Replacement of SF6 switches at 6 kV switchgear

IGNALINA NUCLEAR POWER PLANT (INPP)

In order to ensure electrical power supply to auxiliary consumers, including security systems, and their proper operation both in normal and emergency situations, auxiliary switchgear was designed for Ignalina Nuclear Power Plant.

When the power plant unit operates at full capacity, electrical power to the 6 kV auxiliary switchgear is provided from 24/6 kV primary transformers, which are supplied directly from turbine generators (TG). If the turbine generators stop, auxiliary switchgear automatically switches to supply mode from PRT 110/6kV (backup transformers), connected to the electrical power supply system. In emergency cases, when power supply from external sources is interrupted, the automatic transfer switch disconnects the sectional and input connectors of the auxiliary switchgear, starts the diesel generator and connects it to the corresponding section.

VEM-6 type switches contained in 6 kV auxiliary switchgear and manufactured by Konstantinovsk High Voltage Equipment Plant (Ukraine) and Rovensk High Voltage Equipment plant (Ukraine) are used in the first Power Plant Unit. The second Unit uses switches of VMPE type, manufactured by Shymkent Plant of Electric Equipment (Uzbekistan).

The reconstruction of 6kV switchgear equipment must be performed at Ignalina Nuclear Power Plant. Part of this equipment is related to the power supply to security systems (switchgear of reliable power supply) and the other part is related to the general operation systems, which are important from the safety point of view (switchgear of general power supply).

The main objectives of this project were as follows: the replacement of morally and physically obsolete and expired equipment; the improvement of reliability of systems intended to supply electric power to auxiliary power plants; the improvement of technical service conditions; and, ensuring electric power supply to the equipment of the nuclear plant in case of seismic influence.

The project envisaged a phased replacement of the 6 kV switchgear switches by replacing old switches with newly produced 6 kV sulphur hexafluoride circuit breakers mounted on withdrawable elements, adapted to the existing equipment and relay protection and alarm systems.

AS PART OF THIS PROJECT, THE FOLLOWING WORKS WERE CARRIED OUT:

• Step-by-step replacement of the following switches of the new certified unit at Ignalina Nuclear Power Plant: Designing, manufacturing, testing, and delivering 16 switches for the 6 kV switchgear system withdrawable factory-assembled switchgear elements, type KXXIV (Inom = 3200А); 40 switches with withdrawable factory-assembled switchgear elements, type KXXV (Inom = 2000А), and 161 switches withdrawable factory-assembled switchgear elements, type KXXVI (Inom = 1000А and Inom = 630А).
• A complete technical design for the replacement of switches complete with withdrawable carriages, including drawings, calculations, specifications and supporting documentation.
• Installation (under supplier supervision), supervision, and consultations during equipment commissioning, start-up, operational tests, and acceptance into service of the installed equipment.
• Training of maintenance personnel on the maintenance methods and regulations of withdrawable carriages with switches.

The technical design was prepared by our subcontractors SPKB PROELEKTRO ООО (specialized design centre PROELEKTRO, a limited liability company, Kiev, Ukraine).

Electrical, electromechanical, resistance, and other tests of the equipment were carried out at OAO NIC-VVA (open joint-stock company Research and Development Centre for High Voltage Equipment Testing) (Moscow, Russia).