Power transmission is the bulk transfer of electrical energy from power plants to sub-stations. A wireless sensor network is a promising technology for transmission line monitoring due to its low cost, easy installation, large-scale coverage, and fault tolerance characteristics. A wireless sensor network is application-specific; therefore, we investigate the new features and requirements of the wireless sensor network used in transmission line monitoring. Then, we propose an efficient wireless sensor network framework, which includes a clustering algorithm to simplify network management and to balance the network's energy consumption and a hybrid media access control (MAC) (H-MAC) protocol to handle traffic variability. The framework takes advantage of the features of network topology and traffic pattern to optimize the protocols' performance on real time and energy efficiency. The results indicate that the H-MAC shows a significant improvement in the network's reliability, real-time performance, and energy efficiency, and the cluster hierarchy can balance the network's energy consumption. Furthermore, the cluster hierarchy also prolongs the network's lifetime.