Replacement of the Generator Circuit Breaker of C.N. Trillo

Nowadays, due to the high level of availability requirements of Nuclear Power Plants, there is a need of minimizing all those variables that can compromise plant production.

The availability of the generation circuit breaker, an electrical cut-off device located in the generator output, has a direct impact on the plant’s production. In 2014, ABB, manufacturer of Trillo NPP generation switch, officially communicated the obsolescence of the equipment due to the cessation of spare parts manufacturing and unavailability of specialized staff in the technology. Consequently, Trillo NPP generation circuit breaker has been replaced in the R434 (2022) outage.

DR 36 de BBC circuit breaker representation.

During the specification process of the new circuit breaker, several factors were taken into account. On the one hand, the requirements imposed by the existing installation, in order to have the minimum possible impact on the plant. On the other hand, the technical innovations arisen in this type of technology since 1988 (the year in which the plant came into operation).

The new generator circuit breaker, Hitachi HEC 10, brings numerous innovations with respect to the existing circuit breaker. It incorporates a hydraulic spring drive common to all three poles, natural ventilation, SF6 arc extinction and real-time monitoring equipment. In this way, the plant avoids the disadvantages that existed with the compressed air and water cooling system of the previous technology, among other positive aspects.

The assembly process has been mainly conditioned by the time window available within the R434 outage, as well as by the space available in the Turbine building, since the generation switchgear is integrated in the isolated phase busbars, inside an enclosure of very limited dimensions.

Circuit breaker HEC 10 of Hitachi.

Prior to the start of the replacement, it was necessary to make several modifications to allow the installation of the new generator circuit breaker during the R434 reload. In 2021, during the previous outage, the bridge crane and monorail beam located over the switchgear and auxiliary equipment were replaced by other devices with a higher load capacity. Additionally, during 2022, the interferences existing in Turbine building were also resolved in advance. This required cutting pipes, removing handrails, reinforcing tramex, purchasing a trolley with high load capacity but low height to move the equipment through enclosures with limited height and installing a rail beam as an auxiliary element for lifting the equipment.

Finally, assembly and commissioning tests of the equipment and its interfaces with the plant were carried out within the time window foreseen for this purpose, within the R434 Recharge of Trillo NPP. During plant start-up, stator earth fault protection 64.1 tripped due to the increase of earth leakage current through the new capacitor banks incorporated in the new circuit breaker. This event required resetting the relay.

Eventually, the new generation circuit breaker is in operation. Its implementation has led to an increase in the reliability of the system and a significant reduction in maintenance work, which will result in an improvement of the system availability and significant economic savings in the future.

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