SELECTION OF METHOD FOR REGULATION OF TRACTOR PROPULSION ASYNCHRONOUS ELECTRIC MOTOR AND CONSTRUCTION OF MECHANICAL CHARACTERISTICS

Nowadays the work is in progress to develop wheeled and caterpillar tractors with electromechanical transmission. Range of changes in transmission gear ratio while using propulsion electric motor depends on mechanical characteristics of a tractor propulsion electric motor which is equipped with electromechanical transmission. In case when the range is rather high then it is possible to minimize number of gearings in the tractor gearing box or exclude its usage at all. Type of the applied propulsion electric motor and regulation method specify type of mechanical characteristics (characteristics family) of the propulsion electric motor.

The paper considers a propulsion asynchronous electric motor with frequency control. While using frequency control it is possible to regulate electric motor revolutions by mutual changes in voltage and voltage frequency. There are various laws of mutual changes in voltage and frequency (regulation laws). Selection of a regulation law influences on type of mechanical characteristics of a propulsion electric motor. Application of any law can be admissible only for some specific range of voltage frequency otherwise it is possible to exceed some parameters (for example, admissible voltage in the winding of electric motor stator). It is necessary to ensure the required moment within wide range for a tractor propulsion electric motor. In this case losses in the electric motor must be minimal. Losses in the rotor of the propulsion asynchronous electric motor are directly proportional to its sliding and its best propulsion and mechanical properties of a mobile machine will be ensured in the case when sliding is preserved at a constant value. According to these reasons selection of regulation laws has been carried out for operation of the propulsion asynchronous electric motor with nominal sliding and mechanical characteristics at nominal sliding is conventionally called a nominal characteristics.

The paper analyzes the possible laws of mutual application of voltage and voltage frequency and their application boundaries. A combination of laws for regulation of the propulsion asynchronous electric motor has been selected in the paper. The combination ensures the widest operational range of the electric motor with high moment value at nominal sliding and due account of limitations on application of every used regulation law. The following mechanical characteristics family has been constructed for the propulsion asynchronous electric motor regulated in accordance with the proposed law: at nominal sliding, at critical sliding, at changeable sliding and without changes in voltage and frequency.

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