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14.08.2017

Extra safety for the Beznau Nuclear Power Station

BENNING’s modular power supply systems help ensure the Beznau Nuclear Power Plant continues to supply around three million people with reliable electricity.

Located in Switzerland, in the Lower Aare valley near the parish of Döttingen, Beznau Nuclear Power Station (KKB) consists of two largely identical blocks equipped with pressurized water reactors with a capacity of 385 MW each.

KKB is owned and operated by Axpo Power AG (formerly Nordostschweizerische Kraftwerke AG). It has generated around 250 m MWh of electrical energy since it was commissioned in 1969 and 1971.

The installed UPS systems, rectifiers and inverters form a network of connected power supply systems, with corresponding batteries that power key nuclear power plant loads, both when the grid is working and if it fails. These include:

When the grid is live, the UPS systems supply loads at the existing mains voltage and supply batteries with charging and maintenance current. This ensures batteries are always available at full capacity in the event of a power failure, ensuring loads continue to be supplied with clean power during the switchover period.

Retrofitting the power supply

For retrofitting the secure power supply, Axpo Power AG also relies on BENNING’s power devices and systems. Thanks to their modular technology, which has been used successfully in various applications for many years, the availability of the secured power supply can be easily maximized.

Close to the customer

The partnership between Axpo Power AG and BENNING started in 2012. After the Swiss energy group made the initial contact, various meetings and conferences followed - both at KKB and at BENNING Switzerland’s offices, located just 50 kilometres away, and at the BENNING Bocholt company’s headquarters.

Being close to their provider meant the customer could easily discuss its demanding safety requirements collaboratively when developing customised, bespoke solutions. The 1E-rated power supplies were first supplied in January 2015, not long after all the required tests such as earthquake, EMC, type and climatic conditions were successfully passed. For each of the two power station blocks, BENNING provided 15 modular power supply units. These included UPS systems from the ENERTRONIC modular range (60 - 80 kVA), INVERTRONIC modular inverters (30 - 60 kVA) and rectifier systems (24 V / 140 - 1120 A, 110 V / 220 - 300 A), all installed in earthquake-proof system cabinets. Additional product deliveries are planned depending on the next scheduled overhaul times.

Hot-plug-in systems

Before adopting the BENNING products, KKB used a multi-strand system with secured power supplies made of monobloc systems. Compared with the new modular power supply systems, monobloc systems are relatively heavy, bulky and not easily scalable. If one of the monobloc systems fails, the whole supply line can fail - a scenario that is prevented by the modular technology now used. BENNING modular systems consist of parallel power supply modules, using hot plug-in
technology. Switching in parallel gives an n + 1 or n + 2 redundancy system with maximum availability and reduced MTTR (Mean Time to Repair). The system performance can be increased or decreased at any time by adding or removing plug-in modules, without interrupting the supply – a principle that meets the highest demands on availability and ease of maintenance. As well as increasing redundancy, the multi-strand design of the power supply units was maintained, according to the motto: Twice as safe is stronger.

Training, Maintenance & Service

Thanks to the intensive and successful cooperation with Axpo Power AG, several follow-up projects were made possible. BENNING provided reliable power supplies (255 kVA UPS) for the PRW project and supplied several 1E-rated ventilation motors with the support of its Electrical Machines division. There were also several training sessions at BENNING’s training centre in Bocholt at which KKB employees were shown how the new modular power supply systems work. There are also plans for BENNING Switzerland to provide local support in the maintenance and service sector for KKB in the future. It deals with defined response and access times for the maintenance required to keep a high availability. This is another major contribution to ensuring safety at KKB in the future.

The power station control room is where it all comes together. BENNING's modular power supply systems ensure the various systems are always available.
The power station control room is where it all comes together. BENNING's modular power supply systems ensure the various systems are always available.
Each nuclear power station block has four of the UPS systems shown on the left with the appropriate battery cabinets. They supply the plant information system of the control room and are based on the ENERTRONIC modular series.
Each nuclear power station block has four of the UPS systems shown on the left with the appropriate battery cabinets. They supply the plant information system of the control room and are based on the ENERTRONIC modular series.

The installed power supplies are designed to be earthquakeproof to class 1 E. In the adjacent picture, this can be seen, for example, in the cross struts of the walls and ceilings. This system contains up to 20 rectifier modules from the TEBECHOP 3000 HDI series (26 V / 1400 A).

This inverter system provides emergency lighting. The supply is redundant and is taken from the 120 V rail. Each inverter cabinet contains three INVERTRONIC modular modules.
This inverter system provides emergency lighting. The supply is redundant and is taken from the 120 V rail. Each inverter cabinet contains three INVERTRONIC modular modules.

The power supply shown on the left is part of the so-called VITAL system. Each power station block has four of these systems, supplying the control room instrumentation, the emergency oil pump and the 118 V rail. The system cabinets contain, from left to right:

  • The input field with network priority switching and AC distribution
  • The rectifier field with up to 15 TEBECHOP 3000 HDI modules and up to four rectifier modules of the ADC series
  • The inverter field with up to four INVERTRONIC modular modules
  • And the output field with the AC and DC distribution

The 120 V DC network (e.g.: the emergency oil pump and control voltage for switchgear) is supplied via the rectifier. The inverters supply the fire detection system, TXS and the measurement and reporting systems.

Further Information

author/contact: Paul-Gerd Demming
telephone: +49 2871 93 410
e-mail: p.demming@benning.de

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