Application Analysis of Distance Protection in DFIG Access System
The impact of large-scale access of new energy on the traditional relay protection in the system has appeared,and the sensitivity and reliability of the relay protection in some areas have decreased in the near area failure.Focusing on application of distance protection in the doubly-fed fan access system,this study analyzes fault characteristics of the doubly-fed fan in follower inverter.Under the assumption that the electromotive force of the fan is unchanged,the equivalent impedance of the system is calculated by the superposition principle,and the voltage phase mutation is transformed into the equivalent impedance change of the system,and then the behavior of positive-sequence voltage polarization impedance relay is analyzed.The impedance relays on the wind farm side and the system side of the tie lines are studied respectively.The results show that the changes of the equivalent impedance of the doubly-fed fan system will lead to the shift of the impedance circle sensitivity angle when the fault occurs,so that the wind farm side distance protection may misoperate in the case of forward fault,and the system side distance protection may have the risk of reverse misoperation in the case of reverse fault.In addition,when a fault occurs on the tie line,the changes of the equivalent impedance of the system may also cause the misoperation of the adjacent lines without fault.Finally,a simulation model is built based on the field wiring diagram to verify the fast distance protection on the wind farm side,system side and load side,and the experimental results are consistent with the previous analysis.
distance protectiondoubly-fed induction generatorpositive-sequence voltage polarizationimpedance relaysystem equivalent impedance