The hidden cost of engine failure and the value of early diagnosis.

When an electric motor driving a pump, fan, compressor, or conveyor fails, much of the loss isn't in the motor itself, but in the downtime: unplanned production stoppages, damaged products, delayed shipments, and the cost of emergency repairs far exceeding routine maintenance. Furthermore, winding insulation degradation often progresses gradually over months, not instantly; humidity, temperature, vibration, and electrical stress slowly wear down the insulation.

The good news is that much of this degradation can be measured while the motor is still running. Measurements such as insulation resistance, polarization index, winding resistance, and partial discharge can indicate that the insulation is absorbing moisture, becoming contaminated, or aging before any visible failure occurs. The goal isn't to label the motor as 'pass/fail'; rather, it's to establish a trend by comparing the measured values to historical records and standard thresholds, and to shift the maintenance window to a planned date rather than an unplanned shutdown.

• Early diagnosis transforms unplanned downtime into planned care.
• Measurements are taken while the motor is running or with a brief stop, without damaging the winding.
• It's not a single measurement, but the trend over time that makes the decision.

Which engines are we testing?

The service covers rotating electrical machinery. Measurements can be performed on low-voltage (LV) and medium-voltage (MV) motors, both asynchronous (squirrel cage/slip ring) and synchronous machines. In practice, we most frequently encounter pump, fan, compressor, conveyor, crusher, and mixer drive motors.

In MV motors, additional measurements such as partial discharge are important because the winding insulation operates under higher voltages; in LV motors, insulation resistance, PI, and winding resistance are the primary indicators. The motor's label information (rated voltage, power, insulation class, protection class) and, if available, the manufacturer's test report directly influence the measurement plan and threshold interpretation.

• LV and MV asynchronous/synchronous motors
• Pump, fan, compressor, conveyor, crusher, mixer drives
• New commissioning, post-revision inspection, or periodic monitoring scenarios

Measured parameters: insulation, polarization index, and winding.

We assess the condition of the coil insulation using several complementary measurements. Insulation resistance (using a megger) indicates the instantaneous resistance of the insulation between the coil and the fuselage; however, it is very sensitive to temperature and humidity alone, so it is interpreted in conjunction with time-dependent tests.

The polarization index (PI) and DAR (dielectric absorption ratio) measure the change in insulation resistance over time: PI is typically the ratio of the resistance at 10 minutes to 1 minute, while DAR is the ratio of the resistance at 60 seconds to 30 seconds. These ratios provide more information about the dryness and cleanliness of the insulation than the absolute resistance. IEEE 43 defines the general framework for these measurements; however, since threshold values can vary depending on the insulation type, temperature, and age of the machine, instead of simply memorizing a single number as the 'limit,' we consider generally accepted thresholds and the machine's own historical data together.

Winding resistance measurement can reveal phase-to-phase imbalance, loose connections, or in-coil problems; a phase difference can be an early sign of a hidden short circuit or faulty connection.

• Insulation resistance (megger) — interpreted by correcting for temperature and humidity.
• Polarization index (PI, ~10 min / 1 min) and DAR (~60 sec / 30 sec) — IEEE 43 frame
• Winding resistance and phase imbalance control.
• Evaluation of the permissible temperature range according to insulation class.

Partial discharge: especially for MV engines.

In medium-voltage motors, insulation operates under a high electric field. When small gaps, cracks, or separations occur within the insulation, tiny electrical discharges called partial discharges begin in these gaps. Partial discharges do not cause immediate failure on their own, but they slowly erode the insulation, eventually leading to a complete breakdown.

Partial discharge measurement aims to detect these events in the early stages, and the IEC/EN 60034-27 series on partial discharge measurement in rotating electrical machinery is used as a general reference. This measurement is more meaningful for MV motors; for LV motors, insulation resistance, PI, and winding resistance usually provide sufficient information.

• An early indicator of insulation aging in OG motors.
• The IEC/EN 60034-27 series is used as a reference.
• In most cases, it is not necessary in AG motors.

Integrated assessment with vibration and thermography.

The health of a motor is not solely electrical. Bearing wear, imbalance, coupling failure, or loose assembly manifest as vibration; the IEC/EN 60034-14 framework is used for vibration assessment of rotating electrical machinery. Vibration measurement completes the picture by capturing mechanical problems that electrical testing might miss.

Thermography (infrared thermal imaging) shows abnormal heating in the motor housing, connection terminals, and power supply board without physical contact. A loose connection, unbalanced load, or inadequate cooling often manifests itself first as temperature. At AES, thermography is an accredited measurement; when combined with electrical testing expertise, the motor's insulation, connections, and mechanical condition can be comprehensively assessed in a single report. We cover predictive maintenance and vibration analysis in more detail on our respective service pages.

• Vibration measurement (IEC/EN 60034-14) detects mechanical problems.
• Connection with thermography and contactless detection of body temperature.
• Electrical, thermal, and mechanical data in a single integrated assessment.

Legal requirement or good practice? Honest distinction.

We want to clearly distinguish between these two aspects without confusing them. An electric motor is a piece of work equipment in the workplace; periodic inspection of work equipment in terms of electrical safety is a legal obligation under the Regulation on Health and Safety Conditions in the Use of Work Equipment (Regulation dated Official Gazette No. 18627 and current amendments). This inspection covers topics such as power supply, grounding, protective devices, and the electrical safety of the equipment, and is carried out by authorized personnel. An accredited organization can undertake the role of 'inspection/equipment control' within this scope, and contractual work is possible through the OHS-KATIP system.

In contrast, measurements such as polarization index, DAR, detailed winding insulation analysis, partial discharge tendency, and thermography-based trend tracking are not necessarily part of the 'fail/fail' decision of the statutory periodic inspection. These fall under predictive maintenance and good engineering practice: they are performed to foresee failure, extend motor life, and reduce unplanned downtime. In our report, we show these two layers separately; we clearly indicate which finding belongs to the statutory safety inspection and which belongs to good practice/predictive maintenance.

• Legal: Periodic electrical safety inspection of the motor as work equipment (Work Equipment Regulation)
• Good practice / predictive maintenance: PI/DAR, detailed winding analysis, partial discharge trend, thermography monitoring.
• The report presents these two layers separately and transparently.
• Legislation dates and numbers may change over time; current regulations should be confirmed with the relevant official source.

Who prepares the period, methodology, and report?

The inspection period is determined according to the criticality of the motor, the operating environment (humidity, dust, temperature), the load profile, and the manufacturer's recommendations, if any. The intervals stipulated in the legislation for legal electrical safety periodic inspections are used as a basis; predictive maintenance measurements, however, are generally performed more frequently and at regular intervals to generate meaningful trend data.

Measurements are performed by qualified electrical engineers and expert personnel using appropriate measuring devices in a manner that does not damage the winding. The output is a test report by a qualified electrical engineer containing the measured values, applied test voltages, temperature corrections, standard references, comparison with the previous period, and recommendations. The report clearly separates the findings and the recommendations based on them; the decision to repair or replace is justified in a way that will guide the company's planning.

• The period is determined according to criticality, environmental conditions, and regulatory ranges.
• The measurement is carried out by a qualified electrical engineer and a team of experts.
• Output: Engineering report containing measurement values + standard reference + trend + recommendations.

Engine testing and maintenance with AES

AES Innovation is a Type A Inspection Body accredited by TÜRKAK under TS EN ISO/IEC 17020, and its accredited area covers electrical installation inspection. Our strength in electric motor testing comes from the natural combination of two areas: accredited thermography expertise and electrical testing/inspection specialization. When these two are combined, the insulation status, junction temperatures, and mechanical behavior of the motor can be evaluated within a single, consistent framework.

Our approach is unbiased and educational: we don't steer you towards a specific product or brand, we clearly explain the measurement results and what they mean. We distinguish between legal requirements and best practices, ensuring the decision remains within the business.

• TURKAK accredited Type A Inspection Body (TS EN ISO/IEC 17020, electrical installations)
• A combination of accredited thermography and electrical testing expertise.
• Impartial, educational, and transparent reporting.

Related Services

• Vibration
• MCC Inspection
• Thermography

Frequently Asked Questions

Can it be tested without disassembling or stopping the engine?

Insulation resistance, polarization index (PI/DAR), and winding resistance measurements are taken after the motor power is cut off and safely isolated, during a brief shutdown without disassembling the motor. Vibration and thermography measurements, however, are usually taken while the motor is running. Therefore, in most cases, extensive disassembly is not necessary.

What should the polarization index (PI) be?

PI is a ratio that shows the change in insulation resistance over time, and generally accepted thresholds are evaluated within the framework of IEEE 43. However, acceptable values can vary depending on the insulation type, temperature, and age of the machine; therefore, instead of memorizing a single number as the limit, we interpret both general thresholds and the motor's own historical measurement data together.

Is a partial discharge test necessary for every engine?

No. Partial discharge measurement is particularly meaningful in medium voltage (MV) motors because the insulation operates under a high electric field. In low voltage motors, insulation resistance, PI/DAR, and winding resistance measurements usually provide sufficient information.

Does this test replace the legally mandated periodic inspection?

Two things need to be distinguished. Periodic electrical safety inspections of the motor as work equipment are a legal obligation and can only be carried out under accredited scope. Predictive maintenance/good practice, on the other hand, includes detailed winding analysis, partial discharge trend, and thermographic monitoring. Our report clearly and separately demonstrates these two aspects.

According to which standards is the evaluation being carried out?

For rotating electrical machinery, the IEC/EN 60034 series is used as a basis (e.g., 60034-1 for ratings, 60034-14 for vibration, 60034-27 for partial discharge); IEEE 43 is used as a general framework for interpreting insulation resistance and polarization index measurements.

Who signs the report and what are its contents?

The output is a test report prepared by a qualified electrical engineer. The report includes measured values, applied test voltages, temperature corrections, standard references used, comparison with previous periods (trend), and reasoned recommendations.