Exploitation characteristics of the retrofitted thyristor rectifiers in an uninterruptible power supply system of a thermal power plant

Thyristor rectifiers are still the most numerous power supply devices in the internal consumption systems of the power plants and transformer substations of the Electric Power Industry of Serbia. The most of the mentioned devices were commissioned during the seventies and eighties of the last century, having analogue electronic control circuits. Many of the thyristor rectifiers were, in the meantime, retrofitted, with the basic intervention being the replacement of the old analogue electronic control units with a digital one, based on microprocessors. In this way were, with modest investments and actions, procured devices with the novel technical characteristics, yet retaining the robustness and simplicity of the old rectifiers. Nevertheless, following the multi-year exploitation of the retrofitted rectifiers, a question arises regarding the possible duration of their further use, as well as the potential for the further reconstruction of the existing thyristor AC/DC converters with analogue electronic control circuits.
In the paper was described the experience obtained during the thirteen-year exploitation of fourteen retrofitted thyristor rectifiers, operating in the thermal power plant “Nikola Tesla B”. The perceived circuit faults were described, and their causes were analysed. Opportunities for a further retrofit of the old thyristor rectifiers were evaluated, and the procedures for their implementation were proposed.