This Section provides an overview of the systems and components which serve to deliver the power generated by the plant and which assure that internal plant needs for electric power are met. The internal power supply must provide electric power to components of safety related systems for all conditions, this includes accident conditions and loss of off-site power events.
8.1 Off-Site Power System
Connections to external 330 kV power grids are provided using an open 330 kV switchyard. The plant is connected to the Lithuanian power grid using two transmission lines L-454 and L-453, 330 kV each, to the Belorussian power grid using three transmission lines L-450, L-452 and L-705, and to the Latvian power grid using one transmission line L-451.
Connections to external power grids at 110 kV are provided using the first section of the open 110 kV switchyard. The plant is connected to the Lithuanian power grid using one transmission line “Zarasai” 110 kV, and to the Latvian power grid using one transmission line L-632.
Connections between the open switchyards at 330 kV and 110 kV are established using two coupling auto-transformers AT-1 and AT-2, types ATDCTN-200000/330. Power of each autotransformer is equal to 200 MV×A. The autotransformers have a device for voltage regulation under load. The device type is RNOA-110/1000. 15 positions are provided to regulate voltage in a range (115 ± 6) kV.
The open 330 kV switchyard is designed using "4/3" principle (four circuit breakers per three connections) and consists of two sections. Circuit breakers are placed in two rows. The first section of the open switchyard 110 kV is designed using “Double system of buses with bypass” structure. The second section of open switchyard 110 kV is connected to the first section through two circuit breakers C101 and C102. The second section has the same design as the first one. The following transmission lines are connected to the second section: L-Vidzy, L-Opsa, L-Statyba, L-Dukstas. These transmission lines are intended for district power supplies, so they are not essential for electric power supply for the plant in-house operation.
Air circuit breakers of VNV-330/3150A type are used in the open 330 kV switchyard. Air circuit breakers of VVBK-110B-50/3150U1 type are used in open switchyard 110 kV. To supply power loads on voltage level 330 kV and 110 kV, aerial transmission lines are used. Electrical connections of external grids 110 and 330 kV are presented in Fig. 8.1.
Fig. 8.1 Circuit diagram of power supply at units 1 and 2
AT-1, AT-2 - autotransformers 330/110 kV, T-1, T-2 main transformers, 1TR - 4TR - unit service transformers, 1PRT - 4PRT - unit auxiliary transformers, 1BA - 1BH - working buses (6 kV), 1BU - 1BZ - safety buses (6 kV), TG-1, TG-2 - turbogenerators