Units 1, 2 and 4 at Russia’s Kalinin NPP – all VVER-1000 reactors – were automatically disconnected from the network on 18 July due to a short circuit in one of the transformers at the open switchgear, nuclear utility Rosenergoatom said. Units 1 and 4 were reconnected the following day and unit 2 on 20 July.  Rosenergoatom established a commission to investigate the incident.  

Rosenergoatom spokesman Andrey Timonov said in the same statement that the fault was not nuclear-related. "There is a transformer near every power plant, regardless of how electricity is generated, the purpose of which is to change the characteristics of the electrical current generated at a plant so that it can be transferred to the grid,” he explained. “There is a device on the transformer that switches on or off in different modes. This morning, there was a short circuit in one of the switches. As a result, the entire transformer was disconnected, which in turn caused the disconnection of power lines from the plant.”  

Earlier, on 12 July unit 4 at the Beloyarsk NPP (a BN-800 fast reactor unit) was shutdown after an automatic safety mechanism was triggered. The unit restarted on 16 July "after establishing and eliminating the causes of the electrical generator disconnection", Rosenergoatom said. Beloyarsk 3 - a BN-600 fast reactor - was unaffected and continued to operate as normal.