Motors and drives are the literal driving force in plant operations. Controlling the operating speed for different products, motors, and drives is what keeps materials and work moving. These motors and drives are subjected to an array of stresses that over time lead to faults. These faults in turn become downtime – a double-whammy of increased cost and lost production. Mitigating downtime efficiently and avoiding it altogether are important cost-saving measures that process plants and manufacturing facilities have an opportunity to improve upon with minimal investment.
It’s important to understand that motor and drive faults originate for a variety of reasons: electromagnetic and thermal stress in motors from frequent high-current surges that result from cycling; mechanical and hydraulic stresses; and perhaps most significantly, heat. No matter the objective cause, symptoms of an impending fault almost always appear in advance – it’s simply a question of whether or not you’re paying attention.
So, how do you pay attention with minimal investment and without having to change workplace culture? First, work toward bringing all of your motors and drives into a centralized SCADA system if possible. A SCADA system can independently monitor the voltage and current of each drive. As the bearings begin to wear out, the current will increase – an indication of the motor working harder to maintain its given set point. Understanding load imbalance will allow you to accurately configure fault codes that identify signs of increased wear and automatically notify you of required maintenance before a system fault occurs.
A properly configured SCADA system can automatically rotate the lead and lag of motors and drives, reducing the overall stress on any one given motor and distributing it across many. Whether you opt to wear down your motors rapidly in succession or slowly and simultaneously is an organizational decision based on your process and one that will directly affect your planned and unplanned downtime.
Regardless of whether your motors and drives are connected to a SCADA system, load and line reactors are an excellent option for absorbing power disturbances that can damage or shut down drives as well as other electrical equipment on the same distribution circuit. Load and line reactors are great at reducing nuisance tripping and voltage distortion caused by harmonic current distortion that in turn leads to overheating and shorter operating life. Preventing unplanned downtime associated with motors and drives is also significantly improved by adhering to a routinized maintenance schedule. Inspecting, lubricating, and replacing bearings goes a long way toward preventing unplanned downtime.
The final, simplest, and perhaps most important method for avoiding unplanned downtime caused by motors and drives has to do with heat – specifically, avoiding it at all costs. Improperly ventilated drives housed in cabinets will cause the fastest and most preventable types of degradation that lead to immediate and permanent system damage. Cooling-fan failures in drive enclosures must be fixed immediately. Heat is enemy No. 1, and while most large drives and MCCs come prefabricated with fans and ventilation ducts integrated into a central control, simply checking their operation through routine maintenance is a stitch in time that can save you nine.
Active cooling (air conditioning) of drive enclosures or electrical rooms should be considered if heat-related trips are occuring during the hottest time of year.
Of course, all of the preventive maintenance in the world is unlikely to prevent all motor and drive failures and the unplanned outages resulting in downtime that will occur. How rapidly you recover from these will depend on your level of preparedness.
To operate a given motor connected to a drive, the drive must be configured to a set of parameters specific to that motor and process. These include values for your horsepower, ramp speeds, full load amperage, voltage, RPMs, and so on. These parameters are stored directly on the drive or in what is called a human interface module (HIM). HIMs exist in a variety of flavors (including basic and advanced), and over the years they have evolved to store parameters in a way that allows them to be downloaded and saved. Rapid recovery of a failed drive can be as simple as removing the HIM from the failed drive and replacing it in the new drive or restoring saved drive parameters to a new HIM. Your ability to recover rapidly from unplanned downtime that results from drive failure is only as guaranteed as the completeness of your understanding of your HIM parameters' storage capabilities or other backups of parameter information.
Not all HIMs are capable of storing parameters or loading them. Knowing the difference as well as which ones are equipped on your drives is crucial. If your drives have advanced HIMs, make sure your operators and maintenance staff know their capabilities and which motor/drive combinations work. A single drive is capable of controlling many different motors and how they’re configured. Maintenance of operations depends on ensuring that specifications remain up to date. If your drives are not equipped with advanced HIMs, having a comprehensive and current list of which parameters on your drives have been changed from default will at the very least allow you to manually reconfigure a replaced drive and get it back into operation. In some cases, drive parameters can be stored and downloaded via laptop computer or directly from a compatible programmable logic controller (PLC). As you can see, there are many ways to manage drive parameter programming. It's crucial to have a plan in place for your particular situation.
The correct number of parameters required for a given motor/drive combination may number only in the tens from a menu of 1,000 or more. Not knowing the correct parameters can render a drive useless until you are able to track down the OEM or the original programmer – an arduous and time-consuming exercise that can unnecessarily prolong unplanned downtime. Further, if your drives are network-facing, it’s important that you document network node addresses. This includes TCP/IP, Profibus or Modbus, CAN and others. Knowing the correct network address is critical to restoring functions of a network-controlled drive.
Operations and maintenance teams have a great understanding of how things are supposed to operate day to day, and they are the first ones tasked with avoiding unplanned downtime from motor and drive faults. Being mindful of the benefits of simple preventive maintenance, the importance of accurate records for reconfiguring motor/drive parameters, and the need to manage heat is a critical first step in helping prevent motor and drive faults.