Power system security is one of the major challenges to utilities. Some of the power system loads can be critical that require uninterrupted supply all the time. Supply security can be at risk specially when there are project works that require outages of substation equipment. Operator actions are not always adequate to maintain system security. Therefore, utilities develop System Integrity Protection Schemes (SIPS), which could help operators to automatically monitor the risks and take appropriate actions relatively faster. This paper presents development of SIPS for real-time overload protection of a critical feeder in a large utility transmission system. The scheme is developed considering various factors such as the measurement quality, time behaviour, controlled switching, and operator inputs. The effectiveness of the scheme is tested in various overload scenarios of the critical branch. The results show that the scheme can effectively alleviate the feeder overload by controlled switching of surrounding feeders and re-configuring the power flow on the network.