CURRENT MUTATION AND PHASE DIFFERENTIAL FAULT IDENTIFICATION ALGORITHM BASED ON SUPPLY AREA SAMPLING CALIBRATION METHOD FOR ACTIVE DISTRIBUTION NETWORK
More distributed energy resource (DER), regarded as clean energy source, become accessed into the distribution power system. However, it brings different influence on the judgement of protection act and fault location as before. This paper mainly focus on how to use these clean energy sources more effectively and to ensure safe operation of power system without the introducing of other facility. This paper proposes unified-sampling calibration method in which data of all the interconnected feeders in supply area is collected. Without changing the original network topology, the concept of “directed graph” is introduced to carry out of current direction calibration. With the results of such sampling calibration method, current mutation is to be the startup condition to locate the fault precisely. Through local communication in distributed FA and GPS time synchronization, current wave data is transferred between adjacent FA controllers. Fault identification algorithm based on current mutation and phase differential is proposed. INTRODUCTION Active Distribution Network (ADN) not only accepts DER into the distribution network, but also actively manages the system operation, which may alter the oneway power flow in traditional distribution network. Such operation management brings fundamental alteration of primary system as well as secondary system of distribution network, and requires better operation in ADN. Feeder Automation (FA), as one of the key techniques in the operation of distribution network, also needs improvement on its traditional concept in secondary system to meet the demand of technology enhancement brought by ADN. The protection coordination with DG isolation protection has to be considered due to isolate operation is allowed in active distribution network. There is many research has work on these. By studying the relay based on the rate of frequency change and mismatch rate of load and DG to analyze the sensitivity and reliability of protection is proposed in [1]. An active distribution grid protection scheme combined over-current protection and voltage protection is proposed in [2]. An active distribution grid fault location solution that only use current signal to identify the fault line by artificial intelligence algorithms is proposed in [3]. A radial active distribution network protection scheme is proposed in [4] by using directional over-current protection as a primary feeder protection and setting the appropriate current threshold with the appropriate trip time. An active management and protection coordination concept is proposed in [5] based on flexible active distribution network topology and adjustable over-current protection method. This method can provide more flexible and efficient mode of operation, and it is also applicable to islanding operation. It is first proposed in [6] that how to introduce the operation and protection of active distribution network in UK. But at that time, distributed generation is the major consideration. Once a fault is detected, protection action to protect distributed generation. An index called the maximum level of fault transient voltage shock is proposed in [7]. It is found that the index has linear correlation with fault distance. So it is very useful to fault location in single fault of micro-grid. A new method of impedance-based fault location by matching the voltage of substation bus and the voltage of each DG is proposed in [8]. It can be used in unbalanced threephase distribution network. The influence of synchronized phasor measurement and the sensitivity of fault location based on the voltage drop with distributed generation is proposed in [9]. The main problems affecting the distribution network fault location accuracy is: too many branch lines, load changes too fast, the system imbalance, unbalance three-phase system, the presence of branch line and load tap. So the four main issues of active distribution network protection is [10]: (1) It is need to replace the switch due to the increased level of fault currents; (2) Decrease the sensitivity of protection equipment and the normal operation of the feeder will be malfunction due the failure; (3) It is need to introduce new protection device, in particular islanding protection (loss of mains protection); (4) It is need to introduce new protection concept to meet in some islanding operation cases that may be achieved. The operation in traditional topology of secondary system mainly takes consideration of forward mode in which power is applied only by substation. However, it neglects the two-way power flow in ADN, which cannot take one-way flow for granted to set one single current direction as forward direction. This paper proposes unified-sampling calibration method in which data of all the interconnected feeders in supply area is collected. Without changing the original network topology, the concept of “directed graph” is introduced to carry out of CIRED Workshop Helsinki 14-15 June 2016 Paper 0178 Paper No 0178 Page 2 / 4 current direction calibration. With the results of such sampling calibration method, current mutation is to be the start-up condition to locate the fault precisely. Through local communication in distributed FA and GPS time synchronization, current wave data is transferred between adjacent FA controllers. Fault identification algorithm based on current mutation and phase differential is proposed. The method presented in this paper is verified by fault location simulation in China's 863 Project. This method is able to solve the efficiency problem in the operation of ADN with mass DER asserted, and to enhance economic performance by reduce the facility number as much as possible. SUPPLY AREA SAMPLING CALIBRATION METHOD FOR ACTIVE DISTRIBUTION NETWORK The traditional distribution system topology is radial network, so it can be interpreted as a multi-tree structure. Multi-tree structure changes only in the case of changing the operating mode through changing tie-switch status with the other one multi-tree or more multi-trees. However, in this case the new grid structure must still be a multi-tree structure. The conversion is shown in Fig.1: