grounding, electromagnetic coupling)
 Smart Grid Engineering Studies
– Advanced Metering Infrastructure (AMI)
– Utility Communication Architecture
– Security
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2
Outline
Motivation
Fundamentals of Power Quality
Changing Energy Consumption and Changing Loads
Characteristics of “New” Lighting Technologies
Case Studies
Conclusions and Recommendations
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3
Motivation
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Background
 Higher penetration of “new” load types:
–
–
–
–
Energy-efficient lighting
Consumer electronics
Residential appliances
Plug-in Electric Vehicles
 What is the impact?
– Wiring requirements
– Efficiency, reliability, power quality
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NEC Wiring Requirement
NEC 310.15(B)(5)(c)
No information regarding harmonic limits for which the
neutral has to be considered a current carrying conductor
No information regarding required size of neutral
conductor in the presence of harmonics
Old buildings have undersized neutral or neutral size equals
the size of the phase conductor.
New commercial buildings commonly employ oversized
neutral.
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Fundamentals of
Power Quality
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What are Harmonics?
 Harmonics are sinusoidal voltages
and currents with frequencies that
are integer multiples of the
fundamental frequency (60 Hz in the
United States).
 Value of the multiplier corresponds
to the harmonic order.
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General Effects of Harmonics
Harmonics can cause
 Transformer overheating resulting in the shortening of the
expected lifetime
 Capacitor can failure due to excessive harmonic currents or
overvoltage stress on dielectrics
 Increased ohmic losses and shortened lifetime of cables
 Overloaded neutral conductors (odd harmonic currents do
not cancel in the neutral conductor)
 Nuisance tripping of breakers and fuses
 Motor heating
 Control misoperation
 Communication system interference
 Degrade meter accuracy
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Effects on Wiring Requirements
Measure of heating in conductor is product of squared
current I and impedance Z (I2Z)
Harmonics increase heating in conductors due to
– additional load current flowing throughconductor
– current redistribution inside conductor (skin effect)
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10
What is special about 3rd Harmonics?
 Add arithmetically in the Neutral
(assuming balanced 3-phase system)
 Many electronic loads produce them.
 Neutral size in commercial building of
particular concern.
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How to Quantify Harmonics
 Individual Harmonic Distortion (IHD) Level
Percentage of individual harmonic relative to
fundamental
 Total Harmonic Distortion (THD) Level
Percentage of RMS of all harmonics relative 𝑇𝐻𝐷 =
to fundamental
 IEEE 519 specifies limits
IHD for Odd Harmonic Currents
ISC/IL
h < 11
11 ≤ h < 17
17 ≤ h < 23
23 ≤ h < 35
35 ≤ h
<20
20-50
50-100
100-1000
>1000
4.0%
7.0%
10.0%
12.0%
15.0%
2.0%
3.5%
4.5%
5.5%
7.0%
1.5%
2.5%
4.0%
5.0%
6.0%
0.6%
1.0%
1.5%
2.0%
2.5%
0.3%
0.5%
0.7%
1.0%
1.4%
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2
𝑛
𝑖=2 𝐻𝑖
𝐻1
∙ 100%
THD for
Odd
Harmonic
Currents
5.0%
8.0%
12.0%
15.0%
20.0%
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Changing Energy Consumption
and
Changing Loads
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Increasing Electricity Consumption
Residential Electricity Consumption in the U.S.A. 1990-2006
5000
4500
1400
4000
1200
3500
1000
Per-Capita
Electricity
Consumption
800
600
400
Total
Electricity
Consumption
2500
2000
1500
1000
200
500
0
1990
3000
0
1992
1994
1996
1998
Year
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2000
2002
2004
2006
Per-Capita Electricity Consumption (kWh)
Total Electricity Consumption (TWh)
1600
source:
International
Energy Agency,
2009
14
What consumes Electricity?
Distribution of USA Electricity Consumption in 2005
source:
Energy
Information
Administration,
2008
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15
Changing Electricity Consumption
Change in Electricity Consumption (TWh)
Changes in Electricity Consumption in the USA from 1998 to 2008
120.00
100.00
80.00
60.00
40.00
20.00
0.00
-20.00
-40.00
-60.00
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source:
International
Energy Agency,
2009
16
Changing Electricity Consumption
Global CE and ICT Electricity Consumption 1990-2030 (Business As Usual)
Electricity Consumption (TWh)
2000
1800
1600
Miscellaneous
1400
PCs and Monitors
1200
Set-top Boxes
Televisions
1000
800
600
400
200
0
1990
1995
2000
2005
2010
2015
2020
2025
2030
source:
International
Energy Agency,
2009
Year
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Changing Electricity Consumption
Global CE and ICT Electricity Consumption 1990-2030 (BAU, LLCC, BAT)
Electricity Consumption (TWh)
2000
1800
1600
1400
Business As Usual (BAU)
Least Life-Cycle Cost (LLCC)
Best Available Technology (BAT)
1200
1000
800
600
400
200
0
1990
1995
2000
2005
2010
Year
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2015
2020
2025
2030
source:
International
Energy Agency,
2009
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Lighting
Lighting is 16% of residential load
Most incandescent lamps phased-out by 2014
Compact Fluorescent Lamps
– Color Rendering Index around 80
– Some are dimmable (most are not)
– Some are high power factor / low harmonics (most are not)
White LED
– Even more efficient than CFL
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Characteristics of
“New” Lighting Technologies
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Increased Energy Efficiency
250
Electricity Consumption (Watt)
Incandescent Light (750 to 4,000 Hours)
Compact-Fluorescent Light (8,000 to 12,000 Hours)
200
White LED (30,000 to 50,000 Hours)
150
100
50
0
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Initial Luminous Flux (Lumen)
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How does a CFL work?
Electronic Ballast in Energy-Efficient Lighting
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Harmonic Characteristics
Incandescent
Compact
Fluorescent
White LED
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Case Studies
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Currents and Voltages Measured at
Different Locations (PQube Data)
Comp. 1: Office Building in Knoxville, TN
Transformer Configuration
Nominal Line-to-Neutral Voltage
Nominal Line-to-Line Voltage
Nominal Frequency
Wye/Star
120V
208V
60Hz
Comp. 2: Manufacturing Facility in Alameda, CA
Transformer Configuration
Nominal Line-to-Neutral Voltage
Nominal Line-to-Line Voltage
Nominal Frequency
Wye/Star
277V
480V
60Hz
Comp. 3: Office Building in Santa Clara, CA
Power Configuration
Nominal Line-to-Neutral Voltage
Nominal Line-to-Line Voltage
Nominal Frequency
Wye/Star
120V
208V
60Hz
Comp. 4 Manufacturing Facility in Karlsruhe, Germany
Power Configuration
Nominal Line-to-Neutral Voltage
Nominal Line-to-Line Voltage
Nominal Frequency
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Wye/Star
230V
400V
50Hz
25
Phase Currents
Industrial
Commercial
Industrial
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Industrial
Commercial
26
Neutral Currents
Commercial
Industrial
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Industrial
Commercial
27
Conclusion and
Recommendations
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Conclusions & Recommendations
Electricity consumption and load characteristics changing
3rd harmonics produced by power electronics are concern
NEC does recognize neutral as current carrying conductor,
but no guidance/requirement regarding size.
Neutral sizing requirements should be based on statistically
significant data from measurements of neutral currents in
different environments (office buildings, residential
building, etc.)
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Backup
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Power Factor: Displacement vs. True
Not all Power Factors are alike
Im
S
jQ
q
P
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Re
31
Resonances
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Series Resonance
Distribution Substation Bus
High
Voltage
Distortion
High
Harmonic
Currents
Customer
Power Factor
Correction
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Parallel Resonance
High
Voltage
Distortion
Magnified
Harmonic
Currents
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Non-Linear
Loads
34