Sand-dust Prevention and Greening Governance Project

1.Conditions and Requirements Before Retrofit

Bayin Reservoir in Delingha, Qinghai Province supplies domestic water for tens of thousands of people in Delingha City.Due to seasonal and climatic changes, the water level of the reservoir changes continuously. When the water pump runs at a constant speed, the water output also changes accordingly.After heavy rains, the reservoir water level rises sharply, causing a corresponding increase in pump output; conversely, the water output decreases.

Since the water pumped from the reservoir must undergo sedimentation, aeration and other treatment processes, the treatment capacity is limited. Therefore, regardless of the reservoir water level, the pump output is required to be roughly constant.This avoids excessive sediment content in the water after rainfall, which, combined with limited water treatment capacity, would lead to excessive water turbidity and affect the quality of tap water.

2 Retrofit Scheme and Implementation

To achieve constant flow control, a flow transmitter could be installed on the pump outlet pipeline, and the pump driven by an inverter, with the flow signal fed back to the inverter to form a closed-loop flow control system.

In this project, a pressure transmitter was installed on the pump inlet pipeline under the dam. The output signal of the pressure transmitter reflects the reservoir water level.If the reference point of this signal is the same as that of the inverter input, it cannot be directly connected to the inverter.When the water level is high, the output of the pressure transmitter is also high, which would cause the inverter to speed up, increasing rather than reducing the water output.

Therefore, the output signal of the pressure transmitter is inverted before being sent to the inverter. This method is simple and the system operates in open loop.Practice has proven that this method is convenient to use and reliable in operation.

Since the system operates in open loop, commissioning is very simple.Almost no inverter parameters need to be changed; only the gain of the inverter needs to be adjusted appropriately to ensure that the pump output flow is basically constant when the water level is at maximum, minimum, or intermediate positions.

3 Experience from Application

This system is a typical application of Rihong inverters.During project implementation, to save costs, closed-loop flow control was not adopted; instead, open-loop pressure control was used, achieving the same effect.The system functions fully meet the needs of water supply.