Reliable Rate-of-Change-of-Frequency Measurements: Use Cases and Test Conditions

Based on user expectations and requirements, this article discusses three use cases (UCs) for measurements of power system frequency and rate-of-change-of-frequency (ROCOF) measurements, specifying accuracy and latency requirement for each UC. Furthermore, a set of realistic test conditions are proposed, extending those of the present IEC/IEEE 60255-118-1 standard, to ensure ROCOF measuring instruments are adequately tested on their suitability for reliable ROCOF measurements in power systems. Target worst case ROCOF errors (RFEs) are given for each test waveform and UC. Several published ROCOF algorithms are tested using the proposed test conditions. A selection of the test results is reported and compared against the target RFEs. The results show that the defined tests are indeed helpful in evaluating the ROCOF algorithms, and furthermore that the algorithms can be designed to meet all the requirements on RFEs for the tests proposed in this article.