FEATURE Drives, Controls & Motorsy
Effi cient motors for effi cient plants Marek Lukaszczyk of motor and drive manufacturer WEG discusses ways to improve motor energy efficiency
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any electric motors in use are either low effi ciency or not properly sized for the application, resulting
in motors working harder, and hence using more energy. Similarly, older motors may have been rewound a few times during maintenance, lessening their effi ciency. In fact, it is estimated a motor loses 1-2% effi ciency every time it is rewound. Because energy consumption accounts for 96% of the total life-cycle cost of a motor, paying extra for a premium- effi ciency motor will result in return on investment over its lifespan. However, 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-defi ned schedule ensures the motor exchange is carried out quickly and with minimal downtime. Opting for industry standard footprints streamlines the process.
Obviously, if there are 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 fi rst, and plan a schedule of replacements over two to three years to avoid signifi cant downtime.
Motor performance sensors To keep motors running optimally, plant managers can install retrofi t sensors. With important metrics such as vibration and temperature monitored in real time, built- in predictive maintenance analytics will identify future problems. With sensor-based applications, such as WEG Motor Scan, motor data is extracted and sent to a smartphone or tablet. One manufacturing plant in Brazil implemented this technology on motors driving four identical air-recirculating machines. When alert popped up that one had higher than permitted vibration levels, the heightened vigilance enabled the company to solve the problem; otherwise, this could have led to factory shutdown. 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 stiff ness are crucial to reduced
20 October 2020 | Automation
A slower start uses less energy and results in less mechanical stress on the motor and shaft
vibrations. By resolving the non-optimal performance rapidly, this wasted energy was kept to a minimum. Secondly, by preventing a full factory shutdown, the higher energy requirements to restart all machines was not required.
Install soft starters
For machines and motors that don’t 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. 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 Sometimes referred to as a variable frequency drive (VFD) or inverter drive, a variable speed drive (VSD) adjusts the speed of an electric motor, as required. Without this control, the system simply brakes when less force is needed, expelling the wasted energy as heat. In a fan application, for instance, VSDs reduce airfl ow as per requirements, rather than simply cutting it off whilst at maximum capacity. Combine a VSD with a super-premium
effi ciency 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, when properly sized, provides an energy cost reduction up to 80% and average water savings of 22%. While the current regulation states that
IE2 motors must be used with a VSD, this has been diffi cult to enforce. This explains why the regulations are becoming stricter. As of July 1, 2021, three-phase motors will need to meet IE3 standards, regardless of any VSD additions. These changes are also holding VSDs to higher standards, assigning this product group IE ratings, too. They will be expected to meet an IE2 standard, although an IE2 drive does not represent the equivalent effi ciency of an IE2 motor — these are separate rating systems.
Make full use of VSDs Many VSDs are packed with useful features that plant managers don’t know exist. Pump applications are a good example. Fluid handling can be turbulent; between leakages and low fl uid levels, there’s a lot that can go wrong. Built-in control, such as Pump Genius in WEG VSDs, enables more eff ective use of motors based on production demands and fl uid availability. Automatic broken-pipe detection in the VSD can identify fl uid leakage zones and adjusts motor performance accordingly. Additionally, dry-pump detection means if fl uid runs out, the motor is automatically deactivated and a ‘dry pump’ alert issued. In both cases, the motor reduces its energy consumption when less energy is required to handle available resources.
If using multiple motors in the pump application, jockey pump control can also optimise the use of diff erent sized motors. It may be that demand requires just a small motor to run, or a combination of a small and large motor. Pump Genius gives increased fl exibility to use the optimal sized motor for a given fl ow rate. VSDs can even perform automatic cleaning of the motor impeller, to ensure deragging is carried out consistently. This keeps the motor in optimal condition, which has positive eff ects on energy effi ciency. If you’re not happy to pay 30 times the motor price in energy bills over a decade, it’s time to make some of these changes. They won’t happen overnight, but a strategic plan that targets your most ineffi cient pain points will result in signifi cant energy effi ciency.
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