On a power network, events are desired to be monitored to find its reasons and to take preventive action. Today, power quality measurement devices are used to obtain synchronous measurement data of network, however these devices are expensive and it is not considered a practical option to place one on each node of the network. Therefore, methods estimating voltages and currents at non-measured points of the network are required. In this study, a new power system transient state estimation method is designed to estimate transientsin a power network in which some of the loads are unknown. By this method, reduction of measuring devices is aimed considering measurement noises. In addition, the developed method can also be applied on a small area of a power system, and this contributes reducing the amount of measuring devices and calculation time in estimation. The method is applied to a specific region of the IEEE 14 Bus System, and simulation results show that the method gives satisfactory results despite noises.