High-performance drives for port facilities

Cranes perform a simple job: they pick up a load at a specific position, and put it down again at another. In order to reliably accomplish and ensure a sufficient level of precision during this operation, they do depend on drives that are ideally adapted to this task. "Cranes are equipped with geared motors featuring integrated brakes. These are combined with frequency inverters for centralized acceleration and speed profile control," explains XXX name XXX, local Managing Director at NORD Drivesystems. Since port cranes handle extremely large loads, their geared motors are designed to withstand high radial and axial forces. They also provide a range of key functions: enable a soft start with a high starting torque, ensure virtually shock-free motions, facilitate the synchronization of several drives, provide a powerful hoist function, and allow for efficient generative braking via parameterizable ramps. “After a manufacturer has decided on a pre-selection of drives for the overhead crane and trolleys, we as a drive supplier will suggest suitable drive ratings according to customer specifications”, says XXX name XXX.

Geared motors under extreme loads
For this purpose, NORD can specify and deliver helical shaft geared motors and frequency inverters, all from in-house production. The geared motors for cranes and trolleys cover performance ranges up to 160 kW with a wide choice of gear ratios. Available as two- or three-stage designs with a hollow or solid shaft, users can choose between models with a foot mount, flange models and shaft-mounted models. All types are equipped with the same space-saving housing which allows for easy integration. Motors used in cranes and trolleys often operate around the clock in very busy ports. However, if the turnover decreases due to market conditions, some loading facilities may stand still for long periods of time. The build standard of the drives must, of course, ensure that normal operation can be directly even after such prolonged standstill. In addition to these changing load factors, recurring harsh climatic conditions and extreme temperatures as well as the salt water in maritime environments, all call for suitable long-term corrosion-proof material. If required, gear units from NORD are available with IP55 or IP66 protection. Moreover, all models are also available as ATEX versions.

User-friendly drive electronics
Frequency inverters from NORD's SK 500E line are an ideal match for geared motors used in cranes. The robust, high-performance units provide an efficiency of more than 95% and a typical overload capacity of 200% for 5 s. Compatible with all standard bus interfaces, the units are easy to operate and program. Basic models feature an integrated brake chopper with management for brake motor control, which is ideally suited for use in hoist applications. The inverters operate with sensorless current vector control. Alternatively, speed feedback can be used in applications with elevated requirements for speed control precision and overload capacity. The Posicon extension enables these inverters to perform intelligent position control tasks, rendering additional modules for such functions in higher-level controllers unnecessary. The cost-efficient “Safe Stop” feature according to EN 954-1 and EN 13849-1 is optionally available.

Tried-and-tested combinations
NORD's drive solutions, which are installed in a wide range of crane facilities with different capacities, have proven their reliability for years. One example is the transtainer crane at the Scandinavia quay in Travemünde, Germany. With more and more cargo runs in the Baltic Sea, boosted by the eastern expansion of the EU, the port authorities have considerably extended the Scandinavia quay in the last few years. Now the largest part of the port, the facility comprises cranes with a load capacity of 56 t which act as hubs for all kinds of goods that arrive on trucks, in containers or in swap bodies and must be transferred. In total, 60 NORD drives are used in this application. The installation of the world's biggest shipyard portal crane, “Goliath”, in Odense, Denmark, was a considerably larger enterprise still. For this application, NORD developed a drive concept with a sophisticated control system and a total of 68 helical bevel geared motors. The drives for the shipyard crane, which master a maximum load of 100 t, ensure precise directional stability. Controlled DC drives in the crane hoist and inverter-controlled three-phase asynchronous motors in all trolleys ensure stageless and smooth speed control. Combined with continuous brake monitoring through micro switches, this ensures high positioning precision and plant safety.

Interview: Crane drives for every port
NORD Drivesystems pursue an ambitious goal: “We would like to see at least one crane in every major port worldwide equipped with our drive solutions”, says XXX name XXX.

Question: Which special challenges are you faced with in selecting drive mechanics and electronics for cranes installed in shipyards or container terminals?
XXX name XXX: Drive systems used in crane hoists and trolleys must combine a robust, wear-resistant design with characteristics such as great dynamics and precise motions. At the same time, of course, users ask for economical TCO. For crane builders and operators, getting complete solutions from specialized suppliers is the easiest route to fulfilling these requirements.

Question: Are cranes comparable to series machines or special purpose machines?
XXX name XXX: Insofar as you can make that comparison, there are only a few crane manufacturers who build a giant ship-to-shore crane per day. Therefore, crane building is comparable to manufacturing modular special purpose machines – and our drive solutions are an optimal match for such applications.

Question: NORD is specialized provider of drive systems for cranes. What do these complete packages consist of?
XXX name XXX: We provide cost-efficient, reliable drive technology for all types and sizes of crane hoists and trolleys. Our extensive range of mechanical, electric and electronic products allows us to create drive solutions from a single source. Products with IP55 and IP66 protection as well as corrosion and dust-protected versions with a special coating ensure high reliability and a long operating life even under demanding environmental conditions and during long-term standstill periods, such as in seasonal operation. Various frequency inverter models with a performance of up to 160 kW are available to provide functions such as Soft Start, generative braking, synchronized operation and high positioning accuracy. One more thing: we have established a new microsite dedicated to drive solutions for crane applications at http://cranes.nord.com.

Question: Other than container terminals, what are typical applications for cranes equipped with NORD drives?
XXX name XXX: Industrial cranes are used e.g. in foundries, in steel building applications, in shipbuilding, power plants and heavy engineering. Smaller types are also used in workshops. Currently, there are approximately 700 machine builders who manufacture cranes. Out of those, about 15 build giant port cranes.

Figure 1: Cranes in shipyards, container terminals and other port facilities require highly reliable, powerful drive mechanics and electronics
Figure 2: The SK 500E line of frequency inverters is available in six sizes
Figure 3: Drive solutions for port cranes must provide excellent dynamics