A shovel excavator more than 20yrs old was recently equipped with modern electrical technology by ABB. This offered more advantages for Lafarge Zement than the purchase of a new excavator. The rugged shovel excavator, used by Lafarge Zement at its Karsdorf location in Saxony-Anhalt, was not yet ready for the scrap heap. However, the electronics of the machine, which was built in 1986, were antiquated and worn.
After a comparative study of the operating costs and the technology, Lafarge, one of the leading German cement manufacturers, decided not to replace the old electric cable excavator with a modern hydraulic excavator. Instead, the company decided on an electrical reconstruction and commissioned ABB to equip the EKG 5A excavator with new electrotechnical systems.
“Electrotechnical reconstruction offers an alternative to a new purchase, which is increasingly used,” says Steffen Weise of ABB Automation in Cottbus. Most of the shovel excavators in operation today are of the type EKG 5 and date from the 1970s and 1980s. Owing to their robust construction and regular maintenance, they can be used for around 30yrs without any problems, but then the mechanical system and electrical technology reach their wear limits. The shovel excavator is used by Lafarge in open-pit mining and was manufactured in the Soviet Union. Uralmasch (UHM), the manufacturer, equipped the construction machine with a 6kV switchgear and a Ward-Leonard set. The drive motors are regulated by transductors for setting the generator field.
In order to modernize the excavator, the machine room was first of all prepared for the new drive technology. In this respect, safety and reliability were of paramount importance, because machinery in open-pit mining has to endure severe conditions: moisture, dust and variations in temperatures between -25ºC and +40ºC. The cabinets for the low voltage switching system were also specially tailored to open-pit mining conditions and the space in the machine room. The old switchgear and the Ward-Leonard set with transductor then made way for the new DC drive technology with programmable logic control (PLC) from ABB.
The ACS800-207 dynamic reactive power compensation is an important component of the newly installed electrical technology. It automatically ensures that the considerable amount of control reactive power in the 415V converter supply system is immediately compensated for at the point of origin. An impermissibly high load on the upstream power transmission equipment and the transformer is thereby prevented.
Undisturbed operation is top priority for the customer, so reliability and efficiency were the most important aspects in the reconstruction of the electronic system. The fully digitized static converter and its drive logic and loop control provide the required high functional reliability. Torque monitoring and operating characteristics, which protect the gearbox, reduce the wear.
The power converters, the reactive power compensator, the control panel and the switchgear were installed in a separate electronics compartment in the machine room with heating and air filtering. Heating elements with an automatic control system are provided for operation at low temperatures. If the appliance cools down, both the electronics compartment and the switchgear bays are automatically pre-heated to 5°C. After preheating, the control voltages for the electronic devices are automatically connected to the system. These conditions ensure low-stressing operation and reduce the maintenance requirements.
The decision for a reconstruction of the electronics also secures further advantages for Lafarge Zement. Firstly, the concept is reasonably priced because the existing DC motors can continue to be used owing to modern converter technology. Secondly, the digital control system guarantees high functional reliability and increases the productivity. Last but not least, spare parts are reasonably priced and available on a long-term basis. Under these conditions, the 20yr-old shovel excavator can do its job for many more years to come.