On reverse control action of on-load tap-changers

The on-load tap-changer (OLTC) is one of the major elements participating in voltage instability. To assess unstable behavior of OLTC, that is, the reverse control action, the sensitivity of load voltage to tap position, dv/dn, is investigated in two different situations: One is a realistic situation where the exact load characteristics including voltage dependence are used to compute dv/dn. The other is the more ideal situation where dv/dn is calculated assuming constant power lends. It is demonstrated that both sensitivities can be used to assess the occurrence of reverse control action. Line and transformer reactances are the most important factors affecting this condition. The validity of these results is verified through numerical simulations where the dynamic characteristics of OLTC and time varying loads with static nonlinear voltage dependence are taken into account. (C) 1997 Elsevier Science Ltd.