Variable Frequency Drives (VFDs) and Programmable Logic Controllers (PLCs) are the technological pillars that support modern industries. Alongside controlling the motor speed, they are responsible for the critical process control, accuracy, and consistency of production. Despite their daunting design and functionalities, VFDs and PLCs share one vulnerabilityyou guessed it, the most ignored factor.
Just a tiny turbulence in the system, for instance, a voltage sag, surge, harmonics, or electrical noise, is enough to disturb the performance of VFDs and PLCs. They usually start as a barely visible phenomenon, eventually, they contribute to abnormal system behavior, unplanned stoppages, system breakdowns, and to downtime that is both costly and frustrating. At times, a manufacturer may replace the sensors, motors, and PLCs without knowing that the real culprit behind such problems is poor power quality.
This blog will first discuss how power quality issues can be detected in advance. Then it explains how these issues affect VFDs/PLCs and finally, how you may respond to such problems. If you wish for your automation equipment to be free of any breakdowns, then you must understand this aspect.
Common Power Quality Issues That Affect VFDs and PLCs:
Power quality greatly impacts the reliability of VFDs and the operational effectiveness of PLCs. VFDs and PLCs require clean, stable electrical input without any noise. When the power quality drops, even by a small amount, VFDs and PLCs will operate abnormally and in fact, they will issue faults, along with gradually damaging themselves.
Below are the main power quality issues that lead to VFD and PLC damage and their effects.
1. Voltage Sags and Dips:
A temporary reduction in voltage that is shorter than normal and lasts only a few moments.
Impact on VFDs:
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Under-voltage trips
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DC bus undervoltage
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Motor torque loss
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Drive shutdown during acceleration
Impact on PLCs:
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Unexpected reboots
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Loss of program execution
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Input/output modules malfunction
Voltage dips are among the most frequent reasons for PLC restarts and production line stoppages.
2. Voltage Surges and Spikes:
A voltage rise is seen for a very short time (a few milliseconds).
Impact on the VFDs:
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IGBT failure
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Blown input rectifier
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Overvoltage fault codes
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Damage to control boards
Impact on PLCs:
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Burnt power modules
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Power supply failure
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Memory corruption
3. Harmonic Distortion:
Distortion of the standard sinusoidal waveform.
Impact on the VFDs:
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Excessive heating
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Nuisance overcurrent trips
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Transformer and cable overheating
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Reduced drive efficiency
Impact on PLCs:
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Power supply noise
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Unstable I/O readings
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Control module heating
4. Electrical Noise (EMI/RFI):
Unwanted electromagnetic or radio frequency interference that degrades the signal.
Impact on the VFDs:
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Erratic motor speed
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Encoder misreadings
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Random fault trips
Impact on PLCs:
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Analog signal fluctuations
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False triggering of digital inputs
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Loss of communication (Ethernet/RS485/Profibus)
5. Phase Imbalance:
This is a situation where voltage or current magnitude differs between the three phases.
Impact on VFDs:
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Increased current in one phase
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Reduced torque and efficiency
Impact on PLCs:
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Overheated power supply
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Reduced lifespan of components
6. Poor Grounding and Bonding:
Physically weak, corroded, or improperly done grounds leading to an unstable electrical reference.
Impact on VFDs:
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Nuisance tripping
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Overcurrent & ground fault alarms
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Noise entering control circuits
Impact on PLCs:
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Communication dropouts
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HMI freezing
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Erratic I/O behavior
7. Transients and Switching Disturbances:
Fast, energetic voltage pulses that occur as a result of switching.
Impact on VFDs:
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DC bus overvoltage
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Damaged input bridge
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Sudden drive shutdown
Impact on PLCs:
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Power supply resets
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Corrupted memory
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Unpredictable logic execution
How to Identify Power Quality Problems That Affect VFDs and PLCs
- Watch for Frequent VFD or PLC Fault Codes
- Check for Excessive Heating in VFDs, PLCs, and Motors
- Monitor Voltage Fluctuations in Real Time
- Inspect Analog Signal Instability
- Look for Communication Dropouts
- Perform Power Harmonic Analysis
- Inspect Grounding and Shielding Quality Physically
- Analyze Event Logs and Historical Trends
- Use Thermal Imaging to Detect Hidden Issues
Ironically, power quality is often overlooked. In fact, it is one of the factors that contribute the most to the reliability and lifespan of VFDs and PLCs. These units may be made with high precision and robustness, but even the slightest signal: voltage sag, surge, distortion, noise, imbalance, and/or grounding error, may cause them to fail and get into an unstable condition. A minimal signal that leads to unstable condition may soon trigger recurring warnings and production downtimes.
The knowledge of recognizing early signs is the secret to sudden failures avoidance. Maintenance personnel would have to monitor voltage characteristics, detect abnormal heating, check communication signal stability, and perform harmonic and grounding tests to locate problems before they impact operations.
Power quality is a matter of electrical engineering that directly influences production reliability. If the power supply to your automated system is clean, stable, and properly grounded, your VFDs and PLCs will operate correctly, accurately, and predictably. An effort to analyze and remedy power problems in your system today is a complete protection environment that is not only more efficient but much less prone to catastrophic failures.
