This chapter presents a hybrid magnetic, thermoelectric and vibrational energy harvesting (EH) system, which is oriented to power grid applications. The systemcan energize low-power wireless sensor networks (WSNs) that serve for conditionbased monitoring of grid-connected power apparatus. Simulation and experimental results on the characteristics of the energy scavenging methodologies and the system are presented. Experimental evidence is provided to indicate the system’s usability by observations on energy-autonomous Zigbee nodes, which are developed for proof-ofconcept trials. This chapter is dedicated to giving an integrated case study for understanding the feasibilities and potentials of representative energy harvesting technologies, which can be promising as novel alternative power supplies in WSNs.