USING A NEW FAULTED SYNCHRONOUS MACHINE MODEL FOR HARDWARE-IN-LOOP TESTING OF A GENERATOR PROTECTION RELAY

This paper presents the results of a study into the use of a new faulted synchronous generator model for testing generator protection schemes using a real-time simulator. The paper presents results of tests on stator differential, loss of excitation and 100% stator ground fault protection schemes. INTRODUCTION Hardware-in-loop testing of relays connected to realtime simulation models of protected plant has become a well-established method of analysis and testing in many sub-disciplines of the field of protection. However, until recently even the most detailed dynamic models of synchronous generators that were available in simulation programs were very limited when it came to the particular requirements demanded by protection studies. Recently though, a new model has recently become available that allows representation of internal winding faults in the stator circuits of a synchronous machine as well as faults in the excitation systems feeding the field circuits of these machines in real-time simulation studies [1,2]. In large synchronous generators, different stator winding protection schemes are recommended in practice depending on the particular grounding method used on the machines [3]. The particular measurement requirements of these different protection schemes, in turn, have implications for the extent to which it may be possible to test their hardware and settings using a realtime simulator. This paper presents the results of a research study currently being conducted to evaluate the use of this new faulted synchronous machine model for conducting hardware-in-loop testing of a number of protection functions on a practical generator protection relay [4]. STUDY SYSTEM AND METHODS Fig. 1 shows a schematic diagram of the study system that is being used for this research project. The system comprises four 555 MVA generators at a power station connected to a remote system (represented as an infinite bus) via two transmission lines. This system was chosen for study since it is a well-known benchmark for the study of generator stability [5] and as such has documented parameters that are not only representative of large generators but also of their controllers; the availability of detailed and realistic controller information is important for studies into many aspects of generator protection that are influenced by, and in turn inter-related with system stability issues. The diagram illustrates that for these studies, all four generator and step-up transformer units in the study system of [5] have been represented explicitly within the real-time model, both to allow connection of a protection relay to the real-time model of a single generator for study (Unit 1), but also to allow further studies into the influence of faults on other generators in the station, and the resulting inter-machine swings, on the protection of the first generator. Fig. 1 – Single line diagram of the full study system. The diagram in Fig. 1 also illustrates how hardware-inloop studies are carried out on the real-time simulator. All the electrical plant in the power station and the remote system is modelled mathematically on the realtime simulator. For the particular generator and transformer unit whose protection is being studied, instrument transformers are included in the real time model to measure the voltages and currents required by the protection, and the secondary variables from them are exported for injection into the external hardware relay being used to protect the generator. The trip signals from this external relay are then fed back into simulator and used to operate the appropriate circuit breakers within the real-time model of the plant. The particular relay hardware being used for these studies is a multi-function generator protection relay [4] that had been donated to the research centre where the studies are being conducted. Table 1 shows a summary of some of the elements available on this relay, but the particular elements focused on in this paper are the loss of field (LOF) protection (40), and two distinct types of stator protection, 100% stator ground fault protection (64G) and phase percentage restrained differential Infinite bus Transmission lines UNIT 1