Modernization of transmission and distribution power grids, so-called smart grids , requires thousands of monitoring sensors to be installed within the grids. The main requirements in development of sensors for smart grids are self-powering and plug-and-play features. Wireless sensor nodes are among promising devices for smart grid applications. They are low power sensor devices which require power sources range from hundreds of micro watts up to a few milli-watts. Battery is the easiest and most common source of power for wireless sensor nodes. However, due to the limited life of batteries and high cost of maintenance, a combination of battery or super-capacitors with a micro-power generator has been recently considered a more attractive solution for powering of sensors. Micro-power generator or energy harvesters are energy converging devices which convert available source of energy in surrounding environment into electricity. Vibration-to-electricity is among the widely used techniques for harvesting energy. So far, three types of energy harvesters including piezoelectric, capacitive and electromagnetic devices have been developed to convert mechanical vibration energy into electricity. In this thesis after a brief introduction of different types of energy harvesters and comparing their features for powering of smart grid sensors, electromagnetic micro-generators are selected and investigated in details. This investigation covers the basic principles for design of vibration-to-electricity energy harvesters and presents an analysis and design method for electromagnetic micro-generators. The method deals with the dynamic model of mechanical vibrations and equivalent electric circuit of the electromagnetic micro-generator. Then, two electromagnetic energy harvesters are designed and presented which are suitable for low frequency applications. The designed energy harvesters use the electromagnetic field around a transmission line as the main source of energy. The field energy is converted to the mechanical vibration energy via using a small permanent magnet installed at the tip of a cantilever beam. The first design is established based on a combination of static transformer with an electromagnetic vibration to electricity energy harvester. The second proposed device is designed based on a linear synchronous generator using an array of small permanent magnets with opposite polarities. This arrangement of magnets increases the flux gradient which increases the induced voltage level compare to the first topology. An experimental test setup and prototype of the proposed micro-generators devices have been developed to verify the design method and evaluate the performance of the devices. To verify the model, the experimentally measured voltage and captured power compared with those obtained from analytical model and numerical analysis based on 2D finite element. The test results show the validity and accuracy of the model with an error less than 5% in the measured induced voltage. The analytical model also predicts a matching condition for capturing the maximum output power that is also verified experimentally. Keywords: Electromagnetic energy harvesters, Low frequency vibrations, Smart grids sensors, Vibration to electricity, Wireless sensor nodes.