Justification of main design parameters of asynchronous electric motor current protection
2021
Victor Petko, Orenburg State Agrarian Univ. (Russian Federation) | Rakhimzhanova, I., Orenburg State Agrarian Univ. (Russian Federation) | Ushakov, Yu., Orenburg State Agrarian Univ. (Russian Federation) | Fomin, M., Orenburg State Agrarian Univ. (Russian Federation) | Kononets, V., Orenburg State Agrarian Univ. (Russian Federation)
The article considers the issues of current protection circuitry of asynchronous motors operating from the AC mains of standard frequency. It is noted that in the vast majority of cases transformer current sensors operating in idle mode (transreactors) or in short circuit mode (current transformers) are used as current sensors in such protections. Current transformers have a more stable linear “input-output” characteristic, less current and angular errors, so they are most widespread. The purpose of the work is to substantiate the parameters of the universal current transformer and methods of setting setpoint currents for the protection unit of asynchronous motors having a wide range of rated currents. It is shown that nominal currents of protection units for different groups of electric motors with the multiplicity of the maximum to the minimum nominal currents equal to four will be determined only by the number of turns and the section of the primary winding installed in each specific unit of the current transformer. Moreover, with the maximum possible nominal current for a particular design of the protection unit, which allows direct switching into the controlled current circuit without intermediate current transformers, the number of turns of the primary winding should be equal to one. Under these conditions, it is technically possible to change the nominal current of the current protection device by changing the number of turns of the primary winding of current transformers with a discrete coefficient equal to 2:1 turns, 2 turns, 4 turns, 8 turns, etc. At the same time, it is proposed to set the actuation current of the protection unit for each specific motor by discrete change in the conductivity of the load included in the secondary winding of the current transformer.
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