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The iron core of the oil pump motor in operation will produce iron loss in the alternating magnetic field. When the winding is energized, copper loss will occur, and other stray losses will occur. These will increase the temperature of the motor and on the other hand the oil pump will dissipate heat. When the heat and heat are equal, the equilibrium state is reached, and the temperature does not rise and stabilizes at a level. When the heat is increased or the heat is reduced, the balance is broken, the temperature continues to rise, the temperature difference is increased, the heat is increased, and a new balance is reached at another higher temperature. However, the temperature difference at this time, that is, the temperature rise has increased more than before, so that temperature rise is an important indicator in the design and operation of the motor, which indicates the degree of heat generation of the oil pump motor. During operation, if the temperature rise of the motor suddenly increases , indicating that the motor is faulty, or the air duct is blocked or the load is too heavy. Now Dalang Motor Xiaobian explains the methods of fault analysis and measurement.
First, the relationship between temperature rise and temperature
For a normal operation of the oil pump motor, the theoretical temperature rise under the rated load should be independent of the ambient temperature, but it is actually affected by environmental temperature and other factors.
(1) When the temperature drops, the temperature rise of the normal motor will decrease slightly. This is because the winding resistance R is lowered and the copper loss is reduced. For every 1 °C drop in temperature, R is reduced by about 0.4%.
(2) For self-cooling motors, the temperature rise is increased by 1.5 to 3 °C for every 10 °C increase in ambient temperature. This is because the copper loss of the winding increases as the temperature rises.
(3) The air humidity is 10% higher. Due to the improvement of heat conduction, the temperature rise can be reduced by 0.07~0.38°C, with an average of 0.19°C.
(4) The altitude is 1000m, and 100m per liter, the temperature rise increases by 1% of the temperature rise limit.
Second, the limit working temperature and the maximum allowable working temperature
Generally speaking, the ultimate operating temperature of Class A is 105 °C, and the maximum allowable operating temperature of Class A is 90 °C. So, what is the difference between the extreme operating temperature and the maximum allowable operating temperature? In fact, this is related to the measurement method. Different measurement methods reflect different values ​​and have different meanings.
(1) Thermometer method: The measurement results reflect the local surface temperature of the winding insulation. This number is on average about 15 °C lower than the actual maximum temperature of the winding insulation, the "hottest spot". This method is the simplest and most widely used in medium and small motors.
(2) Resistance method: The measurement result reflects the average value of the copper temperature of the entire winding. This number is reduced by 5 to 15 ° C depending on the actual maximum temperature. The method measures the cold state and the thermal resistance of the conductor, and calculates the average temperature rise according to the relevant formula.
(3) Buried thermometer: The copper or platinum resistance thermometer or thermocouple is embedded in the winding, core or other parts that need to measure the highest temperature expected during the test. The measurement results reflect the temperature at which the temperature measuring element contacts. Large motors often use this method to monitor the operating temperature of the motor.
The temperature measured by various measuring methods has a certain difference from the actual maximum temperature. Therefore, it is necessary to subtract the difference from the "limit operating temperature" of the insulating material to be the "highest allowable operating temperature".
Third, the temperature limit of each part of the motor
(1) The temperature rise of the core in contact with the winding (thermometer method) shall not exceed the temperature rise limit of the winding insulation (resistance method), that is, Class A is 60 °C, Class E is 75 °C, Class B is 80 °C, Class F is 100 ° C and Class H is 125 ° C.
(2) The temperature of the rolling bearing should not exceed 95 °C, and the temperature of the sliding bearing should not exceed 80 °C. If the temperature is too high, the oil quality will change and the oil film will be destroyed.
(3) The surface of the squirrel-cage rotor has a large stray loss and a high temperature, which is generally limited to the extent that it does not endanger the adjacent insulation.
Fourth, the motor heating fault elimination
When the motor temperature exceeds the maximum operating temperature or the temperature rise exceeds the specified or the temperature rise does not exceed the specified, but the temperature rise suddenly increases at low load, the motor is faulty.
The method of judging and eliminating is that the temperature rise does not exceed the temperature rise limit under the rated load, and the motor temperature exceeds the maximum allowable working temperature only because the ambient temperature exceeds 40 °C. This phenomenon indicates that the motor itself is normal. The solution is to artificially reduce the ambient temperature. If it is not possible, the load must be reduced.
----- Editor-in-Chief: Dalan Oil Pump Motor 02-Procurement Consultant
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