Customer application 31 August 2020
Modernizing with Vision

The modular WAGO-I/O-SYSTEM and the WTG Protocol Converter enable easy management of the complex district heating system in Greifswald.

Greifswald relies on district heating. Almost 20,000 residents – about 70 % of the population – use it for heating and for hot water, which is an astonishing statistic in comparison to the national average of 14 %. The first thermal plant went online in 1958, and more have been added over time. Starting in 1983, one of the two nuclear plants in the GDR supplied the city with both waste heat and electricity. Up until 1990, a district heating line extended 24 kilometers between the Lubmin nuclear plant and Greifswald.

The end of the GDR sealed the fate of the nuclear reactor. Serious safety infractions were revealed, and conforming to FRG standards would have been prohibitively expensive. In 1990, the power plant was taken off line, and the aboveground supply line was dismantled four years later. From 1990 to 1993, an oil heating plant at the Lubmin location temporarily supplied Greifswald with district heat.

Following the shutdown of the nuclear plant, Greifswald maintained its district heating and established Fernwärme Greifswald GmbH in 1991 to supply it. This entity introduced a new energy concept: Downtown pipeline systems were renovated, and four new power plants were built in just five years. Three CHPs with internal combustion engine systems, and one thermal plant with a gas turbine engine and waste heat boiler, now supply thermal energy and electrical power. Electricity is generated exclusively by the high-efficiency CHPs located within the city limits.

Managing district heating systems – here’s how WAGO supports you:

  • The WAGO-I/O-SYSTEM 750 combines the functions of a telecontrol station and data concentrator in one system.

  • The telecontrol gateway records data from the heat regulators in the transfer station via serial channels.

  • New elements are added via FTP and Web-Based Management.

Heat regulators and overvoltage protection technology come from different manufacturers. The WAGO WTG allows manufacture-independent connection of substations.

Frank Reißmann, supervisor for network control technology at the Greifswald municipal utility

Highly Efficient Power–Heat Coupling

The complex district heating network requires an intelligent management system for efficient operation and for the (highly unlikely, yet conceivable) possibility of accidents or disruptions. Therefore, the two generating plants that are responsible for the central network are linked together thermally by a network coupling station in the city center. This is where heat is transferred between the two primary networks. Since the maximum supply temperatures and the pressure are different for historical reasons, the coupling initially takes place via a heat exchanger.

To guarantee an efficient and error-free supply, the transmission of the amounts of heat is automated. The outside temperature is detected, and the supply temperature is automatically adjusted to the level necessary for heating demands. This turns district heating into heating energy for private consumption with demand-based control.

When their previous telecontrol hardware was discontinued, the Greifswald municipal utility decided to replace both of the components in the telecontrol station and the data concentrator with WAGO solutions. The WAGO-I/O-SYSTEM 750, with its find-grained modularity and fieldbus-independence, has been used since October 2016. Greifswald is unusual in that a WTG Telecontrol Gateway is integrated as an application for the I/O system. Whereas the modules previously operated as a telecontrol station or data concentrator required an individual interface to the network control station, this is now accomplished through a common bidirectional interface.

Manufacturer-Independent and Scalable

Because local control of the network gateway to the analog and digital input and output arrays of the I/O system is not possible, the WTG from WAGO records data from the heat regulator in the transfer station via serial channels. This demonstrates a central feature of the telecontrol gateway: “Heat regulators and overvoltage protection come from different manufacturers,” explains Frank Reißmann, Supervisor for Network Control Technology at the Greifswald municipal utility. “Using the WTG from WAGO allows manufacturer-independent connection of substations.”

The protocol translation is carried out in the WAGO WTG using the PLC functionality. Data from up to nine telecontrol lines, each with a maximum of 16 substations, can be recorded this way. Operators can independently add elements and carry out system adjustments via FTP data transfer and Web-Based Management – i.e., using a Web browser, so the process is platform-independent.

Together with the open structure, this leads to a high degree of flexibility and offers the Greifswald utility a sustainable future – after all, modernization is a continuous process, and they currently have one telecontrol station with 31 heating controllers as substations. Nine additional telecontrol stations are to follow in the next few years – which will be easy to implement, efficient and reliable thanks to the open and scalable solutions from WAGO.

Text: Daniel Wiese | WAGO

Photo: Thorsten Sienk

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