Effective model reduction methods are required to deal with new challenges in active distribution network simulations that are on a large scale and have complicated structures. In the development of advanced electromagnetic transient simulation programs

automated model reduction plays an important role. This paper proposes an automated realization algorithm for the Krylov subspace based model reduction methods of an active distribution network with which the reduced model can be automatically established according to a given threshold of reduction error. The combined state-space nodal analysis framework is employed to apply the automated model reduction algorithm in popular EMTP-type simulation programs. Simulations are performed using PSCAD and a self-developed program to show the feasibility and validity of the proposed methods.