It is known that following disturba

It is known that following disturbances, on-load tap changers act to restore the load bus voltage and thus restore the load power to near pre-disturbance level. As the system is probably weakened by the contingencies, this will often over-tax existing supplies due to increased losses and reduction in power plant ability, and thus voltage collapse may result. This paper discusses the less emphasized effect of on;load tap changers from another point of view, i.e., how the maximum power transfer limit is affected by on-load tap changers. In addition to restoring the load, on-load tap changers also extend the power transfer ability. Whether the overall effect is beneficial or counter-productive depends on the system ability to balance the amount of extended power transfer limit and the amount of restored load by the same tap changers.