Not only at the breathtaking St. Gotthard tunnel, currently under construction, but all over the world, Herrenknecht tunnel boring machines are burrowing through soft and mixed ground as well as hard stone. The Herrenknecht Group, based in Schwanau, Germany, is the technology and market leader in mechanized tunneling technology.
Herrenknecht tunneling technology is used worldwide in the construction of transport tunnels as well as supply and disposal tunnels. The demand for high-performance tunnel infrastructures is driven by megatrends such as ongoing urbanization, global economic networking, population growth, and climate change.
Founded in 1977, the company had around 5000 employees by 2011, generating a total turnover of 1.1 billion euros. Herrenknecht develops, builds, and sells tunneling systems in diameters up to 19 meters. In October 2010, the Herrenknecht tunnel boring machine known as “Sissi” made headlines with the final breakthrough of the eastern tube in the Gotthard Base Tunnel project of the century.
“We only have a few months in which to complete the entire manufacturing process for a tunnel boring machine,” explains Volker Rastetter, Workshop Foreman for control cabinet manufacturing at Herrenknecht in Schwanau. “The machine control consoles, control cabinets, and junction boxes are all assembled and prewired by us here in Schwanau.” Final electrotechnical installation on the machine then takes place in the factory in Schwanau. Here, the machine is commissioned and thoroughly tested.
The machines are split into transportable units for transfer from the Schwanau factory to the tunnel construction sites. Wires and cables are disconnected at predefined interfaces and then reconnected at the destination. “With our old terminal blocks, connection was somewhat harder,” recalls Rastetter, looking back to the time before the company made the switch to this technology. “Sometimes they couldn't be reconnected and had to be replaced.”
The machines, together with their built-in components, are exposed to extreme loads and strong vibrations during tunnel boring work. Interrupting work and experiencing downtimes during tunneling as a consequence of poor contacting is unacceptable for machine suppliers and construction companies – time is big money here.
Terminal blocks from Phoenix Contact's CLIPLINE complete range are designed to withstand even extreme loads. Shock and vibrations are taken into consideration in their design through material selection and appropriate manufacturing methods. With load testing to DIN EN 50155 intensity (German railway standard), the shock and vibration performance of the terminal blocks is proven.
Even if the tunnel boring machines are sometimes enormous – electrical installation can still be a squeeze. Elements for the drive and boring process, for transporting spoil, and for moving the so-called segments, which often construct the tunnel wall – these must all be accommodated in a space-saving way.
“In the confined installation conditions, the front connection technology of the spring-cage terminal blocks makes our job easier,” explains Rastetter. “Our installation engineers have a constant view of the actuation of the terminal block as well as the conductor connection.” Thanks to the front connection technology, cable ducts can be mounted close to the terminal blocks meaning that additional room to connect the conductor is not needed. This saves space in the control cabinet and enables higher wiring density. Despite the compact design, all conductors up to the nominal cross section can be conveniently wired with a ferrule – a further advantage of the spring-cage terminal block.
Even comprehensive and complex power supply potential distribution to all the control cabinet devices, sensors, actuators, and loads can be achieved quickly and easily with the simple jumper system. Thanks to CLIPLINE complete's uniform jumper system for all terminal blocks, bridging between non-adjacent terminal blocks is also possible.
In addition, unnecessary contacts can be cleanly removed with needle-nose pliers at a predetermined breaking point. The installation engineer then only needs to cut the bridge to the required length and mark the assembled bridge with a felt marker on the circuit diagram on the top. User-specific components can therefore be created from standard bridges, saving storage and logistics costs.
Being able to connect and disconnect conductors numerous times, vibration-proof contacting, easy wiring via a front connection, practical bridging – these were the main reasons why Herrenknecht chose to make the switch to spring-cage terminal blocks.
Advice and support from the terminal block manufacturer also played a decisive role. “Phoenix Contact's specialists were on hand throughout the various phases of this transition,” explains Rastetter, as many drawings and parts lists had to be altered. “Our factory team accepted the new connection technology straight away – this was also because our colleagues were part of the decision-making process right from the beginning,” summarizes Rastetter.