Condition Monitoring (CM) has long been used to improve plant performance and reduce costs, by helping to diagnose faults and optimise maintenance schedules. There is a well-understood kit of CM tools and techniques, of which the leading method is vibration analysis, with thermography, ultrasound, oil analysis, motion amplification and others also widely used. No single tool provides a universal solution to every situation. Like any kit of tools, the skilled practitioner understands the capabilities of each, and selects the most appropriate tool, or combination of tools, for the task in hand.
Nowadays, with the increasing emphasis on sustainability and reducing carbon footprint, there is a new generation of condition monitoring solutions that also provide energy monitoring and energy optimisation capabilities, based on electrical measurements to give information on electrical, mechanical and operational problems all in one go.
What Is MBVI?
MBVI stands for Model-Based Voltage and Current. The acronym uses I rather than C because I is the standard engineering symbol for electric current.
MBVI is a powerful condition monitoring and diagnostic technique for equipment driven by electric motors. It uses the motor itself as a sensor, measuring the voltage and current drawn at the motor starter cabinet to identify a wide range of faults in both the motor and the driven equipment, covering mechanical, operational, and electrical domains.
Because all connections are made in the switchgear, which is almost always in a clean, dry, non-flammable area, MBVI systems avoid the need for expensive ATEX-rated sensors. There is no need to fit accelerometers to each bearing, run sensor cabling to rotating equipment, or access machinery during operation.
MBVI systems can be supplied as a portable kit for quick assessments, or as permanently installed hardware for continuous 24/7 monitoring.
How MBVI Works
Most engineers know that a motor draws more current under higher load and less under lower load, even when supply voltage is constant. What is less widely appreciated is that this current variation applies not just to major load changes, such as a pump discharge valve opening, but also to smaller, faster phenomena occurring several times per shaft rotation, including rolling element bearing defects.
MBVI systems build a mathematical model of the relationship between the voltage and current waveforms. This model is used to identify distortions on the current waveform that have not been caused by distortions on the voltage waveform, and which therefore must have been caused by the behaviour of the motor and driven equipment.
This residual current signal is directly equivalent to a raw vibration signal, and can be analysed in the same way, examining the magnitude and frequency of distortions to identify underlying fault causes and their severity.
This approach also blends the benefits of established electrical techniques such as Motor Current Signature Analysis (MCSA) with the fault-detection capabilities more associated with vibration analysis, giving broader coverage than either technique alone.
What Faults Can MBVI Detect?
MBVI systems provide useful diagnostic information across a wider range of fault types than vibration monitoring alone:
Mechanical faults
- Rolling element bearing deterioration
- Belt drive problems
- Mechanical looseness and rubbing
- Shaft and coupling stress
Electrical faults
- Motor rotor bar damage
- Stator winding problems
- Phase imbalance
- High harmonic distortion
Operational and energy issues
- Energy efficiency assessment
- Quantification of energy wasted by developing faults
- Total Harmonic Distortion on voltage and current
- Power factor and phase angle
The system automatically compensates for variations in load and speed, and makes automated allowances for distorted waveforms present with inverter-driven equipment.
MBVI analysis shares several principles with electrical signature analysis (ESA), a closely related technique for detecting motor and drivetrain faults through electrical measurements.
Why Electrical Measurements Catch Faults Vibration Misses
Several electrical parameters have direct implications for mechanical reliability that are not visible to vibration sensors.
Phase imbalance on a three-phase supply, where not all phases carry the same amplitude, creates a twice-per-cycle oscillation in motor torque. This puts additional stress on shafts and couplings that vibration analysis would attribute to imbalance or misalignment without identifying the electrical root cause.
Harmonic distortion represents current flowing in and out of the motor but not doing effective work in turning the shaft. This creates additional heating in the motor windings. A widely used rule of thumb in motor reliability is that a 10°C rise in winding temperature halves the operational life of the insulation.
MBVI identifies both the fault and its energy cost, displaying the proportion of total energy consumption attributable to each fault detected. This allows cost-justified decisions on corrective action.
MBVI vs MCSA: What Is the Difference?
Motor Current Signature Analysis (MCSA) is an established electrical technique that analyses current signatures to identify specific motor faults. MBVI extends this in two important ways.
First, MBVI models the relationship between voltage and current together, rather than analysing current alone. This allows it to separate distortions caused by supply quality from distortions caused by the machine itself, significantly reducing false positives in environments with noisy or distorted supply waveforms.
Second, MBVI incorporates energy monitoring and efficiency assessment alongside fault detection, providing information that MCSA does not.
Faraday Predictive MBVI Solutions
Faraday Predictive supplies MBVI systems in both portable and permanently installed forms.
P100 Portable Equipment Health Assessor: The P100 connects temporarily at the motor starter to deliver a rapid condition assessment. It is well suited to periodic surveys across a fleet of assets, or for building familiarity with the technology before committing to permanent installation.
Inpod Condition and Energy Monitoring System: For 24/7 continuous monitoring, the Inpod is designed for permanent installation inside the motor starter cabinet. It provides ongoing condition trending, fault progression forecasting up to three months ahead, and automated maintenance planning outputs.
Both systems provide:
- Current and predicted condition at overall equipment level
- Current and predicted status of individual fault types
- Fault descriptions, detection rationale, impact assessment, and recommended corrective action
- Detailed electrical parameters including power factor, active and reactive power, phase imbalance, and THD on both voltage and current
Faraday Predictive also offers an on-site assessment and diagnostic survey service, which provides a fleet health report across several items of equipment and allows you to evaluate the depth of information available before committing to a full monitoring programme.
What to do next
If you are interested in applying MBVI condition monitoring to your plant, call us on 0333 772 0748 or email info@faradaypredictive.com.
To build your business case for investment, use our predictive maintenance benefits calculator.
To learn more about our condition monitoring systems, visit the Faraday Predictive homepage.
For a deeper technical reference, download the MBVI systems white paper.