for low wind penetration the capacity credit can be approximated by the capacity factor for larger wind injections the capacity credit decreases with increasing wind power capacity and this decrease goes faster for small regions the consequent variations and disturbances on the grid voltage and frequency are experienced daily by power generators and electricity end users each tso publishes in a document called grid code the performances that each generating unit must meet to be connected to the system also generating plants should be able to ride through certain transient events in the transmission system without tripping such as a sudden step change in the voltage a typical requirement is a voltage step of