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.