Analysis of the Causes of Increased Motor Fault Factors and Selection of Protective Devices

In the modern industrial environment, the increase in motor failure rates is not caused by a single factor, but rather the result of the combined effect of multiple trends and challenges.

I. Reasons for the increase in motor failure factors

1. Deterioration of power supply quality

Voltage fluctuation and three-phase imbalance: The complexity of grid loads (such as the integration of new energy sources and the increase in nonlinear devices) leads to excessive voltage amplitude fluctuation (±5%) and three-phase imbalance degree exceeding the standard (> 5%), causing motor overcurrent, heating and efficiency decline.

Phase loss operation: Aging of distribution lines or poor contact can easily lead to phase loss. When a phase is lost, the remaining two-phase current suddenly increases to 4 to 7 times the rated value, accelerating insulation aging and even burning out the windings.

2. Mechanical and environmental factors

Bearing wear and rotor imbalance: Long-term high-load operation or insufficient lubrication can cause abnormal noise and jamming of the bearings. Rotor imbalance leads to intensified vibration, affecting the motor's lifespan.

Poor heat dissipation: Dust accumulation, ventilation duct blockage or high-temperature environment leads to a decrease in heat dissipation efficiency, and the winding temperature rise exceeds the standard (for example, for every 10℃ increase, the insulation life is halved).

3. The operating conditions become more complicated

Frequent start-stop and overload: Modern equipment has increased requirements for the start-stop frequency and dynamic response of motors. Frequent inrush currents (up to 6-8 times the rated current) lead to the accumulation of thermal fatigue.

Diversified load types: Abnormal loads such as idling of water pumps and locked-rotor of fans intensify the mechanical stress on motors, requiring more precise protection logic to deal with them.

4. Insulation aging and electrical faults

Inter-turn short circuit and ground fault: Partial discharge caused by moisture, aging or overvoltage breakdown of insulating materials can lead to winding short circuit or ground. It is necessary to monitor insulation resistance and leakage current in real time.

Ii. Selection Principles and Types of Motor Protection Devices

1. Principles for selecting protective devices

Match motor capacity with operating conditions: For small-capacity motors, economical thermal relays can be selected; for high-power or critical equipment, intelligent comprehensive protectors should be adopted.

Comprehensive functional coverage: It needs to cover core fault types such as overload, phase loss, locked rotor, imbalance, and leakage, and support multi-parameter monitoring (current, voltage, temperature).

Anti-interference and reliability: In industrial environments, EMC standards (such as GB/T17626) must be met, and industrial-grade components should be used to ensure high/low temperature stability.

2. Common types of protective devices and applicable scenarios

Type

Features

Applicable scenarios

Typical product

Thermal relay

It has low cost, reliable overload protection, but low sensitivity of phase loss protection and no real-time monitoring function

Ordinary small-power motors, non-frequent start-stop environments

JR36 type, ABBT series

Electronic overcurrent relay

Supports inverse-time characteristics, has a wide setting range (3-4 times In), and can display fault types

In places with large load fluctuations such as mines and compressors

UL-E2 series, Schneider M series circuit breakers

Intelligent comprehensive protector

It integrates protection, monitoring and communication functions, supports the Modbus protocol, and can record historical fault data

Key equipment, automated production lines

Intelligent integrated protector WDH-31-503K-100A, D30M measurement and control device

Solid state relays and soft starters control the starting current through thyristors and are equipped with built-in locked-rotor and leakage detection modes

For high-power motors or industrial equipment blocks that require soft start, reduce mechanical shock

Schneider ATS48 and Eaton PKZMX circuit breakers

Temperature detection type protector

Directly monitor the winding temperature (such as PTC thermistors) to avoid the lag of current protection

Submersible pumps and compressors with high-precision temperature control requirements

JW9 series, SPB type thermal protectors

3. Protection schemes under special working conditions

High-voltage/high-frequency environment: Differential protection (such as the 9698 generator differential device) is adopted to prevent phase-to-phase short circuits in the stator windings.

Flammable and explosive environments: Select flameproof protectors and combine residual current monitoring (30mA threshold) to prevent electric leakage fires.

Long-distance power supply lines: Low-voltage protection (0.5-0.7Un action) is configured to prevent insufficient torque caused by under-voltage operation.

Iii. Development Trends of Protective Devices

1. Intelligence and integration: Predict faults through AI algorithms (such as bearing wear trend analysis), and combine edge computing to achieve local decision-making.

2. High-precision sensing technology: Utilizing Rogowski coils or optical fiber current sensors to enhance sampling accuracy (±0.5%), it ADAPTS to the complex harmonic environment of frequency converter power supply.

3. Cloud platform linkage: Supports 4G/5G remote monitoring, and uploads data to the cloud in real time for energy efficiency analysis and health management.

Iv. Summary

The increase in motor faults is the result of the combined effect of power quality, mechanical load and environmental factors. It is necessary to select matching protection devices according to specific working conditions. Traditional thermal relays are still suitable for simple scenarios, while intelligent integrated protectors have become the mainstream trend due to their multi-functional integration and communication capabilities. In the future, protection solutions that combine predictive maintenance with Internet of Things (iot) technology will further enhance the reliability of motor systems.

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