Synchronising with continental Europe
Connecting two power systems is not a matter of closing a switch. The engineering behind Ukraine joining the European grid is worth understanding properly, because it explains why it could not have been done in a week.
Two alternating current systems can only be joined if they run at the same frequency, in phase, and can hold that relationship under disturbance. Everything else follows from that requirement.
What has to be true first
Frequency control. Both systems must regulate to the same nominal frequency with compatible response characteristics, so that when demand changes somewhere, generation responds in a coordinated way rather than fighting itself.
Reserve provision. A synchronised area shares the burden of a sudden loss of generation. Joining one means committing to hold reserves to the same standard and release them on the same signal.
Protection coordination. When a fault occurs, protective devices must trip in a defined order so that the smallest possible section is isolated. Two systems with incompatible protection philosophies connected together will cascade.
Communication and metering. Cross-border flows have to be measured, scheduled, settled and observable in real time by both operators.
The isolated-mode test
Before synchronisation, a system must prove it can hold frequency entirely alone, without leaning on any neighbour. That is what the test beginning on 24 February 2022 was for. It was scheduled long in advance as one step in a programme running to 2023.
The system passed it and then continued in island mode for three weeks, which was not the plan and demonstrated the capability more thoroughly than the test would have.
Why the achievement is real
ENTSO-E compressed the remaining approvals and technical steps into three weeks. Everything that made that possible had been built over the preceding years: the control systems, the metering, the protection settings, the regulatory alignment. You cannot compress preparation. You can only compress the last step, and only if the preparation is done.
A habit left over from an engineering education: in work like this I read the acceptance test rather than the announcement. The isolated-mode trial was the result of years of preparation rather than of a political decision, and most of that preparation was measurement, protocol and paperwork that nobody reports. That it was completed in the first days of the invasion remains one of the pieces of technical work I respect most in twenty years here.
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