Case Study
Invertek Drives gives South African power station a boost
Problem
Cranes used for moving turbines at a power station needed to be controlled more accurately and precisely.
Solution
The retrofitting of Optidrive P2 variable frequency drives into the process allows the cranes to be operated at different speeds, even when single speed motors are fitted, and minimises maintenance costs by eliminating shock loading. The drives can also be used to prevent load swinging during start up and stopping.
Morris Cranes
The Optidrive P2 delivers 100 per cent torque at 0.0Hz allowing this unique open loop drive to be used without any feedback device in traditional closed loop applications. The latest success story from South Africa concerns the complete retrofit of two 100 and 25 tonnes turbine cranes for Grootvlei power station, where the main hoist has a maximum lifting capacity of 100 tonnes and the auxiliary hoist has a maximum lifting capacity of 25 tonnes. Morris Cranes undertook the project with Invertek Drives providing the VFD technology.
The project required an upgrade of every crane in the power station so that all the motion elements, including main hoist, auxiliary hoist, cross travel and long travel, would be controlled through VFDs. Introducing the Optidrive P2 allows the cranes to be operated at different speeds, even when single speed motors are fitted, and minimises maintenance costs by eliminating shock loading. The drives can also be used to prevent load swinging during start up and stopping.
With a gantry length of approximately 400 metres, a span of 30 metres and a lifting height of 40 metres, these cranes provide an ideal application for variable speed drives.
Used to maintain the steam turbines within the power station, the running speeds of these cranes was previously very low. With an Optidrive P2 fitted the crane operators were given a choice of three different speeds and they had greater confidence in being able to move the extremely valuable cargos with a greater degree of control
By far the most challenging part of the project however was using the Optidrive P2 to maintain total control throughout a 105 ton load test over a lifting distance of 40 metres. The most impressive part being able to demonstrate the 100 per cent torque from zero speed without an encoder.
An Invertek Drives spokesperson said: "Being able to offer 100 per cent torque from zero without the use of an encoder is most certainly a major benefit for hoisting applications and we have shown that the results that can be achieved with this drive are truly amazing."
