The Multilingual Transformer Station

The security of the power supply can be easily endangered – for example, when an overly enthusiastic backhoe operator damages electrical lines during an excavation. In such cases, a fast and, above all, targeted diagnosis of the electrical grid is essential, both along long spans and also in the distributed transformer stations. In the transformer station in the Wittmund wind farm, ENERCON relies on the WAGO PFC200 Telecontroller for signal processing and data transmission.

ENERCON, headquartered in Aurich in northern Germany, is among the international technological leaders, with more than 26,300 wind turbines. In Wittmund, ENERCON constructed the facility, and it also operates the wind farm and transformer station. “There is increasing demand for turnkey solutions for wind farms from a single source, from planning, to construction, to supplying the electrical grid,” explains Gerd-Evert Meyer, Project Manager at ENERCON. Consequently, the company is seriously considering how to link wind farms into the smart grid and, above all, how to ensure the availability and monitoring of the systems, including the transformer stations.

With this goal in mind, the WAGO PFC200 Telecontroller plays a central communication role in the transformer station. First, it establishes the link between the network operator and the wind farm controller. It’s important to understand that the network operator uses a different language than is used within the wind farm and between the facility and its operator – namely ENERCON. The multiple languages are a result of different protocol standards for telecontrol technology. A serial, point-to-point connection, based on IEC 60870-5-101, is established between the network operator and the wind farm regulator. The data to be transmitted typically consists of requests for active power or reactive power. In addition to the acknowledgment of the setpoints, the actual output, wind strengths and additional weather data are then sent back “to make it possible to derive the output capability of the wind farm,” explains Meyer.

Virtually everything is monitored in a transformer station. While door contacts serve primarily to detect access, for example to prevent break-ins, linking the fill level sensors in the transformer base increases operating safety and protects both employees and the environment. The base must always be able to capture all of the oil from the transformer. If the water level were too high, for example, due to rain water or ground water in the foundation, the oil could no longer be captured, which could damage the environment.

To ensure that signals are transmitted with no physical interruptions, ENERCON uses fiber optic cables within the transformer stations, which collect all connected components using a star coupler and in turn are connected to the PFC200 using a serial interface module. The switching devices for medium voltage are isolated using SF6 gas. If this gas escapes through a leak, then the switch is blocked by a locking mechanism. This is reported by the protective device via the IEC 60870-5-103 protocol to the PFC200, and from there via IEC 60870-5-104 to the ENERCON control center.

To program these functions, ENERCON uses the standardized languages of IEC 61131-3, which are included in the standard equipment of the PFC200. Programming via CODESYS offers Meyer the advantage that he can more easily adapt to the specifications of the network operator in the area where his wind farm and transformer station are located. This detail has recently become more important for systems that supply electricity outside of the Central European time zone, where it is necessary to combine different time stamps with each other. Based on Meyer’s experience with the high voltage systems, he can thus “easily program the second time stamp” within the WAGO controller. “I retrieved the variables and added or subtracted the time difference.” The PFC200 sends the data with the original time stamp to ENERCON in Germany and corrects it with the local time for the network operator. Features like this are why Meyer values the PFC200. “We have more options – we can make the programming easier and still retain standard communication despite individual adaptations.”

The overall solution is based on having the telecontrol configurator automatically supply the relevant information and variables for data transmission from the depths of Linux^® itself. “This is our great advantage. We can program freely, but we can also take advantage of a certain degree of standardization by using the telecontrol configurator.”

One System, Three Communication Protocols In light of the trend in building technology and automation towards standardizing communication and linking everything using ETHERNET, it is worth asking: Why do the three different universes even have to be linked at this point? The ENERCON employee justifies all this on the basis of differences in security requirements. “Communication inside of the station is implemented using the IEC 60870-5-103 protocol for serial data transmission, which is an economical standard in the area of protection technology. The signals are then sent to the ENERCON control center via a VP tunnel using TCP/IP, the IEC 60870-5-104 protocol. The network operator, in contrast, prefers a serial end-to-end connection, which is more difficult to influence than the TCP/IP protocol. We use the IEC 60-870-5-101 protocol here, which is usually converted by the network operator into IEC 60870-5-104 in its own network.” As a consequence, using three protocols is completely justified.

Meyer and his team also like the fact that WAGO offers visualization in addition to the telecontrol and controller functions of the PFC200. “We would have to buy it for some cases anyway,” says Meyer and estimates that the visualizations created can be easily carried over to other projects, which ultimately will reduce the time required for development. The new device in Aurich has also received positive feedback, because the PFC200 can send SMSs or emails within the context of management. “This is unusual for a telecontroller,” says Gerd-Evert Meyer. Because the telecontroller can also process two separate communication networks, service technicians can now send messages over their own channel, while ENERCON operates a VPN tunnel in parallel. As part of further development, WAGO has also equipped the PFC200 with an integrated 3G modem. “Now we have three separate access points,” says Meyer with satisfaction.

Text: Heiko Tautor | WAGO

Photo: Thorsten Sienk