Artesis’ unique patented technology utilizes model-based voltage and current system approach to detect wide range of faults on electric motors. This model-based approach works on the principle that the current drawn by an electric motor is affected by not only the applied voltage but also the behaviour of both the motor and the driven equipment. It identifies the distortions of the current waveform that have not been caused by distortions on the voltage waveform and therefore must have been caused by the behaviour of the motor and driven equipment system. The frequency of these distortions indicates the nature of the cause, and the magnitude of the distortions indicates the severity of the cause.
How does Model-Based Voltage and Current system analysis compare with VA?
Compared to Vibration Analysis, Artesis technology is more sensitive to torsional phenomena, whereas Vibration systems are more sensitive to radial phenomena. Model-based system can detect a wide range of mechanical phenomena inside the motor and driven equipment, not only related to bearings but also to common issues such as misalignment and unbalance. It also detects a range of electrical problems such as broken rotor bars and loose motor windings.
Model-based voltage and current analysis measure a range of electrical parameters such as Total Harmonic Distortion (THD), Voltage Imbalance and Current Imbalance that can themselves contribute to longer term mechanical as well as electrical problems. These parameters can also give rise to vibration signals, that can sometimes be misinterpreted by Vibration Analysis as mechanical faults such as bearing problems. Because these electrical parameters are being directly measured by Artesis technology such false diagnosis can be avoided.
As with Vibration Monitoring, the signals identified by model-based system approach increase when the equipment is working under greater load. Just using the increased vibration levels only, one might falsely conclude that a problem was developing. Because model-based system measure Voltage and Current, they also calculate power, and use this load information to normalise readings to avoid such fase diagnoses.
MCSA (Motor Current Signature Analysis) is a well-established technique that relies on the same fundamental principle as Model-based voltage and current analysis, that the current drawn by a motor is affected by a number of factors, that each occur at specific, identifiable frequencies. MCSA is classically used for identifying rotor-bar problems in induction motors, a phenomenon that model-based system can also identify, with generally better resolution than MCSA.
However, model-based system is much more powerful than MCSA at identifying and diagnosing a wide range of phenomena. The key differences between Artesis technology and MCSA systems are:
MCSA performs a spectral analysis on the full motor current – which is dominated by the 50Hz or 60 Hz supply frequency; rotor bar faults are detected as the difference in height between the supply peak and pole dominant pass frequency, typically 60dB for a good condition motor falling to 30dB a very bad one.
- MCSA is generally based on Current only.
- MCSA often uses one phase only.
Model-Based Voltage and Current Analysis
Model-based approach analyses the “residual current” – the distortions on the current waveform that have not been caused by distortions on the voltage waveform. This eliminates the dominant supply frequency, and focuses on the signals that indicate the faults right across the spectrum.
- Model-based approach measures both voltage and current to remove distortions from current waveform that have been generated by distortions on the voltage waveform.
- Model-based system measures all three phases of current and all three phases of voltage.
- Model-based system is much more sensitive to a wide range of phenomena because its spectra is not dominated by the mains supply frequency peak.
- Distortions on the voltage supply would lead to MCSA identifying spurious faults Such distortions are quite common on many industrial electricity supplies, and can be enormous on inverter-driven equipment.
Issues that can be revealed by the unbalance between phases are invisible when only a single phase is measured.