The difference between soft start and variable frequency start of centrifugal pump
In the design of water treatment process, we usually use the corresponding booster pump for the equipment with no water flow. In order to avoid the impact on the circuit and electrical components when the pump starts, we need to select the power size.
Corresponding starting mode: If the pump motor power is less than 15KW, the electromagnetic control (contactor, etc.) can be started directly; the pump motor power 15-30KW can be started at the star angle. If the stable start is required, the soft start or variable frequency start mode can be adopted; the pump power is greater than At 30KW, soft start or variable frequency start mode must be used. We introduce the difference between high-power soft start and variable frequency start for your reference:
Frequency conversion start of centrifugal pump:
When starting, the AC power whose frequency and frequency are fixed by the inverter is converted into AC power with variable voltage and frequency, which is used to reduce the impact load caused by the motor starting, control the motor speed, and lengthen the starting time. Smoothing the current to achieve the purpose of soft start, while also improving the efficiency of the grid and motor. In fact, the inverter is mainly used in energy saving, and the output voltage, current and frequency are changed by adjustment.
The disadvantages of frequency conversion start:
1. High cost, the price is much more expensive than microcomputer protection.
2. Because the current inverter almost adopts PWM control mode, such pulse modulation form makes the inverter produce high harmonic current on the power supply side during operation. And causing distortion of the voltage waveform. After the power system is subjected to harmonic interference, it will affect the operating efficiency of the system, and damage the equipment and even the safe operation of the power system.
3. The overload causes the inverter to jump more frequently, and when the overload occurs normally. Generally speaking, the motor has strong overload capability. As long as the motor parameters of the inverter parameter table are properly set, the motor overload is generally not expected. The inverter itself is prone to overload alarm due to poor overload capability.
The soft start of the centrifugal pump is connected between the power supply and the controlled motor in series, and the internal thyristor is triggered by the microcomputer to trigger the conduction voltage to realize the AC voltage regulation, so that the input voltage of the motor gradually increases from zero to the preset function relationship until the start is completed. Give the motor full voltage, that is, soft start. During the soft start process, the motor starting torque is gradually increased, and the rotational speed is gradually increased until the thyristor is fully turned on, and the motor works on the mechanical characteristics of the rated voltage to achieve smooth start and reduce startup. Current. Avoid starting overcurrent trips. When the motor reaches the rated number of revolutions, the starting process ends and the rated voltage is supplied for the normal operation of the motor.
Disadvantages:
1 Can not adjust the power frequency, so it can not start the motor from zero voltage zero frequency, can not achieve zero impact start;
2 Can not speed;
3 The soft starter exits the system after starting the motor, loses the protection function.
The difference between soft start and variable frequency start of centrifugal pump:
☆Inverter controls the start and run of the pump by adjusting the frequency. The soft start is to change the resistance connected in the circuit to make the current from small to large. This way is used to start the high-power motor to reduce High-power motors directly start to cause fluctuations in the grid, or cause some unimportant load unloading troubles;
☆Inverter is used for the need of speed regulation, the output of the inverter not only changes the voltage but also changes the frequency at the same time;
☆The soft starter is actually a voltage regulator that protects the motor. When the motor is stepped down, the soft starter output only changes the voltage without changing the frequency.
☆Inverter has the function of all soft starters, and the pump can control its output pressure and flow to save energy during operation;
☆ If you only need to consider the control at startup, you can use soft start, but if you need to consider the control at runtime, you need to use inverter control.
