Failure Mode Effects Analysis (FMEA): Electric Motor for Pumps
Activity 1
Failure Mode Effects Analysis is carried out to identify the possible failures in a design system, assembly or manufacturing process of the electric motor used in pumps. Through the analysis, it is possible to identify possible errors or defects of a product. The errors are identified and corrected to prevent them from affecting the customers. However, the main goal of the analysis is to study the consequences or the effects of failures that might render the electric motor not to operate effectively. Therefore the purpose of FMEA is to take actions that are critical in eliminating or reducing failures by prioritizing the adverse failures. FMEA is employed to control and prevent failures during the design process. There are several cases when FMEA is utilized. For instance the process can be conducted when designing or redesigning a product and application of a product in a new way.
During the process of design and operation, different data is necessary for the implementation of all the processes. The data include motor current, Voltage levels, Service factor and safety, overloading, and troubleshooting. The amount of current is necessary to determine the level of torque output. The amount of current is proportional to the level of output. The amount of current determines the rise in the temperature of the equipment. Data on voltage is a determinant factor because of the effect of low and high voltages. The low voltages produce high amount of current which causes the rise in temperature while the high voltage causes less amount of current which reduces the overheating process and therefore causing cooling process. Data from the voltage test is critical in determining the unbalancing or balancing of the system. The data are used in assessing the performance of the electric motor. The determination of the frequency at which the motor operates is important in examining the operations of the system. Most of the electric motors are connected to the utility power line and therefore the design process should correspond to the frequency of utilization. The service factor determines the conditions at which the electric motor will operate; the factor should be applied in controlling other factors such as temperature. The other types of data include safety, overloading, and troubleshooting. For instance, for safety purposes there is need for guards such as couplings gears, sheaves among others. In the cases of overloading, there must be data that determines the limit of overloading.

Figure 1. Functional Block Diagram for Electric Motor Pump
The pump is digitally controlled using a simple logic circuit. In the block diagram, four positions are utilized in determining the direction of current in the coil or on and off current in the mover coil.

Figure 2: The Reliability Diagram for Electric Motor Pump
The reliability block diagram is used in the identification of the potential areas of poor reliability or where improvements can be made. The method can be used at both operational and design phases. The diagram shows the logical connections between the electric motor pump. A formula is employed in the calculations of the reliability which later guides the design and operation process.

Figure 3: Diagrammatic Representation of Rotor Bar

Table 1: Work sheet
System Electric Motor
Equipment Rotor
Drawing Rotor Arrangement FAILURE MODE EFFECTS ANALYSIS WORKSHEET Date Today’s Date
Sheet 1 of __
Complied By Reliability Improvement Team
Approved Engineer in Charge
ID No Item Description Functions of Item Function Failure Mode Failure Mode Causes Failure Effect
Damages/Costs/Losses/Safety Symptoms of Failure Mode Failure Mode Detection Method Rectification on Failure Action to Prevent Failure Causes
The Item Its Neighbors Whole System CM Technique
1 Rotor bars To vary the speed of toque characteristics in the induction electric motor of the pump Broken Rotor bar Mechanical Issues Overworking of the item The Rotor bars interact with radial flux
Toque produce acts in the same direction as the rotating field The eventual rotor failure
Failure in the transmission of current Noise
Arcing Vibration analysis
Current measurements Replace a new rotor bar Monitor the rotor bars time to time to prevent it from damage or avoid the overworking of the equipment
2 Rotor Core To carry the rotating magnetic field that induces due to 3-phase supply Thermal stress
Thermal overloading
Unbalanced phase voltage Poor location or uninsulated rotor core Incorrect fitting/ Lack of insulation The electric system
Interaction between rotor core and ventilating duct The eventual failure of rotor
Uneventful winding wire Noise
Overheating of the motor Analysis of the temperature
Analysis of the current flow Install a replacement rotor core Insulating of the device
Motor designed with the NEMA standards
3 Rotor Shaft Passes rotational movement from the rotor and the power on downstream elements Rotor shaft misalignment
Corrosion and wear and tear Friction between parts which cause corrosion Incorrect installation or not firmly installed The overheating of the other parts of the rotor Eventual Rotor failure

Overheating The fatigue or working abnormally
Install a new rotor shaft Greasing/ oiling of the parts to prevent corrosion

Table 2: Failure Mode for a Rotor defect
Failure Mode Failure Effect Failure cause Failure Case Cause Occurrence Current controls Detection
Rotor defect Damage of the rotor Brocken rotor bars
Eccentric rotor Imbalance
Thermal stress
Assembly issues Aging

1 Checking air between the gaps of the rotor and stator 10

Item Sub-Assy DAFT Cost Rating Likelihood Criticality by Risk Matrix Required Operating Practice Required Maintenance Criticality after Mitigation
Total Loss Cost
$ Partial Loss Cost
$ Time to Rebuild
Days Failure Rate – MTBF From CMMS Equipment History Consequence ; Likelihood = Risk Rating Must be substantial reduction in level or chance of stress on item
Electric Pump Motor 550,000 120 TOTAL RISK
= 480000 1. Too expensive to carry emergency spare ?3; 3 > M
Rotor Bars 20,000 25 1 in 40,000hr 3 ; 3 = M 1. Replace the Rotor bas
2. Conduct a check on the bars frequently 1. Inspect and test the working mechanism
2. Replace the rotor bars 3 ; 2 = M
Rotor Core 45,000 30 1 in 10,000hr 3; 4 = H 1. Replace the rotor core
2. Monitor current flow 3. Use best practice for rotor core management methods

4. Rotor core tests 4: 3 = M
Rotor Shaft 250,000 10 1 in 60,000hr 4 ; 3 = H 1. Operator trained to not overload truck and over-rev motor
2. Install wireless engine monitoring and reporting 5. Inspection of the shaft 3: 2= M
End Ring 140,000 32 1 in 50,000hr 3; 4 =H 1. Replace the rotor ring
2. Diagnose the working condition 6. Ensuring end rings are in position 4: 4= M
Ventilating Duct 25,000 14 1 in 10,000hr 4; 4=M 1. Replace the ventilating duct
2. Check the working condition on frequent basis 7. Monitoring the work condition 2: 2= M