Assessing the necessity of integrated transmission-distribution modelling for voltage stability analysis

This paper presents a novel method to improve the representation of the power flow behaviour of distribution networks in transmission level voltage stability assessment. Traditional voltage stability analysis typically assumes that loads represented at transmission level follow constant power factor during loadability assessments and ignores the nonlinear losses present in distribution networks. This introduces error into voltage stability assessments, resulting in an over-assessment of loadability. Integrated transmission and distribution modelling illuminates this discrepancy by fully modelling all network voltage levels and thus the nonlinear interactions between transmission and distribution networks. This paper proposes a method of distribution network representation at the transmission level that is as accurate as integrated modelling, without the need for integrated modelling and the computational requirements it incurs. The differences resulting from the varying representations are investigated by considering various distribution networks.