Electrical Network Modeling and Electrical Transfer Simulation of C.N. Asco´ I and C.N. Asco´ II, to Obtain Voltage and Frequency Limit Values Allowing the Electrical Transfer From the Main Generator to the External 110 kV Power Grid

Broadly speaking, a simple electrical diagram of Asco´ I and Asco´ II power nuclear plants could be two power supply bus bars for general equipment classified No-1E, three power supply bus bars class No-1E for the Reactor Coolant Pumps (RCP) and two more bus bars classified 1E for safety related equipment. In normal operating mode, all the five power supply bus bars class No-1E are connected to the main generator (GP1) through two unit transformers (TAG1/2), while the two class 1E power supply bus bars are always connected to an external 110 kV power grid through two auxiliary transformer (TAA1/2). The main generator supplies power to an external 400 kV grid through the main transformer (TP1). The main circuit breaker is placed between the high voltage side of the main transformer and the 400 kV grid. With this configuration, the appearance of an abnormal condition that originates the trip of the main generator and the opening of the main circuit breaker from the external network, involves an electric transfer of the supply bus bars connected to the turbo generator to the external 110 kV power grid. The electric transfer to the external 110 kV power grid will be only possible if the frequency and voltage values are within the allowed range allowed by the grid’s protective relays. Two kinds of electrical transfers are possible: fast transfers and slow transfers. It will be necessary then to evaluate the limit values of voltage and frequency of the power grid that makes the electrical transfer possible in each case. In order to obtain the limit values previously mentioned, the electric system of the plant has been modeled. Different scenarios have been analyzed, taking into account the dynamic behavior of the system components and the delay of the protective relays actuation, verifying the electrical transfer for those situations. This analysis will give enough information to take the correct decisions for future design modifications, and it will assure that the electrical transfer will be done always with success.