The measurement of ROCOF is a significant problem with the poor PQ waveforms that particularly prevail in low inertia power networks containing RES. This is because a ROCOF measurement first requires frequency to be found using the d/dt derivative from phase, before ROCOF is itself determined via a second d/dt derivative from frequency. Any noise on the original phase estimate due to poor PQ, transients, fault events, or instrumentation noise are vastly “amplified” by the double derivative causing spurious results.

The problem of the present state-of-the-art in ROCOF measurement is three-fold.

  • The users of ROCOF measurements do not appreciate the potential uncertainty of the measurements under imperfect PQ, and sometimes assume that measurement is instant (Objective 1).
  • The designers of the measurement devices do not fully understand the required accuracy or latency for particular use cases, or the PQ environment (Objectives 3 and 4).
  • Some algorithms for measuring ROCOF are much less tolerant of poor PQ than others. In particular, instruments from different manufacturers exhibit very different performance. This is easy to understand, since there are no workable standards for ROCOF measurement, so the manufacturers’ algorithms performance also varies widely (Objective 2).

So presently there is a big disconnect between the end user expectations, the equipment manufacturers who provide ROCOF-measuring devices, the bodies setting standards, and the real-world context of a power network in which the AC network voltages (and currents) deviate from clean sinusoidal conditions.

The instrumentation used to measure ROCOF is overseen by the IEEE/IEC joint standards committee TC95 WG1 (60255 118-1). There is a critical need to develop a standard for ROCOF which will first require some research to determine algorithms that can operate reliably over the range of normal to exceptional power quality scenarios that exist in power networks. Such research is a necessary foundation on which to build a credible, practical and defendable standard that will command the confidence of the international power systems community (Objective 5).