Measure the current and voltage of the motor to ensure that they are within the rated range. Use a megohmmeter to test the insulation resistance of the motor windings to ensure that it is above 100 megohms. Temperatures exceeding 100°C or excessive vibration may cause motor failure. Regular inspection and maintenance can extend the life of the motor and improve operating efficiency.
Engine inspection
Suppose we have a 15 kW motor. When running at full load, the current should be around 32 amps. If the current exceeds 40 amps, the motor may face overload and its life span will be more than 50% shorter than that of a normally operating motor.
Take a 100 kW motor as an example. If its efficiency is less than 90%, at least 10 kW of energy is wasted in the conversion process for every 100 kW of input power. According to data, a 1% drop in efficiency usually leads to a 5% to 10% increase in annual energy consumption.
According to industry reports, more than 80% of motor failures are directly related to excessive temperature, especially when the temperature exceeds 100°C for a long time. Studies have shown that when the temperature of the motor rises by 10°C, the life of the motor will be reduced by about 50%.
The vibration speed of the motor during operation should be controlled within 2mm/s. Studies have shown that the maintenance cost of motors that exceed the standard vibration level may be about 30% higher than that of normal motors. For example, in a large factory, a motor that frequently exceeds the standard vibration level may incur tens of thousands of yuan in maintenance costs each year.
If a motor that was originally running quietly suddenly makes a loud noise (for example, more than 70 decibels), there may be a fault inside the motor. The current fluctuation amplitude of a 5-kilowatt motor under no-load conditions should be controlled within 5%. If the fluctuation exceeds 10%, the motor’s electrical system needs to be checked. Data shows that current fluctuations caused by electrical faults account for about 15% of all motor failures.
Taking a 50-kilowatt motor as an example, if the bearing is severely worn, the motor speed may be reduced by 10% to 20%. According to market research, about 30% of motor failures are caused by bearing problems.
Data shows that the failure rate of improperly lubricated motors is twice that of normal motors. The replacement cycle of motor lubricants is 6 months to 1 year. Surveys show that about 20% of motor failures are related to the control system.
Power supply test
Taking a common 100-kilowatt motor as an example, the power supply voltage should be within the range of 380 volts ±10%. If the voltage fluctuates by more than 5%, the motor will face the risk of reduced efficiency and overload of the electrical system. Research shows that about 30% of motor failures are directly related to power supply problems.
Suppose a factory uses a 55-kW motor. If the current fluctuates by more than 15% during operation, the motor is very likely to be affected. According to statistics, motor failures caused by current fluctuations account for about 18% of total motor failures.
When the power factor of a 30-kW motor is less than 0.8, more than 30% of the electrical energy may be wasted. The starting current of the motor should be 5 to 7 times its rated current. For example, a 7.5-kW motor exceeds the standard range if the current reaches 40 amperes at startup and the normal operating current is 15 amperes.
Taking a 37-kW motor as an example, good grounding can ensure the safe operation of the motor. According to data, about 20% of electrical fires are caused by poor grounding. If the total harmonic content of a 40-kW motor in the power supply exceeds 5%, it may affect the efficiency and stability of the motor.
If the current exceeds the rated current by more than 15% when the motor is running at full load, the motor may be overloaded. Taking a 10-kilowatt motor as an example, its current should be around 22 amperes under full load. If the current exceeds 25 amperes, the motor may be overloaded.
Taking a 15-kilowatt motor as an example, if the voltage fluctuation exceeds 10%, it may cause unstable starting of the motor. During the power supply process, voltage stabilizers and other equipment should be used to reduce the impact of voltage fluctuations on motor operation.
The operating frequency of industrial motors should be 50 Hz. Taking a 20-kilowatt motor as an example, the efficiency of the motor may decrease by 2% to 3% for every 1 Hz deviation in frequency.
Taking a 50-kilowatt motor as an example, its insulation resistance should be maintained above 100 megohms. Regular electrical insulation testing can timely detect potential risks of the motor.
Insulation resistance test
When a 40-kilowatt motor is running, the insulation resistance between the stator winding and the ground of the motor should usually be greater than 100 megohms. When the motor is used for more than 10 years, the insulation resistance may show a downward trend.
Ideally, for a 5 kW motor, the measured insulation resistance should be at least 1 megohm. If the measured resistance is significantly lower than this, for example, less than 0.5 megohm, the motor may have insulation damage. When the motor is running at 50°C, the insulation resistance value will drop by 20% to 30% compared to normal temperature.
High-voltage industrial motors need a comprehensive insulation resistance inspection once a year. Low-voltage motors should be inspected every six months or even quarterly. Studies have shown that early detection and repair of insulation resistance problems can reduce motor failure rates by about 25%.
For a 100 kW motor, for example, the insulation performance of the motor will deteriorate, resulting in current leakage. When testing the insulation resistance of a motor, if it is below the standard value, the efficiency of the motor will usually decrease by 10% to 15%. Taking electricity costs as an example, if a 100 kW motor is running with abnormal insulation resistance, it may cost about 10,000 to 20,000 yuan more in electricity costs each year. A 20 kW pump motor with an insulation resistance of less than 2 megohms may have a winding short circuit in a high humidity environment.
Taking a 10-kilowatt motor as an example, when the insulation resistance decreases year by year and the decrease exceeds 10%, there may be water leakage or lubricating oil leakage inside the motor.
For low-voltage motors, the test voltage should be 500 volts, and for high-voltage motors, the test voltage can be increased to 1000 volts. Taking a 30-kilowatt high-voltage motor as an example, using a 1000-volt test voltage can more effectively detect the aging of the motor insulation material.
If the insulation resistance of a 20-kilowatt motor is 100 megohms, 80 megohms, and 60 megohms in three tests, it means that the insulation performance of the motor has gradually decreased. According to the trend, the staff can repair or replace the insulation material in advance.
Measuring current
For a motor with a rated power of 50 kilowatts, the current should be close to the rated current marked on the motor nameplate during normal operation. If the current measured during the test is 100 amperes, and the rated current is 90 amperes, then the motor is overloaded. According to relevant research, when a motor is overloaded, it may lose 10% to 20% of its energy efficiency.
When a 200-kilowatt motor is running at high load, the current may reach 400 amperes, while under normal load the current should be controlled within 350 amperes. According to statistics, about 20% of industrial motors will have current overload during operation.
Some motors that require high starting torque may have a current of 5 times or even higher than the rated current when starting. For example, a 300-kilowatt motor may have a current of 1500 amperes at the moment of starting.
If a motor with a nominal power of 100 kilowatts runs at full load with an actual current of 200 amperes and a nominal current of 180 amperes, the motor will have a large current loss during operation. In a large factory that requires 10 50-kilowatt motors to work together, if the current of one motor is much higher than that of the other motors, then the load of this motor may be too large.
A 15 kW motor has an overload protection setting of 150 amps. If the current exceeds 150 amps during operation, the protection device should immediately activate and cut off the power supply. Testing the responsiveness of the protection device can ensure that the motor can be shut down in time when an overload occurs.
If the current measurement of a 50 kW asynchronous motor shows a low power factor (less than 0.8), it indicates that the load efficiency of the motor is poor. In an environment with a temperature above 40 degrees Celsius, the current of a 100 kW motor may be 10% to 15% higher than the current during normal operation.
Under normal circumstances, the current of the motor at startup is about 5 times the rated current, and within a few seconds after startup, the current gradually decreases to the rated current. For example, for a 200 kW motor, the current should be controlled within 1000 amps at startup and should quickly drop to less than 500 amps after startup.
Evaluating system performance
For a 100 kW motor, if its efficiency under load conditions is 95%, then it is running efficiently. If the motor is overloaded or the system is not matched, it may lead to reduced efficiency.
The motor drive system power of a production line is 500 kilowatts. In the test, the actual power loss was about 50 kilowatts, and the system loss rate was 10%. 10% of the energy is lost in the system as heat.
Take a 1000-kilowatt large pump motor as an example. If the load fluctuation exceeds the set range (such as more than 10% fluctuation), the system may be abnormal. Through continuous monitoring and data analysis, problems can be discovered and intervened in time.
The power factor of industrial motors should be kept above 0.8. A 200-kilowatt motor has a rated power factor of 0.9. If the test results show that the power factor drops to 0.7, it indicates that the motor has performance problems.
If a high-power crane motor has a current peak of 6 times the rated current at startup, the starting circuit design may be improper or the motor itself may be faulty. By testing the starting peak of the current, technicians can help evaluate whether the motor starts smoothly.
Some motors should be kept below 80°C during normal operation. If the temperature exceeds 100°C when the load increases, the motor may overheat. By using a temperature sensor to monitor the operating temperature of the motor in real time, overheating can be effectively prevented.
If a 500 kW motor is frequently subject to grid fluctuations, the motor current and power factor will fluctuate accordingly. If a load test is performed on a 150 kW motor, if the efficiency remains above 90% when the load increases to 80%, then the motor has good load adaptability.
