Operational HVDC round power 1st May 2014 1 What is round power ? • round power is the ability to operate each pole of the HVDC link in opposite directions • this will circulate power through each pole without necessarily providing a net power transfer between the islands. 2 What is round power mode of operation ? • enabling round power as a mode of operation is far more than just the ability to operate the two poles on opposite directions • round power mode is a fully automated Bi-pole control mode that will automatically start and stop poles as required • round power control mode allows seamless dispatch from 1200MW DCN to 750MW DCS through zero. 3 Round power configurations Net Pole 2 Pole 3 • DCN >200 MW • DCN 41 to 199 MW • DCN 40 MW to DCS 40 MW • DCS 41 to 199 MW • DCS >200MW 4 Round Rower Configurations Net Pole 2 Pole 3 • DCN >200 MW • DCN 41 to 199 MW • DCN 40 MW to DCS 40 MW • DCS 41 to 199 MW • DCS >200MW 5 Round power close up Example: Net P2 P3 45 MW 10MW DC north of 10MW • Note: The pole opposing the net MW will always be on minimum MW 35 MW 6 Round power configurations Net Pole 2 Pole 3 • DCN >200 MW • DCN 41 to 199 MW • DCN 40 MW to DCS 40 MW • DCS 41 to 199 MW • DCS >200MW 7 Round power close up Net Example: DC north of 170MW Pole 2 170MW Pole 3 170 MW 0 MW 8 Round power close up Example: DC north of 170MW 170MW 170 MW 0 MW • If Pole 3 trips 170MW 170 MW 0 MW • Pole 2 starts and replaces lost MW within 250ms • DC provides its own reserve using the standby pole. 9 Round power close up Example: DC south of 55MW • If large NI generator trips. Net -55MW P2 55 MW P3 0 MW 10 Round power close up example DC south of 55MW Net -55MW • If large NI generator trips • Pole 2 backs off to minimum • Pole 3 starts and north within 250ms • DC provides Hz stabilizing even near its minimum ~ P2 55 MW P3 0 MW 115 MW 80MW -35 MW 11 Current dead band • Current dead band • No dead band +35 +35 0 0 -30 -30 12 Modelling in market system • scheduling time no change • interim manual DC dispatch modelling process HVDC transfer >100MW we will model full bi-pole (max risk subtractor) HVDC transfer <100MW will model round power (no risk subtractor) • losses while in round power at low transfer minimal (<1MW) • fully automated round power dispatch modelling tool, post operation trial. 13 Voltage control • Bi-pole filters will be kept in service at low transfer • low load periods with low HVDC will become more challenging (high volts) reduced voltage removal of AC circuits disabling round power. 14 When is round power not used? • during a Pole outage (requires full Bi-pole) • reclose blocks on HVDC equipment • high volts become unmanageable • Grid Owner withdraws the round power offer. 15 Summary • seamless HVDC dispatch through zero • reduced chance of price separation between islands • better Hz stabilization (no minimums) • easier SI Hz keeping • no HVDC start / stop disturbances • better reserve sharing between islands • lower risk of IL event with monopole operation • harder to manage volts at low load • interim DC dispatch modelling process. 16 Future with round power • • • • automated dispatch modelling national Hz keeping market national Reserve market increased reserve sharing. 17 Questions 18