A reliable and straightforward index to avoid nuisance trip of the conventional Z‐based loss‐of‐field relay in synchronous generators

Abstract

The conventional impedance (Z)‐based relay which is the well‐known relay to preserve the power plant's synchronous generator (PPSG) against loss of field (LOF) accident may fail during some stable power swing (SPS); on the other hand, most of the previously introduced schemes may fail during the happening of hybrid events. In this paper to overcome the raised problems, a straightforward index is developed for reliable detection of the hybrid events, and it is combined with an AND‐logic cluster with the Z‐relay to avoid its spurious trip during SPS events. The reactive power (QSG) of the faulty PPSG is continuously decreased during LOF, while it oscillates under both SPS and hybrid events, leading to non‐detection of the hybrid event. Hence, using the integral operator and arithmetic mean value are suggested to eliminate the swinging variations of QSG as a Z‐relay blocking function (ZRBF). Thus, QSG decreases during both LOF and hybrid events and does not decrease under SPS events. Therefore, by combination of ZRBF with the Z‐relay, the PPSG is properly tripped out during the both LOF and hybrid events, and wrong tripping under SPS is reliably hindered. The reliable performance of developed scheme is completely approved thorough performed simulation studies.

Using dynamic state estimation to detect loss of excitation in synchronous generators

“…Measurements from a PMU augmented by system inputs ( T m , E fd ) will be used as inputs of the EKF. Also, Pt and Qt are used as measurable outputs of the system as (14).…”

“…Despite the widespread use of these types of relays in industry, it is susceptible to malfunctions under conditions of SPS [11]. Other types of LOE protection methods exist that are modelled on the impedance-based method, such as the admittance scheme, and the active-reactive power scheme [12], and all of them are vulnerable to system disturbances [13], but to avoid mal-operation of the conventional impedance relay, a relay-blocking function is added to the conventional method with the approach of eliminating the swinging change of the reactive power [14]. Artificial intelligence-based approaches are proposed to improve the robustness of LOE fault detection algorithms.…”

A multi‐variables loss of excitation protection scheme to improve the factors of accuracy and speed of detection than the conventional impedance relay

“…The main drawbacks of this scheme are its dependence on parallel SGs being in service and its wrong performance when the under-study SG operates alone (in the absence of parallel generators). The introduced strategy in [21] implements the integral of reactive power of the SG in an AND-logic format with the conventional impedance relay to prohibit the nuisance trip during the power system disturbances. This strategy improves the performance of the impedance relay, though it may still fail during some power system disturbances.…”