7/29/2019 High-Phase Order Power Line Relaying

http://slidepdf.com/reader/full/high-phase-order-power-line-relaying 1/5

HI GH-PHASE ORDER POWER T RANSM ISSION L INES R E L A Y I N G APPROACH BASEDON THE WAVELET A N A L Y S E OF THE FAULT GENERATED TRAVELING WAVES

Ammar A. Hajjar “ I , Mohamed M . Mansour ‘*’,Hosam A. Talaat ”’(1) Tishrcen University, Syria (2) Ain Shams University, Egypt (3) K ing Saud University, Saudi A rabia

ABSTRACT

This paper introduces a high-speed relaying approach based on the wavelet anlaysis of the fault generated traveling

waves dedicated for high-phase order power transmission lines. In this approach, a suitable wavelet is chosen and tunedat a suitable band of frequencies to capture the fault generated high frequency traveling waves superimposed on thepowcr frequency waves in a modal domain. Then, the energies of thc captured signals are used for making a tripdecision. The introduced approach is tested and validated by a computer simulation using an ElectroMagnetic TransientProgram (EMTDC). T he results show that the approach has the abil ity for high-speed fault detection, cIassification andfaulted phase(s) selcction irrespective of the fault inception angle, fault resistance and line termials.

K eywords: High-phase order power transmission lines, traveling waves, rvavdet andvsis, high-speed relaying

INTRODUCTIONThree-phase transmission system faces some problems

such as increasing demand, costs, and restrictions onright of way (ROW), One possible solutions of theaforesaid problems, is the use of high-phase order(HPO) power transmission systems (more than three-phases systems). In this regard, HPO transmission hasseveral advantages over three-phase transmission such

as HPO has the capability to transmit the same electricpower as three-phase system on smaller ROW, for thesame electric field and audible noise criteria, withsmaller structure and reduced overall cost. On the otherhand, HPO can transmit higher electric power thanthree-phase transmission system, on the same ROW forthe same electric fjeld and audible noise criteria.

Moreover, HPO is more economic than three-phasesystem and compatible with it [I-31.

One of the important aspects in applying the HPOtransmission systems is the design of an adequate

protective schemes. But the additional phases increasethe number of possible faults highly and cosequentlycomplicate the protection schemes. For instance, thenumber of the shunt faults in a six-phase system is I20

whereas it isonly I 1 in a three-phase system [4].

So far, there is a few relaying schemes suggested forHPO power transmission lines [3,5].So that, this paperintroduses a high-speed relaying approach based on thewavelet analysisof the fault generated traveling waves,

Wavelet is a short duration wave which can be definedby any fast decaying oscillatory function that has zeroaverage value. So that it is more suitable for transientsignals analysis. Wavelet analysis (WA) is a windowingtechnique with variable-sized windows. I t allows the useof long time windows when i t is required to have aprecise low frequency information, and a short timewindows when i t is required to have a high frequencyinformation. One majore advantage afforded by W A isthe ability to analyze a localized area of a signal andrevealing aspects of data that other signal processing

techniques miss [7,8,12]. Due to the aforesaid featuresWA was used in transient signals analysis in powersystem [8-lo].

This paper introduces a high-speed relaying apprachdedicated for HPO power transmission lines based on

the WA of the fault generated traveling waves. I n thisapproach, a suitable wavelet is chosen and tuned at asuitable band of frequencies to capture the faultgenerated high frequencies (HF) traveling wavessuperimposed on the power frequency waves in a modaldomain. T he energies of the captured H F signals areused for making a trip decision. A computer simulationof the introduced approach show that it has the abilityfor high-speed fault detection, classif ication and faultedphase(s) selection irrespective of the fault inception

angle, fault resistance and line termials.

WA V E L E T ANALYS IS

Wavelet analysis is relativdy a new mathematical toolfor nonstationary signal analysis. WA , similar to Fourieranalysis, breaks up a signal into shifted (translated) andscaled (compressed or dilated) versions of the originalwavelet or the so-called “mother wavelet”.

Similar to Forier Transform, the Continuous WaveletTransform (CWT), is defined as the sum over all timesof a signal flrl multiplied by a scaled and shifted

versions of the mother wavelet y(t),which is given by;

where “a” and “b” represent the time dilation andtranslation, respectively. The coefficients Cf (a,b) , or

the CWT, aredefined by the following inner product:

+m

- x!

where “*” refers to a complex conjugate.

805

7/29/2019 High-Phase Order Power Line Relaying

http://slidepdf.com/reader/full/high-phase-order-power-line-relaying 2/5

Generally, wavelet transform consists of succcssive

pairs of low and high pass filters [7]. For each pair thehigh-scale, low frequency components of the signal‘If(?)” are called approximations (CA), while the low-scale. high frequency components of the same signat‘y(t)” re called details (CD).

After each fi ltering stage a downsantyling process,throwing away every second data point, is achieved to

avoid redundant data. The two stages filtering processof a signal ‘?(I)’’ isdepicted in Fig. 1.

PhaseSelection +Truth *.

Fig.1 T he two stages filtering process of a signal f{Q

FAULT GENERATED TRA V E L ING WA V E S A NDMO D A L TRANSFORM

When a fault occurs on a power transmission line, HFtraveling waves of currents and voltages are generatedat the fault point. T hese HF signals travel away towardboth the h e ends then they reflect back and forthbetween the fault point and the line terminals until thepost fault steady state is reached. However, these HFsignals, which contain an imponant information aboutthe fault location, direction and its type, are

superimpose on the power frequency signals of thefaulted and unfaulted phases due to the mutual coupl ingbetween phases. Therefore, modal transformation is

used to decouple these HF signals into their respectiveaerial and ground modes. The relation between the

phase signals and the modal signals given by:

TripDecision

where, T is the modal transformation matrix and Sp~,,,,

S,,,, are the phase and modal (voltages or currents)vectors, respectively. In this study, the n-phasetransmission line is assumed ideally transposed;

therefore the K arrenbauer’s constant and realtransformation matrix isused [6].

Tablerb

/f 7

Fault CIassification

(4)I. . ...Q 1 ... 1-9

The first mode (mode 0) is frequency dependent andrefers to a ground mode that is usually presents io theground faults. The other (1-n) modes (model ... moden-I) are frequency independent and refer to the aerialmodes that are present for any type of fault.

WAVELETS FOR HIGK PHASE ORDERPOWER TRANSMISSION LINES RELAYING

The introduced approach uses wavelet transform as a

fault detector. For this purpose, a suitable wavelet ischosen and tuned, at frequency ranges between (50-100)

kHz, to extract the fault generated H F currentssuperimposed on the power frequency currents in amodal domain. In this respect, the so-called “B-Splinewavelet of order I (n=l)”, which is more suitable fortransient signals analysis in terms of speed and time-frequency localization, is used. Fig. 2  depicts theaforementioned waveiei with its transfer modulus [121.

transfer modulus high-pass-spl ine wavelet (n=j)0.8 I I ’

0.6-

0.4

0.2.

0 .

- 0. 2.

- 0 . 4 .

0.6

0.4 .

0 5 f 0 0 0.2 0.4 0. 6 0.8 1

Fig. 2B-Spline wavelet and its transfer modulus

Fig. 3 depicts a block diagram of the introducedrelaying approach. It is worth to note that the introducedapproach is completed with a fault 1ocation.techniqueto

confirm that the fault is on aprotected line 193..- -CT’s Modal Waveletoutput Transform Transform

cv

Faultdetecrion

&Confirmation- - ’ I

Fig. 3 A block diagram of the proposed approach

Faulted Phase(s) Selection and Fault Classification:Faulted phase(s) selection, and hence selective pole

tripping and autoreclosing, is an important relaying

capability since it increases the system stability as wellas its availability. Fault type classification is a relaying

feature, which enhances the protection scheme. In thissection the fault detection, classifi cation and faultedphase(s) selection principles are developed based on themodal currents, fault conditions, and WA .

Substituting by the fault conditions, for each type offault, in the phase currents vector we obtain a vector of

the modal currents. These modal currents cannot beused as a discriminant components, because they aredepend on the fault inception angle, fault resistance andline terminals. To avoid this problem wavelet transform

806

7/29/2019 High-Phase Order Power Line Relaying

http://slidepdf.com/reader/full/high-phase-order-power-line-relaying 3/5

is used to capture the fault generated HF travelingwaves of the currents, superimposed on the powerfrequcncy currents in a modal domain, with frequenciesof (50-100) kHz. The obtained HF signals arecalled thewavelet coefficients Wi . The spectral energies of theseHF signals, Ei ,can be calculated as follows:

k=

where, m is the number of samples in a chosen window,the duration tiinc of the window is chosen between (1-2)ms for a sampling frequency of 200 kHz, the subscript i

refers to the mode number and n i s the number of

phases in the HPO system. From Eqn.(5) thediscriminant components can be derived as follows:

1 for Ei > E

0 for E, 5 E

(6),={where, E isa threshold value that can be determined by aprecalculation for relay setting for each individualsystem, Li is logic value that will be used as a

discriminant component for fault detection,classification, and faulted phase(s) selection. By virtueo f these discriminants, the truth tables are establishcd

for all types of shunt faults for HPO systems (e.g. six-and twelve-phase systems) and for different bases(phase a, b, c , d,and etc...).

However, due to space limitation, the truth Tables forsingle line to ground faults for six- and twelve-phase

power transmission systems are presented here, Tables1,2. Thc value of spectral energy function E, whichcorrespond to Li = 0 is very small relative to thatcorrespond to L , = 1. This indicates the highly’

discrimination nature of this relaying principle.

From Table I , one can observe that there is nodiscrimination for phase ‘a’ to ground fault when phase‘a’ is chosen as a basis for L i calculatation, this problem

is solved by a recalculation of L i w.r.t another basis(phase ‘ c ’ in this case).

Based on the truth Tables, decision fl owcharts for faultclassification and faulted phase(s) selection for HPOsystems, are developed. Fig. 4.  for instance, depicts aflowchart for fault type classification in a twelve-phasesystem. Fig. 5 depicts a flowchart for faulted phaseselection for single line to ground “LG” fault in a six-phase system. Decision flowcharts for other types offaults are obtained in the samemanner.

Table I : T ruth table for L G ault w.r.t phase ‘a’and phase ‘c ’ bases for a six-phase system

Table2: Truth table for L C ault w.r.t phase ‘a’basis for a twelve-phase system

Calculate L ,L la , ... ,L L I l a

3%ind no. of zeros (2 )of L l , L z, ...,L I O , II

L

Change the base andcalculateL I , .. L I O , L I I

4

11 L O R 12 L O R

12L-G Fault

, &-;I O L I G Z=2 9 L / G

Fig. 4 Flowchart for fault type classification in atwelve-phase system

In Fig. 4 the term (2L / G) represents a double line faultwith or without ground according to Lo value. I n truthtables (1,2), ’1’ refers to fault existance (e.g. in table 1

L I =1 refers to fault on phase ‘b’ and so on)

807

7/29/2019 High-Phase Order Power Line Relaying

http://slidepdf.com/reader/full/high-phase-order-power-line-relaying 4/5

1rip e

2 3C

3g 2.

," I -fEL - I .P-v, -2

6 - 1 ripf

' 4 w p Lo=L,=lI.

"

I '

--- . r . , ,j f ;% ,

0 , I , ' I .

.'

- I'

Time in ms

+orip a

Fig.5 Flowchart for faulted phaseselection for singleline to ground %LG" ault in a six-phase system

COMPUTER SIMULAT ION

A verification of the developed relaying approach withpractical cases is done with the help of anelectromagnetic transient program (EMTDC) [1 ].

Algorithms for the introduced approach and W A areprogrammed under MATLAB environment.

Among the HPO transmission systems, the study isconducted on a six-phase transmission system due to

space limitation and because it i s the most promisingdue to the existing of double-circuit three-phasetransmission lines, which can be fairly converted to a

six-phase lines. However, the study is applied on a 230kV six-phase transmission system shown in Fig. 6. The

lines parameters are considered to be frequencydependent. The impedances of the sources S1 , S2, 53

are 20,10,20 R, espectively. The sampling frequency of200 lcHz is used. T he WA at scale 1 is used to capturethe HF currents superimposed on power frequencycurrents in a modal domain. For all casesEqns. (4-6) areused to calculate the discriminant components L3..

Fig. 6 Six-phase power transmission system

The system is simulated under various types of faults aidifferent locations, fault resistances, l ine terminals andfault inception angles. The results of these studies areshown In Figs. (7-1 ) . Fig. 7 (a,b) shows the HF modalcurrents (W, or WTC's) corresponding to phase 'a' toground fau\t at 180 km fromSI for 90" fault inceptionangle. Fig.7a corresponds to the sources S1, 52, S3

impedances of 20,10,20 n, respectively. Fig.7b

corresponds to equal sources impedances of 20 zl.Thecalculated discriminants L, for high states are shown in

the upper right corner of each figure. However, since

Z=4 (L I=L 2=t3=L 5=0) w.r.t the base IC', the fault i s

classified as a single line to ground and since (Lo=L4=1

the phase 'a ' will be tripped (see Table 1). Comparingthe results of Fig. 7a and Fig 7b one can observe thatthey are coincident. This assures that the introducedapproach is insensitive to the line terminals. This is dueto the busbar capacitances, which act asa short circuit attheconsidered range of frequencies.

Fig.8Wi for phase 'f toground fault at 25km from

S1 with cp =13S0,Rr =40 0 Cl.'

808

7/29/2019 High-Phase Order Power Line Relaying

http://slidepdf.com/reader/full/high-phase-order-power-line-relaying 5/5

Fig. 9depicts the WTC’s corresponding to phase ‘b’ to

ground fault at 50 km from S1 for a zero voltage

inception angle and 0.5 Cl fault retistance. As expected,the WTC’sare smaller than those i n Figs. (7,8)! but theunique features are also still existent, and this assure

that the introduccd approach does not suffer from the

limitation of a zero voltage fault inception angle asother traditional approaches.

2 0. 03-

g 0 0 2 -

,D5

V

001 -

$ -001

!i002-

“._ I

-

’: t (a’w, 1&=i

h:

T i m n m 1-0 03 I

3.4 3.6 3.8 4

Fig.9Wi for phase ‘b’ toground fault at 50km f rom

SI with ‘p =O, Rr =0 .5 0 .

Fig. 10depicts the WTC’s for twophase to ground fault

:: w pTime inms

4.9 5. 15 5. 4 5. 65

Fig. 10Wi for tw o phase ‘de’ toground fault with

cp =90aand Rr=0.50,.

Fig. 11 depicts the WTC’s for three phase fault.

2. 65 4.8 4. 95 5.1 5. 25

Fig. 11 Wi for three phase ‘bcd’ fault without ground

I t is worth noting that 5L , 6L, or 6L-G faults areconsidered as one category for a chosen modaltransform. I t is practically accepted, since the mostcommon fault is single line to ground fault.

CONCLUSION

This paper introduces a high-speed relaying approach,based on the wavelet analysis of the fault generated(raveling waves, dedicated for HPO transmission lines.I n this approach, the wavelet is used to capture the HFtraveling waves of currents superimposed on the powerfrequency currents in a modal domain. By virtue of thespectral energies o f the captured HF currents the truthtables are established for the entire types of shunt faults.The results of computer simulation show that the faultdetection, classification and faulted phase selection canbe realized within a quarter of cycle irrespective of the

fault inception angle, fault resistance, and line terminals.Hence, the approach ishighly decisive and reliable.

REFERENCES

[ I J J . R. Stewart et al, “High phase order transmission-Afeasibility analysis ’’ IEEE Trans. On PAS, Vol. 97, No. 6,Nov./Dec. 1978, pp. 2300-23 t 7.

[2] J . R. Stewartet al, ”Economics of EHV high phase order

transmission” IEEE Trans. On PAS, Vol. 103, No. 1 I ,November1984,pp. 3386-3392.

[3] J . R.Stewart and I . S. Grant, “High phase order- eady for

application”” EEE Trans. On PAS, Vol. 101,No. 6: une1982, pp. 1757-1767.

[4] S. S. Venkata e al, “138 kV , six phase transmissionsystem: ‘fault analysis”, IEEE Trans, On PAS, Vol. 101,No. 5,May 1982,pp. 1203-1218.

[5] R. V . Rebbapragda et al, “Selection and application of

relay protection for si x phase demonstration project” lEEE

Trans. On Power Delivery, Vol. 7, No. 4, October 1992.

[6] H. W. Dommel, “Digital computer solution ofelecrromagnetic transients in single- and muliphasenetworks” IEEE Trans, On PAS, Vol. 88 , No, 4, April

[7] S. G. Mallat.“A theory for multiresolution signal

deconiposition: the wavelet representation”, IEEE Trans.On Partem and Machine Intelligent, Vol. 11, No 7, J uly1989.

[ XI D. C. Robertson et al, “Wavelets and electromagneticpower system transients”, IEEE Trans. On PowerDelivery, Vol. 11, No. 2,April 1996,pp. 1050-1058.

[9] Ammar A . Hajjar, M . M . Mansour,H. A. Talaat, “ A NewApproach for High-speed Distance Protection Based onFault Induced High Frequency Currents and Wavelets,”The 51hJordanian International Conference on Electrical& Electronic Engineering JIEEECO3, 13-16 October,2003,Amman, J ordan.

1101 F . H . Magnago et al, “Fault location using wavelets”IEEE Trans. On Power Delivery, Vol. 13, No. 4, Oct.1998,pp. 14751480,

pp. 1900-1911.

1969,pp,388-399.

[I I ] HVDC Research Center, Manitoba,Canada, 1999.

[121 MATLAB User’ Guide,TheMath Work Inc.

AUTHOR ADDRESS

Dr. A mmar A. Hajjar

Deptartment of Electrical Power EngineeringFaculty of Mechanical & Electrical EngineeringTishreen University, Latakia, Syriaemail: ammarhajjar@hotmail.com

or aahajjar@scs-net.org mmsmansour@ieee.org

809