The installation of electric motors for lifting machinery is a crucial process that requires careful attention to detail to ensure the safe and efficient operation of the lifting equipment. There are two main points to consider during the installation process.
Before installation, thorough inspection is essential. Firstly, check whether the data on the motor nameplate is consistent with the drawings. The nameplate on the motor provides important information such as the motor’s power rating, voltage, current, speed, and other specifications. By comparing this information with the drawings for the lifting machinery, it can be ensured that the correct motor has been selected for the specific application. Any discrepancies between the nameplate data and the drawings could lead to improper functioning of the lifting equipment or even safety hazards.
After confirming the nameplate data, rotate the motor rotor by hand. This step is crucial for detecting any mechanical issues with the motor. The rotation should be flexible without jamming or abnormal noise. A smooth rotation indicates that the bearings and other moving parts of the motor are in good condition and are properly lubricated. If there is any jamming or abnormal noise, it could indicate a problem with the bearings, rotor alignment, or other internal components. In such cases, further inspection and troubleshooting may be required before proceeding with the installation.
For wound rotor motors, an additional step is to check the contact condition between the carbon brush and the slip ring. The carbon brush and slip ring are important components that transfer electrical current from the power source to the rotor windings. A proper contact between the carbon brush and slip ring is essential for efficient electrical conduction and smooth motor operation. Check for signs of wear, damage, or improper alignment of the carbon brush and slip ring. Ensure that the carbon brush is making good contact with the slip ring and is not worn down to the point where it needs to be replaced. Any issues with the carbon brush and slip ring contact can lead to electrical problems, reduced motor performance, and potential damage to the motor.
For example, imagine a large crane with a powerful electric motor for lifting heavy loads. If the motor nameplate data does not match the requirements of the crane’s design, it could result in the motor being unable to handle the required load, leading to overheating, reduced lifting capacity, or even motor failure. Similarly, if the rotor is jammed or there are problems with the carbon brush and slip ring contact in a wound rotor motor, it could cause the crane to operate erratically or fail to lift loads properly, posing a significant safety risk to the operators and surrounding personnel.
Measuring insulation resistance and handling low insulation values. Use a 500-volt megger to measure the insulation resistance between phases and to the ground of the motor. Insulation resistance is a critical parameter that indicates the electrical integrity of the motor’s windings and insulation system. A high insulation resistance is necessary to prevent electrical leakage and short circuits, which can damage the motor and pose a safety hazard. The insulation resistance of the stator and rotor must not be less than the specified value. This specified value is typically determined by the motor manufacturer and is based on the motor’s design and intended application.
If the insulation resistance is lower than the specified value, drying should be carried out. Drying is necessary to remove moisture from the motor windings and insulation, which can reduce insulation resistance and lead to electrical problems. There are several methods for drying the motor, and the choice depends on the actual situation and relevant conditions. Electric heating drying method involves using electrical heaters to warm up the motor and drive out moisture. This method is effective but requires careful control of the heating temperature to prevent damage to the motor. Low voltage (36 volts) copper loss method uses a low voltage current to pass through the motor windings, generating heat and drying out the insulation. This method is relatively safe but may take longer to achieve the desired drying effect. Idling self-drying method involves running the motor at a low speed without load to generate heat and evaporate moisture. This method is simple but may not be suitable for motors with severe moisture problems.
The maximum temperature during drying must not exceed 70°C. Exceeding this temperature can damage the insulation materials and reduce the lifespan of the motor. Careful monitoring of the temperature is essential during the drying process to ensure that the motor is not overheated.
When the factory delivery period of the motor exceeds the specified value or there are internal defects or suspected defects, disassembly inspection and treatment can be carried out. Before disassembling the motor, make assembly marks at the joint seam. These marks will help ensure that the motor can be reassembled correctly after inspection and treatment. Remove the motor end cover carefully to expose the internal components. Let the rotor fall into the stator bore gently to avoid damage to the windings and other parts. Extend one end of the motor rotor with a sleeve and lift the rotor so that it does not collide with the stator. Move the rotor out of the stator bore carefully for comprehensive inspection.
During the inspection, look for signs of damage, wear, corrosion, or other defects in the windings, bearings, rotor, and stator. Check for loose connections, broken insulation, or other electrical issues. If any defects are found, they should be repaired or replaced as necessary. After treatment, add lubricating oil to the bearing to ensure smooth rotation and reduce wear. Perform insulation treatment on the coil as appropriate to restore the insulation resistance to the required level.
For instance, if a motor has been in storage for a long time or has been exposed to moisture, it may have a low insulation resistance. By using the appropriate drying method and conducting a thorough inspection and treatment, the motor can be restored to a proper working condition and safely installed in the lifting machinery.
In conclusion, the installation of electric motors for lifting machinery requires careful attention to detail and adherence to proper procedures. By checking the motor nameplate data, inspecting the mechanical and electrical components, measuring insulation resistance, and taking appropriate measures for low insulation values and potential defects, the installation can be carried out successfully, ensuring the safe and efficient operation of the lifting equipment.
