Power-swing detection logic for systems with low inertia

Distance protection elements face security problems during power-swing conditions because the swelling power may cause the apparent impedance to encroach on the element operating characteristics. To address this problem, line distance protective relays include a power-swing blocking logic to secure their distance elements during power swings. Avoiding undesired line tripping keeps the transmission network intact and gives the system time to stabilize through inherent transient stability margins and dedicated transient stability schemes, including load and generation shedding, power system stabilizers, and remedial action schemes. From the protection perspective, however, assertion of the power-swing blocking logic hurts protection dependability during power-swing conditions. Symmetrical faults that cannot be detected by using sequence directional elements in a pilot protection scheme are of particular concern. To maintain protection dependability during power swings, it is desirable to remove the power-swing blocking signal for faults that occur during power swings, especially for three-phase symmetrical faults. Characteristics of power swings continue to change as more unconventional low-inertia sources are added to the power system. These sources are modulated by their control algorithms rather than by the inertia of the rotating masses and synchronous machine torques. This paper presents a power-swing blocking and out-of-step tripping logic suitable for systems with low inertia. The presented logic does not require settings and derives its operating parameters from the basic line parameters and distance protection settings. As a result, application of the presented logic does not need transient stability studies. The logic presented in this paper has been implemented and deployed in the field since 2020.