Any network expansion demands intensive planning studies and redesign of control and protection systems in order to maintain a reliable, system behaviour. Applying a control architecture, which enables the operation of a controlled transmission path without affecting the rest of the system, can eliminate these problems. This non-intrusiveness is the key issue of the proposed non intrusive system control (NISC^TM) architecture. In this paper the basic requirements and structure of this new control-architecture. are described first. A second focus is given to the problem of controller interactions in abnormal operation situations where the NISC^TM architecture helps to avoid malfunctioning or adverse reactions. The overall efficiency and robustness is shown in connection with a case study.