Proving a Concept of Flexible Under-Frequency Load Shedding with Hardware-in-the-Loop Testing

It is widely recognized that in the transition from conventional electrical power systems (EPSs) towards smart grids, electrical voltage frequency will be greatly affected. This is why this research is extremely valuable, especially since rate-of-change-of-frequency (RoCoF) is often considered as a potential means of resolving newly arisen problems, but is often challenged in practice due to the noise and its oscillating character. In this paper, the authors further developed and tested one of the new technologies related to under-frequency load shedding (UFLS) protection. Since the basic idea was to enhance the selected technology's readiness level, a hardware-in-the-loop (HIL) setup with an RTDS was assembled. The under-frequency technology was implemented in an intelligent electronic device (IED) and included in the HIL setup. The IED acted as one of several protection devices, representing a last-resort system protection scheme. All main contributions of this research deal with usingRoCoFin an innovative UFLS scheme under test: (i) appropriate selection and parameterization ofRoCoFfiltering techniques does not worsen under-frequency load shedding during fast-occurring events, (ii) locally measuredRoCoFcan be effectively used for bringing a high level of flexibility to a system-wide scheme, and (iii) diversity of relays andRoCoF-measuring techniques is an advantage, not a drawback.