Better safe than sorry: AC and DC power supply for critical systems in Sweden’s transmission grid

Modular, battery-supported BENNING power supplies provide round-the-clock security at the Forsmark substation

Sweden flag and map with neighbouring countries

Svenska Kraftnät (SVK) operates the Swedish high-voltage transmission grid – and , as a state enterprise, does not accept any compromises with regard to the safety and reliability of the infrastructure entrusted to it.
This is why the authority counts on reliable uninterruptible AC and DC power supplies with modular 19” TEBECHOP SE rectifiers and INVERTRONIC compact inverters from BENNING – most recently at the substation in Forsmark in the province of Uppland, where these systems reliably supply power to its monitoring and control systems, among other things.

19” rack with TEBECHOP 3000 SE power modules: Each rectifier module provides a maximum output power of 1800 W or 3000 W. Up to 5 power modules can be installed in a 19” rectifier rack, covering the power range from 1800 W to 15000 W

The area around Forsmark is characterized by central elements of the Swedish electricity grid. After all, one of the country’s three nuclear power plants and the converter for the Fenno-Skan high-voltage direct current (HVDC) transmission line to Finland are located there.*¹ In order to fulfill its mission – the reliable operation and safe, environmentally friendly and cost-efficient expansion of the Swedish transmission grid*² – Svenska Kraftnät decided at the beginning of the decade to build a number of additional substations for the 400 kV and 220 kV grid levels, including the new station in Forsmark.

The grid operator was established in 1992 by splitting Vattenfall into a generation and distribution company, which continues to operate under the name Vattenfall, and the current grid company Svenska Kraftnät. The latter operates around 15,000 kilometers of high-voltage lines, runs 16 connections with neighboring countries and is mainly financed by grid usage fees.

Auxiliary power supply in Forsmark substation

2 rectifiers TEBECHOP 3000 SE (110 V/196 A)
2 distributions 110 V
2 DC/DC converters TEBECHOP 3000 SE DC/DC 48 V/2 x 1200 W + 48 V/3600 W
2 INVERTRONIC compact 4500 VA inverters with distribution
2 EXIDE 10 OPzS 1000 LA (1140 Ah) batteries with 54 cells each, with battery stands

Focus on grid and supply reliability

In line with its focus on grid and supply security, Sweden’s transmission system operator developed detailed requirements for a high-performance and reliable power supply when building the substation.

It is intended to protect the 110 V grid of the substation against a blackout and thus ensure that the substation can carry out all control and switching operations even if the public grid fails.

This also includes, for example, the operation of the 400 kV switches, which are particularly important for the stability of the transmission grid.

19” rack module with INVERTRONIC compact output modules – 19” rack: 5 inverter modules, output voltage of 230 V AC, output power of up to 7.5 kVA at 110 V and 220 V, 12.5 kVA at 48/60 V, 5.5 kVA at 24 V

Project schedule Svenska Kraftnät

First offer: September 2021
Final offer: October 2022
Order: November/December 2022
Delivery: August 2023
Lead time: 30 weeks

Tailor-made, efficient and safe

At various sites operated by SVK, power supply systems from BENNING have been in use for more than 10 years. However, there is no direct customer-supplier relationship between SVK and BENNING. Instead, deliveries have been and continue to be made within the scope of “Engineering, Procurement and Construction” or EPC for short. In this form of project realization, general contractors – as “builders” of turnkey grid components such as transformer stations – stand between Svenska Kraftnät as the grid operator and BENNING as supplier of power supply solutions.

Therefore, in 2021, BENNING received an invitation to submit a quote from the EPC contractor responsible for building and equipping the substation.

For many decades BENNING has been supplying high quantities of modular power systems for business critical installations. These modular systems allow capacity adjustments in small steps (scalability) and cost effective redundant solutions.

The modular system design with parallel operating hot-plug power modules (plug and play) provides high availability, can be upgraded and is easy to install and to maintain.

Above/from left to right: Rectifier cabinet, 110 V main distribution cabinet, 48V DC/DC converter cabinet

Efficiency and output line of TEBECHOP 3000 SE and TEBECHOP 13500 SE

The modules are especially designed to meet the specifications required in the industrial sectors, such as the petrochemical industry, the power distribution and power generation industry and the automation control industry.

After examining the various offers, the decision was made in favor of the customized AC/DC power supply solution proposed by BENNING. In addition to the cost-effectiveness of the offer, the decisive factor was that the power supply specified for the quote exactly met the desired technical requirements. Therefore it offered the best prerequisites for ensuring the operation of the new substation even in the event of a breakdown of the public grid.

The block diagram shows the principle of the modular architecture of a power supply system with modular rectifiers, inverters and DC converters

Advantages of Industrial Modular Power Systems

High power density with low volume and weight
Reliable hot-plug design
Very short MTTR (Meantime to Repair)
Capacity adjustments in small steps
Excellent energy efficiency
Remote monitoring and preventive maintenance

Dream team for electricity supply security

The modular inverters, rectifiers and DC/DC converters from the INVERTRONIC compact and TEBECHOP SE series, in combination with lead-acid, NiCd or Li batteries connected in parallel, provide a flexible and economical platform for the construction of complete battery-supported backup power supplies with maximum availability. These systems are particularly suitable for reliably supplying sensitive and process-critical equipment with high-quality electrical energy.

Two 54-cell batteries, each with a capacity of 1140 Ah, are used as power storage units in Forsmark. In addition, an MCU 3000 is integrated to operate and remotely monitor the power supply systems.

This version has a 10.4” touch display and features an integrated web server, among other things. In addition to remote maintenance, for example as part of the proactive 360° service offered by BENNING, this also enables connection to various customer network topologies. This solution, which was individually tailored to the requirements of the Swedish transmission system operator, provides another significant example of the advantages offered by the modular architecture of a BENNING power supply system. – And the partnership-based collaboration during the implementation of the “Forsmark substation” project adds another chapter to the success story between Svenska Kraftnät, the responsible EPC contractor and BENNING.

Further Information

author/contact: Anders Jansson
telephone: +46 8 623 95 06
e-mail: anders.jansson@benning.se

_{*1 Source: https://de.wikipedia.org/wiki/Forsmark}
_{*2 Source: https://www.svk.se/en/about-us/}
_{*3 Source: https://de.wikipedia.org/wiki/Svenska_kraftnät}