FAULT FINDING ANALYSIS
Fault finding analysis forms a critical part of electric motor condition monitoring. Aside from having a well-established testing and condition monitoring program, it may become necessary from time to time to delve further into a specific fault zone for further analysis.
Since testing is best performed from the motor control center (MCC) to measure the motor, cable and capacitors as one circuit, it may become necessary to split the circuit components to isolate a potential fault.
It’s recommended using the same equipment for condition monitoring and fault finding to ensure the accuracy of specific measurements during the process of repair and retesting after the repair has been done. This will ensure proper recording of data for future analysis and record keeping.
When testing from the MCC, fault finding may become necessary when readings deteriorate or significantly change from the baseline readings.
Fault finding is a critical part of condition monitoring to ensure the seamless operation of equipment and ensuring the highest possible production output. It does however take time and effort to follow correct procedures, therefore extra time should be factored in when considering the possibility of doing fault finding.
1. POWER CIRCUIT
The power circuit refers to all of the conductors and connections that exist from the point at which the testing starts through to the connections at the motor. It can include circuit breakers, fuses, contactors, overloads, disconnects, and lug connections. Research on industrial power distribution systems has shown that connectors and conductors are the source of 46% of the faults reducing motor efficiency.
2. POWER QUALITY
The Power Quality fault zone focuses on the condition of the voltage and current in a motor’s branch circuit. Poor power quality can greatly affect the operation and health of an electric motor. During operation several stresses are brought to bear upon key components of the motor. Variances or distortions in the voltage powering a motor results in increasing both thermal and electrical stresses to the stator windings and in some cases components of the rotor.
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3. AIR GAP
The Air Gap fault zone describes the measurable distance between the rotor and stator within the motor. If this distance is not equal throughout the entire circumference air gap eccentricity occurs. The varying magnetic flux within the air gap creates imbalances in the current flow, which can be identified in the current spectrum.
4. INSULATION
The Insulation fault zone refers to the condition of the insulation between the windings and ground. For electrical equipment to operate properly and safely, it is important that the flow of electricity take place along well-defined paths or circuits and that it not be leaking from one path to another. Deterioration of the insulation systems can result in an unsafe situation for personnel exposed to the leakage current.
5. ROTOR
Rotor health refers to the integrity of the rotor bars, rotor laminations, and end rings of the squirrel cage induction motors. In a joint study by EPRI and General Electric, rotor defects were estimated to be responsible for approximately 10% of the motor failures. The rotor, although responsible for only a small percentage of the motor problems, can influence other fault zones to fail.
6. STATOR
The stator fault zone is often considered one of the most controversial fault zones due to the significant challenge of early fault detection and the prevention of motor failure surrounding the stator windings. Stator windings are the heart of the motor, producing the rotating magnetic field, induction current, and torque to turn the rotor and shaft.