Fault diagnosis and cause analysis of Roots blower motor burning out within half an hour
1、 Electrical system failures (accounting for approximately 45%)
1. * * Abnormal power supply voltage**
-Voltage deviation ＞ ± 10 (such as 380V system measured ＜ 342V or ＞ 418V)
-Three phase imbalance>2 (phase to phase current difference)
-Case: A factory experienced voltage fluctuations up to 410V due to a transformer malfunction, resulting in a threefold increase in motor temperature rise rate
2. * * Protection device failure**
-The setting value of the thermal relay is incorrect (should be set to 1.05-1.2 times the rated current of the motor)
-Circuit breaker instantaneous protection not activated (failure to trip in time during short circuit)
-Actual test case: The rated current of the motor is 52A, but the thermal relay is set to 80A
3. Insulation damage**
-Winding insulation resistance<1M Ω (measured with a 500V megohmmeter)
-Partial discharge capacity>10pC (indicating insulation degradation)
2、 Abnormal mechanical load (accounting for approximately 35%)
1. Overload operation of the fan**
-The actual pressure exceeds the nameplate value by 10 (if calibrated at 58.8kPa but running at 64.7kPa for a long time)
-Current overload characteristic: continuous>1.2 times the rated current (e.g. the rated current of a 55kW motor is about 100A, and the measured current reaches 130A)
2. * * Rotating components are stuck**
-Bearing damage leads to a 3-5 times increase in friction torque
-Radial sweeping of rotor (friction power consumption increases by 800W/cm2 when clearance<0.1mm)
3. * * Transmission system malfunction**
-Coupling misalignment (radial deviation>0.1mm/m)
-The belt is too tight (when the tension is greater than 350N, the bearing load increases by 40)
3、 Cooling system issues (accounting for approximately 15%)
1. * * Cooling failure**
-The air-cooled motor fan is damaged (with a decrease of 60% in air volume)
-Water cooling motor water channel blockage (flow rate<rated value 70)
2. * * Environmental temperature exceeds the standard**
-When the temperature in the computer room exceeds 40 ℃, the rated power of the motor needs to be reduced by 15 degrees for use
-Actual test case: The temperature in a confined space reaches 52 ℃, and the temperature rise of the motor accelerates to 130 ℃/h
4、 Equipment selection errors (accounting for approximately 5%)
1. * * Power mismatch**
-The actual required power is 55kW, but a 45kW motor is selected (underload rate>18)
-Inappropriate starting method (when starting directly, the surge current reaches 7 times the rated value)
2. Insufficient protection level**
-IP54 motor for use in dusty environments (IP65 required)
-Ordinary motors are used in corrosive gas environments
5、 Fault diagnosis process
1. Power outage detection**
-Measure winding resistance (abnormal if three-phase deviation>2)
-Manual turning inspection for mechanical resistance (normal torque<5N · m)
2. * * Trace analysis**
-Bearing cage melting (temperature>300 ℃)
-Winding insulation carbonization (local temperature>180 ℃)
3. * * Data traceability**
-Retrieve the historical curve of the frequency converter (view changes in current and temperature)
-Check the action record of the protective device
6、 Preventive improvement measures
1. * * Electrical system**
-Install voltage monitoring relay (action value set ± 8)
-Measure insulation resistance quarterly (trend analysis)
2. * * Mechanical system**
-Install vibration monitoring device (alarm value set to 4.5mm/s)
-Monthly inspection of coupling alignment (calibration of laser alignment instrument)
3. * * Thermal management**
-Add forced ventilation system (air exchange rate>20 times/hour)
-Important motor configuration PT100 temperature sensor
4. * * Operation and Maintenance Standards**
-A 4-hour no-load test must be conducted before the first operation
-Establish a motor health record (including baseline data for current and temperature)
7、 Typical Case Analysis
**Accident at a certain sewage treatment plant:**
-Phenomenon: The motor of the 55kW Roots blower burned out after running for 27 minutes
-The investigation found that:
-Export valve mistakenly closed (system pressure reached 98kPa, exceeding the rated value of 67)
-Current continuously at 160A (rated 100A)
-The thermal relay is short circuited
-Direct loss: motor scrapped (38000 yuan)
-Indirect loss: 36 hours of shutdown (loss of 96000 yuan)
conclusion
Short term motor burnout is often caused by multiple factors, and it is recommended to take the following steps:
1. Immediately save operational data (current and voltage records)
2. Conduct professional disassembly and analysis (with a focus on inspecting bearings and windings)
3. System investigation of associated equipment (valves, pipelines, control systems)
After rectification, a 72 hour trial operation monitoring is required
The key to preventing such accidents lies in establishing a comprehensive preventive maintenance system, with particular emphasis on regular calibration of protective devices and status monitoring of mechanical components. For important equipment, it is recommended to configure motor intelligent protectors (such as Schneider TeSys series), which can monitor 15 types of faults in real time and provide early warning.
