Assessing voltage collapse

Several cases of voltage collapse can be modeled by so-called turning paint s of the stationary states of special ordinary differential equations. Volt age stability is identified with the margin between the current operating p oint and the collapse point. Assessing voltage stability then amounts to ca lculate turning points. This contribution describes different classes of me thods to estimate the location of collapse points. One class of approaches is based on test functions, another on curve fitting. The latter approach i s the least expensive one.