IMCA Testing, Induction Motor Current Signature Analysis
There are various external conditions that can adversely effect the operation of electric motors. These range from operational, environmental to electrical and mechanical. With the application of ERIKS Condition Based Monitoring techniques it is possible to monitor measure and identify these factors prior to them becoming catastrophic. The aim of this being the increased plant availability and increased production capability it offers to our customers. With the capability to detect conditions, which damage a machine, store this information for detailed analysis we can 'trend' developing machine faults.
The application of Current Spectrum Analysis ( IMCA Testing ) techniques allows ERIKS to measure, manage and detect the following fault parameters.
- Abnormal performance and operation
- Motor Starts
- Running Current
- Running hours
- Rotor Bar Faults
- Rotor Eccentricity
Broken or cracked rotor bars will develop severe high resistance connections. These high resistance connections require the current to increase in the nearby bars to supply the torque required for start-up and operation of the motor.
During start-up very high temperatures will develop around the crack or open bar causing potential damage to the rotor core as well as the stator insulation. Thermal expansion of the copper can change the severity of the defect.
The electrical effect of the broken or cracked rotor bar is an increase in the rotor circuit impedance and, therefore, the stator impedance also.
Damage to the rotor laminations is another effect that can be catastrophic to the motor. There are numerous causes of lamination damage, ranging from the rotor being dropped during transit, rotor/stator rub, overheating during a locked rotor condition etc. A stator/rotor rub can slowly push iron from the laminations over ventilation slots in the rotor. This effects the normal circulation of cooling air and can cause severe overheating of the stator insulation. This damage may only be evident on one side of the motor due to many motors having split airflow cooling. General damage from the overheating of a broken bar or overloading is less obvious.
Individual rotor laminations are insulated from each other and are designed to prevent excessive I²R losses. When this insulation is damaged, high currents can flow through the iron, doing no real work but creating excessive heat. These high temperatures lead to abnormal thermal growth creating imbalanced, and worse case, stator/rotor contact. It can also result in excessive temperatures being applied to the stator insulation, which will eventually develop into a stator insulation failure.
All of the above critical failures can be detected and avoided with the application of ERIKS's Current spectrum analysis techniques