Merging unit accuracy testing

Digital devices are controlling, protecting and monitoring increasing numbers of electric power systems. One such device that delivers needed measurements is the merging unit (MU). The function of an MU is to merge different types of measurements in one device and generate a digital data stream from measured values, which can then serve as an input signal, e.g. for a protective relay. Apart from communication, its accuracy of parameter capture is another of this device's features and is instrumental in controlling other devices. The authors propose a test procedure, which enables testing a merging unit under differing conditions, and discuss the test stand itself, its construction and functionality, test scenarios, the method of analysis and the results.