In the industrial and mining enterprises, the higher the motor power, the more heat is generated, so the temperature of the motor winding is higher. In order to make the motor work normally, the cooling water is used to the motor. Perform heat exchange to achieve cooling and cooling.
However, in actual work, often due to improper operation or accidents, such as forgetting the water valve for a while, accidental water cut or insufficient water flow during operation, the motor temperature will rise sharply in a short time, causing its insulation to age. If it is found to be untimely, there will be a possibility of burning the motor.
Our company's No. 7 and No. 8 cement mills use a 2500 kW water-cooled asynchronous motor produced by Lanzhou Electric Machinery. The schematic diagram of the electric start control is shown. Since the trial production of the cement mill in 1997, within one year, due to the negligence of operation and accidental water cut, the temperature of the motor winding has been raised twice, causing certain damage to the motor.
In March 1998, the author added the water-breaking protection interlocking device to the No. 7 and No. 8 cement mill main motors. The occurrence of similar incidents was eliminated and good control effects were received.
Two kinds of simple control circuits for water cut protection applied in practice are introduced for peers.
1 use the crystal triode circuit as a water cut protection switch can use the microphone plug connector as a water flow probe, but the best way is to use a car spark plug (sold at the auto parts store), because the car spark plug housing is a metal conductor and has a mounting thread, Easy to install â–¡ Tang Quansheng installation. In addition, the housing and the intermediate electrode are insulated from each other. After the spark plug is tapped on the water pipe, the casing is in communication with the pipe, so that the entire pipe can be used as the other electrode of the control circuit, as shown.
Note: The horizontal position of the pipe is selected as the installation point of the spark plug, and the spark plug should be installed vertically. The purpose of the spark plug is to prevent the residual water droplet from hanging between the middle electrode and the casing and the base of the triode and the negative pole of the power supply. Turn on.
Working principle: When the pipeline has cooling water, the base of the triode V is connected to the negative pole of the power supply, the triode V is turned on, the DC relay KA is pulled in, and the normally open contact is closed, allowing the motor to be closed; when the pipeline is waterless The base of the transistor V is open, the transistor V is cut off, and the DC relay KA is released, so that the motor cannot be closed or the motor is tripped during operation. Note: (丨) 10\1, 12 are respectively the cutter motor (or hoist) The intermediate relay interlocking points KA0 and KI of the oil pump motor are respectively the pressure loss and overcurrent intermediate relay interlocking point <3 is the oil circuit breaker auxiliary contact S (J is the closing position auxiliary travel switch SA is the transfer switch main motor control) Circuit diagram address: Guangdong Yingde Nanhua Cement Co., Ltd., Guangdong Yingde 513049;:2002-08-10;Editor: Shen Ying uses three-stage pipe to cut off water protection switch electric contact pressure gauge with electric contact pressure gauge for water shortage protection The switch thus provides timely water shortage protection for the motor.
2 Using the electric contact pressure gauge as the water-deficient protection switch. The practical experience proves that the use of the crystal triode as the water-breaking protection switch has the following disadvantages: First, the spark plug is improperly installed, there is no vertical installation, and it is easy to hang the water droplet between the middle electrode and the casing. The second electrode and the shell electrode may be severely oxidized after being used for one year or so, so that the motor cannot be closed, and it is difficult to replace the spark plug due to serious oxidation; the third is when the water flow is insufficient. The goal of water shortage protection cannot be achieved.
In view of the above situation, the author improved the control circuit and adopted another effective method, that is, using the electric contact pressure gauge as the water shortage protection switch. In the past three years, there has been no damage to the motor caused by the temperature of the motor winding due to water cut or water shortage, and the control effect is very satisfactory. In order to use the electric contact pressure gauge, the conduction defect caused by the oxidation of the surface of the metal electrode can be effectively prevented. For example, the electric contact pressure gauge is vertically installed above the cooling water horizontal pipe, and the movable contact of the electric contact pressure gauge is low. The two contacts of the static contact of the water pressure set point are taken out. (1) When there is water pressure in the pipeline, the pressure gauge has a pressure indication (the hydraulic pressure action value can be set according to the actual situation). When the water pressure is sufficient, the moving contact is connected to the set static contact, the intermediate relay KA is actuated, the normally open contact is closed, the closing circuit of the motor is turned on, the motor is allowed to start 3 (2) when the pipe is broken or When the water flow is insufficient, the moving contact of the electric contact pressure gauge is disconnected from the set static contact, and the intermediate relay is de-energized, so that the motor cannot be closed or the motor is tripped during operation, thereby timely shutting off the water or missing the motor. Water protection, slightly modified, this circuit can also be applied to other places where water shortage control.
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