The starting method of the cooling tower dedicated motor is the key link to balance the starting current and the instantaneous load demand of the cooling tower. Its design needs to deal with the current impact when the cooling tower dedicated motor starts, as well as the urgent need for power of the cooling tower at the moment of starting. By optimizing the energy transfer during the starting process, the coordination and unity of the two can be achieved.
The direct starting method can quickly respond to the instantaneous load in specific scenarios, but it needs to deal with a large starting current. When the cooling tower is in a low-load state and the grid capacity is sufficient, direct starting can allow the cooling tower dedicated motor to quickly reach the rated speed to meet the cooling tower's instantaneous air volume increase needs. At this time, the stator winding of the cooling tower dedicated motor is directly connected to the power supply, and the strong starting torque can drive the fan to quickly overcome the inertia and realize the power supply of the instantaneous load. However, in this way, the starting current will be significantly higher than the rated current. In order to avoid impact on the power grid, it is usually necessary to strengthen the current resistance of the winding in the design of the cooling tower dedicated motor, and match it with a grid protection device to control the current impact within the allowable range while meeting the instantaneous load.
The step-down starting method reduces the starting current by reducing the voltage at startup, while taking into account the response to the load. The common star-delta start-up reduces the voltage at the beginning of the start-up by changing the connection mode of the cooling tower dedicated motor winding, so that the starting current can be reduced, and the excessive current can be avoided from causing damage to the cooling tower dedicated motor and the power grid. When the speed of the cooling tower dedicated motor is close to the rated value, it is switched to the rated voltage operation. At this time, the torque increases accordingly, which can meet the load requirements of the cooling tower during normal operation. This method sacrifices part of the torque in the early stage of starting in exchange for the stability of the current, but through the later switching, it ensures that sufficient power is provided in the load rising stage, which is especially suitable for those cooling tower systems that are sensitive to the starting current and whose instantaneous load is not extremely large.
The soft start method realizes the progressive control of the starting process by smoothly adjusting the voltage and current, and perfectly balances the relationship between the two. The soft starter can set the starting time and current curve according to the load characteristics of the cooling tower, so that the voltage of the cooling tower dedicated motor gradually increases during the start-up, and the current increases steadily accordingly, avoiding peak impact. In this process, the torque also gradually increases, just matching the load change of the cooling tower fan from static to rotating. It will not affect the stability of the power grid due to excessive current, nor will it cause slow start due to insufficient torque, and fail to meet the instantaneous load requirements. This method is particularly suitable for large cooling towers, which have large instantaneous loads and high requirements for grid stability. The gradual nature of soft start allows the two to achieve a balance in dynamic adjustment.
The variable frequency starting method achieves precise matching of starting current and load demand by changing the power supply frequency. At startup, the inverter outputs a lower frequency, the speed of the cooling tower dedicated motor rises slowly, and the starting current is always kept at a low level to avoid impact. At the same time, the gradual increase in frequency drives the speed to increase steadily, and the air volume generated by the fan increases accordingly, just meeting the transition of the cooling tower from low load to high load, ensuring that the torque at each stage is adapted to the instantaneous load. When the cooling tower needs to increase the load quickly, the inverter can appropriately increase the frequency rise speed to speed up the starting process while controlling the current; if the grid pressure is large, the frequency rise speed is reduced to prioritize current stability. This flexible adjustment capability allows the startup process to fully fit the actual load changes of the cooling tower and achieve a dynamic balance between the two.
Torque regulation in the starting method is the core technology that takes both into account. When starting, the cooling tower dedicated motor needs to overcome the inertia of the fan and the air flow resistance in the cooling tower, which requires the starting torque to meet the minimum value of the instantaneous load. Different starting methods adjust the torque output curve to make the torque at the beginning of the start slightly higher than the instantaneous load demand, ensuring smooth start-up while controlling the current within a reasonable range. For example, in step-down start-up, by optimizing the winding parameters, the torque after the voltage is reduced can still cover the load demand; in soft start-up, by dynamically adjusting the voltage, the torque and load increase synchronously to avoid current waste caused by excessive torque or start-up failure caused by insufficient torque.
Time control during the start-up process also affects the balance effect of the two. If the start-up time is too short, the cooling tower dedicated motor needs to reach the rated speed in a short time, which will inevitably lead to a surge in current in exchange for sufficient torque; if the start-up time is too long, although the current is stable, it may not be able to meet the cooling tower's demand for instantaneous air volume in time, affecting the cooling effect. Therefore, the design of the starting method will set a reasonable starting time according to the load characteristics of the cooling tower, so that the speed of current rise matches the rhythm of torque increase, neither rushing to achieve success to cause current shock, nor delaying to affect load response, and achieving coordination between the two in the time dimension.
In addition, the matching of the starting method with the characteristics of the cooling tower dedicated motor itself is the basis for achieving balance. The rotor design and winding materials of the cooling tower dedicated motor will affect the current and torque performance at startup. For example, the use of high-conductivity winding materials can generate greater torque at the same current, so that the starting method can still meet the load requirements when controlling the current; optimizing the slot design of the rotor can reduce eddy current loss at startup, reduce starting current, and improve torque output efficiency. This coordination between the characteristics of the cooling tower dedicated motor itself and the starting method allows the goal of balancing the starting current and instantaneous load to be achieved more efficiently.
In practical applications, the choice of starting method also needs to be combined with the operating environment of the cooling tower. In areas with unstable power grids, soft start or variable frequency start is preferred to ensure that the starting current does not cause excessive impact on the power grid; in scenarios where frequent starts and stops are required, the starting method must have a fast response capability and control the frequent fluctuations of current to avoid overheating of the cooling tower dedicated motor. Through this targeted selection, the starting method can adapt to the limitations of external conditions and meet the inherent requirements of the instantaneous load of the cooling tower, ultimately achieving a perfect balance between starting current and load requirements.
