A VFD (variable frequency drive) controls the speed, torque and direction of an induction motor. A VFD takes fixed motor voltage and AC frequency and converts it to a variable voltage and frequency AC output. In very small VFDs, a single power pack unit may contain the converter and inverter modules. Preventive maintenance VFD programs preventmanufacturing downtime while maintaining optimal production performance.
Clean Environment– Preventive Maintenance VFD:
Most VFDs fall into the NEMA 1 category or NEMA 12 category. Drives that fall in the NEMA 1 category are susceptible to dust contamination. Dust on VFD hardware can cause a lack of airflow resulting in diminished performance from heat sink and circulating fans. Dust on an electronic device can cause malfunction or even failure. Dust absorbs moisture, which also contributes to failure. Periodically spraying air through the heat sink fan is a good PM measure. Discharging compressed air into a VFD is a viable option in some environments, but typical plant air contains oil and water. To use compressed air for cooling, you must use air that is oil-free and dry or you are likely to do more harm than good. A non-static generating spray or a reverse-operated ESD vacuum will reduce static build-up. Common plastics are prime generators of static electricity. The material in ESD vacuum cases and fans is a special, non-static generating plastic. These vacuums, and cans of non-static generating compressed air, are available through companies that specialize in static control equipment.
Control boards and other electronic components can be damaged when subjected to periodic moisture or water. Some VFD manufacturers include a type of condensation protection on certain product versions. If you operate a VFD all day every day, the normal radiant heat from the heat sink should prevent condensation. Unless the unit is in continuous operation, use a NEMA 12 enclosure and thermostatically controlled space heater where condensation is likely.
Keep Connections Tight – Preventive Maintenance VFD:
Checking connections is a step many people miss or do incorrectly, and the requirement applies even in clean rooms. Heat cycles and mechanical vibration can lead to sub-standard connections, as can standard PM practices. Reusing torque screws is not a good Idea, and further tightening an already tight connection can ruin the connection.
Bad connections eventually lead to arcing. Arcing at the VFD input could result in nuisance over voltage faults, clearing of input fuses, or damage to protective components. Arcing at the VFD output could result in over-current faults or even damage to the power components.
Loose connections can cause erratic operation. For example, a loose START/STOP signal wire can cause uncontrollable VFD starting and stopping. A loose speed reference wire can cause the drive speed to fluctuate, resulting in scrap, machine damage, or personnel injury.
Additional Considerations – Preventive Maintenance VFD:
- As part of a mechanical inspection procedure, don’t overlook internal VFD components.
- Check circulating fans for signs of bearing failure or foreign objects.
- Store spare VFDs in a clean, dry environment, with no condensation allowed.
- Power spare VFD’s every 6 months to keep the DC bus capacitors at their peak performance capability.
- Regularly monitor heat sink temperatures.
- Inspect DC bus capacitors for bulging and leakage. Either could be a sign of component stress or electrical misuse.
You wouldn’t place alaptop computer on the roof of a building or in direct sunlight, where temperatures could reach 115 degrees Fahrenheit or as low as -10 degrees Fahrenheit. A VFD, which is basically a computer with a power supply, needs the same consideration. Some VFD manufacturers advertise 200,000 hours-almost 23 years-of Mean Time between Failures (MTBF). Such impressive performance is easy to obtain, if you follow these simple procedures.
By integrating a preventive maintenance VFD program, you can ensure your drives provide minimal repair service while maximizing production.Always call certified variable frequency drive integrators or experienced technicians to perform preventive maintenance VFD services to prevent injury or death.
To learn more about preventive maintenance VFD programs or for VFD repair and replacement quotes, contact Precision Electric.