Case Study: ALL-TEST PRO saves $1 million

The equipment at risk

The motor formed part of the bearing cooling system for a large generator. The installation used two cooling-pump motors so that one could take over if the other failed.

The standby unit was a:

• 50 HP electric motor
• 3,600 RPM motor
• 480 V motor
• Delta-connected motor
• Generator bearing cooling-pump motor

The team had already installed the standby motor and confirmed its direction of rotation. It remained available until the primary cooling motor failed.

Once called into service, the standby motor displayed several warning signs:

• An 11% current unbalance between phases
• Excessive operating temperature
• Electrical vibration at 120 Hz
• A load reading of approximately 90%
• Less than 0.5% voltage unbalance

The balanced supply voltage helped rule out a serious incoming power-quality problem. The uneven current, heat, and vibration pointed towards an internal motor condition. If the standby motor had also failed, the generator would have needed to shut down within two minutes.

What did the ALL-TEST Pro find?

ALL-TEST Pro motor circuit analysis compares the electrical characteristics of each motor phase. It can help identify abnormal differences in the windings, rotor, connections, insulation system, or electrical circuit.

In this case, the test readings showed a clear phase-to-phase difference inside the motor. The maintenance team tested two more motors with the same design and similar serial numbers. Those motors produced comparable results, which suggested that the condition extended beyond one isolated unit.

The investigation considered several possible causes:

• Supply-voltage quality
• Incorrect test readings
• Loose or poor connections
• Rotor defects
• Winding faults
• A motor design or manufacturing issue

The team confirmed that the incoming power, test instruments, and external connections were satisfactory. Further investigation traced the unbalance to a change in the manufacturer’s winding process.

The root cause: unequal winding construction

The manufacturer had increased the size of one set of coils to improve the winding’s physical appearance and mechanical construction.

That change affected factors such as:

• The coil’s distance from the rotor
• The dimensions of the coil
• The conductor arrangement
• The electrical inductance of that phase

The motor met the manufacturer’s existing acceptance requirements, but its phases were not electrically balanced under operating conditions. The motor had passed earlier checks. It had been delivered, installed, and kept ready for critical standby service. The hidden winding difference only became clear when the motor was placed under load and then assessed with more detailed motor circuit analysis.

What did early diagnosis prevent?

The facility removed the affected motors from critical service and introduced incoming inspection for new and repaired motors.

ALL-TEST Pro testing gave the maintenance team evidence that the motors contained an internal electrical problem. They could act before another motor entered service and threatened the generator cooling system.

The diagnosis helped the facility:

• Avoid relying on a defective standby motor
• Prevent a possible forced generator shutdown
• Reduce the risk of generator-bearing damage
• Identify other motors with the same design issue
• Improve its acceptance process for new and repaired motors
• Add electrical condition data to its maintenance decisions

The case carries a clear lesson for any industrial operation: a new, repaired, or unused motor can still contain a fault.

How CAW uses ALL-TEST Pro motor testing

CAW uses ALL-TEST Pro equipment to support motor fault finding, condition assessment, incoming inspection, and repair verification. The test takes place while the motor is de-energised. This allows our technicians to assess the electrical circuit without running the motor under production conditions.

Depending on the motor, access point, and type of test, the findings can help us identify or investigate:

• Phase-to-phase unbalance
• Developing winding faults
• High-resistance or loose connections
• Insulation concerns
• Contamination within the winding
• Open circuits
• Rotor abnormalities
• Differences between similar motors
• Changes from previous baseline readings

The test results do not sit in isolation. CAW combines them with visual inspection, insulation testing, mechanical checks, vibration findings, operating information, and other relevant diagnostic methods.

This gives you a clearer basis for deciding whether to monitor, repair, rewind, refurbish, or replace the motor.

Test a new motor before you install it

A new motor can contain a manufacturing, winding, connection, or rotor defect.

Incoming motor inspection gives you an independent view of its electrical condition before you:

• Accept delivery
• Move it to a remote plant
• Install it in a difficult-to-access location
• Allow the warranty period to pass
• Place it into critical standby service

This matters when the motor has a long replacement lead time or supports equipment that can stop your plant.

Verify a repaired motor before returning it to service

A repaired motor should undergo proper testing before it returns to your operation. Motor circuit analysis can help verify whether the phases are electrically consistent and whether there are signs of an unresolved winding, connection, insulation, or rotor problem. This reduces the risk of transporting, installing, and commissioning a motor that still requires further attention.

CAW can also carry the process through from diagnosis to repair, rewinding, balancing, refurbishment, and final testing where required.

Investigate recurring motor problems

Repeated motor failure often points to an underlying condition that has not yet been addressed.

Arrange further testing when a motor:

• Continues to run hot
• Draws uneven phase current
• Trips without a clear cause
• Develops unexplained electrical vibration
• Fails repeatedly in the same application
• Performs differently from an identical motor
• Returns from repair with the same symptoms
• Shows abnormal readings during routine maintenance

Detailed testing helps separate an internal motor fault from problems elsewhere in the circuit or driven equipment.

Build baseline readings for condition monitoring

A baseline test records the motor’s electrical condition at a known point in time.

CAW can compare future results against that baseline to identify changes. This helps your maintenance team see whether the motor remains stable or whether a fault may be developing.

Baseline motor testing is particularly useful for:

• Critical production motors
• Standby and emergency equipment
• High-value motors
• Long-lead-time motors
• Motors in remote locations
• Equipment exposed to moisture, dust, chemicals, or heat
• Motors with a history of repeat failure

Trend data also helps you plan maintenance around shutdowns rather than waiting for the motor to determine your schedule.

When should you arrange motor circuit analysis?

Contact CAW when:

• You receive a new critical motor
• A repaired or rewound motor returns to your site
• A standby motor has remained in storage
• A motor runs hotter than expected
• You measure uneven phase current
• A motor develops unexplained vibration
• The same motor or application fails repeatedly
• You need baseline readings for condition monitoring
• You are preparing for a planned shutdown
• You need evidence before deciding whether to repair or replace

You do not need to wait for a breakdown. Testing while the motor remains de-energised can give you time to plan the next step.

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