Careful cabling considerations

Bespoke solutions are more often than not the case in energy and data transmission cable systems. Common factors include the considerable length of travel over which power must be supplied at a constant rate, and the often harsh environmental conditions in which the equipment to be powered has to operate.

A good recent example is a transmission system for the steel pan, scrap, and slag transport cars of the Tulachermet Steel Company in Tula, Russia, developed and delivered by Conductix-Wampfler. 

Located 200 km south of Moscow, Tulachermet (which is part of the SMS Group) specialises in systems and machines for processing steel and non-ferrous metals. The project presented a number of challenges: six double-spiral motor driven cable reels for cables totalling over 1,000m in length, as well as a hose reel for carrying argon for use in a plant with particularly harsh atmospheres. The specific electrical requirements demanded close cooperation with the cable manufacturer. 

The special reeling cable developed in collaboration with the cable manufacturer is unique, claims Conductix-Wampfler. With six shielded energy strands for frequency-controlled drives, 20 control strands, two shielded twisted-pair
control lines, and six type 50/125 optical fibres, the special cable is specifically adapted to the application and local regulations.

The reels, with their unusually long winding lengths, were installed in protected areas above the working environment. The cables and hoses are suspended and guided by roller bearings every 3m. The reels are driven by AC motors, in combination with the MAG-Drive magnetic clutch developed by Conductix-Wampfler.

Harmonious balance

Jürgen Schmidt, sales and application engineer at the cable firm, says this provides a “harmonious balance” between the motorised reels and the special cable, all driven through the robust magnetic clutch. Schmidt adds that this “guarantees” long-term reliable use in an environment, which is both hot and aggressive. 

The steel plant solution developed makes use of rotary fibre optic transmitters (TFO), which are best suited for transmitting large volumes of data over larger distances. They can be equipped with single mode (9/12) or multi-mode (50/125 and 62.5/125) fibre optic cables, a single mode (<1.5 dB) or multimode (<1.0 dB) damping, and in variants for 40, 80, or 120 turns, and 6, 12, 18, or 24 fibres. The standard connector is a Type ST, but FC, SC, and other types are also available on request.

Using standardised cable reel components for simple spare parts stockpiling helps maintain smooth, consistent operation of the transport cars. “For Tulachermet, reliability is top priority, since every unplanned stoppage leads to costly losses in productivity,” says Schmidt. 

In China, Conductix-Wampfler delivered two slip-ring assemblies  for Shanghai Electricity and Environment Protection Equipment Plant (SEEPEP).

The slip rings will be installed at the Tianjin Beijiang power station, where they will be used to transmit electrical power, control signals, data and fluids from the stationary to the rotating units in two circular stacker/reclaimers.

As at Tulachermet Steel, this was a bespoke system designed to meet the requirements for safe and reliable transmission in the harsh environment of a coal-fired utility. Any such solution has to be capable of withstanding frequent and severe acceleration forces, and thereby ensure that process-critical pieces of machinery can continue to operate reliably and without interruption under extreme conditions. 

The slip ring assemblies supplied to SEEPEP are rated  for voltages up to 400V and currents up to 1,000A. In addition, the unit also handles 24 x 250V, 10A channels for machine control signals, and a fluidic rotary joint offering a 2ins orifice for dust suppression water and 0.5ins bore for compressed air. Data transmission is carried out using a six-channel optical slip ring to handle the 100 Mb/s data flowing through 62/125 μm multi-mode optical fibres.

The two slip-ring units were designed to match the customer’s requirements exactly, where availability is critical to keep the power flowing. The order also included the supply of System 0360 heavy-duty I beam festoon components and cables from the firm’s Germany site at Weil Am Rhein, which will be used on other bulk handling equipment. 

Most recently, ConductixWampfler delivered the power supply units for the world’s largest offshore overhead gantry crane. 

The special crane is being used in the construction of a new road around the Indian Ocean island of Réunion. When completed in 2018, the six-lane highway – dubbed by French media as “the most expensive road in the world” – will connect the capital, Saint Denis, with the smaller town of Possession, a distance of about 12 km. 

Spectacular 

The most spectacular section is a viaduct leading 5.4 km off the coast into the Indian Ocean. It must withstand cyclones with speeds of up to 144 kph, as well as waves up to 10m high.

The construction project involves the installation of heavy equipment for the construction of the viaduct, including 16 different crane types, for which the key component is the offshore gantry crane from Enerpac. Enerpac has already successfully completed testing with the special crane at its production sites in the Netherlands.

The gantry comprises two pairs of lifting traverses with a total width of 30m and a load-bearing capacity of 4,800t for lifting, moving, and lowering the concrete blocks that are needed to build the coastal highway. The blocks are lifted and lowered using a reeving hoist system based on eight grooved drum winches. The longitudinal movement of the portal is conducted using a roller trolley system, with two roller trolleys per lifting traverse. Engines drive each
roller trolley with hydraulic drive and planetary gears. The wheels run on two parallel rails that are mounted onto the runway beam on the barge. Long-stroke cylinders affect the continuous lateral movement of the portal winches.

Conductix-Wampfler is providing the six motor-driven cable reels for high loads that supply the gantry crane with energy. Two monospiral motor reels with a magnetic coupler (MAG Drive) provide the power for the longitudinal travel of the crane bridges on the barge, while four random wind reels ensure the supply of the load handling attachments.

In port cranes, cable management has traditionally been handled with festoon systems or standard cable carriers. But Tsubaki Kabelschlepp believes both methods have drawbacks. 

That is why the firm last year launched its roller supported chain (RSC) system. RSC does not use rollers built into the cable carrier, because having the wheels as part of the link construction can cause excessive vibration and jams that could lead to accelerated wear, and eventually total replacement of the cable carrier, the company says. RSC was designed so that the  upper run of the cable carrier never comes in contact with the lower run. 

RSC uses maintenance free ball bearing rollers that are mounted onto the side of the cable carrier. The rollers are fully exposed, and roll on the smooth top surface of the guide channel. With this design, no bounce or vibration is caused by the wheels rolling on top of each other. Not only does this ensure low noise and vibration during operation, it also reduces the tow forces by 90% compared with traditional cable carrier systems, and by an even greater amount in comparison to festoon systems. 

This reduction in tow force  minimises the wear on the cable carrier, which greatly increases the life. The design also ensures that all components on the RSC are easily accessible. Recesses in the guide channel make it easy to reach the rollers and modular side parts. This allows for easy inspection of the rollers without lifting or touching the cable carrier. Worn rollers can be replaced individually during maintenance, if necessary. 

RSC vs. festoon

The use of an RSC cable carrier addresses several concerns compared with festoon systems that go beyond crane operating speed, says Tsubaki Kabelschlepp. With a standard festoon system, each cable needs to be approximately 115% of the length of crane travel. With the RSC cable carrier system, each cable only needs to be approximately 52% of the length of travel. On a long travel port crane system, this reduction in required cable length can translate into substantial cost-savings. 

The RSC cable carrier system also requires a much smaller operating space. A typical long travel festoon system can require space as much as 15ft high and  5ft wide. An equivalent long travel RSC may only need 3ft in height and 2ft in width.

Even more important to crane operators is the ‘parking station’ that a festoon requires. A long travel festoon system often needs up to 10% of total travel distance for this. On a ship-to-shore crane, this requirement could easily be more than 60ft. In comparison, an RSC virtually eliminates this requirement, and on an equivalent system would require less than 5ft of parking space.

An RSC system was included in a tender won last year from Indonesian fertiliser manufacturer Pupuk Kaltim. The basis of the winning tender was an MC1300 cable carrier equipped with Traxline drag chain cables. 

“One of the decisive aspects for the customer was that Tsubaki Kabelschlepp was able to supply cable carrier and cables from one source,” explains Winfried Sambale, product specialist for cables at Kabelschlepp. “Only a few suppliers are able to offer this, particularly as this project required the use of special medium-voltage cables.”

These are continuous bending hi-flex 10,000V drag chain cables, which are specially designed for long travel lengths. The active power cable is only a few millimetres thicker at the same weight as a 1,000V cable, but it can transmit up to 10 times the electrical power. 

“Based on the required travel length, in combination with the associated cable package, we immediately decided to use a rolling chain application,” adds Thorsten Serapinas, engineering manager project at the cable firm. “260m is one of the longer travel lengths we have ever implemented with a rolling system.”

The RSC has been running successfully at Pupuk Kaltim, which is located on the island of Borneo. It is installed on the transverse axis of a new crane system used for shiploading and unloading. 

Due to the low pull/push forces, the required driving force is reduced, and thereby the power of the drives is scaled down as well. 

Monitoring

Increasingly, technology is being put to use to monitor performance in energy transmission systems, whether in cable reels or drive chains. 

Last year, Tsubaki Kabelschlepp launched a new push/ pull force monitoring unit aimed at ensuring greater reliability and safety for its cable chains in crane and other long travel applications. 

The system takes constant measurements on the drive end connection, which can prevent damage to the overall system and costly unexpected downtimes if the cable carrier is blocked by external material, such as dirt, metal
or wood shavings – a common issue in dry bulk applications.

The force limitations of the system (lower and upper limits) can be programmed freely, and there is no travel speed limit. The output signal can be used as a PLC input signal, allowing an emergency stop, a slowdown or an acoustic signal to be triggered when the programmed force limits are exceeded.

Tsubaki Kabelschlepp says the system is maintenance free (e.g. there is no need for battery changes) and complies with protection class IP67. The heavy-duty version of the system box is resistant to sea water, and is therefore suitable for use in maritime ports. 

The monitoring unit is optionally available with a data memory, allowing users to save and evaluate the development of the forces. 

As the control box is integrated directly into the drive section of the system, this ensures short cable lengths. “It is particularly suitable for cranes in container ports, cement works, steelworks, foundries or waste incineration plants, but also for handling bulk materials such as coal, ore or spoils,” says Tsubaki Kabelschlepp.