Power supply description

The water pump station is located in the village. The external power supply is supplied by the 10KV overhead line of the rural power grid. After passing through a 250KVA transformer, the voltage is stepped down from 10KV to 400V to supply power to the station, as shown in the figure below.

The water pump uses two soft start drive boxes, which are started separately. During soft start control, the voltage is slowly increased from zero to the rated voltage, so that the starting current of the motor during the starting process is controllable instead of the uncontrollable overload impact current in the past. The figure below shows the water pump soft start and related low-voltage distribution box.

There are 4 water pumps in total, with a power supply of three-phase 380V, 2 75KW and 2 15KW. When in use, 1 75KW and 2 15KW pumps are used, totaling 105KW, and another 75KW water pump is used as a standby. The daily operation is generally 2 4-hour shifts during the day and 8 hours from afternoon to evening, totaling 16 hours.

Current Problems

After on-site measurements, when the water pump is not working, the three-phase line voltage is around 306V. According to feedback, the lowest voltage reaches 270V, which is far lower than the water pump starting voltage, so the water pump cannot operate normally. The diesel engine generator involves interference with the surrounding environment and is temporarily stopped.

Cause Analysis

We learned from the staff that the voltage of the primary side line of the external power supply, that is, the transformer, is about 8KV, and the single-phase voltage of nearby farmers is less than 220V. Then we conducted a survey along the 10KV transmission line of the water pump. In just 2KM, there are four or five transformers, and it can be clearly seen that two are newly added transformers. Therefore, it can be determined that the main reason for the voltage drop is insufficient power supply capacity, mainly the 10KV circuit of the rural power grid, with many newly added transformers and heavy loads. The load has increased a lot compared to the initial design of the power network, the structure is more complicated, the line loss and transformer loss are large, and the power supply capacity is seriously insufficient.

Improvement plan

Solve the problem on the user side, and use a three-phase AC voltage stabilizer to increase the secondary low voltage to about 380V. Because the water pump has a small power and soft start, it has little impact on the power grid and can effectively solve the on-site problem. The voltage stabilizer parameters are as follows:

Input voltage: 250-400V

Output voltage: 380V

Capacity: 300KVA

Heat dissipation: natural cooling

Size: 1000*800*1900 (width*depth*height)

Installation method: on-site installation

Install in place

Connecting the main cable

Start running

Normal running