Differences Between Variable Frequency Starting And Soft Starting Of Electric Water Pump

June 16 17:14 2022

People may know that direct starting of an electric water pump will cause the water hammer effect, which means that water impacts the pipe and cause a serious water hammer when the water pump starts and stops. If people are familiar with water hammer, people must know that it can generate the force that may be great and damage valve or pump. Therefore, to avoid or reduce the negative effect of water hammer effect, the water pump’s rotation speed should be increased to the rated speed slowly when it’s started, so that the water pump will start gently, instead of starting at once.

But how to start the water pump gently? people can try two methods to start people’s water pump slowly and completely avoid the water hammer effect. The first method is variable frequency starting, and the second is soft starting.

1. Variable frequency starting

When starting the electric water pump, transform the AC current with constant voltage and frequency into AC current with variable voltage and frequency through variable frequency drive, to reduce the impact load caused by the motor starting, control the motor speed, and lengthen the starting time, thus achieving soft starting and improving the efficiency of power grid and motor. In fact, the variable frequency drive is mainly used in energy saving and changes output voltage, current and frequency by adjusting.

Features: It can adjust motor speed and is suitable for the application where the speed requires to be adjusted. But its cost is high. High harmonic current will be generated at the power side when it is running. Due to the harmonic interference, operation efficiency of power system may be affected.

2. Soft starting

Connected in series between the power supply and the motor, the soft starter controls the internal thyristor through microcomputer to trigger conduction angle and realize voltage regulation, thus gradually increasing the motor input voltage till the end of starting, and gives the motor full voltage. This process is soft starting. During the soft starting process, the motor starting torque and speed gradually increase till the thyristor is fully conducted. The motor works on the mechanical characteristics of rated voltage, to realize smooth starting, reduce starting current and avoid overcurrent tripping.

Features: It integrates motor protection function, thus eliminating the cost of microprotector. But it cannot adjust the speed, and is suitable for electric water pumps, fans and crushers that do not require speed regulation.

Soft starter is not as versatile as variable frequency drive, but it is targeted to solve the current impact problem of pump start, and can operate stably and reliably. What’s more, soft starting is not as expensive as variable frequency starting, so soft starting is the most practical and feasible way to start people’s water pump.

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