Harmonic Reduction Techniques
Department of Electrical
HK Polytechnic University
What is a power quality problem?
What are harmonics and triplen harmonics?
What are the major causes of harmonics?
What are typical harmonic current and voltage
What are the future trend?
What are the effect of harmonics?
“Don’t think there are no
crocodiles because the
water is calm”
Power electronics technology has become widely accepted
in industrial, commercial, and municipal facilities.
In high rise buildings, almost every office has a computer,
a printer etc and every floor has a photocopy machine, a
fax machine etc, all driven by power electronics.
With these increasing installed base comes inevitable
problems, like reduced power quality, harmonic distortion
problem with its disruptive effect and low power factor with
its costly consequences.
In this talk, we’ll try to explore these problems and see how
power electronics can actually solve many of these
What is a power quality problem?
A Power Quality Problem is:
Why is Power Quality Important
Load Equipment Sensitivity
POWER QUALITY MEANS PRODUCTIVITY
Categories of Power Quality
Voltage Variations (Sags) and
Harmonics are currents or voltages at higher frequencies
than the fundamental power frequency (50Hz)
Most significant harmonics are the low order integral
harmonics, typically from the 2nd to the 31st.
The use of newer devices such as cycloconverter,, slip
recovery drives etc. has produced frequencies which are
integer multiples of the supply frequency, I.e. non
characteristic harmonics with possible side band and
they are often refereed to as ‘inter
Harmonics results from the distortion of sine wave caused
naturally by non
Harmonics distortion can affect voltage or current or both
These disturbances can cause significant problems within a facility
Often harmonic remains an unknown problem until major
Harmonics can even flow back into the supply line and create
havoc at other locations
Harmonic is a problem that needs to be addressed ideally during
planning stages but certainly as soon as signs of its occurrence is
“Even if you are on the right track,
you’ll get run over if you just sit
A classic example, a high rise building in Sydney, Australia
During its design stage, it appears that there are ample capacity in the
transformer to meet the the total demand of the building and the
wiring is perfectly adeaquate to meet the projected peak load with
A few weeks later when people moves in and everybody adds
computer, fax machine, printer etc to their desk, the transformer that
supplies the building was overloaded and very hot, yet the actual watt
loading in the building is very low.
The heating that was taking place in the transformer is totally due to
Success comes from good judgment
Good judgment comes from
Experience comes from bad
In the past, the ideal goal of the the utility is to have the power factor
near unity or around 0.9 and the customer then make business
judgment on the best way to meet this requirement due to his own
load and that’s the end of the problem.
However, now power factor is not only due your own load, it also
depends on the utility’s quality of supply and due to your neighbour’s
With the competitive electricity supply industry, the utility are now
being forced more and more to provide quality service at a reasonable
cost to the customer
The customer’s responsibility is first to minimise his cost and then to
be a good neighbour.
Classifications of harmonics:
positive sequence etc.
Triplen harmonics are all the odd harmonics which are multiple of
third harmonics. In 3
phase 4 wire system, they are in phase with
each other and add numerically in the neutral conductor wire.
Major Causes of Harmonics
Power Electronics Converters
DC power supplies in Computer, TV, Fax machines, printers etc
Uninterruptible Power Supplies (UPS)
Solid State Rectifiers
Electronic Process Control equipment, PLC’s etc
Electronic Lighting Ballasts, including Light Dimmer
Reduced Voltage Motor Controllers
Electrical Traction System
Variable speed ac motor drives
Electrochemical and electro
Major Cause of Harmonics(cont.)
Discharge Lighting, e.g. Fluoro, Sodium or Mercury Vapour
Transformer operating near saturation level
Magnetic Ballast (saturated iron core)
Static Var Compensator
Slip Recovery Drives
Typical Harmonic Current and VoltageDeviation
Standard Personal Computers
Signs of Harmonic Problems
Customer capacitor or transformer failure
Capacitor fuse blowing
Transformer overheating at less than full load
Clocks running fast
PLC and Computer Failures
Faulty Operation of relays and meters
Hard disk data corruption
Switch mode power supply failure
High Neutral Currents
Signs of Harmonic Problems
These disturbances can cause significant problems
within a facility
Often harmonic remains an unknown problem until
major disruption occurs
Harmonics can even flow back into the supply line and
create havoc at other locations
Harmonic is a problem that needs to be addressed ideally
during planning stages but ceratinly as soon as signs of
its occurrence is detected.
Electronic Loads Cause Excessive Neutral Current
Why harmonics are now being recognised as a a major
Exponential growth of electronics loads in recent years
More intelligent buildings over last decade
Information super highway and Internet
Lack of awareness and understanding
Numerous reported problems on harmonics and power quality
from various existing electrical installations in different major
Harmonics now form an integral part of the mandatory EMC
regulations in USA, European community, Australia, etc.
Why harmonics are the future trends in power system
More prevalent because:
The application of sophisticated electronic controlled equipment would
dominate over a wide area
Future buildings will be more intelligent especially the high rise premises.
Many countries are constructing or planning to build the world tallest smart
21st century information super highway with next generationcomputers
with speed of 10
100 times faster than the current technology and space age
linear loads in USA has increased from 5% in1960 to
30% in 1990. It is estimated that it will reach 60% by the year
Symptoms of Voltage Variation Problems
Tripping of sensitive loads
(PLC, motor controls, process
controls, machine tools etc.)
Arc Lighting drops out
Remote Transmission Fault
Causes Sensitive Loads to trip
Symptoms of Interruptions
loss of loads
Multiple trips (reclosing operations)
Symptoms of Transient Problems
ASD’s & process loads tripping frequently
Equipment failures during lightning storms
Distribution transformers fail during storm
Customer capacitor failures/fuse blowing
Equipment failures on the network
TV failures with cable connection
Utility Capacitors Switching
causes drives to trip
Why is equipment sensitive
Low signal voltage levels
Fast processing speed
Electronic circuit design without shielding or
Lack of Energy Storage in power supplies
Source of the problems can be anywher
Equipment sensitivity determines
ent of problems
Solutions must be developed using SYSTEM
System Approach to solving Power Quality
Identify the Problem
Characterise the problem
What is the Source?
What are the possible solutions?
Cost of the
Cost of the Solutions
Active filters are proving to be a viable option
for controlling harmonic distortion levels in
The application of passive tuned filters creates
new system resonances which are dependent
on specific system conditions.
Also, passive filters often need to be
significantly overrated to account for possible
harmonic absorption from the power system.
Passive filter ratings must be coordinated with reactive
power requirements of the loads and it is often difficult
to design the filters to avoid leading power factor
operation for some load conditions.
Active filters have the advantage of being able to
compensate for harmonics without fundamental
frequency reactive power concerns.
This means that the rating of the active power can be
less than a comparable passive filter for the same
nonlinear load and the active filter will not introduce
system resonances that can move a harmonic problem
from one frequency to another.
The active filter concept uses power electronics to
produce harmonic components which cancel the
harmonic components from the nonlinear loads.
These active filters are relatively new and a number
of different topologies are being proposed.
Within each topology, there are issues of required
component ratings and methods of rating the
overall filter for the loads to be compensated.
Active Filter Configuration
One leg of the active Filter
Source strength at transmission supply point = 200 MVA 138/13.8
kV Transformer: 10 MVA, 7% impedance
Substation capacitor bank size = 3.0 Mvar (switched)
Equivalent load for parallel feeders = 3.0 MW
Modeled feeder circuit: 3.0 miles to example customer
Feeder capacitor bank on 13.8 kV side at example customer:
different sizes evaluated
Customer low voltage capacitor bank: varied
Customer service transformer: 1500 kVA, 6% impedance
Customer load = 1.0 MW
Active Filter size = 400 Vrms, 30 Arms
Nonlinear load: different loads evaluated