Three-legged centrifuge is chemical industry, light industry, textile, food industry, one of the main equipment, its main role by centrifugal force to solid-liquid separation, generally by feeding, washing, dehydration, knife, discharge and so on several parts, including feeding, washing, knife, discharge part is controlled by electromagnetic valve, pneumatic valve, centrifugal kettle is a major part of the realization of solid-liquid separation, by a three-phase ac motor through a belt drive. According to the characteristics of the process, the material is mainly a solid-liquid mixture at the beginning stage, and the load is relatively large at the beginning. When a certain speed is reached, the liquid flows out of the centrifuge under the action of centrifugal force, so that part of the liquid is separated first. With the further increase of the motor speed, the load also decreases accordingly. According to the process requirements, generally divided into several different speeds to achieve the separation effect. 

Principle of centrifuge: after adding materials into the rotating barrel of the centrifuge, the rotating barrel will start driven by the external motor and gradually accelerate to the rated relay. The material will be separated through the filter cloth or filter screen by strong centrifugal force. The brake can be controlled by hydraulic brake or manual brake pad, but the maintenance cost is high. And centrifuge in the traditional start up the current is very large, the impact on the power grid.

Centrifuge load for constant torque large inertia load, here choose the AMB300 series universal frequency converter produced by ambition letter company. Taking the motor power as 22kW and 4 as an example, amb300-022g / 030p-t3 is selected, whose external control circuit is shown in figure 1. One of K1 start signal control inverter X1 multi-function terminal, K2 multistage speed by frequency converter 1 X3, K3 multistage speed by frequency converter 2 X4, K5 multistage speed by frequency converter 3 X5, according to the need to choose three speed which is running at low speed, medium speed and high speed operation, specific speed can by setting the corresponding parameter.

Ambition inverter main parameters set

The main circuit of the universal inverter is shown in figure 2.

FIG. 2 schematic diagram of main circuit of frequency converter

According to the load characteristics of the centrifuge, set the following main parameters:

Table 1 setting parameters of inverter operation

According to the load characteristics of the centrifuge, attention should be paid to:

(1) centrifuge load higher starting torque requirements, likely starting difficult situation, then can boost converter torque compensation value, appropriately AMB300 F5.01 set parameters for 5 series, not too big, but the starting torque compensation or possible flow (fault code E.O.C.), overload (such as fault code for E.O.L.) call the police, if the acceleration in the over-current alarm should be appropriately extended time;

(2) the big inertia centrifuge, parking for frequency converter according to deceleration time, must be equipped with brake unit, the choice of the braking resistor are on general frequency converter manufacturers instruction manual, can choose according to operation manual, would be normal work when braking resistor as the energy consumption and fever, over-voltage alarm occurs if slowing down (fault code E.O.U.) can be appropriately extended deceleration time F0.02 F0.03 parameters;

(3) general centrifuge installed at the scene of the operation, frequency converter, and more than concentrated in the control room, if the scene and centrifuge distance than frequency converter allows scope shall adopt corresponding measures, such as reasonable distribution main return route and the line of control, reactor with output or filter, to prevent the attenuation of the inverter output voltage, or considering increase the capacity of the inverter.

Application benefit analysis of centrifuge inverter: manual mechanical braking has the disadvantage of large consumption of brake pads, good brake pads can be used for 2 weeks, poor only use for 5 days or so, it takes 2-3 hours to replace a brake pad. The maintenance cost of traditional centrifuge is high and the production efficiency is low. The starting current is large, which has a great impact on power grid, line and transformer.

After the centrifuge USES the frequency converter, USES the energy consumption brake, the soft start and soft stop, does not have the impact to the power grid. Every year, the cost of each brake pad can be saved about 3,000 yuan, and the replacement of the brake pad will take 300 hours per set. The production efficiency was increased by 15% and the comprehensive benefit was greatly increased.

Centrifuge adopts frequency control of motor speed can speed according to different process requirements, depending on the material can easily choose the multistage speed operation, using variable frequency control of motor soft start at the same time, reduce the impact on the grid, the inverter has the rich such as overcurrent, overload, overvoltage protection function, when the abnormal load or motor frequency converter for downtime and rapid blockade output, so that can timely protect motor.