Steps To Prevent Faults Attributed To VFD
What is a VFD?
VFD is an acronym for Variable Frequency Drive. A Variable Frequency Drive is a motor controller that drives an electric current by alternating the frequency of the voltage supplied to that motor. VFD helps machines improve tasks in automated plants and industries. This device helps optimize performance and lower machinery lifecycle costs, it supports a wide range of machine types and robotics in automation processes and industrial plants.
Although VFDs are very helpful in the automation industry, they are not immune to developing faults. These faults can reduce machine efficiency and could also escalate into costly downtime.
In order to avoid downtime, steps must be taken to prevent these faults from setting in or quickly address them when they do.
Here are some steps required to prevent faults and failures in a Variable Frequency Drive:
PROPERLY DERATE VFDs
The first step to take in preventing faults in a VFD is to right-size the device. Single-phase input voltage on a VFD with a 3-phase input is common in many automatic applications.
For proper drive sizing, the output current should be derated by 50%. For instance, a drive rated 10hp and has an output of 29A will be derated to produce an out output of 14.5A but the rating remains the same.
WIRING AND FILTER PROTECTION
A VFD generates a plus-width modulate output waveform containing high-frequency components including Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI). Cable lengths exceeding 33ft can pick up noise, stray capacitive effects, and have resistive voltage drops. It is important not to exceed the maximum length recommended for the cable. Always check your device manual for recommendations.
COMMON FAULT PARAMETERS
A VFD will generate low-voltage faults when the voltage drops below set parameters. A VFD may record low-volts fault when the drive DC link voltage drops below 62% of the nominal level for the high setting (480V ac) and 50% of the nominal for the low setting.
VFDs are equipped with surge guards in the input rectifier circuit. Additional safeguards against voltage swings such as surge arrestors and other external protection can prevent severe input disturbances. Ignoring the guidelines can blow the input fuses, trip the breaker or even damage the charge relay circuit.
A voltage monitor with time delay can provide protection trip levels to shut down the drive in the event of under-voltage, over-voltage, loss of phase and voltage imbalance between phases.
DEPLOYING ISOLATION TRANSFORMER
A Drive Isolation Transformer can isolate grounding and noise related input power problems that can potentially affect drive performance and operation. A drive Isolation Transformer between the VFD and the power source offers several benefits by ensuring that no direct electrical connection exists between the source and the load. The placement of grounded electrostatic shielding between and around the primary and secondary windings makes a Drive Isolation Transformer unique. This provides up to a million-fold decrease in the capacitive coupling involved in transferring common-mode voltage disturbances.
