辽宁科技大学本科生毕业论文 第12页Digital Drive Crane Hoist ConversionWhile working on the bridge of a crane, I remember feeling the intense heat of the speed reduction Resistors. I looked over the prints and tried to figure out how to reduce this energy loss. As I understood, heat is the product of energy lost (). I was new to crane maintenance in 1990 and, having an electrical/electronic background,Crane panel manufacturers desired a novel method of crane control that combines new technology with some of the oldest. The new crane panel resulted in lower costs, increased productivity and reduced wear on components, as well as energy savings.I believed new technology existed. Several of the newer devices needed alternating current input. SCRs, VFDs and PMWs were becoming common acronyms in newer plants. The possibility of upgrading our pre-existing 250 VDC distribution was cost-prohibitive, Various transistors could run DC, but not at the ampere demands we needed. With crane panel replacement under consideration, we challenged our panel suppliers to develop new crane control technologyDigital Hoist ConversionSeverstal North America Inc. is an integrated steel mill dating back to 1917, when Henry Ford built it to supply his Ford Motor Co. auto manufacturing enterprise. It was operated as Ford Steel Division urti11982, when it became Rouge Steel Co. In 2004, OAt Severstal Steel purchased the assets of Rouge Industries and Rouge Steel. Figure1.A digital drive controller was installed Figure2. Preliminary setup of DDC hoist panelon this 135-ton-capacity slab-handling craneThe market price for steel was flat in the early part of the new millennium, forcing departmental groups to look for cost-saving improvements. One improvement was the installation of a new type of digital electronic control panel in 2003. This panel represented the introduction of DC electronic crane control to Rouge Steel and the largest duplex crane hoist controller (dual 200-hp) of its type in North America. The original panels were built on a P&H 135-ton slab-handling crane having standard DC hoisting contactor controls. They were industrial and functional, designed to handle the loads of this crane in 1972. The loads are greater now with heavier slabs, runing the crane at maximum limits and higher production rates. This caused premature equipment failures and production down-time. With three aging cranes in this bay, maintenance costs were rising to new highs. Those involved in maintenance were finding that distributors and manufactures were downsizing or had gone out of business, making replacement parts costly or obsolete. The market drivers of today are forcing the change to newer technologiesFigure3. Digital panel installed on crane trolley deck Figure4.Prewired resistors reduced start-up timeA novel design approach was asked of the crane panel manufactures. They replied with a proposed partnership and an effort to add some of the newest technology to the oldest methods of crane controls. The result was high-current transistor switching with a 250 VDC input. The design was well-thought-out and included integrating the original motors, limits, switches and wiring. Now speeds are controlled by sending the motors only enough current to safely lift and lower the load. The motors are soft stopped (reverse plugged) before the brakes close. This saves wear on components, reduces costs and increases productivity. Without the need for reduction resistors, there is no energy wasted, maximizing the energy savings. The panel installation of the SY-4 crane was completed in 2003 and is still running. The results are smoother movements with little energy loss (heat).The new panels were designed for installation on the trolley deck, as opposed to the bridge deck. This aids in troubleshooting and reduces excessive wiring mainly at the weak point of the cable powertrack. This allowed the time and ability to perform all setup work during mini-downturns without disabling the original hoist. The original panel was left in place as a backup, as failures could not be predicted. To date, the fail-safe panel has not been required.The panels were pre-wired and pre-tested prior to crane installation, further reducing crane downtime. When the transfer day came, only the master switch, motors and limit leads needed to be rerouted to the new system. On-the-job tuning and monitoring were vital for the first couple of days. It was important to have crane operators involved for that “personal feel” and to obtain their buy-in to the project, to increase awareness and productivity. No-load and full-load current tests were run with great results.An aded benefit to this control is the electrical current savings. Without reductin resistors for speed points, and with the added benefit of power produced when regenerative lowering, this single crane installation saves more than 25000 in electricity