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Should lifting and metallurgical motors be star-connected?

source:未知   time:2024-06-28 09:51nbsp;  click:



   There are two connection methods for three-phase asynchronous motors: delta connection and star connection. For many series of motors, according to the appropriate power division, small power uses star connection, and large power uses delta connection; and for hoisting and metallurgical motors, regardless of power, most of them are connected in star connection. So the question is, why do all series of hoisting and metallurgical motors such as YZ, YZR, and YZP use star connection?

   We understand the difference and connection between the two connection methods from the most common dual-voltage motor. When the rated power of the same motor is , the rated voltage in the star connection state is higher than the rated voltage in the delta connection state (the star connection voltage is the square root of 3 times the delta connection voltage), and the line current corresponding to the star connection is smaller than the line current of the delta connection. In general, customers use the star connection with high voltage and low current to start the motor, and the delta connection with low voltage to run the motor; and for the motor body, the phase voltage and phase current under the same power conditions are the same under the two connection methods. When the three-phase winding and the three-phase power supply are completely symmetrical, the two connection methods only involve changes in the line current size, and there will be no difference in operation.
 
   However, the absolute symmetry of the three-phase winding or the three-phase power supply is not very likely, especially when there are electrical problems or manufacturing defects in the motor; once the three-phase winding or the three-phase power supply is asymmetrical, it will cause circulating current in the three-phase winding of the delta connection.

   From the analysis of motor winding reliability, compared with other motors, the frequent forward and reverse characteristics of hoisting and metallurgical motors will cause the temperature of the motor winding to rise. If there is a circulating current in the motor winding, it will naturally affect the temperature rise of the motor. For this reason, star connection should be selected to eliminate the influence of circulating current on the motor temperature rise, and at the same time avoid the aging of motor winding insulation and avoid the problem of shortening the service life of the motor.
 
   From the analysis of the working conditions, hoisting and metallurgical series motors are usually used for frequent starting and forward and reverse working conditions, which have a very strong impact on the motor windings. Some specifications of the JZR series motors used in the steel rolling environment were once called "one-week motors" because they would burn out in less than a week, reflecting the harsh operating environment or working conditions; on the other hand, the application of lifting machinery has very strict safety requirements, and any defects in the operating characteristics may lead to major safety accidents.

   Based on the above reasons, the winding connection method of lifting and metallurgical motors (commonly known as crane motors) usually does not use the triangle connection method, and avoids various factors that may cause circulating currents as much as possible, thereby eliminating reliability and safety risks such as severe heating due to unexplained reasons and torque oscillation on the output shaft.

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