Akademik Veri Yönetim Sistemi
Teknik Rapor, ss.1-66, 2018
Inverter based resources (IBR) have different and, in some cases, complex fault current characteristics compared to conventional synchronous generators. Hence, legacy protection schemes—set under the assumption of a conventional power system with synchronous generators—may malfunction under operating conditions with high levels of generating power from IBR. It is therefore necessary to study the performance of the protection system to ensure its efficiency in the presence of IBR. This technical update studies the impact of IBR on communication-assisted protection, fault identification (FID) scheme, distance, frequency, and power swing protection functions.
The report first studies the impact on negative-sequence-based communication-assisted protection and FID. Wind turbine generators (WTGs) exhibit a substantially different negative-sequence fault current characteristic compared to synchronous generators; negative-sequence current contribution is substantially lower for a WTG compared to a synchronous generator due to WTG controls, and the phase angle relation of negative-sequence voltage and current is different. These effects may cause misoperation of a negative-sequence-based element employed in a communication-assisted protection or FID resulting in their misoperation.
Next, the report investigates the impact of IBR on the performance of line distance protection. Due to memory polarization, the mho zone of a distance relay may dynamically expand and shrink during a fault. This dynamic characteristic depends on the source impedance, which is different for a WTG compared to a synchronous generator, and depends on variables such as wind speed and the operating conditions of the wind park. As a result, the dynamic characteristic becomes dependent on these variable quantities, leading to possible misoperation issues. The report provides examples of such a misoperation, and studies the impact of the operating conditions of a wind park, wind speed, grid strength, and memory polarization scheme on the dynamic characteristic to determine key parameters that should be taken into account.
Finally, the report studies the impact of wind generation on rate-of-change-of-frequency (ROCOF) and power swing protection. WTGs have no inherent rotational inertia provided to the system. Therefore, the rate of change of frequency under a high share of wind will be different than that under synchronous generation resulting in possible misoperation of ROCOF relays. Further, faster power swings due to reduced system inertia and changed swing trajectory due to the control of WTGs may cause the misoperation of power swing protection. The report provides examples to show such misoperations, and potential solutions to circumvent the issues.