Abstract
Power utilities worldwide commonly use the radial distribution system because of its advantages of being simple in structure and having relatively inexpensive installation costs. It has a disadvantage in that its power supply reliability is low because the load side of the fault section will suffer from an outage in the event of a fault in the system. However, recently, with ICT (Information and Communication Technologies) development, system reliability is required to be high as the outage-susceptible loads increase. In addition, the increase in the connection of distributed resources such as renewable energy and electric vehicles is making it impossible to predict the power flow and reducing line utilization. Therefore, a loop power distribution system is proposed as a measure to solve this problem. Because all buses (nodes) in a loop distribution system have two or more power supply routes, they are more reliable than the radial system. It allows them to improve line utilization by connecting lines with different load peak times. However, in the case of a fault in the loop distribution system, the fault current is supplied from both directions, making it impossible to properly isolate the fault section with the protection method of the conventional distribution system. The permissive overreach transfer trip (POTT) method using communication to compensate for the limitations of conventional protection devices, and the other method using directional distance relay, is proposed. However, these methods operate by determining the direction of the fault current but have a disadvantage. It is difficult to detect a fault due to the effects of ground faults and distributed generation (DG) occurring in other lines. Therefore, in this paper, we propose a protection coordination algorithm that uses the negative-sequence component of voltage and current that occur when an unbalanced fault occurs, rather than the determination of the directionality and use of communication. To validate this, we configured a system using PSCAD/EMTDC (Manitoba Hydro International Ltd., Winnipeg, Manitoba, Canada), a system analysis program package and verified the results depending on the type of faults with the proposed algorithm.
Highlights
The radial distribution system currently accounts for more than 99% of distribution lines used by power companies worldwide because of its advantages of being simple in structure and having relatively inexpensive installation costs compared to other methods
We modeled a PCS-based distributed generation (DG) interconnected to a loop distribution system by using the PSCAD/EMTDC program tool
The protection methods in the conventional loop distribution system are communicationbased, and methods of isolating a fault section by exchanging a trip and blocking signal by detecting a forward fault current were mainly applied. They were methods of using directional distance relays to detect the fault section by measuring impedance. These methods have the disadvantage of not detecting a fault or causing a malfunction resulting from the fault current flowing through the grounding of the interconnection transformer of DG
Summary
Using the distance relay has the disadvantage of not accurately detecting the fault location since it affects the equation for determining impedance to the fault location when DGs are interconnected to the distribution line, or the size of the fault resistance becomes large Another method is to isolate the fault section using the ratios of the zero-sequence component and positive-sequence component of the fault current [17]. It detects and isolates the fault section using the ratios of the positive-sequence component and zero-sequence component [18,19,20] This method activates the circuit breaker without considering the load interconnected to the line in the process of converting the system into a temporary radial system. The method we propose has the advantage of isolating the fault section without determining the direction of the fault current, reducing additional facilities because it does not use communication
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