Abstract
Considering the problem of energy saving at industrial enterprises, attention should be paid to the fact that about 70 ... 80% of all electric motors are asynchronous, and most of them are installed in unregulated drives. Most of these electric drives are equipped with asynchronous electric motors with a squirrel-cage rotor (AM SC). Energy saving problem in such cases can be solved by using a frequency converter (FC), however, all FC models are intended for AM SCs, while until the mid-90s the most common variable AC drives were electric drives equipped by an asynchronous motor with a phase rotor (AD PR) as they provided easy speed regulation through the rotor circuit. Such drives are usually used in hoisting and transport machines (conveyors, cranes, etc.). Direct transfer of the abovementioned drives to frequency-controlled mode is quite complicated due to the fact that standard inverters are designed to work with AM SCs having no phase rotor winding, and whose short-circuiting leads to additional electromagnetic losses in comparison with AM SC. An upcoming engineering trend is the development and research of synchronized AM control systems.
Highlights
The relevance of the study is determined by the following capabilities of synchronized machines [1,2]: 1) shunt characteristics; 2) reduction in electricity consumption; 3) easy speed maintaining in deep control mode
The synchronous mode of the motor has among others one advantage over the asynchronous mode which is the ability of the motor to change the magnitude and mark of the reactive power when adjusting the magnitude of the excitation current [6]
With direct connection of the stator winding to the supply mains providing motor overexcitation, reactive power is supplied to the supply mains network and, if underexcited, is consumed from the network, there is a fundamental possibility of influencing the energy exchange process between the motor and the power supply system by controlling the excitation current of powerful synchronized asynchronous motors [7,8]
Summary
The relevance of the study is determined by the following capabilities of synchronized machines [1,2]: 1) shunt characteristics; 2) reduction in electricity consumption; 3) easy speed maintaining in deep control mode. The advantage of a synchronized asynchronous electric drive is that a precise speed maintaining does not require a complex computer and the use of speed sensors on the motor shaft. The synchronous mode of the motor has among others one advantage over the asynchronous mode which is the ability of the motor to change the magnitude and mark of the reactive power when adjusting the magnitude of the excitation current [6]. With direct connection of the stator winding to the supply mains providing motor overexcitation, reactive power is supplied to the supply mains network and, if underexcited, is consumed from the network, there is a fundamental possibility of influencing the energy exchange process between the motor and the power supply system by controlling the excitation current of powerful synchronized asynchronous motors [7,8]
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