This paper presents the design, implementation and experimental results of an energy harvesting system to extract energy from power transmission lines. The energy is extracted from a high permeability core clamped on a high alternative current cable. A coil wound on the magnetic core can harvest energy effectively from the power line when the core is operating at the non-saturation region. Little energy can be harvested once the magnetic flux density is saturated in the core. This paper introduces a new method to increase the harvested power level. By adding a switch to short circuit the coil when the core saturates, the harvested power level can be increased by 27%. To drive a device where higher power is needed, a power management circuit is integrated with the energy harvester. The designed system can provide a power of 792 mW from a 10 A power line, which is sufficient to operate many different types of sensors or communication systems.