DOI QR코드

DOI QR Code

Characteristics of Saturation and Circulating Current Based on Winding and Iron Core Structure of Grid-connected Transformer in Energy Storage System

ESS 연계용 변압기의 결선방식 및 철심구조에 따른 순환전류와 포화특성에 관한 연구

  • Tae, Dong-Hyun (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Lee, Hu-Dong (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Kim, Ji-Myung (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Rho, Dae-Seok (Department of Electrical Engineering, Korea University of Technology and Education)
  • 태동현 (한국기술교육대학교 전기공학과) ;
  • 이후동 (한국기술교육대학교 전기공학과) ;
  • 김지명 (한국기술교육대학교 전기공학과) ;
  • 노대석 (한국기술교육대학교 전기공학과)
  • Received : 2020.01.30
  • Accepted : 2020.04.03
  • Published : 2020.04.29

Abstract

Since the fire accident of ESS (energy storage system) occurred at Gochang KEPCO Power Testing Center in August 2017, 29 fire cases with significant property losses have occurred in Korea. Although the cause of fire accidents have not been identified precisely, it should be considered battery and PCS (power conditioning system) as well as unbalance issues in the distribution system. In particular, circulating currents in a neutral line of a grid-connected transformer, which can affect a magnetized current, may have a negative effect on the ESS with unintentional core saturation and surge voltages at the secondary side of the transformer. Therefore, this paper proposes the modeling of the distribution system, which was composed of a substation, grid-connected transformer, and customer loads using PSCAD/EMTDC S/W, to analyze the phenomena of circulating current and surge voltages of the transformer with unbalanced currents in the distribution system. This paper presents a countermeasure for a circulating current with the installation of NGR (neutral grounding resistor) in grid-connected transformer. From the simulation results, it is clear that exceeding the circulating current and surge voltage at the secondary side of the transformer can be one of the causes of fire accidents.

2017년 8월에 발생한 고창 전력시험센터를 시작으로, 현재까지 총 29건의 전기저장장치 화재가 발생하여 많은 재산피해가 보고되고 있다. 이에 대한 원인은 아직 정확하게 규명되지 않았으나, ESS(energy storage system)와 전력변환장치뿐만 아니라, 계통측 불평형 문제도 하나의 원인으로 고려되어야 할 것으로 보인다. 특히, 연계용변압기측의 순환전류가 자화전류에 영향을 미쳐, 의도치 않게 변압기의 철심이 포화되고 서지전압이 발생하여 ESS에 영향을 줄 수 있다. 따라서, 본 논문에서는 부하불평형에 의한 불평형전류 발생시, ESS 연계용변압기로 순환전류의 유입과 변압기 포화로 인한 서지전압 발생 현상을 해석하기 위하여, PSCAD/EMTDC를 이용한 배전용변전소, 연계용변압기 및 수용가부하로 구성된 배전계통의 모델링을 수행한다. 또한, 이러한 문제를 해결하기 위하여, 중성점 접지 저항기(neutral grounding resistor, NGR)를 통해 순환전류의 크기를 일정 값 이내로 저감시키는 방안을 제시하였다. 이를 바탕으로 시뮬레이션을 수행한 결과, 연계용변압기의 결선방식 및 철심구조에 따라 일정 값(10[A]) 이상의 순환전류가 발생하여, ESS에 전기적인 위해 요인이 될 수 있음을 알 수 있었고, 변압기 포화로 인해 2차측에 최대 3[pu]의 서지전압이 발생될 수 있음을 확인하였다.

Keywords

References

  1. "ESS Causes Investigation and Safety Reinforcement Measures Announcement", Ministry of Trade, Industry and Energy, 2019.06. http://www.kats.go.kr/cwsboard/board.do?mode=download&bid=128&cid=20839&filename=20839_201906111437588581.pdf
  2. "Establishing government measures to cope with ESS fire accidents", Ministry of Trade, Industry and Energy, 2019.06. http://kats.go.kr/cwsboard/board.do?mode=download&bid=128&cid=20485&filename=20485_201811281715340631.pdf
  3. G.Morkyani, M.-R.Haghifam, "Analysis of ferroresonance in a 20kV distribution network", International conference on power electronics and intelligent transportation system, pp. 31-35, 2009. DOI: https://doi.org/10.1109/PEITS.2009.5407008
  4. Madhab Roy, Chinmay Kanti Roy, "A study on ferroresonance and its depedence on instant of switching angle of the source voltage", Third international conference on power systems, Kharagpur, pp. 1-6, India December 27-29, 2009 DOI: https://doi.org/10.1109/ICPWS.2009.5442704
  5. S. M. Lee, Y. G. Sun, J. Y. Lee, D. G. Lee, E. I. Cho, D. H. Park, Y. B. Kim, I. S. Sim, J. Y. Kim, "Short-term Power Consumption Forecasting Based on IoT Power Meter with LSTM and GRU Deep Learning", The Journal of The Institute of Internet, Broadcasting and Communication, Vol. 19, No. 5, pp. 79-85, Oct. 2019. DOI: https://doi.org/10.7236/JIIBC.2019.19.5.79
  6. Paul S. Moses, Mohammad A.S.Masoum, Hamid A. Toliyat, "Impacts of hysteresis and magnetic couplings on the stability domain of ferroresonance in asymmetric three-phase three-leg transformers", IEEE Transactions on energy conversion, vol.26, no.2, pp. 581-592, June 2011. DOI: https://doi.org/10.1109/TEC.2010.2088400
  7. L. B. Crann, R. B. Flickinger, "Overvoltages on 14.4/24.9-Kv Rural Distribution Systems", Transactions of the American Institute of Electrical Engineers. Part III: Power Apparatus and Systems, Volume: 73, Issue: 2, Jan. 1954 DOI: https://doi.org/10.1109/AIEEPAS.1954.4498949
  8. P. A. Abetti, I. B. Johnson, A. J. Schultz, "Surge Phenomena in Large Unit-Connected Steam Turbine Generators", Transactions of the American Institute of Electrical Engineers. Part III: Power Apparatus and Systems, Volume: 71, Issue: 5, Dec. 1952 DOI: https://doi.org/10.1109/AIEEPAS.1952.4498573
  9. D. G. Lee, Y. G. Sun, I. S. Sim, Y. M. Hwang, J. Y. Kim, "Comparison of Power Consumption Prediction Scheme Based on Artificial Intelligence", The Journal of The Institute of Internet, Broadcasting and Communication, Vol. 19, No. 4, pp. 161-167, Aug. 2019. DOI: https://doi.org/10.7236/JIIBC.2019.19.4.161
  10. R. H. Hopkinson, "Ferroresonant During Single-Phase Switching of 3-Phase Distribution Transformer Banks", IEEE Trans, on Power Apparatus and Systems, Vol. PAS-84, No. 4, pp. 289-293, April, 1965. DOI: https://doi.org/10.1109/TPAS.1965.4766193
  11. Jin-Geun Shon, Dong-joon Kim, Min-Gu Kang, Hee-Jong Jeon, "Magnetic Flux Saturation Analysis of Matching Transformer Considering Characteristic of Dynamic Voltage Restorer(DVR)", Trans., KIEE, vol.57P, no.3, pp. 236-243, SEP 2008. http://uci.or.kr/G704-001568.2008.57.3.012
  12. M. Salimi, A. M. Gole, and R. P. Jayasinghe, "Improvement of Transformer Saturation Modeling for Electromagnetic Transient Programs," in International Conference on Power Systems Transients, 2013, pp. 16. http://ipstconf.org/papers/Proc_IPST2013/13IPST075
  13. "EMTDC manual," Winnipeg: Manitoba HVDC Research Center, 2003.