1350 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 15, NO. 4, OCTOBER 2000

[4] A. Ametani et al., “A simple and efficient method for including fre-quency-dependent effects in transmission line transient analysis,”Elec-tric Power Energy Systems, vol. 19, no. 4, pp. 255–261, 1997.

[5] A. Ametaniet al., “Comparison of surge simulation by Marti and Nodaline models with field test results,” inProceedings EEUG’98, Prague,Nov. 1998.

[6] T. Adielson, A. Ametani, and R. G. Bergmanet al., “The calculation ofswitching surges—III,”ELECTRA, vol. 62, pp. 45–62, 1979.

Closure to Discussion of “Switching Overvoltage Analysisand Air Clearance Design on the KEPCO 765 kV Double

Circuit Transmission System”

Jeong-Boo Kim, Eung-Bo Shim, and Jeong-Woon Shim

The authors greatly appreciate the questions raised by Prof. A.Ametani. Our response to the questions are as follows:

We have noticed the facts Prof. A. Ametani pointed out, which Martimodel can not represent the vertical double-circuit line characteristicsfully, but the accuracy in a long time range is good enough in a prac-tical application. And we believe there is no significant change of over-voltage factors even though the step response of Marti model in a shorttime range is different from field test result. If we have a chance to havea field test for KEPCO’s 765 kV transmission line, we would like tocompare the result with field test.

In the KEPCO’s TNA line model, only the earth return branch canrepresent the frequency dependent characteristics. We think that thephase conductor do not need to be represented as frequency depen-dant model because the impedance variation according to the frequencychange is not dominant, and the frequencies used in the TNA line modelare the same ones in the EMTP Marti model. We chose the dominantfrequency as 60 Hz for power frequency, 500 Hz and 2000 Hz forhighest frequency, because the KEPCO’s transmission line is consistof two lines, 40 km and 150 km long, respectively.

As same as the discusser’s opinion, the measured value of earth resis-tivity was 600 ohm-meter to over 1200 ohm-meter in the rocky moun-tainous area. In the calculation of EMTP line model, 400 ohm-metersof value was used considering the average value of total route. In the de-termination of conductor height, we considered the average conductorheight and the ratio of tension type tower to suspension tower in thetotal route. In the early stage the average tower height was 85 meters,and finally we have correct it as 95 meters according to the commer-cial line. After the few EMTP calculation according to the change ofconductor height, we found no significant change of overvoltage anddo not need more detailed calculation.

We compared the same case using K. C. Lee model, Semlyn modeland Marti model in the EMTP line model. The result from Semlynand Marti model was almost identical, but we mainly use the Martimodel because the use of Semlyn model was complicated. The fre-quencies used in the TNA, line model for the representation of earthreturn branch were same as those of Marti model in EMTP. We did notperformed the comparison study for the frequency dependence.

Manuscript received January 14, 2000.J.-B. Kim, E.-B. Shim, and J.-W. Shim are with the Korea Electric Power

Research Institute, 103-16, Munji-Dong, Yousung-Gu, Taejon 305-380, Korea(e-mail: jbkim@kepri.re.kr).

Publisher Item Identifier S 0885-8977(00)11145-8.

The study result of CIGRE WG in 1970s which compare the analogmodel and digital simulation shows differences between them, and eventhe TNA result is not identical according to the TNA manufacturer. Wethink that nowaday TNA is improved to be far better than that of inthe year of 1970s. The KEPCO’s TNA was designed to represent thecapacitances for line to ground, line to line and inter-circuits, and thedata acquisition system is better than that of 1970’s. We think the bigdifference of phase to phase overvoltage is due to the difference of linemodel between EMTP and TNA. In EMTP the distributed line modelis possible whereas in TNA the line model can be represented as phisections. So, we think the different wave propagation velocity can makethe difference of phase to phase overvoltage.

In the study of lightning surge of transmission line, we calculatedthe lightning flashover rate based on the arcing horn gap length whichis derived from the switching surge overvoltage factors. Although thatprocedure is not described on this paper,1 calculated the lightningflashover rate as 0.4 flash per 100 km route length per year based onthe IKL of 20. The ground wire arm is longer than the upper conductorarm by 2 meters at each end, which is approximately minus 8 degreesof shielding angle in suspension tower and minus 10 degrees in tensiontype tower.

J.-B. Kim et al., IEEE Trans. on Power Delivery, vol. 15, no. 1, pp.381–386, January 2000.

Discussion of “A Fault Diagnosis Expert System forDistribution Substations”

Yan Liu and Noel N. Schulz

The authors are to be congratulated for this interesting paper.1 Wewould like to comment on several points and the authors’ responseswould be appreciated.

1) In the introduction, the authors mentioned that this fault diag-nosis expert system is for multiple substations, but no exampleor test case for multiple substations was presented. How doesthis system deal with the interaction of the substations? Haveyou tested it on any multiple-substation model? Can you giveany example or test case to support this statement?

2) In Section V, the authors give the relationships between mis-op-eration probabilities. The priority of the solutions is based onthese relationships. These relationships seem to be from a histor-ical data. Is there any documentation to support this? What is therange of the probabilities? Do you have any numerical values forthe probabilities that would indicate a clear separation of them?In your test cases, what percentage included a device mis-oper-ation?

3) The example in Section V indicated that time is not used in theKEPCO system. If this is true, how would the expect system

Manuscript received September 8, 1999.Y. Liu and N. N. Schulz are with Michigan Technological University, Depart-

ment of Electrical Engineering, 121 EERC, 1400 Townsend Drive, Houghton,MI 49931.

Publisher Item Identifier S 0885-8977(00)11148-3.

1H.-J. Leeet al., IEEE Trans. Power Delivery, vol. 15, no. 1, pp. 92–97, Jan-uary 2000.

0885–8977/00$10.00 © 2000 IEEE

IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 15, NO. 4, OCTOBER 2000 1351

come up with a unique solution to given example? It seems thatthis would not be possible without the time information if thereis a mis-operation.

4) The authors’ data representation lacks a node naming structure.How is the location of the over-current relay represented to dif-ferentiate between low side and high side of the transformer?

Closure to Discussion of “A Fault Diagnosis Expert Systemfor Distribution Substations”

Heung-Jae Lee, Bok-Shin Ahn, and Young-Moon Park

The author wishes to thank Mr. Liu and Dr. Schulz for their interestin the paper.1

1) This paper1 focused into the general structure of the expertsystem to be applied to several substations that may havedifferent number of transformers or transmission lines. Theinteraction is considered in [1]. Actually the system was testedin a practical control center, where there are eight substations.

2) We have a report on the project in Korean language. The clearseparation is essentially impossible since the diagnosis is an in-ductive problem in nature. The reason and the range is discussedin [1].

3) Certainly, utilizing time information will improve the perfor-mance of the diagnosis. However it is possible without time in-formation. Reference [2] would also provide good insight for theinference without time information.

4) Value “1” at the location field denotes the primary side, “2” de-notes secondary side of transformers, “3” denotes distributionfeeders. In the target system of my project, some common alarmsare received. For example, when a fault occurs in any primaryside of three transformers, only an alarm “ocr(alpha, 1, o)” isreceived to the expert system. Then the system should identifythe transformer using topological knowledge and circuit breakersalarms. Analog data is also utilized for the better performance.

REFERENCES

[1] H. J. Lee, D. Y. Park, B. S. Ahn, J. K. Park, Y. M. Park, and S. S. Venkata,“A fuzzy expert system for the integrated fault diagnosis,” IEEE Trans.PWRS, to be published.

[2] C. Fukui and J. Kawakami, “An expert system for fault section estima-tion using information from protective relays and circuit breakers,”IEEETrans. PWRD, vol. PWRD-1, no. 4, pp. 83–90, Oct. 1986.

Manuscript received September 30, 1999.H.-J. Lee is with Kwangwoon University, Korea (e-mail: hjlee@daisy.kwang-

woon.ac.kr).B.-S. Ahn is with System Laboratory, R&D Center, LG Industrial Systems

Co., Korea.Y.-M. Park is with the School of the Electrical Engineering, Seoul National

University, Korea.Publisher Item Identifier S 0885-8977(00)11147-1.

1H.-J. Leeet al., IEEE Trans. on Power Delivery, vol. 15, no. 1, pp. 92–97,January 2000.

Fig. D1. The circuit with a linear load.

Fig. D2. The circuit with a nonlinear load.

Discussion of “Evaluation of Single-Point MeasurementsMethod for Harmonic Pollution Cost Allocation”

Shih-Min Hsu

The author has some observations and suggestions about themethods and procedures presented in the paper.1

The paper claimed that the harmonic active power,PH , as defined in(4), was directly produced by the nonlinear loads. This may not be truewhen a linear load is supplied by a nonsinusoidal, or distorted, voltagesource. In this case the harmonic active power is not caused becauseof the load nonlinearity but the source voltage distortion. For example,a circuit with system impedance ofRS andXS , and load impedanceof RL andXL, as shown in Fig. D1, if the supply voltage is distorted,then the terminal voltage and current will be distorted. In this case, al-though the terminal voltage and current contain harmonic components,the load should not be charged for it. On the other hand, a circuit witha nonlinear load can be expressed as a combination of a linear loadand a harmonic current source, as shown in Fig. D2. The nonlinearloads may generate more current harmonic components than the sourcevoltage harmonics. In the other words, the harmonic spectrum of thisharmonic current source may not be the same as the source voltage har-monic spectrum. It seemed the method presented in the paper would notbe able to distinguish who is responsible for the cause of a particularharmonic component.

Moreover, according to the way the nonfundamental apparent power,SN , was defined in (7), namely,

SN = 3(V1IH + VHI1 + VHIH);

Manuscript received June 18, 1999.S.-M. Hsu is with Transmission Planning, Southern Company Services, Inc.,

Birmingham, AL.Publisher Item Identifier S 0885-8977(00)11150-1.

1E. J. Daviset al., IEEE Trans. Power Delivery, vol. 15, no. 1, pp. 14–18,January 2000

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