mechanical inertia. Thanks to gravity, the higher the load, the more potential energy is stored, which can be transferred to regenerative power when lowering the load. Electricity consumption is reduced by the amount of regenerated power, which brings about a significant reduction in energy cost. With typical stacking heights
drastically increasing over the last three to five years from 10m to up to 60m, and with travel speeds of up to 200m per minute or even more, the benefits of regenerative drives are more relevant than ever. In a conventional drive with braking
resistor configuration within a stacker crane, kinetic and potential energy is dissipated as heat and is wasted. The more braking power there is, the more difficult it becomes to handle this waste heat – it may even necessitate the installation of a costly cooling system. In contrast, using a regenerative drive means that no external braking resistor is needed. This makes the drive installation simpler, with fewer wires and spare parts required. Plus, there is no need for extra cooling. Overall, this can reduce the installation footprint. Furthermore, by avoiding the dissipation of excess heat into the environment, operators can also lower the risk of food, beverages, and other temperature-sensitive products from being spoilt or damaged.
MITIGATING HARMONICS Another challenge facing warehouse operators is electrical harmonics. Harmonics are unwanted frequency effects or distortions that can occur in the electrical supply network, which can degrade the quality of the network and lead to degradation or damage to downstream power devices. This in turn can shorten the asset lifetime and increase maintenance costs. Harmonic current is injected to the
supply network from non-linear loads such as drives. System integrators often choose to oversize electrical equipment such as cables and transformers to compensate for the side effects, rather than address the root issue. This is not cost-effective. A more sensible alternative is to identify solutions that deliver low harmonic content and high system efficiency. Fortunately, active front-end regenerative drives offer ultra-low harmonic levels, reducing harmonic content by up to 97% compared to conventional drives.
This reduction in harmonics avoids the
need for excessive sizing of electrical equipment on the network. In addition, operators can enjoy higher total system efficiency compared to other solutions using additional harmonic filters. By minimising the need to upsize other equipment and with higher total efficiency, active front-end regenerative drives help to
reduce both the capital and the operational costs of the whole system. Active front-end regenerative
drives offer a very promising pathway towards high energy efficiency and high performance in stacker cranes. And with the unprecedented cost savings this technology delivers, it might well be the intralogistics industry’s best-kept secret.
Overhead Crane Material Handling Industry Supplement | November 2023 | xiii
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