1.ac harmonic filters

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Ac harmonic filters

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FILTER

FILTER

HVDC Main Components

T8396

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AC Harmonic Filters

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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

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Idealised harmonic currents

Practical harmonic currentsCharacteristic harmonics

Theoretically cancelled harmonics

Non-characteristic harmonics

Types of Harmonic

T8395

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Idealised Current Waveforms….

T8397

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Combined Waveform…..

T8399

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12 Pulse

Practical Harmonic Currents….

T8402

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λ λ 

π ω ω ω ω ω  

λ 

π ω ω ω ω ω  

/

(cos cos cos cos cos ...

/

(cos cos cos cos cos ...

 I I  D

t t t t t  

 I I  D

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

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 I I   D t t t 

t t 

= − +

− +

4 3 1

1 1 1 1

1

1 3 1 3

1

2 32 3

1

2 52 5

π  ω ω ω 

ω ω 

( c o s c o s c o s

c o s c o s . . .

Fourier Analysis

T8400

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9

8

7

6

5

4

3

2

1

10 3020 40

Overlap angle (degrees)

I11

I1

11th Harmonic as a Percentage of Fundamental

T8404

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0.2 0.4 0.6 0.8 1.0

1

2

3

4

5

   H

  a  r  m  o  n   i  c   l   i  n  e  c  u  r  r  e  n   t   %   o

   f

  r  a   t  e   d   f  u  n   d  a  m

  e  n   t  a   l

Transmitted power (PU)

11th

13th

Characteristic Harmonic Generation

T8405

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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)

   H  a  r  m  o  n   i  c   l   i  n  e  c  u  r  r  e  n   t   %   o

   f

  r  a   t  e   d   f  u  n   d  a  m  e  n   t  a   l

Theoretically Cancelled Harmonic Generation

T8407

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100

10

1.0

0.1

0.01

0.00110 20 30 40 50

Harmonic Number 

In

I1%

Typical Spectrum…

T8409

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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

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Filter 

Zfn

System

ZSnIcn

Ifn

VSn

ISn

T8378

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Rmin

   X   (   O   h  m  s   )

R(Ohms)

400kV System Harmonic Impedance

T8381

Rmax

2

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Sasaram Filters

T8379

400kV

Double Damped

Filter 

400kV

Double Tuned Filter 

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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 onlywhen filter is de-energised and earthed.

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AC Filter Layouts Double Damped Filter

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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 1 2 14 1 6 18 2 0 22 24 26 28 3 0 32 34 3 6 38 40 42 4 4 46 48 50 5 2 54

Harm onic

   A   d  m   i   t  a  n  c  e

3/13th Double-Frequency Filter

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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

   A   d  m   i   t  a  n  c  e

11/25th Double-Frequency Filter

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Single frequencytuned filter

2nd Orderbroadband

damped filter

3rd Orderbroadband

damped filter

‘C’ Typebroadband

damped filter

Types of Filter

T8412

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Advantages

Maximum attenuation at single harmonic

Low loss

Disadvantages

May be de-tuned

Off-circuit adjustment

Single Tuned

T8413

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f1 f0 f2 Frequency

High Q

Low Q

Y

Effect of De-tuning 

T8414

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Advantages

Attenuation over a spectrum of harmonics

Less sensitive to de-tuning Disadvantages

Needs higher Mvar to achieve same performance as singletuned

Additional losses in resistor

2nd Order Damped

T8416

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Tuned / Damped Filters

f1 f0 f2 Frequency

Damped filter 

Tuned filter 

Filter admittance

T8417

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Single frequency

tuned filter 

2nd Order 

broadband

damped filter 

3rd Order 

broadband

damped filter 

‘C’ Type

broadband

damped filter 

Types of Filter

T8418

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Advantages

Lower losses in resistor

Disadvantages Poorer performance than 2nd order

Additional cost of capacitor

3rd Order Damped

T8419

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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

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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

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Double Tuned Double Tuned

Double Tuned Filters

T8423

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0.03

0.02

0.01

0

-0.01

0 10 20 30 40 50

Harmonic

   A   d  m   i   t   t  a  n  c  e   (  m   h  o  s   )

G

B

Admittance Characteristic

(G= conductance, B= susceptance)

T1774

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Main Capacitor

Corona Rings

Base Insulators

Horizontal MountedCans

LV Terminal

HV Terminal

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Auxiliary Capacitor

Base Insulators

Steel Frames

HV terminal

LV terminal

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Reactors

Spiders

Terminal

Coil

Base

Insulators

Pedestals

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Resistors

Roof 

Base

Insulators

Bushings

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