600 500 400 300 200 100 Peak SNSP 91.6% -100 -200 -300 -400 -500 12:00:00 a.m. Wind Generation (MW) Basslink (MW) 6:00:00 a.m. 12:00:00 p.m. 16 January 2021 Figure 4. High SNSP operating conditions (and peak nonsynchronous generation) on Saturday, 16 January 2021 in Tasmania. Basslink import into Tasmania is negative in this figure. 100 90 80 70 60 50 40 30 20 10 0102030405060708090 100 Percentage of Year SNSP Level is Exceeded Figure 5. The distribution of Tasmanian SNSP for the calendar year 2021 [5-min supervisory control and data acquisition data (SCADA)]. Managing Loss of the HVdc Interconnector A key operational challenge for the Tasmanian power system is loss of the Basslink HVdc interconnector. As Basslink is a monopole design, loss of power transfer is considered a credible contingency (N - 1 planning criteria). With a ±500-MW rating, this particular event can represent more than half of the Tasmanian system and, if not rapidly corrected, would lead to an extreme rise or fall in system frequency, depending on the direction of the 76 IEEE Electrification Magazine / SEPTEMBER 2022 power transfer. Because of typical system inertia levels and the relatively slow governor response characteristics of hydrogeneration, this event is unmanageable without the use of a fast-acting control scheme, aptly called the frequency-control system protection scheme (FCSPS). The FCSPS dynamically arms either contracted industrial load blocks (for loss of HVdc import into Tasmania) or generators (for loss of export) to compensate for the Basslink power transfer level. The arming of generators or loads is updated every 4 s based on realtime measurements of system conditions. Upon receipt of a lossof-link signal from the HVdc converter station, the FCSPS acts to rapidly disconnect whatever load blocks or generators have been prearmed (within approximately 200 ms). The design of the FCSPS has recently been updated with the introduction of wind farms into the generator arming list for tripping during HVdc export conditions. This ensures that synchronous generation remains online where possible to maximize system inertia after tripping of generation by the scheme. The FCSPS has proven to be very reliable and has correctly acted on all occasions 6:00:00 p.m. 12:00:00 a.m. Instantaneous SNSP (%) Basslink/Wind Generation (MW)