Protection relay testing in smart grids

Smart grids are those electrical transmission and distribution systems that are networked and equipped with computer intelligence. That enables them to employ advanced test strategies requiring special conditions of the grid. In the paper methods and equipment for on-line testing of analog and digital measurement channels of protection relays have been presented. During the test all protection functions of the device are active like during the normal work. Moreover no special hardware is installed inside the protection relay. The methods enable to reveal subtle changes in the measurement channel circuitry frequency characteristic caused for instance by an aging capacitor.