Preventive maintenance for industrial drives and panels
Drives and control panels are the equipment people notice least and miss most. A motor makes noise when it is unhappy. A panel gives almost no warning until something stops. Preventive maintenance on this equipment is unglamorous, cheap relative to the consequences of neglect, and skipped more often than any other item on a maintenance schedule.
The components that age whether you use them or not
Three things in a drive deteriorate with time rather than with duty, which is why a spare drive sitting on a shelf is not necessarily a reliable spare.
Electrolytic capacitors in the direct current link degrade as electrolyte dries, and the process is driven by temperature. This is the most common age related failure in a drive and the reason thermal design matters so much, as set out in our note on heat loss and cooling inside a drive enclosure. A drive stored unpowered for years may need its capacitors reformed by applying voltage gradually before being put into service.
Cooling fans have bearings with a finite life, and a drive fan that has stopped turns a well cooled drive into a poorly cooled one silently. Fans are inexpensive, usually replaceable without removing the drive, and worth changing on a schedule rather than on failure.
Connections loosen. Thermal cycling, vibration and the slow relaxation of conductors under clamping pressure all mean that a terminal torqued correctly on commissioning may not be correct three years later. A loose connection increases resistance, generates heat, and accelerates its own deterioration until it fails or starts a fire.
What to do and how often
Monthly, by walking past
Listen for fans that have stopped or changed note. Look at indication and alarm status. Check that panel doors are closed and latched, because an open door is both a safety matter and a cooling matter, since ventilation designed for a sealed enclosure does not work with the door open.
Quarterly, depending on environment
Inspect filters and replace or clean them. In dusty environments this may need to be monthly. A blocked filter looks identical to a clean one from outside the panel and is the single most neglected item in industrial electrical maintenance.
Review logged data from drives and protection relays. Most report heatsink temperature, trip history, operating hours and current, and a trend toward the overtemperature threshold is visible long before the first trip. This is the cheapest condition monitoring available and it requires no additional hardware.
Annually, with the equipment isolated
Clean dust from heatsinks and internal surfaces, using vacuum extraction rather than compressed air, which merely relocates dust into places it was not previously. Check terminal tightness to the specified torque on power connections. Inspect gaskets and door seals. Verify that fans turn freely. Check that cable glands and blanking plugs are intact.
Thermographic inspection under load is worth the cost on anything substantial. An infrared survey of a panel in service finds loose connections, overloaded conductors and failing components without taking anything apart, and it finds them before they announce themselves. Where panels have inspection windows, this can be done without opening doors at all.
Every few years
Replace cooling fans on a time basis. Consider capacitor replacement or drive replacement as the equipment approaches the end of its expected service life, since planned replacement during a shutdown costs a fraction of unplanned replacement during production.
Records, spares and the things that make a repair fast
The difference between a thirty minute repair and a three day outage is usually information. Drive parameter sets should be backed up and stored where the maintenance team can find them, because a replacement drive with factory settings on a commissioned machine means recommissioning rather than swapping. Many drives support copying parameters to a memory module or a laptop, and doing so takes minutes.
Keep as built drawings inside the panel, updated when modifications are made. An out of date drawing is worse than none, because it is trusted.
Hold spares for what cannot wait. Fans, filters, control fuses and, for critical drives, a complete spare unit. Where the installation uses direct current machines, brush stock is essential and grades are not interchangeable, as noted in our piece on DC motor drives and where they still make sense.
Safety, which is not optional on this equipment
A drive’s direct current link holds charge after the supply is removed. Manufacturers state a discharge time, commonly several minutes, and that time must elapse and be verified before anyone touches the terminals. Isolation, lock off and proof of dead are the baseline, and on larger assemblies arc flash risk assessment determines what protective equipment is required.
Work involving open panels under load, such as thermography, is specialised and should be done by people trained and equipped for it. The safest panels are the ones designed so that routine inspection does not require exposure, which is one of the arguments in our note on what goes inside a motor control centre panel.
Frequently asked questions
Can compressed air be used to clean a panel?
It is best avoided, because it drives dust into components and connectors rather than removing it. Vacuum extraction is preferable.
Why do terminals need re torquing?
Thermal cycling, vibration and conductor relaxation reduce clamping pressure over time. A loose connection heats, which accelerates further deterioration.
Does a spare drive on a shelf stay usable?
Not indefinitely. Electrolytic capacitors degrade in storage, and a drive stored for a long period may need its capacitors reformed by gradual application of voltage before use.
How long after switching off is a drive safe to work on?
Only after the manufacturer’s stated discharge time has elapsed and the absence of voltage has been verified. The direct current link retains charge after the supply is removed.
Is thermographic inspection worth the cost?
On any substantial installation, generally yes. It identifies loose connections and overloaded components under load without dismantling anything, well before failure.