32 n MOTORS May 2023 www.drivesncontrols.com Protect your machinery by monitoring motor loads There are a variety of issues that can cause inefficiencies and defects in production processes. Equipment failures, set-ups and adjustments, idling, minor stops, running at reduced speeds, and process defects can all affect yield and increase costs. One way to avoid such issues is to protect motor-driven machines effectively. These machines are often critical components in manufacturing processes and can be expensive to replace if they fail. It is essential to take steps to protect them against damage. There are several ways to do this, including installing overload protection devices, ensuring effective lubrication and maintenance, and monitoring the machines for signs of wear or damage. By taking such precautions, manufacturers can help to ensure the reliability and longevity of their equipment and to minimise the risks of process defects and reduced yields. Continuing to operate motor-driven machines during abnormal conditions caused by jams or blockages can cause irreparable damage, not only to the motor but also to the machinery. In the past, the extent of damage to machines has been understated compared to the damage to the motor. Overload systems, and motor management and control devices, can protect motors, but what is protecting the machine itself? In pump installations for example, when there’s suction loss or a jam long before the thermal overloads trip, serious damage can be done to the machine as well as the motor. Any abnormal operating conditions can have a detrimental effect on the life of the system. Dry pump, dead head, jammed impellers and even premature bearing wear can all lead to motor and pump failures. To cut upfront costs, motordriven systems are often installed without any means to monitor their operation. As a result, frequent inspections of the motor and the machine are necessary. If an unexpected failure occurs, it can mean irreparable damage to a machine and possibly its motor. But such issues can be eliminated by using simple, but effective, monitoring and control techniques. Adding a small cost to the installation will pay for itself several times over the first time a fault is detected and damage to the machine or motor is avoided. Imbalances To analyse a motor’s health, you need to consider all aspects that can affect it under normal operational conditions. Incoming power quality is one area that is often overlooked – correct, safe operation of motors depends on the power conditions. As voltage levels vary during the day there can be imbalances. Raising voltage levels to reduce the current and achieve a motor’s nameplate ratings can cause excessive heat, degrading the insulation. Harmonic distortion also affects the power quality, much of which is caused by variable-speed drives (VSDs) and other nearby installations that go undetected most of the time. Typically, a motor will draw six to ten times its rated current levels during start-up. Hot starts are more detrimental to the windings, Technologies such as overload devices, and motor management and control systems, can protect motors effectively, but may not safeguard the machinery that they are driving. Amir Sami, business development manager at Charter Controls, looks at how to prevent costly damage and downtime to machinery by monitoring the power consumed by the motor. By measuring when power exceeds a 5% threshold, a start-up surge timer can be used to mask when a motor’s start in-rush current begins. Unipower’s HPL500 digital power monitor is triggered in this way, rather than by power on, and can be connected before or after the motor contactor. The graph shows the protection logic. Digital load monitors with an analogue load transducer. Such devices can help to protect motor-driven machinery from damage.
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