This paper examines the accuracy of frequency measurement-based inertia estimation of different interconnected power networks and the effect of frequency transients due to sudden power imbalance that leads to the estimation error. The knowledge about power system inertia is an important information for the Transmission System Operator (TSO) as it helps them to maintain stable operation of the power network. An inertia estimation method (IEM) on the basis of frequency measurement is carried out in this paper. Based on the frequency transients and the suitable selection of the time ranges, inertia estimation (IE) is done. The inertia is estimated considering the rate of change of center of inertia frequency ( \(\text{RoCoF}{coi}\) ). System inertia estimation is performed on the two simulink models during step changes of static load. The obtained results of the test cases are presented in this paper. The accuracy of the estimation process is quantified from the obtained results. It is observed that different power network models differ in accuracy for the same inertia estimation method which is evaluated in this paper.