Determination of the rational voltage for the induction motor of a blower used for cooling of locomotive traction motors

Abstract

Improving the auxiliary systems of rolling stock responsible for cooling traction electrical equipment is an important direction for enhancing the traction‑energy performance of mainline and industrial railway vehicles. This substantiates the relevance of the present study. Modern rolling stock employs motor–fan units equipped with induction motors to provide cooling for traction electrical equipment. Regulation of the airflow rate in such systems is achieved by varying the rotational speed of the electric motor. At the same time, the line voltage can be modified according to various control laws, which creates the need to determine the rational value of the motor supply voltage at a fixed supply frequency to ensure the highest energy efficiency of the electric drive.

The study considers a three‑phase, six‑pole, squirrel‑cage induction motor rated at 35 kW, with a nominal line voltage of 400 V and a nominal supply frequency of 100  Hz, used to drive the cooling fan of traction motors. It is shown that due to variations in ambient conditions—namely temperature and atmospheric pressure—the motor power may vary in the range from 23 kW to 33 kW. Calculations of motor characteristics under changing power levels indicate that, when the power decreases, reducing the line voltage is advisable because it increases the motor efficiency, with the maximum improvement reaching 0.31%. Under nominal supply frequency, the motor’s line voltage may vary within the range of 360–400 V.

The operation of the motor at a rotor speed equal to two‑thirds of the nominal value was investigated, corresponding to the required cooling airflow rate. Motor parameter calculations show that the highest efficiency values correspond to operation with a line voltage of 199–234 V for a power range of 6.8–9.8 kW. Within this voltage range, the efficiency improvement lies between 1.17 % and 2.76 %. When the motor operates at one‑third of the nominal rotational speed, the maximum efficiency increase reaches 14.1% and 19.82%, achieved at line voltages of 61 V and 44 V for power levels of 1.2 kW and 0.85 kW, respectively.

For more accurate determination of the optimal line voltage—considering converter losses, additional losses in the motor caused by higher current and voltage harmonics, as well as deviations in motor and ventilation‑duct parameters—the use of a research controller is recommended. Such a controller evaluates the power consumed by the motor-fan electric drive.