With all the focus on energy efficiency in manufacturing over the past decade and a half, it’s become common knowledge that motors are the devices responsible for most of the industry’s energy use. Now consider those motors being applied in one of the more energy intensive manufacturing industries—steel making—and you’re looking at some seriously intense energy consumption.
At theSiemensAutomation Summit 2014, Adam Spece, environmental and electrical leader atNucor Steel，分享了他最近在该公司的德克萨斯州Jewett设施的一速电动机和可变频率驱动器（VFD）取代两速电动机的经验。
Describing the legacy set-up at Nucor’s 45,000 gallon-per-minute, non-contact cooling tower, Spece explained that the two cells in the tower are used to cool water used in the steelmaking process. “Each cell has a 28-ft diameter, nine-blade fan attached to a right angle gear box and shaft,” he said. “These fans were driven by 250 hp motors with two-speed starters.”
The control program used to manage the legacy cooling tower system required 45 networks of logic to attain desired operations of cooling fans, Spece said. This made the system complex to program and difficult to troubleshoot, as fans shifted between slow and fast speeds based on temperature inputs. It also required a two-degree deadband to prevent excessive cycling and wear (ranging in two degree increments from 78 to 84 degrees between both motor fans being off and both running at fast speed.)
In March 2012, vibration testing indicated that one of the tower’s two motors was failing. “PdMAtesting confirmed the motor’s problem and we learned that we needed to replace the motor,” said Spece. In the search for a new motor, Spece said Nucor learned that buying a replacement two-speed motor not only had a long lead time, but that it would cost $6500 more than single-speed motor. This lead to the decision to opt for a single speed motor controlled by a VFD.
两个西门子250 hp Micromaster 440驱动器带有线路和负载反应堆的驱动器与电动机的旧两速启动器同一区域。“驱动器是从现有的电动机控制中心馈入的，” Spece指出，轴，变速箱，风扇和电线的电动机保持不变。他补充说，在冷却塔开始运行时，必须更改一些PLC编程才能以快速速度运行电动机。这种变化是必要的，因为在全速下启动电动机会产生高扭矩条件，可能会损害风扇，变速箱，轴和电动机。
Beyond the $6500 cost savings achieved through the purchase of a one-speed motor versus a two-speed motor, electrical cost savings are projected to be nearly $38,000 annually. “Electrical savings alone pays for cost of project in two years,” said Spece.
自2013年安装新电动机系统以来，Nucor的每吨钢的用水量也下降了500万加仑。自从熔融店开始运营以来，该公司现在的钢铁用水量最低。Spece补充说：“较少的用水意味着较少用于治疗化妆水的化学物质。”这也有助于更容易遵守环境法规作为零排放设施。
There have also been significant savings in maintenance costs and downtime due to better control of the cooling tower fans. According to Spece, Nucor spent nearly $44,000 in replacement and rebuilds in the two years prior to the new motor system installation. Since then, wear on components has been greatly reduced by slower ramping up and down. The company estimates it will save $11,000 a year on repairs.
