Editing Chernobyl Nuclear Power Plant (section)

=== Electrical systems ===
The power plant is connected to the 330&nbsp;kV and 750&nbsp;kV [[electrical grid]]. The block has two [[electrical generator]]s connected to the 750&nbsp;kV grid by a single generator transformer. The generators are connected to their common transformer by two switches in series. Between them, the unit transformers are connected to supply power to the power plant's own systems; each generator can therefore be connected to the unit transformer to power the plant, or to the unit transformer and the generator transformer to also feed power to the grid.<ref name="techappr">{{cite book |author=British Nuclear Energy Society |url=https://books.google.com/books?id=oEqd0IeAhccC&pg=PA11 |title=Chernobyl: a technical appraisal: proceedings of the seminar organized by the British Nuclear Energy Society held in London on 3 October 1986 |publisher=Thomas Telford Ltd |year=1987 |isbn=978-0-7277-0394-1 |location=London, England |access-date=June 27, 2010 |archive-url=https://web.archive.org/web/20211214002828/https://books.google.com/books?id=oEqd0IeAhccC&pg=PA11 |archive-date=14 December 2021 |url-status=live}}</ref>

The 330&nbsp;kV line was normally not used, and served as an external power supply, connected to a station's transformer – meaning to the power plant's electrical systems. The plant was powered by its own generators, or at any event got power from the 750&nbsp;kV national grid through the main grid backup feed in the transformer, or from the 330&nbsp;kV level feed in grid transformer 2, or from the other power plant blocks via two reserve [[busbar]]s. In case of total external power loss, the essential systems could be powered by [[diesel generator]]s. Each unit's transformer is therefore connected to two 6&nbsp;kV main power line switchboards, A and B (e.g., 7A, 7B, 8A, 8B for generators 7 and 8), powering principal essential systems and connected to even another transformer at 4&nbsp;kV, which is backed up twice (4&nbsp;kV reserve busbar).<ref name="techappr"/>

The 7A, 7B, and 8B boards are also connected to the three essential power lines (for the coolant pumps), each also having its own diesel generator. In case of a coolant circuit failure with simultaneous loss of external power, the essential power can be supplied by spinning down turbogenerators for about 45 to 50 seconds, during which time the diesel generators should start. The generators were started automatically within 15 seconds at loss of off-site power.<ref name="techappr"/>