Introduction: A disabling symptom that prompts research
Unwanted thermal relay tripping in a production drive system is a common problem that causes production downtime and time-consuming diagnostics. In the case of production in Ukraine, where the lack of temperature regulation in the room and uneven loads on electric motors are common, there is a high risk of incorrect tripping of the thermal relay, even with the appropriate selection of components.
Component overview: function, location, operating conditions
The thermal relay Schneider Electric A9D52610 is used to protect electric motors from overload. It is installed in the electric plate or in the engine housing. The component senses the temperature of the motor windings through thermal sensors that are installed in the housing. Operating conditions include an ambient temperature of 0 to +40 °C, a rated load of up to 100% of the rated current, and a frequency of 50 Hz.
Evidence of a defect: what the technician sees
During the research, it was found that the thermal relay turns off when the load on the motor exceeds 110% of the nominal one. The room temperature reaches 45 °C during operation. Vibration measurements showed values of up to 7.2 mm/s, which exceeds the permissible 5.5 mm/s according to ISO 10816-3:2009. On the corresponding diagrams, there are no connections of additional thermal sensors, which can affect the accuracy of measurements.
Root cause research: a systematic review
The 5-why method and the Ishikawa diagram were used to determine the root cause. The first "why" is the disconnection of the thermal relay. The second is a high load. The third is the high temperature of the environment. The fourth is the insufficient size of the thermal relay. The fifth is incorrect installation or lack of thermal sensors.
Identifying Root Causes: Ranking with Probability and Supporting Evidence
1. High ambient temperature (probability: 45%)
The room temperature is higher than recommended (45 °C instead of 40 °C). This leads to a decrease in the efficiency of the thermal relay, which can cause an unwanted trip.
2. Incorrect size of thermal relay (probability: 35%)
The relay is selected according to the rated current, but the load at the maximum operating mode is not taken into account. This leads to premature shutdown.
3. High load (probability: 20%)
The load on the motor exceeds 110% of the nominal. This causes heating of the windings, which causes the relay to trip.
Western solutions: immediate fixation + long-term prevention
1. Changing the thermal relay to a more powerful one
Choosing a thermal relay with a rated current corresponding to 120% of the rated load. This will provide more accurate protection at maximum loads.
2. Installation of additional temperature sensors
Additional temperature sensors are installed in the engine housing for more accurate temperature measurements. This allows to reduce measurement errors.
3. Room cooling
Installing a ventilation or air conditioning system to reduce the room temperature to the recommended level (40 °C). This will reduce the effect of the environment on the thermal relay.
Quick diagnostic check: 12 points for the technician in the work environment
- Measure the temperature of the environment in the room.
- Check the distance to the temperature sensor from the engine.
- Measure engine vibration.
- Confirm the motor load rating.
- Check the relay installation according to the instructions.
- Determine if additional temperature sensors are installed.
- Check the current on the motor during operation.
- Measure the temperature of the motor windings.
- Check the manufacturer's manual for the thermal relay.
- Perform a vibration analysis using a measuring device.
- Check whether the temperature sensor is installed incorrectly.
- Measure the temperature in the operating mode.
- Check that the motor power relay is correct.
- Measure the engine load.
- Check that the relay complies with DSTU 4174:2018 standards.
- Measure the temperature in the room.
- Check that the relay complies with ISO 10816-3:2009.
Prevention strategy: maintenance intervals, condition monitoring, project improvement
To prevent unwanted disconnection of the thermal relay, it is recommended:
- Calculate the load on the engine taking into account the load at maximum mode.
- Install additional temperature sensors for more accurate measurements.
- Carry out regular temperature control in the room.
- Perform engine vibration measurements every 3 months.
- Use condition monitoring systems to determine deviations.
- Install indoor cooling systems if the temperature exceeds 40 °C.
- Calculate the size of the thermal relay taking into account the load on the motor.
- Periodically check the relay using measuring devices.
- Use components that comply with DSTU 4174:2018 and ISO 10816-3:2009.
Conclusion: Transition to UNITEC-D E-Catalog
To ensure the reliable operation of thermal relays in electric drive systems, it is necessary to take into account the influence of the ambient temperature, the load on the motor and correctly choose the components. Knowledge of dimensions, measurements and the use of standards will ensure the long-term performance of the systems. You can find the required components and preventive elements in the UNITEC-D E-Catalog.
List of references
- DSTU 4174:2018 — Requirements for electrotechnical devices and automation equipment
- ISO 10816-3:2009 — Vibration measurement of machinery — Part 3: Requirements for vibration measurement
- EN 50034:1997 — Requirements for thermal relays
- Schneider Electric - Technical documentation for A9D52610
- Handbook of Failure Analysis for Electric Motors
