In the period September 2019 – January 2020, our team had the opportunity to participate in a significant for the Bulgarian energy project for major repairs and modernization of the two hydro generators * of HPP “Stara Zagora” and one generator of HPP “Devin”.

The total installed capacity is 77 MW, which is equivalent to over 100 solar parks. This allows the supply of electricity to cities such as Yambol, Pleven or Silistra.

Our obligations under this project were in two phases. We started with the initial sandblasting of the stator, which has very hard to reach places.

For this purpose, we made both the necessary devices for reaching them. And then prepared the necessary stands for positioning in a given height and plane. The cleaning requirement was Sa3, because after our work a check was made of the aging of the metal and the strength of the welds.

The technological process of metal control was non-destructive (NDA testing) through penetrant control. After ascertaining their condition, the stator bodies of the hydrogenerators underwent a new cleaning by sandblasting. The requirement reached for the second blasting was up to pure Sa3, as the geometric requirements for laying the magnetic conductors and windings are calculated in tenths of a mm.

The second challenge for us was to deal with the deadlines set by the Contracting Authority. As every day delay in the installation of such production capacity puts at risk the electrical system in Bulgaria.

*Технически данни:

Devin HPP
Vertical generator
Type VSG 435 / 166-16
Power -49000 KVA, voltage – 10.5 KV, speed – 375 rpm

Stara Zagora HPP
Vertical generator
Type VSG 370 / 78-20
Power – 14000 KVA, voltage – 10500 V, speed – 750 rpm