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Zero Sequence Filters For Harmonic Mitigation
Tyrone Ding, Pooya Bagheri tding@ualberta.ca, pooya.bagheri@gmail.com
The proliferation of the energy-efficient consumer electronic
appliances in modern households has resulted in significant voltage
and current waveform distortions in residential distribution systems.
Although each of the consumer electronic appliance is not individually
a big source of harmonics, the collective effect will be considerable and
can become a serious concern of utility companies.
Due to the fact that most of residential loads are single-phase, Zero-
Sequence (ZS) harmonics are expected to be created at the three phase
distribution feeders feeding them. High levels of ZS harmonics could
lead to neutral voltage/current raise and interference problems with the
adjacent telephone lines. Therefore, the ZS harmonics must be
considered when researching the harmonic mitigation solutions for
modern residential feeders.
Introduction
Traditional ZS Filters
Power and Energy Innovation Forum ♦ University of Alberta ♦ November 2013
Zero Sequence Frequency Scan of Designed Filters
A B C
A B C A B C
(a) Star-type (b) Star-type including a
three-phase inductor
(c) Zig-zag
transformer-based
The main drawbacks of traditional ZS filters are:
• The star-type (a) and (b) can affect the fundamental power flow and
may lead to positive or negative sequence resonances at other
frequencies.
• The zig-zag transformer-based type needs a nonstandard
transformer.
Transformer-based ZS Filters
Here the transformer-based ZS filters is developed from the concept
of grounding transformer. Such filters behave as an open circuit at
positive and negative sequences so it has no impact on normal power
system operation and non-zero-sequence harmonics.
C
A
B
C
N
A
B
C
N
(a) Single-tuned
Expanding the filter
configuration to trap two
harmonic orders with
just one transformer
(b) Double-tuned
Expanding the filter
configuration to trap
three harmonic orders
with just one transformer
A
B
C
N
(c) Three-tuned
C3
L1
C1
C2 L2
C2 L2
C1
Telephone Interference Mitigation Case Study
The 240/25 kV
Substation
Downstream
loads
Upstream
loads
Filter Location
Telephone line
sections Monitoring
Location
F
Transformer Size 75 kVA
Single-tuned
version C 10.29kVar
Double-tuned
version
C1 7.00kVar
C2 24.60kVar
L2 40.60µH
Three-tuned
version
C1 16.46kVar
C2 11.57kVar
C3 10.29kVar
L1 206.35µH
L2 293.35µH
3rd 5th 7th 9th 11th 13th 15th0
2
4
6
8
IDD
(%)
Simulation Results
No Filter
Single-tuned filter
Double-tuned filter
Three-tuned filter
The single-tuned filter is tuned to filter 9th harmonic, double-tuned filter
is tuned to filter 9th and 15th harmonics and three-tuned filter is tuned to
filter 3rd, 9th and 15th harmonics.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 300
1000
2000
3000
4000
5000
Harmonic Order
Zero
Seq
uen
ce I
mp
ed
an
ce (
)
Single-tuned
Double-tuned
Three-tuned
Key Design Procedures
Substation
A block of residential loads
(e.g. a neighbourhood)
Filt
er
Normal Harmonic flow
New harmonic flows
after the filter is installed
• Determine ZS filter installation location.
• Assess transformer loading level.
Both of these two key design procedures are based on the harmonic
flow study of the problematic feeder.
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