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A novel autonomous voltage and current measurement unit is presented. Due to its high accuracy, communication interface and self-powering feature it is well suited to operate in Smart Grids. Particular attention was paid to its power supply circuits harvesting energy from measured currents and voltages and to the current measurement circuit accepting Rogowski coils and offering a wide measurement range. In order to achieve long term reliability much effort was spent reducing thermal effects inside the unit in case of excessive input currents used as the source of supply energy harvested from the measured signals.

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.

The proposed implementation of ediagnostics of switchgear equipment aims to improve the reliability indicators of the equipment and to reduce the costs of its exploitation. As far as fundamental diagnostics problems are concerned it is still essential to develop methods of calculating tests and diagnostic procedures, which are a base for an inference on the reliability state of the object. Generally it is done based on symptoms (characteristic for non-stationary acting object), which additionally expose processes of aging and wear, or based on functional model of a discrete object. At the present, in many cases the digital part of IEDs is tested by application of a response function compression method. This method characterizes with relatively small control test effectiveness and it does not enable subordinating the tests results to the specific node of the IEC 61850 standard. The paper introduces diagnostics of the digital part of IED's. It presents a certain inference engine on which one of the elements of the digital circuit is (with determined probability) in the inoperable state, if for any pin, (of some element) a fail result of the functional test has been observed. That conclusion is reached by applying the probability approach and knowledge of the digital circuit information net, being a certain digraph respectively described. The method of determining the important causaleffectual relation between the determined inoperable state of the circuit element and the fail result observed on some pins of the other element, using the information net of the circuit is presented. Thereafter we provide some remarks on how to build the IED digital part functional testing, which may be executed under the command e.g. sent from the data concentrator.