Download PP.AFD.07

Yaskawa Electric
America
Harmonic Currents, Voltages
and
Your Building Power System
7/08/2002
PP.AFD.07 Harmonic Quality
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Discussion
Points
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
Power Factor

Harmonics

The Building Power System

Current Distribution Limits

Power System Solutions
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Power Factor

Power Factor is the ratio of the actual
power (kW) being used to the apparent
power being drawn from the line (kVA)

Measurement of the effectiveness of
power usage
•
7/08/2002
The higher the PF, the more efficient the
system
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Power Factor
 To determine Power Factor,
divide kW by apparent
power (kVA)
 Low Power Factor increases
cost of supplying power
•Overloads generators,
transformers, distribution
lines, etc.
•Utilities penalize large
users for low power factor
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kVA
PP.AFD.07 Harmonic Quality
kVAR
kW
Power Factor = kW / kVA
kVAR is reactive power Maintains the
electromagnetic field
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Power Factor
• AC Drives power factor follows concept
except current not a pure sinewave, they
contain harmonics
• Current closer to a square wave than sine
wave
• Most VFD manufacturers use displacement
power factor
• Displacement PF = The cosine of the angle between the
fundamental kVA and kW
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Power Factor
• The effect of harmonics
reduces true power factor
kVA ( Harmonic)
Harmonic
kVAR
• Power factor measurement
by utilities only measure
fundamental current,
therefore only measure
displacement PF.
kVA
kVAR
kW
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Power Factor
.95
.95
PF
PF
% SPEED
% SPEED
100%
FIG 1
100%
FIG 2
• Fig 1. Six step VFD Power Factor Linear with speed
• Fig 2. PWM VFD PF constant with speed
• Harmonics reduce PF for both but can be improved
using DC Link Reactors, AC Line Reactors, etc
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Power Factor
Summary






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The higher the PF, the more efficient the system
Harmonics may result in reduction in power
factor
All non-linear loads add to harmonics
Utilities may penalize for low power factor
Utilities measure displacement PF.
Bottom Line: Not being penalized? No Problem!
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Harmonics:
What Are They?

Fundamental - the Base Frequency
•

Harmonic - Multiples of the Fundamental
•

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For Power Lines 60 Hz is Fundamental
Fifth Harmonic is (5 x 60) or 300 Hz
Only Associated With Periodic Waveforms
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Harmonics:
What Are They?
IEEE 519 defines harmonics as:
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•
A sinusoidal component of a periodic waveform or
quantity having a frequency that is a multiple of the
fundamental frequency
•
They are steady state state distortion of the AC line,
unlike transients, surges and other things that
typically only last a few cycles. They cause stress in
the distribution system and can cause heating of
motors and transformers
•
Reduces the operational life of these devices
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Harmonics:
What are they?

Harmonics can also affect the power
supplies of other VFDs

Can cause spurious fuse blowing and
circuit breaker trips
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Harmonic
Waveforms
Fundamental
Third and Fifth Harmonic
Seventh
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Harmonic
- 60 hz
- 180 and 300 hz
(420 hz) and Resultant
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of Fundamental,
3, 5, 7
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Calculating
Harmonic Distortion

Harmonic and Fundamental Currents
•
•


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Not Added Directly
“Square Root of Sum of Squares”
Total Harmonic Distortion (THD) =
( I32 + I52 + I72 + I92 + I112 + . . . )) / Ifund
Total Current = Ifund2 + Iharm2 )
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Harmonic
Current and THD
•
•
•
•
•
•
System Voltage - 100 v
Load 1 - A Personal Computer Power Supply
Load 2 - 125 hp HVAC Air Handler Motor
Iharm = Ifund * THD (in %) * .01
Ifund = Watts / Volts
Itot = Ifund2 + Iharm2 )
Computer
Power - Watts
Harmonic Distortion (%)
60 hz Current - amps
Harmonic Current - amps
Total Current
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100
100
1
1
1.41
HVAC Motor
100,000
1
1000
10
1000.05
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Building
Power System

Building Loads
•
•

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Repetitive and Synchronous
Random and Asynchronous
Distribution System
•
Service Entrance/Distribution Transformers
•
The Bus/ Riser System
•
The Power/Lighting Distribution Panels
•
Circuit Breakers
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Building
Load Types


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Repetitive and Synchronous
•
Resistive
•
Reactive
•
Nonlinear
Random and Asynchronous
•
Transients
•
Noise
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Resistive
Loads


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Examples of Resistive Loads
•
Incandescent Lighting
•
Electric Heater Elements
Resistive Load Current
•
I load = V load / R load
•
I Waveform Proportional to V Waveform
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Resistive
Waveshapes
Voltage and Current are In Phase and Proportional
pltivres.cgm
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Reactive Load


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Examples of Reactive Loads
•
Electric Motors
•
Contactors, Relays, Solenoids
•
Transformers, Line Reactors
Reactive Load Current
•
I load = V load /  (R2 load + L2 load)
•
Current Phase Shifted with respect to Voltage
•
I Waveform Proportional to V Waveform
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Reactive Waveshapes
Current Lags Voltage But Waveforms Are Proportional
pltivind.cgm
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Non-Linear Loads

Examples of Non-Linear Loads
•
•

Computers, Faxes, Printers, Phone Systems
Variable Frequency Drives (VFDs)
Non-Linear Load Current (Single Phase)
•
I load = (sin 1f) + (sin 3f) *n3 + (sin 5f) *n5 +
(sin 7f) *n7 + (sin 9f) *n9 + (sin 11f) *n11 + ...
•
I load Characteristics
–
–
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Zero for 120 Degrees of Half Cycle
High Crest Factor Surge for 30 Degrees
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Non-Linear
Waveshapes
Voltage is sinusoidal; Current is high harmonic waveform.
pltivnll.cdr
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Non-Linears
Rich in Harmonics
Non-Linear
Loads
Are Rich In Harmonic
Fundamental
Third, Fifth, and Seventh
(60hz)
(180 hz, 300 hz, 420 hz)
Resultant
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Current
Current
Waveform
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Currents
Harmonic
Currents
nllharm.cdr
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3 Phase
Rectifier Current
%
o
f
Three Phase Harmonic Spectrum
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
31
29
27
25
23
21
19
17
15
13
11
9
7
0
5
F
u
n
d
a
m
e
n
t
a
l
Harmonic Number
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Transient
Load Characteristics


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Examples of Transient Loads
(at turn-on/turn-off)
•
Elevator Motors
•
A/C Compressor Motors
•
Short Circuit / Breaker Clear
Transient Load Current
•
Itransient Is Unpredictable and Asynchronous
•
Itransient Approximates a Step Response
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Transient
Waveshapes
Transient
Voltage
Currents
is Zero
Cause
at High
Large
Current,
Voltage
Spikes
Disturbances
at Current
Decay
f aulti.cgm
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Noise
Characteristics


7/08/2002
Example of Noise
•
VFD Power Converter Switch Spikes
•
Relay Openings and Closures
Noise Currents
•
Inoise Large and of Short Duration (uSec)
•
Inoise May be Common or Differential Mode
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IEEE 519-1992
Table 10-3
Isc/ IL
Harmonic Current (Odd)
% THD
<11
11<h<17
17<h<35
35<h
<20
4.0
2.0
1.5
0.6
0.3
5.0
20-50
7.0
3.5
2.5
1.0
0.5
8.0
51-100
10.0
4.5
4.0
1.5
0.7
12.0
101-1000
12.0
5.5
5.0
2.0
1.0
15.0
>1000
15.0
7.0
6.0
2.5
1.4
20.0
IEEE 519 - 1992 Table 10-3 Recommended Practice Max Harmonic Current
Distortion of the Fundamental
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Current
Distortion Limits

PCC (Point of Common Coupling)
•
•
Most important and most controversial item
in IEEE
Defined as:
–

(ISC) Max Short Circuit Current at PCC
–
7/08/2002
The electrical connecting point between the utility
distribution system and the users electrical
distribution system
Determined by the size, impedance, and voltage
of the service feeding the PCC.
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IEEE 519

(IL) Max demand load current at PCC
–
–

(ISC/IL)The ratio of available current at
the PCC to the max demand load
current at the same point.
–
7/08/2002
Facilities should measure this over a period of
time and average it.
If not possible - calculate the anticipated peak
operation of the facility
Measures the stiffness of the electrical system
relative to the load. The larger the power source
in relationship to the load, the stiffer the system.
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IEEE 519

TDD - Total Demand Distortion
–

PCC 1 as measuring point
–
–
–

TDD allowed to be 12%
5th and 7th 15%
No filtering needed
PCC 2 as measuring point
–
–
–
7/08/2002
The measure of the total harmonic current distortion at the
PCC for the total connected load.
TDD allowed to be 5%
5th and 7th 4%
Filtering needed
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IEEE 519
13,800V
69KV
PCC1
PRIMARY OF SERVICE TRANSFORMER
20,000 KVA
TR-1 8.5%
PCC2
480V
PCC1 - if THE COMPANY
OWNS THE XFORMER,
UTILITY WILL
MEASURE HERE
PCC2- IF UTILITY
MEASURES 480V
PCC 2 IS INTERFACE
200kVA
200kVA
200kVA
VFD
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IEEE 519

Voltage Distortion Limits per IEEE 519

Defines the quality of power on the
electrical distribution system.
–
–
7/08/2002
Individual Voltage Distortion 3%
Total Voltage Distortion 5% allowed
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Harmonic
Solutions

No Filtering
•

Isolation Transformers
•
•
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Loads less than 25%- must be very stiff
Very costly
Not required by PWM drives except as
harmonic filters
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Harmonic
Solutions

7/08/2002
AC Line Reactors - 25% Load
•
Greatly improves voltage distortion
•
Current distortion improvement similar to DC Link
Reactor
•
More cost effective than Isolation Transformer
•
Usually effective means of meeting IEEE requirements
•
Improves power factor
•
Protects VFDs from transients
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Harmonic
Solutions

DC Link Reactor up to 40% Load
•
•
•
•
•

DC Link w/ AC Line Reactor
•
•
7/08/2002
More cost effective than AC Line Reactor
Reduces Voltage Distortion effectively
Reduces Current Distortion somewhat less effectively
Improves PF but not as well as AC Reactor
Smaller than AC Reactors
Somewhat better than either system alone
Similar results as DC Link Reactor
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Harmonic
Solutions

Harmonic Trap Filter - 60% Loaded
•
•
•
7/08/2002
5th Harmonic Trap Filter in series with AC
5% Line Reactor
Effective at reducing Voltage and Current
distortion
Very expensive
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Harmonic
Solutions

7/08/2002
12 Pulse (Dual Diode) Transformer
80% or more
•
Most effective method of Harmonic Distortion
reduction
•
Not as expensive as Trap Filters
•
Similar in size to Isolation Transformers
•
Last resort
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Harmonics
Conclusions




7/08/2002
All non-linear power structures cause
harmonics
Harmonics reduce power factor
Filtering requirements depend on where you
are measuring harmonics
Knowing all harmonic distortion and using
appropriate filtering on a system wide
approach, insures a more reliable, cost
effective solution.
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Typical
Harmonic Contents
Harmonic Content of Typical Commercial
Building Electrical Equipment
Equipment
Harmonic Content - %
1 Phase
3 Phase
Magnetic Ballasts
Electronic Ballasts
Personal Computers
Fax, Phone, Printer
Motors
VFDs
VFDs w/Line Reactors
7/08/2002
19-40
<20
80-140
80-140
-------
PP.AFD.07 Harmonic Quality
>7
<5
+/-40
+/-40
3
25-80
<25
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Distribution System

Service Entrance Transformers

Power Distribution Transformers

Lighting Distribution Transformers

“Isolation” Transformers

The Building Riser System

Power/Lighting Panels, Circuit Breakers
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All Transformers
Are Inductive
Rxfmr
Lxfmr
Zxfmr
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Transformer
Impedance vs. Hz
Transformer
Impedance
Rises Proportionally
With Frequency
1.35 ohm
0.27 ohm
60 hz
7/08/2002
300 hz
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Vdistort Increases
With Frequency

Zxfmr = 2P * freq *
Lxfmr

Vdrop = Iharm * Zxfmr
7
6
5
4
3
2
1
0
Series1
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
Series2
1
Blue - Harmonic Current
Red - Distortion Voltage
Harmonic Spectrum and Voltage Drop (Distortion)
Harmonic Number
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Current Is Problem,
Not THD



Assume all 5th Harmonic Current
Use 1.35 ohm Transformer Z
Vdrop = Iharm * Zxfmr
Computer
Pow e r - W a tts
Ha rmonic Distortion (%)
60 hz Curre nt - a mps
Ha rmonic Curre nt - a mps
Tota l Curre nt
Volta ge Distortion (%)
7/08/2002
PP.AFD.07 Harmonic Quality
100
100
1
1
1.41
1.35
HVAC Motor
100,000
1
1000
10
1000.05
13.5
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Result:
Voltage Distortion
Harmonic
Voltage
Current
Cause
- Blue
and High System
Voltage
Distortion
Current
Impedance
- Red
pltv dist.cgm
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Summary:
Harmonic Current

Total Harmonic Distortion - THD
•
•

Causes Nothing
It Is a Factor, a Percentage
Harmonic Current Can be a Problem
•
•
A Function of Total Current
And Total Harmonic Distortion (THD)
 Iharmonic

Modern Loads on the Power Bus
•
•
7/08/2002
Current Can Cause Voltage
Produce High Harmonic Current
Cause Spikes, Transients, Noise
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Summary:
Distribution

The Power System - Inductive in Nature

Impedance Increases With Frequency

The Bus Distributes to Other Loads:
7/08/2002
•
Distorted System Voltage
•
Voltage Dropouts
•
Voltage Spikes, Surges, Transients
•
System Resonances
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Conclusions
for the Industry

Retrofits Reduce Total Building Current

Harmonics - No Problem w/Lighting Circuit
•
•
•

Harmonics - Problem with Power Panels
•
•
•
7/08/2002
Loads are Typically Balanced
Ballasts Have Low Harmonic Current
Electronic Ballasts Reduce Harmonic Current
Loads may be Unbalanced
Loads Produce High Harmonic Current
Loads are Susceptable to Distorted Voltage
PP.AFD.07 Harmonic Quality
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