Study On Line Protection Scheme For Distribution Network With Dispered Doubly-feed Induction Generator

With the energy and environment problem become more serious,renewable energy will be paid attention.The distribution of renewable energy connected in the medium voltage distribution network is development direction in the future.With distributed electric resource(DER)permeability developing rapidly,traditional configuration of distribution network and current characteristics which is after fault will have big change.It makes the relay protection in traditional distribution network is not satisfied requirement of reliable operation.The disadvantage of DFIG connected position upstream for distribution network is traditional current protection easy to unwanted operation、refuse operation.According to transient derived DFIG fault current and analyze short current component,fault current frequency characteristics is researched when fault happened has crowbar DFIG that lost large power grid.A longitudinal protection of distribution network with current frequency difference is studied.The scheme can judge the faults of the fault line both in and outside the line by comparing the frequency difference between the two ends of the line and protecting the action condition.The DFIG connected in the grid will focus on short current increased on connection downstream point,which will lead traditional current protection range increase,even to a big problem.The relationship of DFIC short current and DFIG output power in fault transient time is deduced.Base on this research,one protective scenario which receives output power from wind farm and adjusts connected position of downstream current cut down is studied.This scenario via adjusted protective operates value to ensure the protection in reasonable and reliable range when the circuit suddenly disconnect.This scenario uses PSCAD/EMTDC software to build distribution network model.Under many faults,the researched protection principle will be tested.