Distributed Generation: towards an effective contribution to power system security

With a continuously increasing penetration in power system, the impact of dispersed generation is getting higher and higher. This paper deals with the contribution of DG to power system security. It focuses more precisely on its behavior in case of severe frequency disturbances and shows how distributed generation can provide an active contribution to power system security. The UCTE represents the continental European TSOs and defines system security rules, among which the required amount of reserves or general load shedding management rules. On the one hand, the paper deals with the decoupling protections in EU countries whose specifications may induce different frequency behaviors across the various interconnected power systems. In case of severe frequency deviation across the European grid, unwanted tripping of DG may occur at a large scale, even if this kind of generation has the ability to remain connected during such disturbances. Such a behavior may jeopardize the whole system security by decreasing the amount of available power for frequency support. As an example, the outage of European grid on November 2006 led to the tripping of a significant DG capacity in the western part of the UCTE (e.g. in Spain with the loss of 2 800 MW of wind power) as frequency dropped at 49 Hz. On the other hand, the paper presents the requirements and the existing frequency control systems for wind farms. Due to the dramatic increase in installed wind power capacity, this may become a key issue for frequency control. DG could thus contribute to frequency support and power system security.