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Ac harmonic filters
FILTER
FILTER
HVDC Main Components
T8396
AC Harmonic Filters
� Idealised harmonic currents
� Practical harmonic currents
� Characteristic harmonics
� Theoretically cancelled harmonics
� Non-characteristic harmonics
Types of Harmonic
T8395
Filter Design Objectives
�Limit voltage distortion
�Minimise reactive power imbalance
�Minimise losses
�Improve system performance
� Idealised harmonic currents
� Practical harmonic currents
� Characteristic harmonics
� Theoretically cancelled harmonics
� Non-characteristic harmonics
Types of Harmonic
T8395
Idealised Current Waveforms….
T8397
Combined Waveform…..
T8399
12 Pulse
Practical Harmonic Currents….
T8402
λ λ
πω ω ω ω ω
λ
πω ω ω ω ω
/
(cos cos cos cos cos ...
/
(cos cos cos cos cos ...
I ID
t t t t t
I ID
t t t t t
= − + − +
= + − + −
2 3 1
55
1
77
1
1111
1
1313
2 3 1
55
1
77
1
1111
1
1313
∆
Fourier Analysis
T8398
I ID
t t t
t t
= − +
− +
4 3 1
1 11 1
1
1 31 3
1
2 32 3
1
2 52 5
πω ω ω
ω ω
( c o s c o s c o s
c o s c o s . . .
Fourier Analysis
T8400
9
8
7
6
5
4
3
2
1
10 3020 40Overlap angle (degrees)
I11
I1
11th Harmonic as a Percentage of Fundamental
T8404
0.2 0.4 0.6 0.8 1.0
1
2
3
4
5
Harm
onic
lin
e c
urr
ent %
of
rate
d fundam
enta
l
Transmitted power (PU)
11th
13th
Characteristic Harmonic Generation
T8405
0.5
0.4
0.3
0.2
0.1
0.2 0.4 0.6 0.8 1.0
5th
7th
Transmitted Power(PU)
Harm
onic
lin
e c
urr
ent %
of
rate
d fundam
enta
l
Theoretically Cancelled Harmonic Generation
T8407
100
10
1.0
0.1
0.01
0.00110 20 30 40 50
Harmonic Number
In
I1%
Typical Spectrum…
T8409
� Orders n = 1, 2, 3, 4 etc.
� AC system unbalance (NPS)
� Transformer reactance phase unbalance
� Pre-existing distortion
� firing angle jitter
Non - Characteristic Harmonics
T8408
Filter
Zfn
System
ZSnIcn
Ifn
VSn
ISn
T8378
Rmin
X(O
hm
s)
R(Ohms)
400kV System Harmonic Impedance
T8381
Rmax
2
Sasaram Filters
T8379
400kV
Double Damped
Filter
400kV
Double Tuned Filter
AC Filter Layouts…
� Components mounted on the ground
� Insulation and magnetic clearances
� Two types of harmonic filter
� Double damped filter
� Double tuned filter
� Key Interlocking System for safety - to permit access only when filter is de-energised and earthed.
AC Filter Layouts Double Damped Filter
Admittance vs frequency for 400kV 112Mvar 3/13 double frequency filter
0.0000
0.0050
0.0100
0.0150
0.0200
0.0250
0.0300
0.0350
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
Harm onic
Adm
itance
3/13th Double-Frequency Filter
Admittance vs frequency for 400kV 112Mvar 11/25 double frequency filter
0.0000
0.0050
0.0100
0.0150
0.0200
0.0250
0.0300
0.0350
0.0400
0.0450
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
Harm onic
Adm
itance
11/25th Double-Frequency Filter
Single frequencytuned filter
2nd Order broadband
damped filter
3rd Order broadband
damped filter
‘C’ Type broadband
damped filter
Types of Filter
T8412
� Advantages
� Maximum attenuation at single harmonic
� Low loss
� Disadvantages
� May be de-tuned
� Off-circuit adjustment
Single Tuned
T8413
f1 f0 f2 Frequency
High Q
Low Q
Y
Effect of De-tuning
T8414
� Advantages
� Attenuation over a spectrum of harmonics
� Less sensitive to de-tuning
� Disadvantages
� Needs higher Mvar to achieve same performance as single tuned
� Additional losses in resistor
2nd Order Damped
T8416
Tuned / Damped Filters
f1 f0 f2 Frequency
Damped filter
Tuned filter
Filter admittance
T8417
Single frequency
tuned filter
2nd Order
broadband
damped filter
3rd Order
broadband
damped filter
‘C’ Type
broadband
damped filter
Types of Filter
T8418
� Advantages
� Lower losses in resistor
� Disadvantages
� Poorer performance than 2nd order
� Additional cost of capacitor
3rd Order Damped
T8419
� Advantages
� lower losses in resistor
� Better performance than 3rd order
� Disadvantages
� Poorer performance than 2nd order
� Additional cost of capacitor
� May require off-circuit adjustment
C - Type
T8421
� Advantages
� Only one HV capacitor bank
� Only one reactor subject to HV tests
� Reduced number of filter arms
� No minimum size
� Improved redundancy
� Low fundamental losses (double tuned)
Multiple Tuned Filters
T8422
Double Tuned Double Tuned
Double Tuned Filters
T8423
0.03
0.02
0.01
0
-0.01
0 10 20 30 40 50
Harmonic
Adm
itta
nce (m
hos)
G
B
Admittance Characteristic(G= conductance, B= susceptance)
T1774
Main Capacitor
Corona Rings
Base Insulators
Horizontal Mounted
Cans
LV Terminal
HV Terminal
Auxiliary Capacitor
Base Insulators
Steel Frames
HV terminal
LV terminal
Reactors
Spiders
Terminal
Coil
Base
Insulators
Pedestals
Resistors
Roof
Base
Insulators
Bushings
Thank You