| Renewable energy power generation has been widely used in recent years.When renewable energy is connected to the distribution network in the form of distributed generation,the distribution network changes from the original single power supply to multi power supply at the same time,which changes the electrical characteristics of the original distribution network.When the distribution network fails,the original distribution network protection may malfunction or refuse to operate.Therefore,it is of theoretical and practical significance to study the protection of distribution network with distributed generation.According to the principle of flux conservation,the voltage source series variable impedance fault model of synchronous generator type distributed generation is derived.According to the operation principle and control strategy of distributed generation,the voltage controlled current source fault model of inverter type distributed generation based on positive sequence voltage component of parallel node is obtained.In PSCAD / EMTDC simulation platform is used to build a distribution network model with synchronous generator or inverter type distributed generation.Three phase short circuit and two-phase short circuit faults are set in the area from distributed generation to the power side of distribution network.The output current law of the above two kinds of distributed generation under different fault types is simulated and analyzed.Secondly,aiming at the problems of poor generality and large amount of calculation of traditional short-circuit current calculation method in the case of distribution network fault,a general fault current calculation method suitable for distribution network with distributed generation is proposed.The synchronous generator and the inverter distributed generation are used as two kinds of excitation sources to act on the distribution network with faults.According to the superposition theorem,the fault components under different excitation sources are calculated respectively.Among them,the output current of inverter type distributed generation model adopts iterative algorithm.The correctness of the proposed method is verified by an example.Finally,the influence of distributed generation in 10 k V distribution network on three section current protection is discussed.The influence of distributed generation on current distribution and current protection action is discussed when the fault occurs in the area upstream of the feeder where the distributed generation is located(between the distributed generation and the system power),in the area downstream of the feeder where the distributed generation is located and in the area adjacent to the feeder where the distributed generation is located.In order to solve the problem that the original protection is not applicable after the distributed generation is connected to the grid,the protection area of the distribution network connected to the distributed generation is divided into two types,and the adaptive current protection scheme and the longitudinal differential main protection based on the amplitude ratio and phase angle difference of current positive sequence fault components are proposed for different areas,The total protection scheme including distributed generation is configured with inverse time over-current backup protection.The correctness of the protection scheme is verified by simulation.In order to further improve the correctness of protection action and the convenience of setting,a distributed regional pilot protection scheme using multi-point information is proposed.When the existing main protection refuses to operate,communication automation can be used to send tripping command to the circuit breaker of the main protection. |
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