Introduction To Harmonics

1
Introduction To Harmonics

• What are Harmonics?
• Causes, problems and symptoms
• Popular harmonic standards and their application
  to industrial power systems

2
What Are Harmonics?

• Higher frequency current or voltage
• periodic (continuous vs. transient)
• integer multiples of fundamental frequency
• (50hz)3rd 150hz, 5th 250hz, 7th 350hz, etc
• (60hz) 3rd 180hz, 5th 300hz, 7th 420hz,
  etc
• Power system distortion
• voltage and current

3
Harmonics
Fundamental
Harmonics
True RMS
Harmonics increase the TRMS current
4
Harmonic Current Distortion
8
?
I2
h
h 2
THID
x 100
I1

• Where
• Ih magnitude of individual harmonic content
  (RMS amps)
• h harmonic order
• I1 fundamental current (RMS amps)

5
Harmonic Current Distortion
RMS value of all harmonic currents RMS value of
Fundamental current
x 100
6
Harmonic Current Distortion

• Fundamental Method
• RMS Harmonic Current
• RMS Fundamental Current
• (B/A)

RMS Fundamental
A
B
RMS Harmonics
C

• RMS Method
• RMS Harmonic Current
• TRMS Current
• (B/C)

TRMS
7
Basic Causes of Current Harmonics

• Loads that draw non-sinusoidal current
• Power supplies operating on a stiff power source
• Rectifiers connected to low impedance power
  sources
• Linear loads operating form a distorted voltage
  source

8
Harmonics are Caused by Non-Linear Loads
Typical input current waveform for six pulse
rectifier
Non distorted waveform (linear load)
9
Equipment That Causes Harmonics

• Variable Speed Drives
• UPS
• Induction Heating Equipment
• Saturated transformers
• Electronic welders

• Single phase rectifiers
• 3,5,7,9,11,13..
• Six pulse rectifiers
• 5,7,11,13,17,19.
• Twelve pulse rectifiers
• 11,13,23,

h kp /- 1
10
Harmonics Distort the Power Supply
(Non-Distorted) Fundamental
Fifth Harmonic only
Fundamental w/ 5th harmonic distortion
11
Problems Caused By Harmonics

• Other equipment may over heat
• Interference with other sensitive equipment
• Interference with sensors and timing devices
• Upstream conductors and equipment see elevated
  higher TRMS amps
• Nuisance fuse/ CB operation
• True PF is low

12
Symptoms of Harmonics

• TRMS current exceeds 50/60hz amps
• Transformers over heat
• Fuse blowing / circuit breaker tripping
• Motor heating
• Equipment life reduction
• Equipment interference

13
Harmonics Depend on Total Input Impedance
14
Typical Harmonic Current Distortion (6-pulse
rectifiers)
Without ac line reactor or dc bus choke
15
Effect of Source Impedance
3 impedance
Low impedance
High peak RMS current
Lower peak RMS current
16
TRMS Input Current depends on Harmonics
60 THID
80 THID
100 THID
Fundamental 1.0
Fundamental 1.0
Fundamental 1.0
Harmonics .60
Harmonics .80
Harmonics 1.0
TRMS 1.166
TRMS 1.28
TRMS 1.414
10 THID
20 THID
40 THID
Fundamental 1.0
Fundamental 1.0
Fundamental 1.0
Harmonics .10
Harmonics .20
Harmonics .4
TRMS 1.005
TRMS 1.02
TRMS 1.077
17
Harmonic Standards

• IEEE-519 (USA, etc)
• EN-61000 (Europe)
• 3-2 (lt 16 amps)
• 3-4 (gt 16 amps)

18
IEEE - 519

• PCC Point of common coupling
• At metering point
• Point where non-linear loads meet linear loads
• TDD Total demand distortion
• THD Total harmonic distortion

19
IEEE - 519
20
Applying IEEE - 519 Harmonic Limits
Isc / I (load) 25

• Isc 25,000 amps
• I(load) 1000 amps

Limit 8 THID
Isc / I(load) 260
Limit 15 THID
I(load) 96 amps
L
L
N
L
21
EN61000-3-2 Harmonic Current Limits

• Odd Harmonics
• 3 2.30 amps
• 5 1.14
• 7 0.77
• 9 0.40
• 11 0.33
• 13 0.21
• 15ltnlt39 0.15x(15/n)

• Even Harmonics
• 2 1.08
• 4 0.43
• 6 0.30
• 8ltnlt40 0.23x(8/n)

Input current harmonics should not exceed the
absolute values shown
22
Draft EN61000-3-4 Recommendations

• Three-phase equipment
• Shall comply with table 3
• Relative value of even harmonics (? 16/n)
• Relative value of triplen harmonics (? 9/n)
• Supply authority may accept connection under
  special conditions

23
Draft EN61000-3-4 Limits
Harmonic Admissible Number n harmonic current
In/I() 3 21.6 5 10.7 7 7.2 9 3.8 11 3.1 13 2.0
15 0.7 17 1.2 19 1.1 21 lt0.6 23 0.9 25 0.8 27 lt0.6
29 0.7 31 0.7 gt33 lt0.6 Even lt8/n or lt0.6
Stage 1 Connections without restriction short
circuit ratio gt 33.
24
Draft EN61000-3-4 Limits

• Stage two limits for three-phase equipment
• Table 3

25
Draft EN61000-3-4

• Total harmonic distortion
• THD ratio of the RMS value of the harmonics to
  the RMS value of the fundamental

40 ?


2
In
THD
I1
n 2
26
Draft EN61000-3-4

• Partial weighted harmonic distortion
• PWHD ratio of the RMS value of a selected group
  of higher-order harmonics, weighted by the
  harmonic order number (n), to the RMS value of
  the fundamental

40 ?


2
In
PWHD
n
I1
14
27
Applying Draft EN61000-3-4 Harmonic Limits

• Isc 25,000 amps I(load) 1000 amps

Rsce Isc / I(load) 260
Limit 35 THID
N
L
L
L
I(load) 96 amps
28
Alternative Solutions

• AC line reactors
• DC link chokes
• AC line reactors DC Link chokes
• Harmonic trap filters
• Low Pass harmonic filters
• 12-pulse or 18-pulse drives
• Active harmonic filters