Study Of The Special Problems Of Relay Protection Of 110kV With Wind Power Neutral Resistance Grounding System

Recently,in order to solve the problems of environmental pollution and energy shortage,large-scale wind power construction has swept the whole country.With the rapid growth of capacity installed,the wind farm is usually connected to the power grid with 110kV or above.Our 110V power system usually adopt the neutral point direct grounding system which cannot meet the growing requirements of sensitive load when the single phase earth fault occurs.Theoretical deduction proves that a suitable grounding resistance at the neutral point can effectively suppress the load-side voltage sag caused by the single phase earth fault.However this neutral grounding method would change the zero-sequence net of the power system which leads to the original relay protection cannot meet the demand.Depending on the study of the math model of double fed induction generation unit and typical structure of large scale wind farm,the equivalent modeling of large-scale wind farms is carried out.On the basis of it,the voltage transfer matrix in 110kV neutral resistance system which contained wind power is derived.Combining with the parameters of system,the constraint condition which can suppress the load-side voltage sag is 11X1?R0?1/?C0.Because the equivalent zero sequence reactance of all components of the system is far less than the neutral point grounding resistance,the value and distribution of zero sequence voltage and current and the phase between them are obviously different from those of neutral point grounding system.Based on these difference,a new setting calculation of zero sequence current protection in 110kV neutral resistance system which contained wind power is proposed,and the operating condition of the zero sequence directional element is modified in both system side and transformer side.Moreover,the adjacent side relay protections do not need change while the method of 110kV neutral grounding changed.All the conclusions have been proved by simulation of Matlab.The schemes and setting principles of 110kV neutral resistance system which contained wind power are put forward.According to this,the protection configuration and setting calculation of the test system have been completed,and the selectivity and sensitivity of the protection are satisfied.