Liberalisation of energy market combined with growing energy demand has led to an exponential growth in the number of embedded power plants. Unlike grids made up of large power plants, grids made of many smaller grids tend to be unstable. To minimise the impact of the unstable grids on the consumer, transmission and distribution system operators worldwide are coming up regulations – Grid Codes that specify performance expectations on power plants and therefore on the generating set and their associated components that make up the power plant. These codes are broadly categorized as static and dynamic. Static codes refer to expectations on steady state conditions and Dynamic codes – the expectations on transient stability and fault ride through capability.
Achieving grid code compliance means that the power plant owners and the manufacturers of the components have to work together and individually. The focus of this paper is to broadly describe the effects of grid codes on design of engine driven generating sets and thereby define the scope of changes within the alternator. The authors specifically focus on key design features of the alternator that can be optimised to help the power plants achieve compliance. The design features that will be discussed have been established as the most significant influencers with power system simulations; some of them helping with achieving static grid codes and some of them with dynamic grid codes.
The global electricity demand is growing at a rate of 2.4% every year and the fastest way to address this demand is embedded generation – ad hoc power plants consisting of engine driven generating sets. Along with renewable, these embedded generation units make up a significant portion of the modern grids. Though there are environmental and economical benefits, distributed generation makes the grid less stable. In order to ensure continuity of power supply, electricity transmission and distribution system operators all over the world, with Europe in the lead are enforcing regulations – grid codes – that define performance expectations on power plants.
The table above summarises the key aspects of a grid code document for Germany – voltage, power factor, frequency under steady state conditions and the required ‘connection period’ during a fault ride through. The grid codes can broadly be classified as static – steady state operating conditions and dynamic – transient operating conditions. Designing power plants and associated components to comply with grid codes is challenging, especially for generating sets smaller than 5 MW.
Follow this link to learn about the nature of this challenge and its impact on the design of alternators for grid code compliant generating sets.