October 2020

30 | Plant & Works Engineering www.pwemag.co.uk October 2020 Energy, the Environment & Water Focus on: Drives, Motors & Controls M any electric motors in use are either low efficiency or not properly sized for the application. Both issues result in motors working harder than they need to, using more energy in the process. Similarly, older motors may have been rewound a few times during maintenance, lessening their efficiency. In fact, it is estimated a motor loses one to two percent efficiency every time it is rewound. Because energy consumption accounts for 96 per cent of the total life cycle cost of a motor, paying extra for a premium efficiency motor will result in return on investment over its lifespan. But if the motor is working, and has been working for decades, is it worth the hassle of upgrading it? With the right motor supplier, the upgrade process isn’t disruptive. A pre-defined schedule ensures the motor exchange is carried out quickly and with minimal downtime. Opting for industry standard footprints helps to streamline this process, as factory layout will not need altering. Obviously, if you have hundreds of motors in your facility, it’s not feasible to replace them in one go. Target the motors that have been subjected to rewinds first and plan a schedule of replacements over two to three years to avoid significant downtime. Motor performance sensors To keep motors running optimally, plant managers can install retrofit sensors. With important metrics such as vibration and temperature monitored in real-time, built in predictive maintenance analytics will identify future problems ahead of failure. With sensor-based applications motor data is extracted and sent to a smartphone or tablet. Over in Brazil, one manufacturing plant implemented this technology on motors driving four identical air recirculating machines. When the maintenance team received an alert that one had higher vibration levels than the acceptable threshold, their heightened vigilance enabled them to solve the problem. Without this insight, unexpected factory shutdown could have arisen. But where are the energy savings in the aforementioned scenario? Firstly, increased vibration is increased energy usage. Solid integrated feet on a motor and good mechanical stiffness is crucial to guarantee less vibration. By resolving the non-optimal performance rapidly, this wasted energy was kept to a minimum. Secondly, by preventing a full factory shut down, the higher energy requirements to restart all machines was not required. Install soft starters For machines and motors that do not run continuously, plant managers should install soft starters. These devices temporarily reduce the load and torque in the power train and the electric current surge of the motor during start-up. Think of this as being at a red traffic light. While you could slam your foot down on the gas pedal when the light turns green, you know this is an inefficient and mechanically stressful way to drive — as well as dangerous. Similarly, for machine equipment, a slower start uses less energy and results in less mechanical stress on the motor and shaft. Over the lifespan of the motor, a soft starter provides cost savings attributed to reduced energy costs. Some soft starters also have built in automatic energy optimising. Ideal for compressor applications, the soft starter judges the load requirements and adjusts accordingly to keep energy expenditure to a minimum. Use a variable speed drive (VSD) Sometimes referred to as a variable frequency drive (VFD) or inverter drive, VSDs adjust the speed of an electric motor, based on the application requirements. Without this control, the system simply brakes when less force is required, expelling the wasted energy as heat. In a fan application for instance, VSDs reduce the airflow as per requirements, rather than simply cutting off the airflow while remaining at maximum capacity. Combine a VSD with a super-premium efficiency motor and the reduced energy costs will speak for themselves. In cooling tower applications for example, using a W22 IE4 super premium motor with a CFW701 HVAC VSD, The energy cost to run an electric motor over ten years is at least 30 times the original purchase price. With energy consumption responsible for the vast majority of whole life costs, Marek Lukaszczyk of motor and drive manufacturer, WEG, explains five ways to improve motor energy efficiency. Thankfully, changes in a plant do not have to be huge to reap savings. Many of these changes will work with your existing footprint and equipment. Five small changes to boost plant efficiency