On the Effect of Tap Changers and Nonlinear Loads on Voltage Stability

Abstract: On 21 June 2024, a severe incident happened in the South-Eastern part of the Continental European power system. After a voltage collapse, large parts of Albania, Montenegro, Bosnia and Herzegovina as well as Croatia suffered from a blackout [1]. The initial tripping of two transmission lines resulted in a voltage collapse in these countries. Investigations have shown that a) transformers with on-load tap changers (OLTC) and b) nonlinear loads, in particular air conditioning systems, played a significant role in this event. Motivated by this, we carry out an assessment of the effect of OLTC on voltage stability in the presence of nonlinear loads. By doing this we hope to further shed some light on the potential instability mechanisms that can be triggered in scenarios like the above-mentioned blackout.