No more batteries to change means more production time
Customized generator provides autonomous power supply for lifting beam
- Objective: Implementation of an autonomous auxiliary power supply for a traversing gear of a crane system to supply power to sensors and a radio transmitter
- Implementation: Use of the rotary motion of the bullwheel on the lifting beam to recharge the battery over a connected generator and a charge controller.
- Result: Higher availability and productivity through the elimination of battery changes as well as a higher operational safety through safe power supply.
In steel works, the process of producing steel from raw materials sees oxygen added to raw iron to remove carbon. A torpedo car fills the pig iron produced in the blast furnace into pig iron ladles. Cranes with a load capacity of several hundred tons transport the ladles to a hot metal desulfurization plant where the sulfur content is reduced prior to further processing. The pig iron ladles are lifted using huge laminated hooks joined to one another by means of a lifting beam.
Special safety sensors are installed in the laminated hooks to monitor if the pig iron ladles are securely attached. Requiring a 12 VDC power supply the sensors as well as a radio transmitter to transmit the sensors' signals are installed on the traversing gear of the crane system. Supplying power via a trailing cable is not an option, because the temperature of the pig iron in this area is about 1300 degrees Celsius. Consequently, power is supplied via a 12 V battery, which is also located on the traversing gear of the crane system. The battery is charged by a Hubner generator to avoid outages and downtimes resulting from the need to change the battery. As specialist for individual energy and drive systems Johannes Hubner Fabrik elektrischer Maschinen GmbH implemented an autonomous auxiliary power supply for such a mobile system operating in a steel works. To achieve this goal the company supplied a customized generator solution and the associated charge controller tailored to the application.
The extremely high temperatures and harsh conditions in steel works are a hugely significant factor when considering the demands placed on the deployed energy and drive systems. All components need to be harmonized to ensure the process runs seamlessly and guarantee the interaction between electric components even under extreme conditions. Each additional maintenance or installation task makes operations more difficult and inevitably leads to delays in production time. Consequently, when installing electric systems in particular it is important to ensure they are able to operate maintenance-free and also have a long service life.
The overall solution developed by Johannes Hubner Giessen for the lifting beam is responsible for supplying a 12 V battery with direct current. "Generally speaking, an external voltage source is required for auxiliary power supplies for mobile components. That often has an adverse effect on operations when maintenance is required or it needs to be replaced", explains Maik Will, Project Engineer responsible for Energy and Drive systems at Hubner Giessen. The battery solution originally installed without recharging equipment on the lifting beam was unable to fulfil operational expectations. Before Hubner Giessen carried out the upgrade the battery had to be replaced and recharged every two weeks – as soon as the voltage fell below 12.2 V. This not only caused downtimes, but also tied up personnel and resulted in the constant loss of valuable production time. In addition, the sudden failure of sensors and the radio transmitter due to undervoltage represents a considerable risk to safety.
Rotary motion provides constant power supply
The permanent magnet three-phase synchronous generator that now supplies the battery with voltage via a charge controller uses the rotary motion of the bullwheels on the lifting beam as a source of energy. This rotary motion drives a roller mounted on the generator. When the crane performs a lifting or lowering movement a gearbox sets the generator in motion. The 20-25 revolutions a minute that the roller generates are stepped up to 350 rotations per minute at the generator. This greater speed makes it possible to supply a higher voltage, which in turn the charge controller requires to charge the battery. The rectifier converts the three-phase voltage from the generator and feeds it to the battery as direct voltage.
Individual generator solution
Users in the steel works no longer need to replace the battery or charge it up externally. Consequently, they are able to manage plant operations even better; they need only carry out a minimum of maintenance work on the battery and they also face less downtimes. The generator bearings are greased for life; equally, there are no carbon brushes and no wearing parts as a consequence. As experts for individual products Hubner Giessen fine-tunes its devices to ensure they always interact seamlessly. However, the challenge this application presented for the manufacturer was above all to harmonize the input speed of the roller with the three-phase synchronous generator to ensure it is able to feed a suitable voltage to the charge controller and, as a consequence, to the battery. It is important that the voltage supplied to the rectifier is not too high, Maik Will emphasizes. That means it is important to ensure the generator windings are calculated to ensure the voltage it supplies to the charge controller at 350 rpm remains below its maximum alternating voltage limit of 160 V. Adapting the windings on the generator as calculated ensures the voltage always remains below this value, reaching a maximum of 70 V at the maximum generator speed of 350 revolutions per minute. However, it were not only the technical characteristics of the generator that needed to match those of the application. The battery management system was adapted to fulfil application requirements so that the charge current is reduced or rather interrupted as soon as the battery is charged. In addition, Hubner Giessen guarantees overvoltage protection. When planning the installation of the generator it was also necessary to take into consideration the high ambient temperatures that can climb far above 100 degrees Celsius when loading the desulfurization plant.
A reliable partner customers can depend on
"As we had already benefited from excellent cooperation working on a different application, the owners of the steel works turned to us when seeking a solution to their problem", Maik Will relates. "At a meeting on site, we noted all of the data and determined the position and accessibility of the radio transmitter station, the battery and the roller.” Following the installation of the prototypes and completion of all tests Hubner Giessen supplied the same combination comprising a permanent magnet three-phase synchronous generator and charge controller for other lifting beams in operation in the steel works.