The glass transition region of novolac phenol-formaldehyde (NPF) resin was investigated by integral and partial thermally stimulated depolarization current (TSDC). The experiments were performed on samples with admixtures which might influence the behaviour of the resin. The analysis of the activation energy vs. temperature showed three relaxation stages. Each stage was characterized by the relaxation map and the compensation temperature (T-c). The T-c2 related to the middle stage coincided with the glass transition temperature (T-g), while the T-c1 and T-c3 were shifted. A model was proposed for unification of T-c1 and T-g by including necessary changes in the relaxation parameters. For this purpose, an additional activation energy had to be introduced which was considered as the measure for the rigidity of the investigated system in certain temperature regions.