Due to fine discretization in space and time, the simulation of transient electromagnetic phenomena results in a large system of equations. To cope with this computational effort, model order reduction techniques can be employed. To assess the accuracy of the solution of the reduced model, an error estimation is crucial. A commonly used approach consists of the evaluation of the deviation between the reduced and the full model. This yields a loss of the a-priori property of the Proper Generalized Decomposition. To overcome this problem two a-priori criteria are presented in this paper.