Online diagnostics in Smart Grids: An approach to the future power grid.

In this study the term smart grid is specified toward online diagnostics. It is investigated which online diagnostics techniques fit well within smart grids and whether existing technologies can be used in a smarter way. Smart grids and online diagnostics Since 2005, the term smart grids is widely used in literature. To assess what smart grid means from a component perspective, five values have been identi- fied that describe smart grids: secure, reliable, safe, economic and efficient. If these values are translated into operational characteristics, it is concluded that asset management and reliability are very important for the future power grid. Interviews with three companies show that online monitoring is an appropriate tool to realize a smart grid. However, the costs of online diagnostics should be reduced and the interpretation of measurements should be done by expert systems to make online diagnostics more attractive. Thereafter, smart grid is analyzed from an outside-in approach by investi- gating the need for data and listing available technologies to provide those data. The most frequently occurring failure modes of components in the transmission grid are listed to assess what technologies are required to fulfill the need for online diagnostics. Partial discharge activity can be measured to assess the aging state and operational conditions of transformers, gas insulated switchgear (GIS) and ca- bles. In addition, for high voltage direct current (HVDC) cables, space charge accumulation measurements can be used for the same purpose. Different on- line measurement techniques are listed and compared. Ultra High Frequency, acoustic and optical partial discharge detection are listed. Furthermore, combi- nations of these methods and the experimental 2-D electromagnetic partial dis- charge detection are investigated. For space charge measurements, the pulsed electroacoustic method is explained. Smart use of existing technologies Besides the development of new online diagnostic techniques, it is attractive to make smart use of existing technologies that are already installed in the grid. Fiber optics that are integrated in an increasing number of cables are used for hotspot monitoring, but can be used in a smarter way. Using distributed tem- perature measurements the space charge accumulation as a result of interfacial polarization in the insulation of an HVDC cable, can be determined. From the space charge distribution the electric field enhancement is calculated. If this analysis is applied to weak parts in a cable, the load can be dynamically controlled and condition-based asset management can be applied. A model is developed that determines the space charge distribution due to a temperature gradient in the cable insulation. Consequently, the electric field enhancement is derived from the space charge distribution. The model is validated afterwards, using measurement data from a pulsed electroacoustic space charge measurement setup. A comparison between the measurements and the model reveals that the model is only valid below the electric field threshold for space charge injection. Above this threshold, a more complex model is required. If the cable is operated below the threshold, the model covers the basic requirements for a temperature-based space charge measurement system.High Voltage Technology and ManagementElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc