fault analysis of voltage source converter based multi terminal vsc hvdc transmission link

R. K. Mallick, Member, IEEE, and R. K. Patnaik, PG student

Abstract— A new detection method for DC line faults in a voltage source Converter based three terminal high voltage DC (VSC-MTDC) systems is proposed in this paper. A three-terminal MTDC model is used to investigate fault behavior and detection of type of fault and the dc line of the model where fault has occurred using the simulation program MATLAB/SIMULINK. The fault clearing must be done very rapidly, to limit the effect of the fault on neighboring DC lines because of the rapid increase in DC current. However, before clearing the line, the fault location must be detected as soon as possible. A rapid fault location and detection algorithm is therefore needed. The detection method proposed in this paper uses wavelet decomposition to detect the type of fault and the line in which fault has occurred, based on local measurements. The energy of the fifth level detailed decomposed coefficients of the positive line dc current is calculated for each case of fault. The final objective is to form a decision tree by analyzing the Energy values of each case and implementing it to a MATLAB program which will accurately detect the type of fault and the dc line of the model where fault has occurred. Simulation results shows that the proposed method is simple and very effective in fault detection on the dc side of a VSC-MTDC system. Keywords—dc faults, Voltage source converters, multi-terminal HVDC systems, MATLAB/ SIMULINK, fault detection, Wavelet Analysis.

I. INTRODUCTION Multi-Terminal DC (MTDC) Transmission links is a fairly new field of research. The MTDC can be said to be a DC equivalent of AC grid which will have DC bus network at their dc networks. MTDC’s have been proposed for off-shore wind farms [1], underground urban sub-transmission and distribution systems [2], ship-board power supplies [3], and as a back-bone for distributed and renewable generation systems. It is a transmission network connecting more than two AC/DC converter stations. A VSC-Multi-Terminal dc Transmission link consists of a number of Voltage source converter’s (VSC’s) which are connected to a common dc network. So it is increasingly being realized that MTDC systems may be more attractive in many cases to fully exploit

This paper work was supported in part by the Multi-Disciplinary Research Lab

situated at Siksha O Anusandhan University, Bhubaneswar. R. K. Mallick is with Department of Electrical and Electronics Engineering,

Institute for Technical Education and Research under Siksha O Anusandhan University (e-mail: [email protected]).

R. K. Patnaik is with the Department of Electrical Engineering, Institute for Technical Education and Research under Siksha O Anusandhan University (e-mail: [email protected]).

978-1-4673-0136-7/11/$26.00 ©2011 IEEE

the economic and Technical advantages of the HVDC systems. When a fault occurs on the dc side of the Multi-Terminal DC links, the dc current values rises to a very high level which can damage the equipments connected across it. It also affects the performance of all the VSC based systems which are interconnected to it at the common dc terminal. This is the main difficulty which is generally faced while detection of faults on the dc side of the MTDC system. Depending on the fact that, DC system does experience currents that do not change in polarity makes it more difficult to extinguish the current arc [4]. The protection system which includes detection, classification and location of fault at preliminary stage, may be the main problem when considering the VSCHVDC Multi Terminal configurations and a complete new method should be developed. Identifying the line in which a fault occurs is not so easy and traditional AC methods cannot be used .It is very much necessary to identify which type of fault has occurred and which dc line is the faulted line so that it can be protected.

II. TYPES OF FAULT ON THE DC SIDE Voltage Source Converter based Multi Terminal DC systems are easily exposed to faults on the DC systems. Classical current-sourced-converter based (CSC) HVDC are naturally able to withstand short circuit currents due the presence of DC inductors which helps in limiting the current during fault conditions [5]. When a fault occurs on the DC side of a VSC-HVDC system the IGBT’s lose control and the freewheeling diodes act a bridge rectifier and feed the fault [6] as shown in Figure 1. The types of faults possible on the dc side of a MTDC system are as follows. 1. Positive line to ground fault, 2. Negative line to ground fault,

Figure 1 VSC Operation (a) Normal. (b) Positive Line-to-Ground Fault. 3. Positive line to negative line fault, 4. Positive line to negative line to ground fault. A line-to-ground fault occurs when the positive or negative line is shorted to ground. In overhead lines faults may occur when lightning strikes the line. This may cause the line to

Fault Analysis of Voltage-Source Converter based multi- terminal HVDC transmission links

break, fall to the ground and create fault. The impact this type of fault is that it discharges the dc capacitor to ground, thus creating an imbalance of power on the dc side of the Converters, which results in reducing the DC link voltage between the positive and negative poles. As the voltage of the faulted line begins to fall, high currents flow from the capacitor as well as the AC grid. These high currents may damage the capacitors and the converter [7]. A line-to-line fault on a cable-connected system is less likely to occur on the cable. In an overhead system, line-to-line faults occur, when an object falls across the positive and negative line or they may also occur in the event of the failure of a switching device causing the lines to short. A switching fault, which is independent of how the converter stations are connected together, causes the positive bus to short to the negative bus inside the converter. A line to line fault may be either temporary or permanent. A challenge associated with the protection of VSC-HVDC systems is that the fault current must be detected and cleared very quickly, due to the fact that converters fault withstand rating is only twice the converter full load rating [6]. Fault detection is also important, especially on multi terminal systems, in order to isolate the fault and restore the system to working order.

III. WAVELET ANALYSIS The Wavelet analysis is a new and powerful method of signal analysis well suited to fault generated signals [8].This method is very helpful to detect abrupt, local changes in a signal(e.g. short time phenomenon such as transient processes etc.).The necessary and sufficient condition for wavelets is that it must be oscillatory, must decay quickly to zero and must have an average value of zero. An important point is that wavelet analysis does not use a time frequency region, but rather uses a time-scale region. The windowing of wavelet transform is adjusted automatically for low and high frequencies i.e.it uses short time interval for high frequency components and long time intervals for low frequency components. Wavelet Analysis is based on decomposition of signals into ‘Scales’ using wavelet prototype function called ‘mother wavelet’. The temporal analysis is performed with a contracted, high frequency version of the ‘mother wavelet’, while the frequency analysis is performed with a dilated low frequency version of the ‘mother wavelet’. This wavelet is scaled and translated to match an input signal locally. The subsequent calculated wavelet coefficients represent the correlation between the (scaled) wavelet and the signal. The generated waveforms are analyzed with wavelet analysis to extract sub-band information from the simulated disturbances. Daubechies four wavelet is used in this paper as the ‘mother wavelet’ for the analysis as it closely matches the signal to be processed, which is of utmost importance in wavelet application. Also, the efficiency of daubechies wavelets based on the accurate reconstruction of power system transient signals as described in [9], and the suitability of daubechies four wavelets for the analysis of power system transients from the family of daubechies wavelets as described in [10] are the basis for choosing daubechies four wavelets. The wavelet transform decomposes signals over dilated and translated wavelets. A wavelet is a function ψ with a zero average value

∞∞ = 0 (1)

A wavelet transformation is characterized by a translation parameter u and a dilation parameter .The dilation parameter determines the size of the window in which the wavelet transform is performed. The translation parameter determines the time corresponding to the centre point of each window. A wavelet is normalised = 1 and centered in the neighborhood of t=0. For each ‘mother wavelet’ ψ, a family can be obtained by scaling ψ by S and translation of ψ by u , √ (2) Also, the scaled and translated wavelets remains normalized. The wavelet transform (W.T) of a signal f(t) at time u and Scale S is calculated by WT (u, S) = ∞

∞ √ (3)

with the complex conjugate of the wavelet function ψ.

IV. SIMULATION MODEL The Figure 2 shows the model of a three-terminal MTDC transmission link, which is simulated in MATLAB /SIMULINK. There are two sending ends (line 1 and 2) and a single receiving end (line 3). The line 1 of the model consists of a 100 MVA, 230 kV, 50 Hz source whereas the line 2 consists of a 50 MVA, 230 kV, 50 Hz source which are interconnected and fed to a third system, line3 which is a 230 kV grid. The parameters of the various model elements are tabulated in Appendix A. The line 1 and 2 consists of Voltage IGBT/Diode based Voltage source converters (Rectifier stations) whereas the line 3 consists of a single IGBT/Diode based Voltage source converter (Inverter station). A circuit breaker along with a fault resistance is used to apply various faults on the DC side of the model. The entire model has been simulated with 50 Hz Frequency. Fixed step Simulation of the models has been carried out using ode3 (Bogacki – Shampine) solver. Sampling has been done with 64 samples per cycle (50 Hz). Therefore Sampling frequency is (64*50) Hz i.e. 3200Hz and Sampling time=Ts= (1 /Sampling Frequency) =0.0003125 seconds. The model is simulated for 0.5 seconds i.e. 25 cycles. DC faults are given for a period of 0.1 seconds i.e. from 0.2s to 0.3 sec i.e. 5 cycles. In the Simulink Models the "Model initialization" function automatically sets the sample times in the MATLAB workspace. The voltage and current of the ac side of the model has been normalized to p.u. value based on peak-value of nominal phase to phase voltage using 100 MVA as base power 230 KV as nominal voltage used for p.u. measurement( phase to phase). The behavior of the three terminals VSC-MTDC model, during ‘positive line to ground fault’ conditions on DC transmission line in Line 1 is being observed as under. As can be seen clearly from Figure3 (a), (b), (c), (d), (e), (f), when a positive line to ground fault in dc transmission line of line 1 occurs , it effects the performance of all the systems which are interconnected to it. As stated before, when a line to ground fault occurs, the voltage across the dc side decrease, whereas the current values are very high as to 2.5 p.u. There is a indication that fault has occurred in the system on observing the waveforms

Figure 2 : MATLAB/SIMULINK Model of the three-terminal MTDC system but it is very difficult to say the type of fault has occurred and in which line the fault has occurred. For this reason, the value of the current in the positive pole of the dc line which is sampled at 64 samples per cycle is recorded and further processed to a MATLAB program which uses wavelet transform to detect and identify the type of fault and line in which fault has occurred. This process has been performed for thirteen cases (as there are 3 systems or lines and in each line four types of faults are simulated, which results to twelve cases, and a case of no fault condition), and each data has been processed through the MATLAB program for detection of fault.

V. WAVELET APPROACH FOR FAULT DETECTION The Waveform of positive line dc current observed under different cases has been recorded in a particular .mat files which stores the values of time and amplitude of the signal in the form of an array. Then the mat file consisting of positive line dc currents of line 1,2and 3 are processed to an m-file (which runs in MATLAB 2010 editor) which decomposes the signals using ‘db4’ as mother wavelet for 5 levels. Then the 5th level Detailed Decomposition coefficients are being plotted which clearly shows that when a line is under fault or not. Under normal operating Condition, the wavelet output is constant. Whenever there is a fault condition, the wavelet output shows an abrupt change in the waveform in the particular area of occurrence of the fault. This confirms us

that a fault has occurred in the system or not. The Energy for the same 5th level Detailed Decomposition coefficients are being computed using another m-file for various faults on dc side is shown in table 1(a),(b),(c),(d) and (e). Finally forming a decision tree by comparing the energy of the 5th level detail decomposed coefficients, the type of the fault and the line in which fault has occurred is determined. The energy of the detailed coefficients of level w ( ) is nothing but the sum of the square of all the coefficients of . Mathematically, ∑ (4) Where are the level wavelet coefficients within the window and n is the window length.

VI. ALGORITHM FOR WAVELET DECOMPOSITION AND ENERGY CALCULATION

Step1: Store the positive line dc current values in mat files using suitable variable names. Step2: Load the particular mat file into an m-file. Step3: Load the particular values of the mat file (which is to be processed) to a temporary variable i.e. y. Step4: Now execute the Wavelet decomposition function on the variable y using ‘db4’ as mother wavelet for 5 levels and store the decomposed coefficients in variable C and corresponding lengths in variable L.

GENERATOR 1

LINE 1

TRANSFORMER 1

A.C LINE 1

SERIES FILTER 1

CONVERTER STATION 1 (RECTIFIER )

DC CAPACITOR BANK 1 AND DC

TRANSMISSION LINE 1

CONV_1_PULSE

SHUNT FILTER

1

CONV_2_PULSE

GENERATOR 2

LINE 2

TRANSFORMER 2

A.C LINE 2

SERIES FILTER 2

CONVERTER STATION 2 (RECTIFIER )


TRANSMISSION LINE 2

SHUNT FILTER

2

GRID

LINE 3

TRANSFORMER 3

A.C LINE 3

SHUNT FILTER

3

SERIES FILTER 3

CONVERTER STATION 3 (INVERTER )

Inv_pulse


TRANSMISSION LINE 3

MEASUREMENT POWER GUI CONTROLLER

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-2

-1

0

1

Time (in seconds) ------------------------>

AC

VO

LTA

GE

(in p

.u.)-

->

Figure 3(a) Response of ac voltage to Rectifier of line 1 for a positive line to ground fault on the dc transmission line of line 1

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-2

-1

0

1Figure 3(b) Response of AC Voltage to Rectifier of line 2 for a positive line to ground fault on the dc transmission line of line 1

Time (in seconds)------------------->

AC

VO

LTA

GE

( in

p.u.

)-->

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-2

-1

0

1

Time (in Seconds )----------------------->

Figure 3(c) Response of AC Voltage from Inverter of line 3 for a positive line to ground fault on the dc transmission line of line 1

AC

VO

LTA

GE

(in p

.u.)-

-->

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1

0

1

2

Time ( in seconds)-------------------->

DC

CU

RR

ENT

( in

p.u.

)--->

Figure 3(d) Response of positive line dc current of line 1 for a positive line to ground fault in dc transmission line 1

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1

0

1

2

Time ( in seconds)--------------------------------->

DC

CU

RR

ENT

(p.u

.)--->

Figure 3(e) Response of positive line dc current of line 2 for a positive line to ground fault on the dc transmission line of line 1

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-2

0

2

4Figure 3(f) Response of positive line dc current of line 3 for a positive line to ground fault on the dc transmission line of line 1

Time (in seconds) ----------------------->

DC

CU

RR

ENT

( in

p.u.

)--->

Figure 4 Wavelet output for 5th level detail coefficients of line 1, 2 and 3 for a positive line to ground fault in the dc side Transmission line of system 1

Step5: From the wavelet decomposition structure (C and L), store the 5th level reconstructed detail coefficients in variable D5. Step6: Now plot the original signal and d5 in a single Figure. Step7: Repeat all the above 6 steps for all the positive line dc current values to get the final output of energy of the 5th level detailed decomposed coefficients Step 8: Now execute sum of the square of D5 and store it in variable for example E_L1. Step 9: Repeat all the above 8 steps for all the positive line current DC currents of all the lines to get the final outputs of energy. As can be clearly seen from Figure 4 the region on wavelet output where there is no fault is constant near zero. Whenever there is an occurrence of fault, the output oscillates rapidly.

VII. TABLE FOR DIFFERENT VALUES OF ENERGY OF LINE 1,2 AND 3 FOR DIFFERENT FAULT CONDITIONS

The energy values of the fifth level detailed reconstructed coefficients have been calculated for various cases which are shown in the Table 1(a),1(b),1(c),1(d),1(e). The base value of the energy has been taken as 400.

no fault Energy

Line 1 energy value in p.u.

3.1030e-005


2.1044e-005


3.8159e-004

Table: 1(a) Energy values of 5th level detailed decomposed Coefficients of negative line dc current for no fault condition

positive line to ground

fault Fault in line

1 Fault in line

2 Fault in line

3 Line 1 energy value in

p.u.0.0501 0.0474 0.0477


0.0139 0.0145 0.0150


0.0669 0.0877 0.0873

Table: 1(b) Energy values of 5th level detailed decomposed coefficients of positive line dc current for positive line to ground fault

negative line to ground

fault

Fault in line 1

Fault in line 2

Fault in line 3


3.1571e-05 3.1647e-05 3.1631e-05


2.1730e-05 2.2039e-05 2.1907e-05


4.3027e-04 4.4202e-04 4.3164e-04

Table: 1(c) Energy values of 5th level detailed decomposed coefficients of positive line dc current for negative line to ground fault

positive line to negative line

fault

Fault in line 1

Fault in line 2

Fault in line 3

Line 1 energy value

0.1159 0.2416 0.2227

Line 2 energy value

0.1289 0.0563 0.0813

Line 3 energy value

0.6977 0.7204 0.5728

Table: 1(d) Energy values of 5th level detailed decomposed coefficients of positive line dc current for positive line to negative line fault

positive line to negative line to

ground fault

Fault in line 1

Fault in line 2

Fault in line 3

Line 1 energy value 0.0586 0.1262 0.1175



Table: 1(e) Energy values of 5th level detailed decomposed coefficients of positive line dc current for positive line to negative line to ground fault

0 500 1000 1500 2000-0.5

0

0.5

1

1.5

2

number of coefficients----->

dc c

urre

nt li

ne 1

------

--->

0 500 1000 1500 2000-1

-0.5

0

0.5

1

number of coefficients----->5th

leve

l det

ail w

avel

et c

eoffi

cien

ts lin

e 1-

--> 0 500 1000 1500 2000-0.5

0

0.5

1

1.5

2


dc c

urre

nt li

ne2-

------

-->0 500 1000 1500 2000

-0.4

-0.2

0

0.2

0.4


leve

l det

ail w

avel

et c

eoffi

cien

ts lin

e 2-

--> 0 500 1000 1500 2000-1

0

1

2

3

4


dc c

urre

nt li

ne 3

------

--->

0 500 1000 1500 2000-1

-0.5

0

0.5

1


leve

l det

ail w

avel

et c

eoffi

cien

ts lin

e 3-

-->

Figure 5 Decision Tree for detecting the type of fault and the line in which fault has occurred in the 3- Terminal model

VIII. DECISION TREE FOR DETECTION OF TYPE OF FAULT AND LINE IN WHICH FAULT HAS OCCURRED

The various values of Energy of the 5th level detailed decomposed coefficients of positive line dc current of line 1, 2 and 3 (table 1(a) - 1(e)) which will be denoted in this paper as E_L1, E_L2 and E_L3 respectively, are analyzed and compared to form a decision tree to find or detect which type of fault has occurred and which is the line (either line1 or 2 or 3) in which fault has occurred which is being shown in Figure 5. Here ‘P’ denotes to positive line, ‘N’ denotes to negative line and ‘G’ denotes to ground.

IX. CONCLUSION Detection of the type of fault occurred and the particular dc line which is faulted, on the dc side of the Voltage Source Converter based three-terminal MTDC system is very challenging. It is due to the fact that unlike the ac side, when a fault occurs on the dc side of a single converter of the MTDC system, it affects the performance of all the VSC’s connected to it. The Voltage drops where as the currents increases to a very large value during the fault condition. From the observations of the waveforms of ac or dc side voltage and currents during the fault condition, we can only

conclude that a fault has been occurred in the system, but this is not enough when we are concerned for the protection of the system. In Protection systems, fast and accurate detection of faults is of utmost importance. Therefore a methodology using wavelets is presented in this paper which allows us for correct detection of the type of fault occurred and the exact line where the fault has occurred. A simple decision tree has been made on analyzing the different values of the Energy of 5 level decomposition coefficients of the positive line dc currents during different fault conditions, which is applied to a MATLAB program for the detection of faults. The obtained results show the effectiveness of the method being developed, for almost all the cases being simulated.

Get the 5th level detailed wavelet coefficients of the positive line dc currents of line 1, 2 and 3 respectively.

Calculate the energy of the above coefficients and store it in variables E_L1, E_L2 and E_L3 respectively.

if E_L1<3.12*10^-5 , E_L2<2.15*10^-5 and E_L3<4*10^-4

if E_L1>0.03,

E_L2>0.01 and E_L3<0.09

if E_L1>3.12*10^-5,

E_L2<2.3*10^-5 and E_L3>4*10^-4

if E_L1>0.1, E_L2<0.2

and E_L3>0.5

if E_L1<0.13,

E_L2>0.03 and E_L3>0.3

If E_L2>0.0146

else

if E_L2<0.0142

if E L1>3.1635*10^-5

if E_L1<3.1600*10^-5

else if

E_L3>0.7

if E L3<0.6

elseif

E_L2>0.05

if E_L2<0.04

else

No

fault

P-G

fault in line 3

P-G

fault in line 1

P-G

fault in line 2

N-G

fault in line 2

N-G

fault in line 1

N-G

fault in line 3

P-N

fault in line 2

P-N

fault in line 3

P-N

fault in line 1

P-N-G

fault in line 3

P-N-G

fault in line 1

P-N-G

fault in line 2

X. APPENDIX The Specification of various components of the three terminal MTDC systems as described in this is tabulated as under

Sl.No.

Elements Line 1 (Sending end 1)

Line 2 (Sending end 2)

Line 3 (Receiving end)

1 Voltage Sources

230KV,50 Hz =0.8929Ω =16.58mH

230KV, 50 Hz =0.8929Ω =16.58mH

230KV, 50 Hz =62.23mH

2 Source Filters

= 62.23mH =13.79 Ω = 31.02mH

= 62.23mH =13.79 Ω = 31.02mH

=13.79 Ω = 31.02mH

3 Transform-ers

100 MVA, 230KV:100KV

50 MVA, 230KV:100KV

120 MVA, 100KV:230KV

4 AC Transmiss-ion Lines

20 Km =0.4054Ω =0.07375Ω =8.9524mH =3.4358mH =0.0044µF =0.0075µF

10 Km =0.4054Ω =0.07375Ω =8.9524mH =3.4358mH =0.0044µF =0.0075µF

10 Km =0.4054Ω =0.07375Ω =8.9524mH =3.4358mH =0.0044µF =0.0075µF

5 Shunt Filters 100 KV, 40 MVAR, High Pass Filters

100 KV, 40 MVAR, High Pass Filters

100 KV, 40 MVAR, High Pass Filters

7 Series Filter =0.7935Ω =2525H

=1.587Ω =0.5051H

=0.125Ω =0.03978H

8 Voltage Sourced Converter

Rectifier 1 3-phase IGBT/Diodes

=1000Ω, =1µF

Rectifier 2 3-phase IGBT/Diodes

=1000Ω, =1µF

Inverter 3-phase IGBT/Diodes

=1000Ω, =1µF 9 DC

Capacitance 1 10 F each 1 10 F each 1 10 F each

10 Smoothing Reactors

=0.0025Ω Ls=0.8mH

=0.0025Ω Ls=0.8mH

=0.0025Ω Ls=0.8mH

11 DC Transmissi-on Lines

200 Km R=0.001Ω/Km,L=0.9867H/Km,C=8.69F/Km

100 Km R=0.001Ω/Km,L=0.9867H/Km, C=8.69F/Km

100 Km R=0.001Ω/Km,L=0.9867H/Km, C=8.69F/Km

13 DC Faults =1mΩ =0.0001Ω

Switching time:0.2s-0.3s

=1mΩ =0.0001Ω


=1mΩ =0.0001Ω


XI. REFERANCES [1] W.Lu and B.T.Ooi,”Optimal acquisition and aggregation of off-shore wind power by multi terminal voltage-source had.” IEEE Trans. Power Del., vol. 18, no. 1, pp. 201-206, Jan 2003. [2] W.Lu and B.T.Ooi,''Multiterminal HVDC as enabling Technology of premium quality park,” IEEE Trans. Power Del., vol. 18, no. 3, pp. 915-920, jul 2003. [3] J.C.Ciezki and R.W.Ashton, “Selection and stability issues associated with a navy shipboard and DC zonal electric distribution.” IEEE Trans. Power Del., vol. 15, no. 2, pp. 665-669, Apr 2000. [4] L Tang, and B. Ooi, “Locating and Isolating DC faults in Multi-Terminal DC Links’’, IEEE Transaction on Power Delivery, VOL. 22, No. 3, July 2007. [5] L. Tang and B. Ooi, “Protection of VSC-multi-terminal HVDC against DC faults,” 33rd Annual IEEE Power Electronics Specialist Conference, vol. 2, pp. 719–724, November 2002.

[6] M. Baran and N. Mahajan, “Overcurrent protection on voltage sourced converter based multi terminal DC distribution systems,” IEEE Transactions on Power Delivery, vol. 22, no. 1, pp. 406–412, January 2007. [7] J. Yang, J. Zhen, G. Tang, and Z. He, “Characteristics and recovery performance of VSC- HVDC DC transmission line fault,” Power and Energy Engineering Conference (APPEEC), pp. 1–4, April 2010. [8] D.Chanda, N.K.Kishore, A.K. Sinha , “Application of wavelets mutiresolution analysis for the identification and classification of faults on transmission lines”, Department of Electrical Engineering , Indian Institute of technology, Kharagpur.doi:10.1016/j.epsr.2004.07.006 [9] L. Angrisani, P. Daponte, M. D’Apuzzo, “A. Test, A New wavelet transform bases procedure for electrical power quality analysis”, Proceedings of the 1996 International Conference on Harmonic and power quality, Las Vegas,NV, 16-18 October, 1996, pp-608-614. [10] S.Santoso, E. Powers, P.Hofmann, “Power Quality assessment via wavelet transform analysis”, IEEE Trans. Power Deliv. 11 (2) (1996) 924-930.

XII. BIOGRAPHIES

R. K. Mallick was born in India in 1972. He received his degree in Electrical Engineering from Institute of Engineers (India) in 1996 and M.E degree in Power System Engineering from College of Engineering, Burla, India, in 2001. He is currently working as an Assistant Professor in

the Department of Electronics and Electrical Engineering, Institute of Technical Education and Research, under Siksha ‘O’ Anusandhan University, Bhubaneswar, Odisha, India. His Research Interest include application of Power Electronics in Power system engineering, control of H.V.D.C Converters, voltage and frequency stability of interconnected power system.

R. K. Patnaik was born in India in1986. He received his Bachelors degree in Electrical and Electronics Engineering from Gandhi Institute for Technological Advancement under Biju Patnaik University of Technology in 2008 and M.Tech Degree in Electrical Engineering with specialization of Power Electronics and Drives

from Institute of Technical Education and Research under Siksha ‘O’ Anusandhan University, Bhubaneswar, Odisha, India in 2011.He is currently working as a Research Associate in Department of Instrumentation and Control Engineering, Institute of Technical Education and Research under Siksha O Anusandhan University, Bhubaneswar, Odisha, India. His Research Interest include protection of Multi terminal HCDC systems, Application of HVDC in interconnection with Distributed generations such as wind, solar etc. and control of VSC interconnected to grid.

fault analysis of voltage source converter based multi terminal vsc hvdc transmission link

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