Over-excitation Relaying for Digital Generator Protection using the 765kV Power System Modeling Data in Korea

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1 Available online at Energy Procedia 14 (20) nd International Conference on Advances in Energy Engineering Over-excitation Relaying for Digital Generator Protection using the 765kV Power System Modeling Data in Korea Park Chul Won, Ban Woo Hyeon,a* Gangneung-Wonju National University, Electrical Engineering, 150 Namwonro, Wonju, ,Korea Gangneung-Wonju National University, Electrical Engineering, 150 Namwonro, Wonju, ,Korea Abstract A large AC generator is an important component of the power system. Researches on the AC generator relaying for the next-generation ECMS and an efficient operation of protection control system are necessary. These require developments on detailed generator modeling and internal fault analysis, and prototyping for multifunctional IED device dedicated to next-generation production. In this paper, over-excitation relaying algorithm is one of the main protection elements which have an important role in DGPS(Digital Generator Protection System), was proposed. This paper first briefly introduces a principles of over-excitation and DFT-based gain compensation algorithm was adopted for the frequency measurement. Subsequently, protection scheme of over-excitation was presented. The 765[kV] modeling data of South Korea using EMTP-RV was used for simulations. The simulation result of over-excitation relaying are also provided Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the organizing committee of 2nd 2011 International Published Conference by Elsevier on Ltd. Advances Selection in Energy and/or peer-review Engineering (ICAEE). under responsibility of [name organizer] Open access under CC BY-NC-ND license. Keywords: DFT; DGPS; EMTP-RV; Gain Compensation; IED; Over-Excitation; 765kV Power System 1. Introduction Protection devices improve the stability of the power system and prevent a damage of the various facilities by detecting and removing the fault quickly and correctly whenever a fault occurs in power system[1]. Recently, the digitization of protection relays has accelerated by the rapid development of protection algorithm and the semiconductor technology. A large AC generator is an important component of the power system. Researches on the AC generator protection relays for the next-generation ECMS(Electrical Equipment Control and Monitoring System) * Corresponding author. Tel.: ; fax: address:cwpark1@gwnu.ac.kr Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the organizing committee of 2nd International Conference on Advances in Energy Engineering (ICAEE). Open access under CC BY-NC-ND license. doi: /j.egypro

2 Park Chul Won and Ban Woo Hyeon\ / Energy Procedia 14 (20) and an efficient operation of protection control system are necessary. However, most of protection and control systems used in power plants have been still imported as turn-key and operated in South Korea[2]. This may cause the lack of the correct understanding on the protection systems and methods, and thus have difficulties in optimal operation. On the other hand, the comprehensive tutorials and standards for the generator protection, which is main element in generation, have been announced in overseas[3,7]. Some companies are working to develop IED(Intelligent Electronic Device) for generator protection and control system[4,5,9]. For over-excitation protection, various factors for the synchronous generators in several power plants including the coordination with a generator control system, and over-excitation limiters design, and over-excitation relays setting have been studied[8,10,11,]. In recent years, attention for advancement of smart grid and ECMS has been increased in South Korea[13,14,15]. The increasing attention on multi-function IED for large generator internal fault protection results in starting a national project in South Korea, the IED prototype development for nextgeneration power units[2,6]. In this paper, the over-excitation algorithm, one of the main protection elements which have an important role in DGPS(Digital Generator Protection System), is proposed. The characteristic equation and setting value of the relay which is used in South Korea power plants is explored. The main reason of overexcitation and basic protection principles are reviewed in Section 2.1. Second, the gain compensation method which improves the conventional DFT method to collect the frequency for over-excitation protection is described in Section 2.2. Finally, the 765kV modeling data of South Korea are used and simulated for the performance evaluation of the relay. 2. Over-excitation Protection 2.1 Basics[2,3,6] The flux is proportional to the voltage within the magnetic circuit and is inversely proportional to the frequency. Thus, the flux can be expressed as Volts/Hertz. When the voltage increases or decreases the frequency is overexcited state. So, excess flux is saturated the iron core and it is leakage around the core and conductors leads to extreme eddy loss. The main reasons of over-excitation are as follows:. When the generator to start and stop, the voltage does not decrease proportionally with the frequency. Failure of AVR(AutomaticVoltage Regulator). Loss of input from the transformer. Sudden load off due to the condition of the grid. Line charging current of long-distance transmission in no-load 2.2 Frequency Estimation Method[13,14,15] The frequency response of the real and imaginary parts corresponding to the fundamental frequency is expressed as follows.

3 826 Park Chul Won and Ban Woo Hyeon\ / Energy Procedia 14 (20) V V rl il 2 ( k) = [ Vk + 0.5( V k 6 k ( V 2 ( k) = [ Vk 9 k ( V k 11 k 8 k ( V k 11 k 10 k 4 k 5 k 7 k 8 k 2 k 1 k 5 k 4 k 1 k 2 )] )] (4) The sample of the real and imaginary parts corresponding to the nth data window can be expressed as the equation (5). V = V rn + jv in (5) The phase difference of the continuous discrete signal passed through the filter can be simply displayed as the equation (6). The final frequency value can be calculated using two phase differences as shown. V 1 rnvi invr θ n+ 1 θ = tan [ ] (6) n VrnVr invi θn+ 1 θn (7) fˆ = 2π F s The gain compensator of the DFT filter can be calculated by the calculation of the magnitude and phase according to frequency, after the z-transform of the sine and cosine filters. Gs (f) = T 0[g(f fsys) g(f + fsys)]/t (8) G (f) = T [g(f f ) g(f f )]/T (9) c 0 sys + sys where, sin(2πft0 ) g(f) =, T 0 = 0.5/f sys 2πfT The compensation of estimation frequency was computed by the gain compensator. 2.3 Protection Scheme of Over-excitation[2,4,5] The over-excitation relay is consists of instant function and inverse function with the delay time characteristic. We note only inverse function. A few years ago, the over-excitation protection used a combination of the over-voltage relay and the under-frequency relay. But now days, the over-excitation protection uses the inverse characteristic equation relay shown as the below 0 T K = V / F ( / ) PU V F nom s second (10)

4 Park Chul Won and Ban Woo Hyeon\ / Energy Procedia 14 (20) K T 2 = V / F 1 ( / ) PU V F nom s T K = V / F ( / ) PU V F nom s second (1 second () where, K = time factor(2), Vnom = nominal voltage(114.3), Fs = system frequency(60), PU = V/Hz pickup(1. To minimize the nuisance alarms, the TIME FAC(time factor) was set as Simulation kV Power System Modeling by EMTP-RV The Republic of Korea 765kV power system modeling data by EMTP-RV based on PSS/E program were used[13]. The modeling for the governor and exciter of Uljin N/P and Dangjin T/P were obtained based on real field data, and T/L between Shin-gapyung and Shin-ansung was simulated based on the places where the construction will be done. The data of during disturbances was collected by changing the load of 100MVA and 400MVA at the Dangjin T/P using the EMTP-RV software. The sampling frequency is 720Hz. The simulation was performed for a total of 40sec and disturbance was occurred at 20sec. From the 765kV T/L system as shown in Fig. 1, voltages were measured of six regions (Dangjin, Shin-seosan, Shin-ansung, Shin-gapyung, Shin-taebaek, and Uljin).

5 828 Park Chul Won and Ban Woo Hyeon\ / Energy Procedia 14 (20) Load Shedding Fig. 1 Power system model of EMTP-RV Fig. 2(a) shows the A phase voltage frequency when the load shedding as much 100MVA at the Dangjin. The RMS of the voltage signal is shown in Fig. 2(b). The over-excitation condition is satisfied by the voltage increased. Fig. 2(c) represents the estimated frequency of A phase voltage by proposed methods and the estimated frequency gradually stabilizing after oscillating each about 0.06Hz, 0.08Hz, 0.08Hz, 0.1Hz, 0.Hz, 0.13Hz in Dangjin, Shin-Seosan, Shin-Ansung, Shin-Gapyung, Shin-Taebaek, and Uljin, during a two cycle. The time of trip occurring in Dangjin is shown in Fig. 2(d). (a) Voltage signal at 6 region (b) RMS of voltage signal at 2 region

6 Park Chul Won and Ban Woo Hyeon\ / Energy Procedia 14 (20) (c) Estimated frequency of 6 region (d) Trip signal at Dangjin Fig. 2 Load shedding about 500MVA Fig. 3(a) represents the A phase voltage frequency when a 400MVA load shedding at the Dangjin. Fig. 3(b) shows the RMS of the voltage signal. The over-excitation condition is satisfied by the voltage increased. Fig. 3(c) shows the estimated frequency of A phase voltage by proposed methods and the estimated frequency gradually stabilizing after oscillating each about 0.07Hz, 0.11Hz, 0.16Hz, 0.25Hz, 0.42Hz, 0.43Hz during a two cycle, in Dangjin, Shin-Seosan, Shin-Ansung, Shin-Gapyung, Shin-Taebaek, and Uljin. Fig. 3(d) shows the occurrence time of trip in Dangjin. (a) Voltage signal at 6 region (b) RMS of voltage signal at 2 region (c) Estimated frequency of 6 region (d) Trip signal at Dangjin Fig. 3 Load shedding about 1517MVA 4. Conclusion

7 830 Park Chul Won and Ban Woo Hyeon\ / Energy Procedia 14 (20) In this paper, over-excitation protection, which is main protection element to design multifunction IED for DGPS, was studied. To measure the frequency, DFT-based gain compensation algorithm was proposed. It has better performance than conventional DFT. The Republic of Korea 765kV modeling data were used for performance evaluations. Simulation results that trip was successfully done in both of two cases. The frequency variation was a serious at the city near the origin of the accidents than the more far. We can see that the time of trip decision occurrence gets the fastest with the inverse characteristic equation T1. When T2 or T3 is used, the sensitivity of the relay gets insensitive. Therefore, T1 is best suited for real power systems. Acknowledgements This work has been supported by KESRI(2010T ), which is funded by MKE(Ministry of Knowledge Economy). References [1] Geoff Klempner, Isidor Kerszenbaum, Handbook of Large Turbo-Generator Operation and Maintenance, IEEE Press, 445 Hoes Lane Piscataway, NJ 08855, pp. 333~372, [2] Chul Won Park et al., Development of Prototype Multifunction IED for Internal Fault Protection of Large Generator, 2010 Knowledge economy innovation project, first year's annual report, pp. 1~286, [3] IEEE Power Engineering Society, Guide for AC Generator Protection, IEEE Std. C pp. 1~167, [4] GE Industrial Systems, DGP Digital Generator Protection System Instruction Manual, pp. 1~C4, [5] General Electric Company, GEK DGP Digital Generator Protection System, pp. PD-1~SO-21, [6] Lee Seung Jae et al., A study on establish the setting for protection relays, final report, pp. 1~442, [7] IEEE Std. C , IEEE Guide for Abnormal Frequency Protection of Power Generating Plants, pp. 1~34, [8] Eli Pajuelo et al., Coordination of Overexcitation Limiter, Field Overcurrent Protection and Generator Control, Power and Energy Society General Meeting, IEEE, pp. 1~7, [9] Siemens, Siprotec Numerical Protection Relays, Part 2, Vol. 11, pp. 1~102, [10] Murdoch, A. et al., Generator Over Excitation Capability and Excitation System Limiters, Panel Session Summary for the JEEE/PES WPM, Vol. 1, pp. 215 ~ 220, [11] Alves, E.F. et al., Analysis of overexcitation relaying set up in synchronous generators for hydro power plants, IEEE/PES T&D-LA, pp. 298 ~ 303, [] G. K. Girgis and H. D. Vu, Recommended Models for Overexcitation Limiting Devices, IEEE Transactions on Energy Conversion, Vol. 10, No. 4, [13] Chul Won Park, Yoon Sang Kim, Advanced Frequency Estimation Technique using Gain Compensation, International Symposium MEPS'10 Session 15, 15.1.pdf, [14] Chul Won Park, Yoon Sang Kim, A Monitoring System Development for a New-type of Korean FNET, International Symposium MEPS'10, P44.pdf, [15] Chul-Won Park, Chul-Hwan Kim et al., Study on Advanced Frequency Estimation Techniques using Gain Compensation, Journal of Electrical Engineering & Technology, pp. 439~446, Vol. 6, No. 4, [16] C.W. Park, C.H. Kim et al., A Comparative Study of Frequency Estimation Method for Fault Disturbance Recorder, ICEE 2011, A153-FP.pdf,