Description: During the HV transfer, Warhol DH 4 power strings B1, B2, B3, B4 and B5 will be supported by generators, witch SC Operations will start manually to manage the intervention safely and minimize risk. The affected power strings are B1, B2, B3, B4 and B5. During this period, redundancy will be temporarily reduced from N+1 to N on grid power level. These works support delivery of the increase capacity of the site and enable civil works for the HV substation upgrades, scheduled for completion in August 2027. The attached single-line diagram identifies the Ziels grid power line that will be offline during this period. This intervention notification covers ongoing HV substation works. To safely carry out the required civil works, one HV power line must be switched off and the load transferred to the second HV power line. To minimize the impact during the transfer, generators will be started sequentially to support the load during critical HV switching. Once the HV operations are complete and grid power is restored, the generator system will transfer the load back to the grid as designed.
Risk: Low
Service impact: 60kV grid power line reduced redundancy from N+1 to N.
Rollback plan: As part of the critical work preparation and change management process, the SC Ops team has implemented a rollback switching plan and EOP to restore power to the affected power string. 60kV grid power line (Monte Feio) unavailability, and critical load transfer to 60kV grid power line (Ziels) with support of generators between the transfers.
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