The purpose of dredging is mainly to clean up the river channel and obtain construction sand. The former cleans the river channel and the river mouth to prevent siltation; the latter is to meet the demand for construction sand.

In China, the dredging vessels are widely distributed in the waters of the Yangtze River, the Pearl River, the Dongting Lake and the Poyang Lake. At present, dredging ship equipment has been widely applied to the variable frequency speed control system, and the control ability of the dredging production is improved. Using stepless speed regulation, various process steps are controlled by the system control to adjust speed. It makes the system is stable and reliable.

2 ．Sand dredging workflow

The dredging ship structure includes: siphon up and down lifting, sand suction pump, clean water pump, side pushing machinery, bucket lifting, bucket azimuth angle, sand feeding belt, etc. The above steps accomplish the whole process of sand excavation.

When the dredger is working, it is parked on the water surface. After the bottom sand is pumped out, it will move to the place where has many sand to continue working. The excavated sand was loaded on the side sand boat, and the sand boat transports back and forth on the dredging boat and the shore.

Figure 1 Sand carrier

The sand conveying belt is stretched overhead the sand boat warehouse. The bow siphon tripod adopts frequency conversion control. The process of downward movement needs to release energy, so need adding braking resistor to release the pumping voltage. The siphon pipe reaches the bottom of the water and starts to suck the sand water. The sand-water mixture is sent to the bottom of the dredging ship. The side-pushing machine swings left and right to mix the sand-water mixture and send it into bucket under the control of VFD.  Bucket drive process is controlled by the frequency inverter, and through controlling tilt angle of the bucket by controller to control the capacity of loaded water and sand.

Large-scale dredging ship usually have the function of removing mud, stones and other debris, can directly produce finished sand.

Figure 2 Sand Dredger

Sand dredging process: When the bucket reaches the top of the transmission frame, the sand settles to the bottom of bucket, and water is above the sand. The drive frame continues to drive the bucket down from the highest point. The bucket mouth slowly faces down and water slowly pours out, and the sand was then poured onto drive belt. Conveyor belt then sent sand to loading boat.  In general, The motor power is 132KW ~ 220 kW, and one sand dredger needs about more than 10 pieces motors.

3 ．EN500 solution

   1.Frequency Inverter and accessory configuration

The frequency inverter used for dredging ship is mainly used to control the transmission bucket, the clean water pump, the siphon pipe rack (some ships do not modify the siphon pipe rack).  Because dredging vessel is powered by generator, and frequency inverter needs to be equipped with DC reactor and AC input and output reactor to increase the power factor and reduce inrush current. The tripod of siphon is very heavy, and the feedback energy generated during repeated lifting process will cause bus voltage of the inverter rising. It is necessary to add braking resistors for energy braking (some time the system has many brake pads, so do not need brake resistors) to ensure the system stable.

The working speed after using EN500 can be adjusted freely, generally it will be 10 HZ according to the actual situation, and it will not reach 50HZ under normal conditions.

2 .Sand Dredger motor power

Generally, the  dredging ship uses high-power ordinary three-phase asynchronous motor, power range: 75KW~280KW, rated voltage 380V, and rotating speed.1390r/min ～ 1460r/min， rated frequency 50HZ.

3  . System wiring diagram

According to the equipment production requirements and system scheme, the following system control wiring diagram is as below:

Figure 3 frequency inverter diagram (control convey )

Figure 4 frequency inverter diagram (control siphon tripod )  

4.EN500 parameter setting

Frequency inverter controls siphon tripod

Bucket conveyor belt inverter (vector control)

5.Product advantages

1. The EN500 series frequency inverter has a wide range of voltage adaptability and can be fully powered by marine generators;

2. Fast current limiting function to avoid equipment damage caused by excessive load current during load fluctuation

3. Automatic voltage regulation and instantaneous power failure non-stop function, can keep the motor power supply stable when the generator voltage is fluctuating;

4. Large torque at low frequency and fast response;

5. Complete protection of lack of phase, under voltage, over voltage and over current;

6. Structurally independent air duct design, PCB board adopts thickened three proof paint to enhance the working ability on water surface and sea surface.

6.Notes

Marine equipment should be well sealed and dried in the electrical room to prevent corrosion damage caused by water vapor and salt spray entering the electrical equipment;

Maintain equipment on monthly, weekly and daily basis, check the parts of heat, oxidation and corrosion to ensure normal operation of equipment.

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7.Conclusion

The EN500 series multi-function flux vector inverter adopts 32-bit DSP hardware platform and advanced flux vector control technology, including speed sensorless vector control, closed loop vector control, optimized V/F control mode, and speed and torque modes. The control method has high precision, fast speed response and superior low frequency characteristics. With original self-learning and speed tracking function, it has compact structure, high power density, easy installation, high cost performance, and perfect intelligent detection and protection etc advantages. This series product has a wide range of networking functions and friendly user habits, designed a variety of operating and display interfaces according to different user needs, rich peripheral bus expansion, terminal expansion, relay expansion, analog expansion and so on.