How to supply power for small farm pumps
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When selecting the type of motor, it is essential to consider the local power supply conditions. In areas with a reliable power supply, squirrel-cage motors are typically preferred due to their simplicity, reliability, and low maintenance. However, in situations where the power network has limited capacity and cannot reliably start a squirrel-cage motor, a wound-rotor motor may be considered. For environments that are dry and dusty, open-type motors are suitable. In areas where dust or splashing water is present, enclosed motors should be used, while sealed motors are necessary for flooded conditions.
If the pump operates under continuous and uniform load, the motor should be designed for continuous operation. Its speed should match that of the pump to allow direct starting. If this is not possible, an indirect drive system with a closer speed ratio can be used. It's important to note that for high-power pumps, motor selection must be done through scientific calculations. However, for small agricultural pumps, experience often plays a key role. The motor’s power should generally be 1.0 to 1.3 times the power required by the pump. For internal combustion engines, the power should be 1.3 to 1.5 times the power needed by the agricultural machinery. Choosing a motor that is too large leads to energy waste, while one that is too small can cause damage due to overload or failure to start.
If existing power equipment has already been purchased, it's crucial to make full use of it. When buying a new agricultural water pump, it's advisable to ensure compatibility with the existing power source. In fixed installations, motors should operate within 75% to 100% of their rated power. A diesel engine with a full-speed governor can adjust its speed and power within its operational range, helping to optimize performance.
The rated speed of the motor should be selected based on the pump’s requirements. However, asynchronous motors typically have a synchronous speed of at least 500 revolutions per minute. Therefore, if the pump requires a lower speed, a speed reduction device must be installed.
The rated voltage of the selected motor must match the grid voltage. Three-phase asynchronous motors can operate normally when the applied voltage is between +10% and -5% of the rated voltage. In rural areas, the low-voltage grid usually provides 220V/380V. As a result, most small and medium-sized asynchronous motors used in agriculture are low-voltage. Single-phase motors typically have a rated voltage of 220V, while three-phase motors are rated at 380V. Ensuring proper voltage matching is critical for both efficiency and safety.