Interview Questions for Stator Testing

Stator testing encompasses a range of procedures designed to assess the health and integrity of a stator winding, a crucial component in electric motors and generators. These tests help identify potential faults before they lead to catastrophic failures. The types of tests vary based on the specific needs and the size/type of the machine, but common tests include:

• Insulation Resistance Test: Measures the insulation resistance between the windings and the core/ground. This helps detect insulation degradation.
• High-Potential (Hi-Pot) Test: Applies a high voltage to the windings to check for insulation weaknesses. It’s a more rigorous test than insulation resistance.
• Turn-to-Turn Test: Detects short circuits between adjacent turns of a coil within the winding.
• Surge Test: Simulates a voltage surge to assess the ability of the insulation to withstand transient overvoltages.
• Winding Resistance Test: Measures the DC resistance of the windings to detect open circuits or shorted turns indirectly.
• Ground Test: Checks for electrical continuity to earth, identifying grounding faults.

The choice of which tests to perform depends on factors such as the stator’s age, operating history, and the severity of suspected damage.

Insulation resistance testing assesses the quality of the insulation separating the stator windings from the core and ground. A low resistance indicates insulation breakdown, which can lead to short circuits and failure. The process typically uses a megohmmeter (also called a megger), a device that applies a high DC voltage to the windings and measures the resulting current. A lower current indicates higher resistance, showing better insulation.

1. Preparation: Ensure the stator is clean, dry, and disconnected from the power supply.
2. Connection: Connect the megohmmeter leads to the appropriate winding terminals and ground.
3. Testing: Apply the test voltage (typically 500V or 1000V DC, depending on the stator voltage rating) and record the insulation resistance in megohms (MΩ).
4. Interpretation: Compare the measured resistance with the manufacturer’s specifications or industry standards. Lower resistance values indicate insulation deterioration and potential problems.

For example, a 5kV motor might have a minimum acceptable insulation resistance of 100 MΩ. If the reading is significantly lower, further investigation is needed. Remember to always follow safety procedures, using proper PPE (Personal Protective Equipment) while performing high voltage testing.

Identifying a shorted stator winding requires a combination of tests. A simple visual inspection might reveal signs of burning or damage, but that’s not always sufficient. Electrical tests are more reliable.

• Low Insulation Resistance: A significantly lower than expected insulation resistance reading is a strong indicator of a short circuit. The megger test will show this.
• Winding Resistance Test: An abnormally low winding resistance might suggest a short circuit within the winding itself. Although this isn’t conclusive on its own, comparing the results to the manufacturer’s specification is crucial.
• Turn-to-Turn Test: This test directly detects shorts between adjacent turns within a coil. A low impedance between two adjacent turns confirms a short.
• High-Potential Test: A failure (breakdown) during a Hi-Pot test usually indicates a short, often a turn-to-turn short if it occurs at a relatively low voltage.

The combination of these tests provides a comprehensive picture of the winding’s condition. Sometimes advanced techniques like partial discharge analysis may be employed for more detailed diagnosis.

Turn-to-turn testing is crucial because it detects subtle faults that other tests might miss. While a short circuit between phases might be easily detected by insulation resistance testing, a short between adjacent turns within a single coil might not show up in these tests.

Such a turn-to-turn fault can cause localized overheating, leading to further insulation degradation and eventual catastrophic failure. Turn-to-turn tests use specialized equipment that injects a low-voltage, high-frequency current into the winding and measures the impedance between adjacent turns. A significantly lower impedance than expected indicates a short circuit between those turns.

Think of it like this: a single frayed wire in a large cable bundle might not cause a noticeable short, but that single wire could still cause significant problems if it touches another. Turn-to-turn testing identifies those ‘frayed wires’ before they create larger problems.

Stator winding failures can stem from several factors:

• Overheating: Excessive current, poor ventilation, or blocked air vents can lead to overheating, degrading insulation and potentially causing shorts.
• Mechanical Damage: Vibrations, impacts, or improper handling can physically damage the windings, leading to abrasions and short circuits.
• Insulation Aging: Insulation materials degrade over time due to exposure to heat, moisture, and chemicals. This reduces its dielectric strength, making it more susceptible to failure.
• Manufacturing Defects: Faulty manufacturing processes can introduce defects in the windings or insulation, leading to premature failure.
• Voltage Surges: Lightning strikes or switching surges can cause high transient voltages that exceed the insulation’s capacity, leading to breakdown.
• Moisture Ingress: Moisture can reduce insulation resistance, increasing the likelihood of a short circuit.

Preventive maintenance, including regular inspections, cleaning, and testing, is crucial to extend the stator’s lifespan and prevent these failures.

A high-potential (Hi-Pot) test applies a high AC or DC voltage to the stator windings to stress the insulation and reveal weaknesses. The results are interpreted based on whether the insulation withstands the test voltage without failure (breakdown).

• Successful Test: If the insulation withstands the test voltage without any breakdown (no sparks or significant current leakage), it indicates that the insulation is in good condition and can withstand the expected operating voltages.
• Failure: A breakdown during the test signifies a weakness in the insulation, indicating potential problems like shorts, cracks, or other insulation damage. The voltage at which the breakdown occurs can provide information about the severity of the problem.

It is important to note that a successful Hi-Pot test does not guarantee perfect insulation. It simply indicates that the insulation can withstand the applied voltage. Other tests are still necessary to get a complete picture of the stator’s condition.

For example, a successful Hi-pot test at 2000V DC doesn’t mean there aren’t small weaknesses that might cause problems at higher operating voltages over time. Therefore, a successful Hi-Pot test must be combined with other methods for a complete diagnosis.

A surge test simulates the impact of transient overvoltages on the stator windings. These overvoltages can occur due to lightning strikes, switching operations, or other electrical disturbances. The surge test helps to evaluate the ability of the stator’s insulation to withstand these events without damage. Specialized equipment generates a high-voltage, high-frequency surge waveform (often a standard impulse wave shape), which is applied to the stator windings.

1. Preparation: The stator should be disconnected from the power supply and properly grounded.
2. Connection: The surge generator is connected to the stator windings through appropriate surge arresters and measuring devices.
3. Application: The surge waveform is applied, and the voltage and current are monitored.
4. Measurement: The response of the stator is carefully observed. This includes checking for any breakdown, excessive current flow, or voltage distortions.
5. Analysis: The results of the test are compared against pre-defined acceptance criteria. Any significant deviations might indicate weaknesses in the insulation.

A successful surge test shows that the stator winding can withstand the defined surge amplitude without damaging the insulation. This is a particularly important test for equipment operating in environments prone to lightning strikes or other voltage surges.

Ground testing in stator diagnostics is crucial for ensuring the safety of personnel and equipment during testing and operation. It verifies the integrity of the stator’s grounding system, preventing dangerous voltage build-up that could lead to electric shock or damage to the stator windings. A proper ground connection ensures that stray currents are safely dissipated to earth, preventing insulation breakdown and potential fire hazards.

Think of it like this: a building’s lightning rod. The rod provides a safe path for electrical current during a lightning strike, protecting the building. Similarly, a proper ground connection in a stator provides a safe path for stray currents, protecting the windings and personnel.

Testing typically involves measuring the resistance between the stator frame and earth ground using a low-resistance ohmmeter. Acceptable resistance values depend on the specific stator design and operational environment, but generally should be very low (ideally less than 1 ohm).

Both partial discharge (PD) testing and high-potential (HIPOT) testing are used to assess the insulation quality of stator windings, but they differ significantly in their approach and what they detect.

A high-potential test applies a high DC or AC voltage to the stator winding to check for insulation breakdown. It’s a relatively simple test that identifies major insulation weaknesses or faults that cause complete breakdown under high stress. Think of it like checking for cracks in a dam – you’re looking for complete failures.

Partial discharge testing, on the other hand, is much more sensitive. It detects small, partial discharges within the insulation that may not cause complete breakdown immediately but indicate progressive degradation. These discharges are caused by microscopic voids or defects in the insulation which lead to localized ionization and energy loss. It’s like finding small cracks in the dam before they become catastrophic. PD testing helps predict potential future failures.

In short, HIPOT testing looks for major failures, while PD testing looks for incipient failures.

Diagnosing an open winding in a stator requires a systematic approach. First, you’d use a megohmmeter to measure the insulation resistance between each phase winding and ground. An open winding will exhibit infinite or very high resistance compared to the other phases. You can also use a winding resistance tester to measure the resistance of each phase. An open circuit will show a very high or infinite resistance.

Next, you’ll need to pinpoint the exact location of the open. This is usually done by using a continuity tester or ohmmeter to trace the winding from the terminal connection toward the end windings. Testing coil-to-coil resistance can further narrow down the location.

Troubleshooting involves careful inspection of the windings for physical damage such as broken wires, loose connections, or damaged insulation. Repair techniques can range from simple soldering or rewiring to complete rewinding of the affected coil or even the entire stator, depending on the extent of the damage and economic considerations.

For example, if you find high resistance between one phase and ground, and then trace the winding and find a break near one of the coil ends, you know that section needs repair or replacement.

Safety is paramount during stator testing. The following precautions are essential:

• Lockout/Tagout (LOTO): Always follow strict LOTO procedures to de-energize the stator completely before commencing any testing.
• Personal Protective Equipment (PPE): Wear appropriate PPE including insulated gloves, safety glasses, and safety shoes.
• Grounding: Ensure the stator is properly grounded to prevent static electricity buildup and shocks.
• High Voltage Awareness: Understand the dangers of high voltage and maintain a safe distance from energized equipment.
• Trained Personnel: Only trained and qualified personnel should perform stator testing.
• Proper Equipment: Use only properly calibrated and maintained test equipment.
• Emergency Procedures: Have a clear understanding of emergency procedures in case of accidents or unexpected events.

Failure to adhere to these safety precautions can result in serious injury or death.

Stator testing utilizes several key pieces of equipment:

• Megohmmeter (Insulation Resistance Tester): Measures the insulation resistance between windings and ground, indicating the condition of the insulation. A low resistance value indicates insulation degradation.
• Surge Tester (Impulse Voltage Tester): Applies high-voltage surges to simulate real-world operating conditions, assessing the ability of the stator winding insulation to withstand transient overvoltages.
• Winding Resistance Tester: Measures the DC resistance of each phase winding. This helps identify open circuits, shorts, or uneven winding resistance which could indicate a problem.
• Partial Discharge Detector: Detects partial discharges within the stator winding insulation, which might not be immediately obvious with other tests. This is a predictive maintenance tool that identifies potentially failing insulation.
• High-Potential Tester (HIPOT): Applies a high DC or AC voltage to detect insulation breakdowns.

Each test provides different information about the stator’s health and together they provide a comprehensive picture.

Stator winding configurations vary depending on the motor design and application. Common types include:

• Concentric Winding: Coils are arranged in concentric layers around the stator core. This design is often used in larger motors and generators. It is a robust and efficient configuration for high power applications.
• Distributed Winding: Coils are distributed around the stator core in a more spread-out pattern. This design produces a more sinusoidal voltage waveform compared to a concentric winding, leading to smoother operation.
• Lap Winding: Coil ends are connected in a lap fashion to form a continuous winding path. It’s frequently used in fractional horsepower motors.
• Wave Winding: The coils are connected to form a winding that appears to progress in a wave-like pattern. It is used when a higher number of poles is needed or in applications requiring a higher voltage output.

The choice of winding configuration affects the motor’s performance characteristics, including voltage waveform, efficiency, and power output.

The results of a stator winding resistance test are crucial in assessing the condition of the windings. The test measures the DC resistance of each phase winding using a low-resistance ohmmeter. The obtained values should be compared to the manufacturer’s specifications or a known good stator of the same type and size.

Interpreting the Results:

• Significant Variations between Phases: Large differences in resistance between phases indicate potential problems such as loose connections, broken wires, or partial short circuits within the windings.
• High Resistance: A significantly higher resistance than expected indicates potential problems such as loose connections, corrosion, increased winding temperature, or deteriorated insulation.
• Low Resistance: An unusually low resistance might suggest a short circuit within a winding or between phases.
• Infinite Resistance: This implies an open circuit in the winding, preventing current flow.

It’s important to note that resistance values can change slightly with temperature. For precise comparisons, the measurements should be taken at a consistent temperature. Any significant deviations from expected values necessitate a thorough investigation and likely further testing.

Determining acceptance criteria for stator tests is crucial for ensuring the reliability and safety of the electrical equipment. These criteria are based on industry standards, manufacturer’s specifications, and the specific application of the stator. We typically consider several key factors:

• Insulation Resistance: Measured using a Megger, this indicates the health of the stator winding insulation. Lower resistance suggests insulation degradation and potential failure. Acceptance limits are often expressed in megaohms (MΩ) at a specific temperature and voltage, and vary depending on the stator voltage and size. For example, a large high-voltage stator might require 1000 MΩ or more, while a smaller low-voltage motor might accept 50 MΩ.
• Dielectric Strength (High-Potential Test): This test applies a high voltage to the stator windings to check for insulation breakdown. The applied voltage is significantly higher than the operating voltage and is usually specified by standards like IEEE. A successful test shows no breakdown and confirms the insulation can withstand transient overvoltages.
• Partial Discharge (PD) Testing: PD testing detects small electrical discharges within the insulation, even before a complete breakdown. These discharges indicate flaws that might lead to future insulation failure. Acceptance criteria are usually based on the magnitude and frequency of PD pulses.
• Grounding and Continuity Tests: These verify the proper grounding of the stator windings and confirm the continuity of the windings themselves. Any open circuits or grounding faults will show up in these tests.
• Vibration Analysis: Stator vibrations can be a sign of mechanical problems. Acceptance criteria consider vibration levels at different operating speeds, referring to manufacturer’s guidelines or relevant standards.

These acceptance criteria are often documented in a test report, providing a clear record of the stator’s condition and suitability for service. Failure to meet these criteria would lead to further investigation and potentially repair or rejection of the stator.

Moisture is a major enemy of stator insulation. Its presence significantly reduces the insulation resistance, leading to increased leakage current and eventually insulation breakdown. This is because water acts as a conductor, allowing current to flow where it shouldn’t.

The effects can range from slightly reduced insulation resistance, detectable with a Megger test, to complete insulation failure resulting in a short circuit, potentially causing damage to other parts of the motor or even a fire. Even small amounts of moisture can accelerate the aging process of the insulation, reducing its lifespan significantly. This is particularly true for cellulose-based insulations which are more hygroscopic (absorb moisture readily).

Furthermore, moisture can facilitate the formation of conductive paths along the surface of the insulation, leading to partial discharges. These discharges, though initially small, can erode the insulation over time, eventually causing a total breakdown.

Stator drying is essential when moisture contamination is detected. The goal is to remove moisture from the stator windings and insulation system, restoring the insulation’s dielectric strength and resistance. Several methods exist, each with its own advantages and disadvantages:

• Vacuum Drying: This method uses a vacuum chamber to lower the pressure, which lowers the boiling point of water, allowing it to evaporate at lower temperatures. This method is effective but can be time-consuming and expensive.
• Warm Air Circulation Drying: This involves circulating warm, dry air around the stator windings. This is a common and relatively inexpensive method, but it can be slower than vacuum drying and may not be suitable for all insulation types.
• Combination Methods: Some drying processes combine vacuum drying with warm air circulation for optimal efficiency and to reduce drying time.

The choice of drying method depends on factors like the size and type of stator, the level of moisture contamination, and the available resources. Throughout the drying process, temperature and moisture levels are monitored carefully to avoid damaging the insulation or causing uneven drying. After drying, the stator undergoes insulation resistance testing to ensure the moisture has been successfully removed and the insulation’s integrity has been restored.

For instance, a large stator with significant moisture may require vacuum drying, while a smaller stator with minor moisture might be successfully dried with warm air circulation.

Both AC and DC high-potential tests are used to assess the dielectric strength of stator insulation, but they differ in their mechanisms and the information they provide:

• DC High-Potential Test: This test applies a high DC voltage to the stator windings for a specified duration. It’s primarily used to detect weak points in the insulation that may not be readily apparent with AC testing. DC testing can more effectively stress insulation, revealing subtle flaws that might lead to long-term failure.
• AC High-Potential Test: This test applies a high AC voltage, simulating the transient overvoltages the stator may experience during operation. It’s particularly useful in detecting surface defects and tracking, which are common insulation problems that can develop over time. AC testing also provides information about capacitance, which can be indicative of insulation condition.

The choice between AC and DC testing depends on the specific needs of the test and the type of insulation. Sometimes, both tests are performed for a more comprehensive assessment. It’s also important to note that the voltage levels and test duration are carefully controlled and vary depending on the stator’s voltage rating and insulation type, always following relevant standards to avoid damaging the equipment.

Analyzing stator vibration data involves identifying the frequencies and amplitudes of vibrations to diagnose potential problems within the stator or the entire motor. This is often done using vibration sensors and data acquisition systems. Here’s a breakdown of the process:

• Data Acquisition: Vibration sensors (accelerometers) are placed on the stator housing at strategic points. Data is collected over time, often while the motor is operating at different speeds and loads.
• Frequency Analysis: Fast Fourier Transform (FFT) is used to convert the time-domain vibration signal into a frequency-domain representation. This shows the dominant frequencies of vibration.
• Amplitude Analysis: The amplitudes of the vibration at different frequencies indicate the severity of the problem. High amplitudes at specific frequencies usually point towards a fault.
• Fault Diagnosis: By comparing the measured frequencies and amplitudes with known vibration characteristics of different motor faults (e.g., bearing wear, rotor imbalance, loose windings), we can pinpoint the source of the problem. There are standard catalogs and software that can assist with this interpretation.

For example, a high amplitude at a specific frequency that is a multiple of the motor’s rotational speed may indicate a rotor imbalance or bearing defect, while high amplitudes at higher frequencies might suggest winding looseness or other structural problems. The analysis should always be done in conjunction with visual inspections and other tests to confirm the diagnosis.

Documentation in stator testing is critical for several reasons:

• Legal and Safety Compliance: Proper documentation ensures compliance with safety regulations and industry standards. It demonstrates that the stator has undergone the necessary testing and meets the required performance criteria. This is vital in case of any liability concerns.
• Traceability and Accountability: Detailed records provide a complete history of the stator’s condition and the tests performed. This enables tracking of any issues over time and helps identify trends that might indicate potential problems.
• Maintenance and Repair: The documentation serves as a valuable reference for future maintenance and repair activities. It enables technicians to quickly understand the stator’s history, any previous issues, and the effectiveness of past repairs.
• Predictive Maintenance: By analyzing test data over time, we can identify patterns and predict potential failures. This enables proactive maintenance, minimizing downtime and reducing the risk of unexpected failures.

Typically, comprehensive documentation includes test procedures, equipment used, test results (numerical values and waveforms), photos of the stator’s condition, and any observed anomalies. Well-organized documentation using standardized formats is crucial for effective analysis and decision-making.

I have extensive experience with various stator insulation materials, each with its own properties and applications:

• Class F Insulation (155°C): A common material, often made of polyester-imide or mica-based materials. It offers good thermal stability and dielectric strength, making it suitable for medium-voltage applications.
• Class H Insulation (180°C): Typically uses polyimide or silicone-based materials. This class provides better thermal resistance than Class F, allowing for use in high-temperature environments and higher-voltage applications.
• Class C Insulation (>200°C): This class consists of materials like mica, ceramic, and silicone. They’re suitable for extremely high-temperature applications, though they might be more brittle and less flexible than other insulation types.
• Epoxy-based Insulation Systems: These are widely used for potting and encapsulation of stator windings, providing excellent mechanical and dielectric protection.

The selection of insulation material is based on factors such as the operating temperature, voltage rating, and environmental conditions. Experience helps to determine the most suitable material for a given application and to anticipate potential challenges related to material aging, moisture absorption, and mechanical stress. For example, in a high-speed, high-temperature motor application, Class H or even Class C insulation might be necessary to withstand the thermal and mechanical stresses involved.

Handling non-conforming stator components involves a rigorous process that prioritizes quality control and minimizing production disruptions. First, we identify the specific non-conformity – is it a dimensional issue, a winding fault, insulation damage, or something else? A detailed report is generated documenting the nature of the defect, its location, and the affected batch. Then, depending on the severity and root cause, several actions are taken.

• Minor Defects: For minor cosmetic issues or tolerances slightly outside specification, repair might be possible. This would involve rework by skilled technicians, followed by retesting to ensure the component meets standards. We maintain meticulous records of all repairs.
• Major Defects: If the defect is significant and repair is impractical or cost-prohibitive, the component is rejected. This involves a formal rejection process that includes detailed documentation and notification of relevant stakeholders. Rejected components are segregated to prevent accidental use.
• Root Cause Analysis: Regardless of the severity, a root cause analysis is crucial. This helps identify systemic issues in the manufacturing process or material supply chain. Corrective and preventive actions are implemented to prevent similar defects in the future. This often involves process adjustments, training refinements, or supplier audits.

For example, if we find a batch of stators with consistently loose windings, we would investigate the winding machine settings, operator training, and the quality of the winding wire. This approach ensures not only immediate resolution but also long-term improvement of stator quality.

My experience with automated stator testing systems is extensive. I’ve worked with several systems, from simple automated testers performing basic resistance and insulation checks to sophisticated systems incorporating advanced techniques like high-voltage tests, turn-to-turn tests, and even automated visual inspection. The benefits of automation are significant: increased throughput, reduced human error, improved consistency of testing, and the generation of comprehensive, auditable data.

For instance, I’ve been involved in the implementation and optimization of a fully automated system that uses robotic arms to handle stators, integrating multiple test instruments, and generating reports automatically. This drastically reduced testing time and significantly improved our accuracy rates. I’m also proficient in programming and troubleshooting these automated systems, ensuring optimal performance and minimizing downtime. This includes experience with various software interfaces, data acquisition systems, and robotic control systems.

Stator winding design is a crucial aspect of motor performance and reliability. It involves carefully selecting the type of winding (concentrated, distributed, etc.), the number of slots and poles, the winding configuration (e.g., single-layer, double-layer, lap winding), and the wire gauge. The design goals are to achieve optimal torque, efficiency, and power factor while minimizing losses and ensuring robust insulation.

Several factors influence the design: the desired motor characteristics (speed, torque, power), the operating voltage and frequency, the cooling method, and the available space within the stator. Advanced techniques like Finite Element Analysis (FEA) are employed to simulate the electromagnetic fields and thermal behavior of the winding, allowing designers to optimize performance and predict potential issues. For example, a high-speed motor might require a different winding design compared to a high-torque motor, involving different coil configurations and wire sizes. Poor winding design can lead to increased heat generation, reduced efficiency, and premature failure. Therefore, a deep understanding of electromagnetic principles and thermal management is essential.

Troubleshooting a failed stator test requires a systematic approach. First, I carefully review the test results, noting the specific tests that failed and the values obtained. Then, I use this information to narrow down the possible causes. For example:

• High Winding Resistance: Could indicate a broken conductor, poor connection, or excessive winding temperature.
• Low Insulation Resistance: Suggests insulation damage, moisture ingress, or contamination.
• Failed Turn-to-Turn Test: Points to a shorted turn within the winding.
• High Capacitance: Might be due to winding defects or proximity to other components.

Once I have identified a potential problem area, I use various diagnostic techniques, such as visual inspection, megger testing, and potentially more advanced methods like partial discharge detection, to pinpoint the exact location of the fault. I also consider the stator’s history and any environmental factors that might have contributed to the failure. Following a careful diagnosis, appropriate repair or replacement actions are undertaken.

For example, if a high winding resistance is detected, I might visually inspect the winding for broken conductors or poor connections. If a specific coil shows abnormally high resistance, I might use a specialized tool to identify and repair the damaged section.

Stator testing adheres to several standards and specifications that ensure consistent quality and safety. These vary based on the application and the specific motor type. Some key standards include:

• IEC 60034: A series of standards covering rotating electrical machines, including testing procedures for insulation resistance, winding resistance, and other critical parameters.
• IEEE standards: Offer similar guidance for different motor types and applications.
• Manufacturer-Specific Standards: Many manufacturers have their own internal standards and specifications that go beyond the general industry standards, reflecting specific quality and performance requirements.
• Automotive Standards: For stators used in automotive applications, there are rigorous standards that address harsh operating conditions, electromagnetic compatibility (EMC), and safety.

These standards provide detailed guidelines for test methods, acceptable limits, and reporting requirements, helping to ensure consistency and reliability in stator testing across different manufacturers and applications. Adherence to these standards is crucial for maintaining product quality and safety.

One challenging situation involved a batch of stators failing a high-voltage test intermittently. The initial tests showed inconsistencies – some stators would pass, others would fail, and the same stator might pass one test and fail the next. This was extremely problematic as we couldn’t identify a consistent defect. Our usual troubleshooting methods were not effective.

After a thorough investigation, we discovered that the problem was not with the stator itself, but with the high-voltage test equipment. A faulty connection in the high-voltage power supply was causing intermittent voltage fluctuations that were impacting the test results. This was tricky to identify because the fluctuations were subtle and unpredictable. We only found it after carefully monitoring the test equipment’s performance and conducting extensive calibration checks.

The resolution involved repairing the power supply and re-testing the entire batch of stators. This highlighted the importance of equipment calibration and maintenance and showed how a seemingly complex problem could originate from an unexpected source. It also led us to implement stricter preventative maintenance schedules for our testing equipment.