Risk-Based Underground Cable Circuit Ratings for Flexible Wind Power Integration

Cable circuit rating methods, used by utilities for connecting wind farms into the grid, neglect the stochastic intermittent nature of wind output and the thermal inertia of the cable. This paper proposes new risk-based rating approaches for windfarm underground cables and suggests a method to evaluate their effectiveness. The novelty stems from integrating cable system thermal inertia and aging models to determine the benefits and risks of time-dependent flexible ratings. These risk-based ratings are compared against standard static cable rating and dynamic rating practices with an aim to identify the value of simple cable operating strategies that minimize wind curtailment, but they could introduce higher aging risks. A wind farm cable tie in Scotland is used to assess the different rating approaches considering wind curtailment and cable aging costs in a multi-year cost-benefit analysis. This case study indicated a 21% increase in wind integration on the existing tie with the proposed Flexible Cable Rating when compared to the Static Rating and with aging equivalent to that of the Dynamic Cable Rating. Thus, the proposed rating approaches and methodology can facilitate risk-based planning and operation practices to increase flexibility at different, operator pre-defined, risk levels.