Why the 6 Fault Zones are Key to Proper Maintenance

Establishing a routine maintenance program is the best way to ensure that your electric motors and other equipment will operate when you need them. The maintenance program must go beyond a visual inspection of the equipment. It needs to use the proper tools and equipment to both test and analyze your motors. Keeping a close tab on the motors is important, they have an impact on all equipment associated with them.

The Six Fault Zones

Tests included in your maintenance program should assess the following six fault zones, which indicate the overall health of the motor:

Power Circuit

Power circuit relates to the various components and connections that are downstream from the motor’s location, including fuses and circuit breakers, overloads, lug connections, disconnects, and contactors. It is possible to analyze the power circuit by measuring its health.

Power Quality

To test power quality, consider both the current and the voltage. This fault zone comes from the electrical system, and when problems occur, they result in damage to the motor immediately or over time. Check the power quality by testing the crest factor, total RMS voltage, current harmonic voltage, and average voltage.

Rotor

There are several issues associated with the rotor fault zone. These include rotor laminations, bars, and end rings. It is unlikely that rotor faults result in direct issues with the motor, but they do cause parts of the motor to experience problems and eventually fail. Some of the tests for this zone include current demodulation, inductive imbalance, and inrush current.

Stator

The connections of the internal coil to the turn-to-turn insulation are associated with the stator fault zone. The tests in this region include analyzing inductive or impedance imbalances.

Although, as the PdMA notes, the stator fault zone isn’t an easy target to find:

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. This challenge is further intensified in higher voltage machines, where the fault-to-failure time frame becomes much shorter. The stator fault zone is identified as the health and quality of the insulation between the turns, coils, and phases within the slots and end turns of the electric motor.

Turn-to-turn or phase-to-phase shorts can be catastrophic to the motor and are not necessarily detected by the standard megohmmeter. Excessive inductive imbalance, resistive imbalance, vibration, partial discharge, or poor insulation quality can lead to stator failure and should be monitored regularly to prevent a shortened life of the electric motor stator. Stator analysis using EMAX technology is performed by evaluating the phase relationship of voltage and current for each of the three phases of an AC induction motor.

Insulation

Motor insulation is responsible for keeping different parts of the motor separated from each other. Heat has an adverse impact on insulation and significantly reduces the lifespan of the motor. Keeping the motor allows the insulation to do its job. In turn, this helps protect the windings and allows the motor to operate indefinitely. Other issues that affect the insulation include vibration, moisture, and contamination. Regular testing of the insulation indicates the overall health of the motor.

Air Gap

The gap between the stator and the rotor is the air gap zone. Two types of faults exist in the air gap: dynamic and static. Analyze the air gap area by using a rotor influence check test (RIC) and current signature analysis.

In Sum

These steps should be part of a routine maintenance program. Be sure that you are not just looking things over. Instead, use proper testing equipment to examine the six fault zones, which shows you just how healthy your motor is.