【Daily Question 2019】Hydrogen production and hydrogenation section – Question No. 009

Cooling water blockage, overload, asymmetrical connection between pump shaft and motor, pump evacuation, etc

1. Poor insulation, moisture. 2. Excessive current, overload. 3. Short circuit in the motor’s power cable. Large voltage fluctuations. 5. Friction between the rotor and stator during operation.

1) Reasons for motor overheating due to power supply issues: There are several reasons why a motor overheats as a result of problems with the power supply: a. Excessively high supply voltage – When the supply voltage is too high, the back EMF of the motor, as well as the flux and flux density, increase accordingly. Since the magnitude of iron loss is proportional to the square of the magnetic flux density, an increase in iron loss leads to overheating of the core. An increase in flux, in turn, causes a sharp rise in the excitation current component, leading to increased copper losses in the stator windings and resulting in winding overheating. Therefore, when the supply voltage exceeds the motor’s rated voltage, it causes the motor to overheat. b. Low supply voltage: When the supply voltage is too low, if the electromagnetic torque of the motor remains constant, the flux will decrease. As a result, the rotor current increases, and the component of the stator current related to the load also increases. This leads to increased copper losses in the windings, causing overheating of both the stator and rotor windings. c. Unsymmetrical supply voltage: When one phase of the power supply wire is broken, a fuse in one phase blows, or the starter device’s contacts are damaged resulting in a break in one phase, this will cause the three-phase motor to operate on only one phase. As a result, the two phases that are in operation experience high currents, which leads to overheating and eventual burnout. d. Unbalanced three-phase power supply: When the three-phase power supply is unbalanced, it causes the currents in the motor’s three phases to be unbalanced, leading to overheating of the windings. As can be seen from the above, when a motor overheats, the power supply should be considered first as the possible cause. After confirming that there are no issues with the power supply, consider other factors. 2) Reasons why load causes the motor to overheat. The reasons for overheating of the motor due to load are as follows: a. Overloaded operation of the motor. When the equipment is not properly matched and the load power on the motor exceeds its rated power, the motor operates under overload conditions for an extended period of time (in other words, trying to pull a heavy load with a weak motor), which leads to overheating of the motor. When repairing an overheating motor, it is necessary to first determine whether the load power matches the motor’s power, in order to avoid unnecessary disassembly. b、The mechanical load being pulled is not operating properly. Although the equipment is complete, the mechanical load it pulls does not function correctly; the load varies in magnitude during operation, causing the motor to overheat. c. Fault in the machine being pulled: If the machine being pulled has a fault, such as inflexible rotation or getting stuck, it will cause the motor to overload, leading to overheating of the motor windings. Therefore, when troubleshooting motor overheating, load-related factors cannot be ignored. 3) Reasons for overheating caused by the motor itself: a. Open circuit in the motor windings – When one of the phases in the motor windings is open, or one of the parallel branches is open, it leads to an imbalance in the three-phase currents, causing the motor to overheat. b. Short circuit in the motor windings: When a short circuit occurs in the motor windings, the short-circuit current is much higher than the normal operating current, which increases the copper loss in the windings, leading to overheating and even burning out of the windings. c. Incorrect motor wiring: When a motor connected in a delta configuration is wired incorrectly in a star configuration, it continues to operate under full load. The current flowing through the stator windings exceeds the rated value, which can cause the motor to stop running on its own. If it remains stopped for an extended period without the power supply being disconnected, the windings will not only overheat severely but may also get burned out. When a star-connected motor is connected in a delta configuration, or when several coil groups connected in series to form one circuit are connected in parallel across two circuits, it will cause the windings and core to overheat; in severe cases, the windings may be damaged. e. Incorrect motor wiring: When a coil, a set of coils, or a phase winding is connected in the wrong direction, it can lead to severe imbalance in the three-phase currents, causing the windings to overheat. f. Mechanical faults of the motor: When the motor shaft is bent, the assembly is improper, or there are problems with the bearings, it can lead to an increase in the motor current. This increases copper losses and mechanical friction losses, causing the motor to overheat. 4) Reasons for motor overheating due to poor ventilation and heat dissipation: a. High ambient temperature, which results in high inlet air temperature. b. Debris blocking the air inlet prevents proper airflow, resulting in a low volume of air intake. c. Excessive dust inside the motor hinders heat dissipation. d. The fan is damaged or installed incorrectly, leading to no airflow or a low volume of airflow. e. No air shroud is installed, or there are no baffles inside the motor’s end cover, which prevents the motor from having an adequate air flow path

1. Overloaded operation, with excessive current. 2. Harsh environment. 3. Unstable voltage, either too high or too low, results in excessive current. 4. 3-phase asymmetry, or phase loss. 5. Motor faults, including winding open circuits, short circuits, leakage current, poor contacts, and bearing wear.

The power supply causes the motor to overheat; the load causes the motor to overheat; problems with the motor itself; poor ventilation and heat dissipation

1. Poor insulation, moisture. 2. Excessive current, overload. 3. Short circuit in the motor’s power cable. Large voltage fluctuations. 5. Friction between the rotor and stator during operation.

1. Poor insulation, moisture. 2. Excessive current, overload. 3. Short circuit in the motor’s power cable. Large voltage fluctuations. 5. Friction between the rotor and stator during operation.

1) Friction occurs between the stator and rotor； 2) The motor is damp, resulting in reduced insulation ； 3) High ambient temperature and poor cooling ； 4) Motor overload ； 5) Operation of the motor with a missing phase.

1 Motor mechanical failure； 2 Power supply voltage fluctuations ； 3 The motor load is too high ； 4 Poor ventilation and heat dissipation.

The bearing is damaged due to excessive stress; there is either too much or too little lubrication in the bearing; the stator windings have low resistance resulting in short circuits; or the load is too high (operating under overload conditions)