Beloyarsk NPP is situated in Sverdlovsk region of Russia, in the town of Zarechny, approximately 60 km east of Ekaterinburg and close to the Ural mountain range. It is one of the oldest commercial nuclear power plants in Russia and started operations in 1964. The first 2 units constructed at the site were AMB100 and AMB200 prototype units, which were forerunners of the RBMK reactors. These 2 units were shut down in 1981 and 1989 respectively. Unit 3 is a 600MWe sodium-cooled fast breeder reactor (FBR) known as BN-600, which started operation in 1980. In addition to the electrical production, the unit produces district heating for the town of Zarechny. Unit 3 is the only unit to have been involved in the TACIS On-Site Assistance. A fourth Unit, also a sodium-cooled FBR (BN-800) has been under construction since 1987, but has suffered many delays, mainly due to the financial difficulties in Russia in the 1990s.
In the frame of the TACIS 2005 nuclear safety programme it was proposed to improve the safety of Unit 3 (BN-600) by replacing a number of the 380 V AC and 220 V DC circuit breakers. An examination of the characteristics of the existing circuit breakers had shown that the reliability was poor and that the protection devices had limited accuracy, considerable variability and strong dependence on the ambient temperature. This was a concern because the cable connections with the motor drives were designed without large margins and could easily be overloaded. Therefore, more accurate and stable protection devices were required. Following an assessment of the characteristics of existing breakers, it was decided to procure a total of around 400 new circuit breakers.
The objective of the project was the provision of new circuit breakers for 380 V AC and 220V DC circuits of the Unit 3.
The 380 V – 50 Hz – 3-phase power network of the power unit is basically divided into 2 levels of switchboards, on the basis of the size of breakers:
- Power centres and
- Sub-distribution cabinets.
Power centres, connected to the 6 kV / 380 V transformers through input circuit breakers, supply motor-drives and sub-distribution cabinets through further breakers. The breakers are installed on retractable racks. Within the sub-distribution cabinets, further breakers are installed in a fixed arrangement.
A number of circuit breakers installed in 220 V DC sub-distribution cabinets were also selected for replacement.
The scope of supply comprised:
- 12 retractable input circuit breakers (1500 A) to be installed in existing 380 V power centres;
- 217 retractable circuit breakers (ranging from 120 A – 500 A) to be installed in existing 380 V power centres;
- 112 fixed circuit breakers (ranging from 15 A – 100 A) to be installed in existing 380 V sub-distribution cabinets (named 'PR');
- 53 fixed circuit breakers (50 A) to be installed in existing 380 V sub-distribution cabinets (named 'RTZO');
- 12 x 1000 A and 3 x 100 A fixed DC circuit breakers to be installed in the existing 220 V DC sub-distribution cabinets;
- 2 complete sets of special tools, instruments and devices required for installation, operation and maintenance of the breakers;
- Spare parts;
- Software for the sort-circuit current calculation.
The rated currents of the breakers specified above (and in the contract) were the nominal values related to the existing breakers. The contractor was required to determine the actual required rated currents of the new breakers based on calculations of the overload and short circuit currents in normal and emergency conditions. The contractor was also required to perform a 'selectivity study' in order to optimise, through the new trip devices of the breakers, the selectivity of the protections of the power circuits taking into account the cable current ratings. The requirements were that:
- the trip of release devices should be selected in such a way as to protect cables, in each plant condition, from the beginning to the end of the connections, from high temperatures in short circuit and overload faults;
- the trip of release devices should be selected in such a way as to obtain a relevant selectivity in breaking the supply of the various loads, motor drives, switchboards and sub-distribution cabinets;
The scope of supply also included documentation; design; calculations; manufacture; testing; delivery; certification; support to licensing; training of End User personnel and supervision of installation, site testing and commissioning.
The Call for Tender was launched in February 2007 and tenders were evaluated in April. Following a period of contract negotiation, the contract was signed with Proras/Schneider Electric consortium on 8 September 2007. The kick-off meeting was held at Beloyarsk NPP in November 2007.
The calculations and analyses were performed in 3 steps:
1. Verification of the required equipment:
- verification of the correct rating of the breakers;
- load flow and short-circuit calculations performed using the software 'DIgSilent', which was part of the scope of supply. The calculation was performed in accordance with IEC 60909.
2. Selectivity calculation of the trip units:
- The final documents detailing the selectivity calculations for the AC and DC breakers were delivered in February 2008.
3. Verification of the results by the design institute 'St Petersburg Atomenergoproekt' (SPb AEP):
- SPb AEP approved the results in April 2008, with minor reserves on the results for the AC breakers;
- The contractor revised the deliverables, taking into account the minor reserves, and delivered the final documents on 10 June 2008.
A number of certification and licensing steps took place from April 2008 until manufacturing of the breakers began in November 2008. Manufacturing, Factory Acceptance Tests and selectivity tests took place late November/early December 2008. Permission to ship the equipment was received from Beloyarsk NPP in March 2009. The equipment arrived in Yekaterinburg customs in April 2009 but customs clearance was not obtained until end of September 2009.
Training of End User personnel took place in January 2010. Thereafter the breakers were installed in several batches at times convenient for the NPP. Due to the delayed installation at the request of the NPP, the contract was amended to allow the Provisional Acceptance Certificate to be signed following equipment delivery, rather than installation. The amendment included a guarantee from the contractor relating to the provision of services for the supervision of installation and commissioning, which was to be provided when the NPP performed the installation of the remaining breakers. All breakers were eventually installed. The Final Acceptance Certificate was signed in February 2012 following satisfactory completion of the warranty period.