1. Working Principle of LSCS Motor Energy-Saving Controller The LSCS motor energy-saving controller is particularly suitable for water pump control. It consists of a Siemens Micromaster 430 frequency converter, a pressure transmitter, a pressure controller, and Mitsubishi contactors, forming a closed-loop circuit for signal and power control (the principle is shown in Figure 1, where the components of the energy-saving controller are within the dashed lines). The Micromaster 430 frequency converter is a series of frequency converters used to control the speed of three-phase AC motors, particularly suitable for water pump drives, with a rated power range of 7.5–250 kW. It is the core component of the energy-saving controller; in this modification, a frequency converter with a rated power of 160 kW was selected. The pressure transmitter is installed on the water supply main pipe, and the pressure value required for the production process is preset in the pressure controller. After the pressure signal is detected by the pressure transmitter, it is transmitted to the pressure controller. After being compared with the set value in the pressure controller, it is sent to the frequency converter. The frequency converter automatically adjusts the output frequency according to the magnitude of the input signal to control the change in motor speed. 2. Major Problems with Production Water Pumps and Production Water Pipeline There are three production water pumps: B02A, B02B, and B02C, each with a 160kW motor. Normally, two are operated at a time. They use direct starting, with a rated operating current of 296A. Even with no-load starting followed by opening the inlet and outlet valves, the starting current still exceeds 1200A, which can severely damage the insulation of the motor contactor contacts and the pump body's structural components. The production main pipeline has a design pressure greater than 0.4MPa. The oxalic acid unit and the demineralized water station are two major water users. Since 1999, after the oxalic acid unit adopted independent cold water pumps B06A and B for water supply, the water consumption of the production water pipeline has been significantly reduced. The rated flow rate of a single production water pump is 735 m³/h, while the actual water consumption in the pipeline network is less than 400 m³/h, resulting in excessively high pipeline pressure. The main pipeline pressure fluctuates between 0.55 and 0.65 MPa, while the normal pressure requirement for the desalination station is 0.45 MPa, but the actual water pressure is between 0.50 and 0.60 MPa. Therefore, the excessively high pressure in the production water pipeline network has long created a situation of "overpowered power," leading to serious energy waste. 3. Modification of the Production Water Pump To address the problems with the production water pump and pipeline network, it was decided to modify the production water pump B02A using an LSCS motor energy-saving controller. The purpose of the modification is to reduce the pressure in the production pipeline network while simultaneously reducing energy loss. The motor energy-saving controller can automatically adjust the output of the production water pump based on the preset pressure setting in the pressure controller and changes in the actual pressure of the production pipeline network to maintain a constant pipeline pressure. The wiring diagram of the modified B01A motor is shown in Figure 2; the area within the dotted line is the wiring diagram of the energy-saving controller. 3.1 Operating Modes of the LSCS Energy-Saving Controller 1) Energy-Saving Operation: When the energy-saving selection switch K3 is closed, and K5 connected to point 20 is also closed, K5 connected to the normally closed auxiliary contact of KM1 is open. The inverter output contactor KMI closes to energize the motor, and the normally open auxiliary contact of KMI closes to start the inverter. This ensures that the output is connected before operation. 2) Mains Power Operation: When the mains power selection switch K5 is closed, the KM2 contactor coil circuit is activated. At this time, K5 connected to point 20 is open, the inverter cannot start, KM1 cannot engage, and KM2 engages to energize the motor. 3) Fault-Bypass Mains Power Operation: Points 18-20 are internal relays of the inverter. Point 20 is the common point, point 19 is a normally open contact, and point 18 is a normally closed contact. When the inverter detects a phase loss, overcurrent, or other internal fault, it stops outputting. Power is cut off at 7 PM and restored at 6 PM. U, V, and W outputs are absent. KMI automatically deactivates after a delay of approximately 1 second. Output stoppage occurs before KM1 deactivates, and intermediate relay KA2 is activated. KM2 only activates after KA2 and KMI resets. KM2 activation takes approximately 20ms, thus preventing simultaneous activation of the inverter output and bypass. 3.2 Signal Mode: Pressure Signal Input: The motor speed and flow rate are automatically adjusted based on the pressure value set by the pressure controller and the actual measured value. 3.3 Reliability: Lower Limit Flow Rate Control: The lower limit frequency for energy-saving operation is set at 35Hz to ensure that even if the input signal is lost, the minimum controlled flow rate remains at 70%. 3.4 Commissioning: Before officially connecting the water pump motor for commissioning, a 10 kW motor is connected to the output of the energy-saving controller for testing. It is tested to ensure normal operation in both energy-saving and mains power modes. Then, the 10 kW motor is removed, and the water pump motor is connected. The energy-saving controller was switched between energy-saving and mains power modes. Process operators performed no-load start-up and shutdown on-site. After both were normal, the water pumps were tested under load. Before the test run, the outlet valve of the running production pump B02B was partially closed to adjust the pipeline pressure to slightly below the set value. Then, B02A was started. After stable operation, the outlet valve of B02B was partially closed to load B02A. The opening of the B02B outlet valve was gradually reduced to 50%, 30%, 20%, 10%, and 5%, every 2 hours. The changes in parameters at each measuring point were observed. Finally, B02B was shut down, and B02A was allowed to carry the full production load for a 24-hour test run. After the test run met the requirements, it was officially put into operation. 4. System Characteristics After Modification 4.1 Comparison of Main Process Parameters (as shown in the attached table) Before the modification, the pipeline pressure was too high. After the modification, the pressure dropped to the normal production range, the main pipeline pressure remained constant, the pump output matched the production load, and the production water network pressure was stable, which is conducive to normal production. 4.2 Soft-start function: After adopting the energy-saving controller, it has a soft-start function, ensuring continuous and smooth starting of the motor. This eliminates the mechanical shock and large starting current generated by conventional starting methods, extends the motor's lifespan, reduces motor operating costs, and significantly improves the service life and fault tolerance of the water pump system, reducing maintenance costs. 4.3 Bypass function: It has a complete bypass function, ensuring that the motor continues to operate normally without affecting production even if the energy-saving controller malfunctions. 5. Economic Benefit Analysis: Assuming an average water pump load rate of 80%, an average of 4 pumps operating per year, operating for 24 hours per day, 360 days per year, and an energy saving rate of 40%, with an electricity price of 0.5 yuan/kWh. 1) The total investment in the energy-saving project is 687,000 yuan. 2) Without energy-saving pumps, the annual electricity consumption is 4 units x 160kW x 80% x 24 x 360 days = 4,423,680 kWh. Annual electricity cost = annual electricity consumption × electricity price 4,423,680 kWh × 0.5 yuan/kWh = 2,211,840 yuan. 3) With 3 energy-saving pumps, the annual electricity savings are 3/4 × 4,423,680 kWh × 40% = 1,327,104 kWh. Annual electricity cost savings are 1,327,104 kWh × 0.5 yuan/kWh = 663,552 yuan. 4) Investment payback period: Total investment / Annual electricity cost savings = 687,000 yuan / 663,552 yuan = 1.04 years. The above calculations only reflect short-term economic benefits; as the company's production scale expands, the energy-saving effect will become more significant.