Trenchless pipelines

The world’s population continues to grow – and with it, the need for higher performing infrastructures. Distribution networks for water, power and communications that function reliably are particularly important in cities. A large number of these networks run underground through tunnels and pipelines. Their installation is becoming costlier and taking longer – especially in densely populated areas where planned sections run underneath buildings or other obstacles.

Such challenges are nothing new to Herrenknecht AG. The company with headquarters in Schwanau, Baden-Württemberg, is global technology leader in the field of tunnel boring engineering and is currently participating in a number of construction projects around the world. The company’s portfolio covers several types of boring methods. For example, the so-called Horizontal Directional Drilling (HDD) facilitates fast, cost-effective and environmentally-friendly installation of pipelines and conduits for oil, gas, waste water, district heating or internet cables underneath rivers and infrastructures.

The HDD method uses a controllable drilling head which starts by making a pilot hole from the launch to the reception point. This hole is then enlarged in several steps until it reaches the required size. During the last step the prefabricated pipeline is inserted. The key benefits here are the elimination of the need to dig a trench and hence the minimal impact on the environment.

Previously, the horizontal drillng machines (also known as rigs) were started using diesel-driven hydraulic power units. These had several drawbacks as Stefan Pabst, head of process engineering at Herrenknecht, explains: “Diesel engines are very energy-intensive, with low efficiency and relatively loud. The latter is a particular problem in residential areas.” This is why – as in many other areas – the trend is towards electric drives.

The HK300TE is an HDD rig powered solely by electric motors and was launched on the market by Herrenknecht in 2022. With a tensile force of 300 tonnes and a torque of 120,000 newtons, it is equal in every way to diesel-driven versions, but is significantly more energy-efficient, zero-emission and quieter. “This means, for example, it can be operated over longer periods of time because it doesn’t disturb the residents so much. Tunnels can hence be completed more quickly and efficiently,” points out Pabst. “Moreover, the speed, forward thrust and torque of the rigs can be set much more precisely.” And there’s another benefit: “The different emission standards for diesel engines which exist in many countries are irrelevant with these machines which means they can be used more flexibly.”

The environment in which tunnel boring takes place is a tough one with adverse weather conditions, humidity, dust, rubble and dirt. High quality cabling is essential to ensure the electric motors work reliably and at full power. “In order to achieve the required performance, we need large currents,” explains Jens Holzwarth, electrical engineer for process engineering at Herrenknecht. “The cables must have a suitable current rating. Electromagnetic compatibility (EMC) must also be guaranteed to avoid disruptions to operations.” Weight and space requirements were also important factors during design as the rigs are transported on trucks and hence need to be as compact and lightweight as possible.

With these requirements in mind, Herrenknecht turned to HELUKABEL. The expert for electric connection technology has been a reliable supplier to the company and a partner in the development of new machinery for about 15 years now. The TOPFLEX series of drive cables which connect frequency converters to electric motors was one of several cables chosen for the HK300TE. “They have the required current rating and are shielded to avoid electromagnetic interference,” explains Michael Huser, head of regional sales at HELUKABEL. Also used is the HELUTHERM series of single conductors which are fitted between the junction box and motor. The HELUKABEL experts developed a special shielded cable with a customised sheathing material for outside installation. The delivery package also includes data cables for measuring the temperature of the motor.

The HDD rig’s main drive unit is the carriage which supplies the torques and forward thrusts required for drilling. The carriage is able to move back and forth several metres thereby forcing the rotating drill string into the stone or soil. Every cable connecting this part to the rest of machine must be fitted into a flexible energy chain to ensure reliable protection against damage from the moving carriage. The chain is a bespoke development from EKD Systems GmbH, a subsidiary of HELUKABEL. “An off-the-shelf plastic chain wouldn’t be tough enough for this demanding type of application so the construction department decided to make one from steel,” explains Stefan Pabst. Thanks to the high level of expertise in the development of bespoke constructions at EKD Systems, it was no problem to optimally adapt the energy supply for use in the HDD machine.