Modernization of generator circuit breakers VVG-20 with the replacement of relay protection and automation at Nizhnekamsk HPS

In Nizhnekamsk HPS circuitry of four integrated units with a connection to the unit transformer of 2 pairs of hydraulic generators through air type circuit breakers VVG-20 is used. In connection with the moral and physical deterioration of these switches, working in difficult conditions (number of switching operations per year is more than 500) in the investment program of JSC "Generation Company" replacement of VVG-20 to gas-insulated ones was provided. In terms of switched-off short-circuit currents on generator voltage busbar (rated short-circuit point K1) it is necessary to apply electric generator switch-off with currents of more than 150 kA. The only switch off on such currents is the Circuit Breaker HEC-7 of the company ABB (Switzerland) with a tripping current of 160 kA. However, the value of HEC-7 is about 1 million dollars. And the dimensions do not allow to install it in an existing camera of VVG-20. Therefore, to replace the VVG-20, it was decided to apply the same gas-insulated switch manufacturer type HECS-130R instead of HEC-7, and the cost of HECS-130R is 3.5 times less than the cost of the HEC-7. But the nominal short-circuit breaking current is only 130 kA, which is less than the calculated short-circuit current - 146.2 kA. To ensure compliance with current short-circuit breaking capacity on the generator, it was decided to apply a stepped switching-off: the first step is to switch off adjacent pair of generators, and then turn off the switch of the damaged pair. In this case, the current declines to 112.8 kA breaking capacity that satisfies the HECS-130R. In 2008 the first project for the replacement of two generator switches with simultaneous replacement of protections of the microprocessor, was implemented.

Group members: "TatNIPIenergoprom", Engineering Centre Energoprogress , "KER-Avtomatika", "KER-Naladka"