Incorporating cost-efficient selection of feeders in a novel adaptive UFLS scheme for application in low-inertia renewable-intensive grids considering voltage stability analysis

Conventional Under-Frequency Load Shedding (UFLS) schemes may lead to over-/under-shedding, and they are not quite reliable for application in low-inertia renewable-intensive grids. This paper proposes an adaptive UFLS scheme suitable for low- and varying-inertia grids. It calculates the frequency event size and executes shedding loads equal to it. The Center-of-Inertia (CoI) Rate of Change of Frequency (RoCoF) is used after estimating it using local frequency measurements. The fast voltage stability indices of loads are used to define their shedding share coefficients according to their level of weakness with respect to voltage stability. Moreover, the steady-state voltage analysis is conducted to determine the maximum limit of active/reactive power decrease at each load bus to limit the shedding amount which avoids violating permissible voltage limits. To maintain the practicality of this scheme, the selection of feeders for disconnection is considered for realizing the calculated shedding amount. To evaluate the proposed UFLS scheme, it is tested on IEEE-39 bus test network with different penetration levels of renewable resources. The realized shedding amount is slightly different from the calculated one considering that the exact amount of load cannot be shedded through feeders’ disconnection. However, the frequency is stabilized in all case studies.