# Fault Detection in Active Magnetic Bearings Using Digital Twin Technology
## 3 Failures in AMB  
To effectively develop a reliable and safe AMB system for different purposes, it is imperative to have a comprehensive understanding of the potential failure mechanisms associated with AMBs. The failure of any component impacts the performance of an AMB. AMB faults must be found at the early stages of expression. There are three essential stages for dealing with faults:  
* Determining the fault's timing.
* Determining the component containing a defect.
* Finding the type of the fault.  
[PERSON], [PERSON], [PERSON], et al. [26] classified faults into multiplicative, bias, and noise addition. They explicitly classified faults in the sensors and actuators, as shown in Figure 5.  
Every failure has a degree of importance to the system's performance that depends on the cause. [PERSON], [PERSON] and [PERSON] [27] used the failure mode and effect analysis (FMEA) methodology to figure out the possible causes of failure for different passive magnetic bearing (PMB) configurations, as well as the resultant impacts of these failures on the overall performance of the bearings. The AMB often experiences problems in the electric systems represented by amplifiers and in the sensors, which are typically brought on by  
Figure 4: Magnetic flux density of the AMB.  
Figure 5: AMB fault types in the sensors and actuators [26].  
rising temperatures, wear and tear, or short circuits. A solid-state amplifier is typically utilized to supply power to each magnetic coil [28]. An amplifier is an important part of the AMB. The amplifiers are set up to operate in either voltage control or current control mode. Amplifier malfunctions can happen as a result of environmental factors, internal thermal effects, or high external load requirements [27]. All AMB systems fail due to the amplifier failures, causing no output power. Initially, a linear power amplifier was implemented in AMBs, but because linear power devices utilize a large amount of energy, they have been replaced with switching power amplifiers (SPAs) [29]. Failure in the position sensor results in errors in the signal feedback to the control system, which causes the rotor to become unstable and finally leads to failure in the AMB system. Failure in the position sensor may be related to the power supply that feeds the sensor and relative damage due to physical contact with parts of the AMB. [PERSON], et al. [30] studied different control techniques and failure modes to increase AMB life, performance, and reliability. They used Failure Mode and Effects Analysis (FMEA) to identify and prioritize system failures in AMB components. This method involves evaluating the severity, occurrence, and detection of possible failures, which results in the identification of important failure modes [31]. The Risk Priority Number (RPN) value was determined for every single cause of failure. The significance of the analysis of causes (RPN) in relation to the failure of the position sensor is as follows:  
* A value of 20 is given to the failure of an electric circuit of the sensor.
* A value of 18 is given to the physical contact between the sensor and the rotor.
* A value of 8 is given to the risk of damage to the shaft.
* A value of 3 is given to the presence of debris.  
Moreover, these failures result in a decrease in speed, causing the rotor to become levitated from its original position.