A Short Note on Harmonics and Filters In

ISSN No. : 2394 – 174X, V – 1, I – 2, 2014

Journal Club for Electrical Engineering (JCEE) Manuscript No: JCEE/REV/2014/13, Received On: 22/10/2014 , Accepted On : 15/11/2014, Published On: 31/12/2014

REVIEW ARTICLE A Short note on Harmonics and Filters in HVDC systems D. Edison Selvaraj1*, K.S. Gouthama Priyan2, Firoz Alam3, Vinay Kumar Singh4, A. Syed Mohamed Meeran5, Dr. C. Pugazhendhi Sugumaran6, M. Raj Kumar7, J. Ganesan8, M. Rajmal Joshi9, S. Dinesh Kumar10, S. Geethadevi11 1

Assistant Professor, Department of Electrical and Electronics Engineering, Panimalar Engineering College, Chennai, India 2-5 BE – Final year, Sri Muthukumaran Institute of Technology, Chennai, India 6 Assistant Professor (Senior Grade), Division of High Voltage Engineering, College of Engineering, Guindy, Anna University, Chennai, India 7 Assistant Professor, Department of Electrical and Electronics Engineering, Dhanalakshmi Srinivasan College of Engineering and Technology, Mamallapuram, Chennai, India 8 Assistant Professor, Department of Electrical and Electronics Engineering, Sree Sowdambika College of Engineering, Aruppukottai, India 9 Assistant Professor, Department of Electrical and Electronics Engineering, Panimalar Engineering College, Chennai, India 10 Research Scholar, Department of Electrical and Electronics Engineering, St. Peter’s University, Avadi, Chennai, India 11 Senior Assistant Professor, Department of Electrical and Electronics Engineering, Aurora Technological and Research Institute, Uppal, Hyderabad, India

ABSTRACT In this paper, the need for filters used in HVDC systems was discussed. The problem of harmonics produced in HVDC systems was given. The method to eliminate the harmonics was discussed in simple manner. Design criteria for different types of filters were briefed to attract the various minds working, studying and doing research in HVDC systems. The harmonic indices were also given in this paper to measure the effect of harmonics in HVDC systems. This paper covers only the basic ideas needed for design of various types of filters, harmonics indices, Effect of harmonics and reduction of harmonics. A special attention was also given to the generation and reduction of carrier frequency and RI noise in HVDC systems. This paper would be helpful for the undergraduate and post graduate students to study about the basics types of harmonics, effect of harmonics and reduction of harmonics using several types of filters. It would be helpful to have some ideas for doing their research works and projects in HVDC systems.

KEYWORDS HVDC, Filters, Harmonics, Radio Interference, Audible Noise INTRODUCTION Harmonics were non sinusoidal component Address for Correspondence: D. Edison Selvaraj, Department of Electrical and Electronics Engineering, Panimalar Engineering College, Chennai, India.

Email: [email protected]

© All Rights Reserved by “Journals Club & Co.”

present in sine waveform. Harmonics would cause serious problems in the power system. So, harmonics were eliminated with the help of filters.

17

A Short note on Harmonics and Filters in HVDC systems Problems of harmonics  AC harmonics 

DC harmonics

i.

Telephone interference

ii.

Power losses

Harmonics were also classified into two

iii.

Heating in machines and capacitors

types based on the order

iv.

Over voltage due to resonance

v.

Instability of converter controls



Characteristic harmonics

vi.

Interference with ripple control systems



Non- Characteristic harmonics

vii.

Extra filter cost

viii.

Suitable filters were needed to suppress carrier and radio frequency harmonics Types of Filters

Characteristic harmonics The harmonics of those orders which were always present in the HVDC system even under the ideal conditions such as 1. Balanced AC voltages

AC filters

2. Symmetric 3 phase network and They were used to filter AC current

3. Equidistant pulses were called as

harmonics. They were also used to supply

Characteristic harmonics.

reactive power. AC characteristic harmonics were of the 1. Band pass Filter

order h= np±1

2. High pass filter  Second order filter  C type filter

Where h=order of harmonics n=Integer

DC filters DC smoothing reactors with DC filters was

p=pulse number AC characteristic harmonics were given as

used to filter DC harmonics. 

Single tuned filter



Double tuned filter

GENERATION OF HARMONICS

I

ho

I 10 

I



10

h

2

6



.I

d

Harmonics were classified into two types based on the supply


18

A Short note on Harmonics and Filters in HVDC systems DC characteristic harmonics were of the Reduction order, h= np. DC characteristic harmonics

Equidistant pulse control was used to

were given as

eliminate residual harmonics. It involves

Vh 



increased reactive power consumption.



Vdo C 2  D 2  2CD. cos2   

1/ 2

Firing angle errors

2

Causes C 

cos h  1  / 2 h 1

D 

cos h  1  / 2 h 1

µ = Overlap angle Non characteristic harmonics The harmonics of the order other than the characteristic harmonics were called as Non-characteristic harmonics. Causes of Non-characteristic harmonics 1. Imbalance in the operation of two bridges-Residual harmonics 2. Firing angle errors 3. Unbalance and distortion in AC voltages 4. Unequal transformer leakage impedances-Residual harmonics Imbalance in the operation of two bridges These were called as residual harmonics.

1. Due to jitter (or) nature of control system 2. Ripple in current feedback signal Properties of non-characteristics harmonics due to firing angle errors 1. There were even harmonics if ∆x or d≠0 i. ∆x, d=parameter showing the deviation of the current waveform 2. The magnitude of the characteristic harmonics were also affected due to this 3. Triple harmonics would fall into odd or even groups defined by h=6n+3 n=0, 1, 2 h=6n n=1, 2 In each of these groups, the magnitude of harmonics decreases monotonically as n increases. 4. Two groups of even harmonics which were not multiples of 3 were given by h=6n+2, n=0, 1, 2 h=6n+4, n=1, 2 In one group, magnitude increases with n while in the other group, it decreases with the increase in n. 5. For higher values of h, the noncharacteristic harmonics would dominate the characteristic harmonics.

Causes 1. Due to the difference in the firing angles in the two bridges. 2. Unequal cancellation of harmonics of order 5, 7, 17, 19


 

Reduction Pulse number should not be increased above 12 EPC cannot reduce harmonics due to jitter Unbalance and distortion in AC voltages

19

A Short note on Harmonics and Filters in HVDC systems Causes E1  Harmonic component of the line to 1. Negative sequence component present in neutral voltage the AC voltage shifts the zero crossing of m InZn  the commutation voltages n 2 D=  100 2. Firing angle dissymmetry due to E1 individual phase control (IPC) system

m  highest harmonic

3. Smoothing reactors will produce second order DC harmonics and third order AC harmonics

D RSS

Reduction EPC firing scheme Unequal impedances   

 m 2   I n Z n      n 2 E1    

1/ 2

 100

Telephone Interference Factor

transformer

leakage

These were also called as residual harmonics. It could generate triplen harmonics and even harmonics Analysis is complex

 m 2    I n Z n Fn    TIF=  n 2 E1    

1/ 2

Where Fn  5  n  f1  p n

Reduction Equidistant pulse control was used

p n  C message weighting ‘C’ message weighting was defined as the

DESIGN OF AC FILTER

frequency dependent sensitivity of the

Criteria for design for AC filters

human ear. It was used in Bell Telephone Systems

The important objective of AC filters was to reduce the telephone interference. This was

measured

by

the

following

(BTS)

and

Edison

Electric

Institute (EEI) in USA. It was maximum at 1000Hz. TIF was used in USA.

performance indices. Telephone harmonic form factor (THFF) Harmonic distortion

Dn 

 m 2     I n Z n Fn    THFF   n 2 E1    

InZn  100 E1

I n  Harmonic current injected Z n  Harmonic impedance of the system


1/ 2

Where

20

Fn 

A Short note on Harmonics and Filters in HVDC systems It was used to filter out two discrete

nf 1 * Wn 800

frequencies. It was also used to eliminate 11th and 13th harmonics.

Wn = psophometric weight It was used by consultative Commission on telephone and telegraph system (CCITT). THFF was used in Europe

Advantages 1. Only one inductor was subjected to full line impulse voltage 2. Reduced power loss at the fundamental frequency High Pass Filter

IT product

Second order High pass filter

It was used by BTS-EET in USA and was given as

It was used to filter out the higher frequencies. Tuning of these filters was not

m

 2 IT   I n Fn    n 2 

1/ 2

critical. C type High pass filter

KIT=

IT 1000

Types of AC Filters

It was used to reduce power losses at the fundamental frequency. Capacitor was connected in series with inductor to provide

The different types of AC filters used in

low impedance path to the fundamental

HVDC systems were as follows

component of current. A third harmonic

1. Band pass filter

filter was used to filter out the non-

2. Single tuned filter

characteristic harmonic of third order. All

3. Double tuned filter

the filter branches were capacitive at

4. High pass Filter

fundamental frequency and supply reactive

i. Second order filter

power.

ii. C type filter

Design of Single tuned filter

Single Tuned Filter It was to filter out the characteristic harmonics of single frequency. It was used to filter out 11th and 13th harmonics in a

Consider In = harmonic current in the converter Zfh = Filter impedance at harmonic frequency Zsh = System impedance at harmonic frequency

converter system. Z f  R f  jx f

Double tuned filter = R f 1  j 2Q  = Z o Q 1  J 2 


21

A Short note on Harmonics and Filters in HVDC systems Q=

Zo ; Rf

Zo 

L C

x

Z sh Z fh  Z sh

δ = Relative frequency deviation x The harmonics current in the filter was given by I fh 

I Z sh Z sh  Z fh

The harmonic voltage at the converter bus is

VC1

I fh Ih

h2  ( 2 ) XV1 h 1

Vch  xI h Z 0 The reactive power generated by the filter at the fundamental frequency was given as

V Vh  I fh Z fh =

Ih

2

Y fh  Ysh

Qopt 

Vh 

Q f  V1  I f 1

1  cos m 2 m sin  m

4 m Z o I h 1  cos m

Minimum cost tuned filters

(V ) h ( 2 ) 1 h 1 Z0

Cost of filter was given as

K  AQ f  BQ f

1

A,B  constants The optimum value of the reactive power

The cost of the reactor and the capacitor

supplied by the filter at the minimum cost

were dependent on their respective ratings.

of filter was obtained as

The ratings of the capacitor was given as





S c  V 2 c1  V 2 ch 1C

The ratings of the reactor was given as



Sl  I 2 f 1  I

2 fh

 L

B Qf      A

1/ 2

The filtering would increase with the increased size of the filter.

1

Where

 h  v1 I f1   2   h 1 zo I fh  xI h


Design of high pass filter Second order high pass filter was usually provided to eliminate 17th and more than 17th order harmonics.

ho 1 

1 LC

22

A Short note on Harmonics and Filters in HVDC systems 2. During switching, the filter current was L

ZO 

C

R  ZO

20 to 100 times that of the normal harmonic current. For tuned filters, it was 20and 100for high pass filter 3. These over currents should be taken into

The following values can be used 0.5<  <2

ho  2hmin

account for the mechanical design of the reactor coils. 4. At the instant of switching, the capacitors present in filters was fully charged

hmin  Minimum value of h Filter impedance was given as

5. These residual over voltages could occur on the bus bars 6. The capacitors were discharged by

2   ho    2  ho   ZO   j      1      h     h    Zf  2  ho  1    h 

a. Short circuiting device b. Converter transformers c. Voltage transformer d. Loaded with resistors 7. Deviation of frequency would result in

The reactive power supplied by the filter

higher currents and losses in AC filters.

was

At this condition, the filters should be disconnected.  h Qf   2o  h 1  o





  V1 2     Z    O

Filtering was improved for the higher values of Q f and ho . High pass filter was not applicable for 6 pulse operation.

DC filters Criteria for the design of DC filters The effectiveness of the DC filter was judged by the following criteria 1. Maximum voltage TIF on DC high voltage bus 2. Maximum induced noise voltage (INV) in mv/km

PROTECTION OF FILTERS Filter was exposed to switching overvoltage 1. The magnitude of overvoltage was

3. Maximum permissible noise to ground in dB Maximum Induced Noise voltage (INV)

dependent on

It was used for the computation of harmonic

i. Short circuit ratio

currents and mutual impedance. It was

ii. Saturation characteristics of converter

dependent on

transformer

i. Earth resistivity


23

ii. Modes of operation 

Mono polar operation



Bipolar operation



Homo polar operation

A Short note on Harmonics and Filters in HVDC systems Computer programmes were used to

iii. Ground (or) Metallic returns

evaluate the performance of filters. CARRIER

FREQUENCY

AND

RI

NOISE 1. HVDC

converter

would

produce

For mono polar operation, INV was 18 to

electrical noise in the carrier frequency

20 mV/km.

band from 20KHZ to 490 KHZ.

Types of DC filters 1. Single tuned filter 2. Double tuned filter 3. High pass filter Single tuned and double tuned filter was used to filter out 6th and 12th harmonics whereas high pass filter was used to filter higher order harmonics.

2. Radio

interference

(RI)

noise

was

produced in the Mega hertz frequency range. However converters were present indoor and hence they were effectively shielded

against

electromagnetic

radiation. Hence, direct radiations from valves were neglected 3. The most important effect of corona that might determine the design of conductor

Choice of DC filter

was

radio

interference.

This

was

The choice of DC filters was affected by

measured at a frequency of 1 MHz with a

i. Over voltage due to DC line resonance

bandwidth of 9 kHz. This RI was mainly

ii. Line fault

due to the positive conductor.

iii. Smoothing reactor

4. The corona discharges from the negative

iv. Surge capacitor

conductor were in the form of Trichel

DC filters would limit the over voltage

pulses which were uniformly distributed

produced by mono polar DC line faults.

over the conductor surface

Design of DC Filters Design of DC filters was similar to that of the AC filters except the value of capacitor used for reactive power compensation in AC but in DC, there was no reactive power compensation. DC filters were stressed by direct voltages and harmonic voltages.


5. Positive corona discharges were of three types a. Herm stein glow b. Plume discharge and c. Steamers 6. Plumes and streamers were randomly distributed and more persistent. They were associated with high stress points

24

A Short note on Harmonics and Filters in HVDC systems due to surface imperfections. These were 16. Operation of core at lower flux densities responsible for RI

would counter balance the harmonics in

7. RI due to positive conductor was given as RI = 25 + 10 log n + 20 log r+ 1.5 (g-g0) 8. RI due to negative conductor was less than 20dB.

not a serious problem in converter stations 17. Effective PLC-RI filters were used to

9. DC - RI were decreased by rain and snow. This was opposite to AC – RI. DC - RI were increased by wind.

due to ion currents. It was very little at the distances greater than 25 meters from the right of way. corona

reduce the impact of RI noise with the power line carrier communication. CONCLUSION

10. Television interference (TVI) was mainly

11. The

converter transformer and hence, AN was

In this paper, the basic points about harmonics were discussed. The different types of filters and design of filters based on performance criteria were discussed to

discharges

from

the

conductor produce compressions and rarefactions. These were propagated through the medium as acoustical energy. 12. The portion of the acoustical energy spectrum that lies between the sonic ranges was called as Audible noise (AN). Audible noise was given as 20 log (P/Pr)

eliminate harmonics in HVDC systems. The

protection

of

filters

against

overvoltage was also briefed. Some of the important methods used to reduce RI, AN, TVI in HVDC systems were also explained for the young readers to encourage their research ideas to reduce harmonics, RI and AN in HVDC systems.

dB. P = Measured sound pressure level Pr = Reference pressure level Pr = 20 M Pascal 13. For ± 600KV DC line, the AN was 45 to 55 dB at 30 meters from ROW. 14. Audible noise varies linearly with the conductor

surface

voltage

gradient.

Positive conductor was responsible for AN. Rain causes a slight reduction in AN. 15. Sources of AN were

REFERENCES 1. www.mhhe.com/kamakshaiah/hvdc1 2. Kimbark E.W. (1983). Direct Current Transmission, (London) Peter Peregrinus. 3. Harraway L. (1985). Electrical Power Systems, (Londan), Peter Peregrinus. 4. Uhlmann. E. (1975). Power Transmission by Direct Current, (Berlin) SpringerVerlag. 5. ABB Systems. http://www.abb.com.in 6. K. R. Padiyar. (1990). HVDC Power Transmission Systems, New Age International.

a. Harmonics in converter transformer b. Magnetostriction in smoothing reactor


25

A Short note on Harmonics and Filters in HVDC systems

HOW TO CITE THIS ARTICLE Selvaraj, D. E., Priyan, K. S. G., Alam, F., Singh, V. K., Meeran, A. S. M., Sugumaran, C. P., Kumar, M. R., Ganesan, J., Joshi, M. R., Kumar, S. D., Geethadevi, S. (2014). A Short note on Harmonics and Filters in HVDC systems. Journal Club for Electrical Engineering (JCEE), 1(II), 17-26.


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A Short Note on Harmonics and Filters In

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