Protection of Distribution Systems with Distributed Generation

Abstract

In recent years the amount of distributed generation(DG) in distribution systems have increased. This poses problems for the traditional protection scheme, with non-directional over-current relays and fuses. When DG is introduced the load flow in distribution systems are often reversed; there is a surplus of power on the radial. Present thesis seeks to determine the most beneficial protection scheme to use in distribution systems with DG.

To investigate the impact of different relays and its settings, two models where made in the simulation tool DigSILENT Power Factory. First a grid with an inverter interfaced wind farm and a smaller DG unit. The second is a multi-machine network with six small synchronous machines. These grids were protected by both distance and over-current relays to determine advantages and drawbacks of the two types.

The simulations indicate that low impedance networks with production will be best protected with directional over-current relays. Long radials with higher impedance and production is best protected with distance relays.