Fault Simulation Analysis And Relay Protection Research Of Wind Farm

Global climate change, environmental pollution and energy crisis have become a hotissue of the governments and people. With the characteristics of wide distribution, hugereserves, low difficulty to be used and rapid development of wind power technology overthe past few decades, wind energy has become the most mature and large-scale commercialdevelopment of power generation technology in the new energy field and will find its placein the future energy field. However, several large-scale accidents of wind turbine generatorsoff the power grid occurring in the past few years have challenged the traditional relayprotection technology seriously. It is urgent to propose relay protection solutions takingaccount of the access of wind power.The thesis firstly established PSCAD simulation model of doubly-fed inductiongenerator (DFIG), to analyze the fault characteristic by the side of DFIG in the singlegenerator-infinity system through digital simulation and physical simulation. Referring tothe typical wiring of the actual wind farm, a wind farm model with a reasonable simplifiedequivalent had been built to set a series of fault points to test its impact on the relayprotection. The studies have shown that the fault transient characteristics near the infinitysystem with DFIG is nearly the same to a regular power system which without, since theimpact of wind power access on relay protection focus on the side of windfarms:(1)three-phase fault current was unable to continue during the DFIG low voltageriding through, leading to current protection with delay difficult to operateaccurately;(2)fault current contained a mass of non-power frequency component whosefrequency relied on rotor speed during riding through low voltage, causing great negativeimpact on phasor distance protection performance;(3)fault line selection for single-phase to ground was difficult since35kV voltage grade were neutral non-grounded system in windfarms.The followed improvements have been made aiming at the influence of wind poweraccess to the relay protection:(1)instantaneous current and voltage comprehensiveprotection was proposed during riding through low voltage;(2)self-adaptive distanceprotection based on solving time domain differential equation with the advantage offrequency insensitivity and high tolerance of excessive resistance;(3)zero sequence currentratio and phase synthesis algorithm was able to select fault line for single-phase to groundcorrectly and even change the neutral point grounding method, increasing the zero sequencecurrent;(4) current phasor longitudinal differential protection would not be affected byspecial transient characteristics of wind farms, becoming the best protection with superiorperformance.