Fortescue earlier this year delivered a prototype Offboard Power Unit to power a converted Liebherr electric R 9400 E excavator previously delivered to the Christmas Creek iron ore operation, part of the Chichester Hub. In a video update this week, the beginning of the electric excavator trial under hydrogen fuel cell derived power is shown with a Fortescue employee stating: “Today we’ll be powering an electric excavator with a hydrogen power supply. Its a bit of a milestone for everyone so its really good. And now we are going to move into further testing.”
The Liebherr R 9400 was originally supplied in 2010 as a diesel machine and was nearing the end of its operating life when Liebherr and Fortescue successfully retrofitted it to electric (cable powered) operation as the R 9400 E. This was Liebherr Mining’s first repower of a diesel-drive machine to electric drive and is also the first Liebherr electric excavator to operate in Australia.
The Offboard Power Unit is described in globally patent pending documents filed by Fortescue as follows: “A power supply system is provided for supplying electrical power for operation of heavy equipment such as mining machinery, the power supply system having: a hydrogen fuel cell module for generating electrical power from stored hydrogen; a power electronics circuit coupled to receive electrical power generated by the fuel cell module, and having at least one output for supplying electrical power generated by the fuel cell module to an external equipment load; a battery module coupled to the power electronics circuit to allow charging of cells in the battery module using electrical power generated by the fuel cell module, and discharging of the battery cells through the at least one power electronics circuit output on demand.”
The document adds: “Mining, particularly open-pit mining, uses large machines for efficiency of scale. In order to power such machines using non-polluting electricity can be challenging in view of the location, environment and mode of use of the machines. Embodiments of the present invention provide an offboard power unit (OPU) for supplying electrical power to operate heavy equipment such as a moveable mining machine. The power unit is designed to be mobile with the equipment being powered. Energy for the OPU is generated from stored hydrogen through use of hydrogen fuel cells (HFCs). By sourcing ‘green’ hydrogen (eg hydrogen generated by electrolysis of water using sustainable electricity), use of the OPU according to embodiments of the invention to power mining operations can be close to ‘carbon neutral’ insofar as neither the energy supplied nor its use in the mining site produces carbon pollution emissions.”
It adds: “The trailing cable in use carries a substantial level of electrical current and/or high voltage between the OPU and the equipment, and should therefore be sufficiently robust and insulated as for use in a mining pit or similar. The trailing cable may have a length in the order of 300 metres, which allows the equipment a range of movement without needing to relocate the OPU. Since the equipment is typically mobile and trails the cable behind it, there is preferably some kind of strong anchoring connection between the cable end and the equipment to prevent unintended disconnection physically or electrically. One way of anchoring is to wind an end portion of the cable around a circular structure that uses friction to maintain lock. The structure is connected to the equipment, but is able to pivot to allow a greater degree of freedom for movement. In addition or alternatively a cable reel of commercial variety may be included, either at the equipment end or the OPU end, for use in managing the length of cable deployed at a given time according to position and/or movement of the vehicle relative to the OPU. In consideration of magnetic flux that may be generated by current flowing through cable wound on the reel, it may be desirable to limit how many layers of cable can be wound on the reel. This is then determined by how large the reel is to accommodate more cable before needing to layer the cable on the drum.”
The document then adds: “Different forms of electrically driven mining machinery may require significantly different electrical supply characteristics. For example, in terms of power requirements, the aforementioned DTH Drill (eg Atlas Copco D65) may require electrical supply power in the order of 400 kW, a large platform drill rig (eg Epiroc PV271 Blast Hole Drill with electric motor option) may need around 700 kW supply, whereas even a small (250 t) mining excavator (eg Liebherr R 9250 E with electric motor option) may require 1,000 kW or more in electrical supply power to operate. Moreover, some equipment needs direct current supply whilst others use alternating current. Supply voltage requirements can vary also, along with duty cycles.”
On scalability the description also states: “The range of power requirements is addressed by embodiments of the invention by allowing each of the fuel cell, battery and electronics modules to be scalable and independently configurable in capacity. This flexibility in design of the offboard power unit provides opportunity to tailor sizing of battery and hydrogen fuel cells, in particular, to suit equipment applications. Hydrogen storage can also be tailored to suit equipment duty cycle and operational requirements.”
Back to Liebherr and the excavator conversion itself. “Approximately 60% of an electric-powered Liebherr mining excavator is the same as a diesel-driven machine, which helps to simplify the repowering process” explained Chris Di-Nardo, Project Manager, New Machine Deliveries, Liebherr-Australia Pty Ltd in a recent article posted by the company. “Once this R 9400 had been removed from its operations in Western Australia, the base machine was returned to our branch in Perth, where the conversion could begin.”
Among the changes necessary for the R 9400 to become an R 9400 E, the diesel powerpack and fuel tank needed to be removed and replaced with their electric counterparts – in this case, an electric-drive powerpack and a high voltage electric cabinet respectively. Components needed in the diesel-drive R 9400 – like the water-cooling radiators, fans, exhaust, and air intake systems – were made redundant with the introduction of the electric-drive powerpack. However, the rotary connection was a unique case: in order to accommodate the high voltage interface between the upper- and undercarriage of the R 9400 E, an entirely new rotary connection needed to be installed.
In order to simplify major machine maintenance for customers, Liebherr recommends that repowers occur when a machine is due for a major service or component exchange. So while the R 9400 was being transitioned from diesel to electric power, major components that had achieved service life were also exchanged. Performing major maintenance in this way also has the benefit of making the process more cost-effective for customers. Once the new electric-drive modules were installed, connections completed, and systems checked, the repowered R 9400 E was then ‘powered up’ to energise the excavator’s operational systems. The R 9400 E requires 6,600 volts at 50 hertz for its power up process and then the electric motor and hydraulics can be ‘started and run up.’ To minimise the inrush current needed to start the electric motor, Liebherr developed a specialised system that consists of high voltage transformers. This system of transformers reduces the current required from the customer’s power grid to avoid excessive network disturbance.
Although the repower process is not overly complicated, specific expertise from Liebherr’s excavator factory in Colmar, France, was required to support the Liebherr team in Australia with its first diesel to electric repower project. “Repowering the R 9400 was an exciting challenge for our team, but one that they quickly overcame,” says Di-Nardo. “Most of the people working on this project had only worked with diesel powered machines previously. However, thanks to the combined efforts of more experienced team members here in Australia and the engineering assistance from our excavator factory, the team was able to complete the project tasks safely and on time.”