In terminals all over the world, old cranes are the main reason for standstill and high service cost. Additionally, the energy costs for these cranes are much higher than necessary because of inefficient motors. More and more terminal operators are recognizing this and would ideally like to exchange the cranes. However, the cost to replace them with a new crane, is often too high. Based on this, the operators modify the existing cranes and build new, modern and efficient equipment into the old cranes. This allows a higher number of containers to be handled, minimizes standstill time, and lowers energy costs.
Efficiently upgrading existing cranes
A lot of existing cranes are equipped with old technology, like DC-technique or AC-slipring-technique. These motors have very high maintenance costs, however, if they could be equipped with modern technology such as the AC-inverter-technique, it would not only be necessary to exchange the whole electrical part of the crane, as the mechanical part would also have to be modified, as the mounting dimensions of the new electrical motors differ from the ones of the existing motors. Franz Wölfer Elektromaschinenfabrik Osnabrück GmbH has a solution for this. The company develops and manufactures custom-built three-phase asynchronous squirrel cage and slipring motors with a power range of 2.0 kilowatts to 2.2 kilowatts. These motors are used in all types of cranes throughout the hoisting equipment and marine sector. If a crane is to be modified, Wölfer designs an electrical motor which is optimized in design relating to moment of inertia, weight, pull-out torque and efficiency. The company calculates the required power and duty cycle based on the crane specification, which is given from the terminal operator. By this, the size of the motors can be optimized and therefore also the moment of inertia. This minimized moment of inertia reduces the energy demand of the motor and therefore the energy cost for the terminal during operation.
Customized designs save energy, time and money
In addition to this reduction of energy cost, the total cost for the retrofit can be reduced as Wölfer is also flexible concerning the mechanical mounting dimensions. For example, if a new AC-squirrel-cage-motor can be delivered in frame size 315, but the existing motor with the old technology is frame size 400, normally the whole machinery house would have to be modified, as the motor feet as well as the shaft height and shaft dimensions are different. Also, a new coupling would have to be used and the motor basement retrofitted. However, with a motor from Wölfer, this is not necessary. The company offers a motor with the electrical data of frame size 315 with minimized inertia and reduced energy cost, but with the identical mechanical mounting dimensions of the old motor – in this example, frame size 400. This is achieved by creating a customized steel welded housing. The change of the motors can be done in one day with this customized solution. When the whole machinery house has to be modified, it can take up to a week to exchange the motors. So the modification work can be done much more quickly with, meaning that the cost of the downtime of the crane is lower. Recent retrofit work includes supplying new motors for a mid-life upgrade of a Morris crane at the Port of Felixstowe. GE Energy's Power Conversion business units were awarded the contract for this job which included replacing the old DC main hoist with a new full AC system. Wölfer supplied new hoist motors for the project, which was completed in March 2012.
Smaller inner-cooled options
This customized design is available in inner-cooled design, which means degree of protection to international standard IP23, as well as in outer-cooled design, for example IP56. If a Rubber Tyred Gantry (RTG) crane is to be modified with an outside mounted motor, Wölfer delivers the relevant exchange motor. Or for a Ship to Shore (STS) crane, where the motor is mounted in the machinery house Wölfer offers an IP23-solution, that means an inner-cooled motor, where the cooling air is directly blown into the motor, where the heat occurs. The heat is blown out of the motor much faster with an IP23-motor. It delivers up to 80 percent more power in the same frame size compared to IP56- motors from other brands. So Wölfer can offer a smaller STS hoist-inner-cooled motor than other companies.
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