Journal of the Korea Academia-Industrial cooperation Society (한국산학기술학회논문지)

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A Study on Operation Method of Protection Device for LVDC Distribution Feeder in Light Rail System

경전철용 LVDC 배전계통의 보호기기 운용 방안에 관한 연구

  • Kang, Min-Kwan (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Choi, Sung Sik (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Lee, Hu-Dong (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Kim, Gi-Yung (Department of Electrical Engineering, Korea University of Technology and Education) ;
  • Rho, Dae-Seok (Department of Electrical Engineering, Korea University of Technology and Education)
  • 강민관 (한국기술교육대학교 전기공학과) ;
  • 최성식 (한국기술교육대학교 전기공학과) ;
  • 이후동 (한국기술교육대학교 전기공학과) ;
  • 김기영 (한국기술교육대학교 전기공학과) ;
  • 노대석 (한국기술교육대학교 전기공학과)
  • Received : 2019.03.12
  • Accepted : 2019.04.05
  • Published : 2019.04.30
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Abstract

Recently, when a fault occurs at a long-distance point in a LVDC (low voltage direct current) distribution feeder in a light rail system, the magnitude of the current can decrease to less than that of the load current of a light rail system. Therefore, proper protection coordination method to distinguish a fault current from a load current is required. To overcome these problems, this paper proposes an optimal algorithm of protection devices for a LVDC distribution feeder in a light rail system. In other words, based on the characteristics of the fault current for ground resistance and fault location, this paper proposes an optimal operation algorithm of a selective relay to properly identify the fault current compared to the load current in a light rail system. In addition, this paper modelled the distribution system including AC/DC converter using a PSCAD/EMTDC S/W and from the simulation results for a real light rail system, the proposed algorithm was found to be a useful and practical tool to correctly identify the fault current and load current.

최근, 출력전압의 제어가 가능하고 양방향 운용이 가능한 PWM(Pulse Width Modulation) 정류기가 도입되고 있다. 그러나, PWM 정류기가 적용될 경우, 전력계통측에서 사고발생하면, 회생전력에 의한 사고전류 공급으로 기존의 사고전류 크기 및 방향이 바뀔 가능성이 있다. 또한, 경전철용 급전시스템에서는 장거리 지점에서 사고가 발생하는 경우, 사고전류의 크기가 크게 감소되고, 부하전류와 비슷하거나 더 작은 경우가 발생할 수 있기 때문에 이에 대한 적절한 보호협조 운용 방안이 필요한 실정이다. 따라서, 본 논문에서는 상기의 문제점들을 해결하기 위하여, 경전철용 LVDC 배전선로의 보호기기 운용 방안을 제안한다. 구체적으로는 LVDC 배전선로에서의 거리 및 단락저항별 사고특성을 분석하여, 다양한 조건에서 사고를 적절하게 판별하는 직류선택계전기의 보호협조 운용방안을 제안한다. 또한, 배전계통 상용 해석 프로그램인 PSCAD/EMTDC를 이용하여 AC 계통, PWM 정류기, LVDC 배전선로로 구성된 경전철용 급전시스템의 모델링을 제시한다. 한편, 제안한 보호협조 알고리즘과 모델링을 이용하여 LVDC 배전선로의 보호기기 특성을 분석한 결과, 제안한 운용방식에서는 전류 경사각의 급격한 감소를 판정하는 보호요소를 추가한다. 따라서, 사고지점의 단락저항이 높거나 장거리 선로인 경우에도, 보호기기가 사고전류와 부하전류를 적절히 판별할 수 있어, 본 논문에서 제안한 보호협조 운용알고리즘의 유용성을 확인하였다.

Keywords

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Fig. 1. Protection Coodination diagram in LVDC

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Fig. 2. Concept of fault and load currents

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Fig. 3. Operation plan of LVDC selection protection relay

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Fig. 4. Operation algorithm of selection protection relay

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Fig. 5. Modeling of power distributions

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Fig. 6. Modeling of MW scaled PWM rectifier

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Fig. 7. Entire modeling of power system

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Fig. 8. Fault characteristics of ground resistance(0[Ω])

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Fig. 9. Fault characteristics of ground resistance(3[Ω])

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Fig. 10. Fault current characteristics of 5km distance

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Fig. 11. Fault current characteristics of 8km distance

Table 1. Detailed parameters

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Table 2. Simulation conditions of Protection relay

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