Practical Sharing on the Automation Transformation of Industrial Water Supply Systems: A Solution Based on S7-400

Having been engaged in the industrial automation industry for 15 years, focusing on the automation transformation of large water supply systems, I would like to share my experience from a municipal water supply system automation project that I led, hoping to provide some reference for friends working on similar projects.

1. Project Background

This is a transformation project for a city water supply system serving a population of 500,000. The original system used relay control methods from the 1990s, which had the following issues:

• High equipment failure rate and significant maintenance costs
• Inability to achieve precise water pressure control
• High energy consumption
• Lack of real-time monitoring and data analysis capabilities

2. System Design

2.1 Hardware Configuration

The core device selected is the Siemens S7-400 PLC, with the following specific configuration:

• CPU: 416-3 PN/DP
• Power Supply: PS407 10A
• Digital I/O: 32 input/24 output modules
• Analog I/O: 8-channel input/4-channel output modules
• Communication Module: CP443-1 for Ethernet communication

2.2 System Architecture

The design adopts a three-layer architecture:

1. Field Layer: Various sensors and actuators
2. Control Layer: PLC control system
3. Management Layer: SCADA monitoring system

Tip: When selecting hardware, it is recommended to reserve about 30% of I/O points for future system expansion.

3. Core Functionality Implementation

3.1 Pump Group Control

This is the most critical part of the entire system. We adopted a PID-based variable frequency speed control scheme:

Variable Frequency Control Strategy:
- Dynamically adjust pump speed based on pipeline pressure feedback
- Use a rotation operation mechanism to extend equipment life
- Set up automatic switching for standby pumps

3.2 Pipeline Pressure Optimization

I remember that in the early stages of the project, we took quite a few wrong turns. Initially, we naively adopted fixed pressure control, only to find that there was an overpressure phenomenon during low water usage at night. We later switched to time-based pressure control:

• Daytime (6:00-22:00): 0.35MPa
• Nighttime (22:00-6:00): 0.28MPa

This small change saved users about 20% on electricity costs annually!

3.3 Fault Diagnosis System

Based on years of operation and maintenance experience, we developed a fault warning mechanism:

1. Real-time monitoring of key parameters
2. Establish a fault characteristic database
3. Set multi-level alarm thresholds
4. Automatically generate fault analysis reports

4. Project Challenges and Solutions

4.1 System Switching Challenges

The most challenging issue was how to complete the switch from the old system to the new one without affecting the water supply. We adopted a gradual switching scheme by area:

1. Prioritize the transformation of the backup system
2. Switch during low peak hours in the early morning
3. Retain manual emergency control functions

4.2 Communication Reliability

Communication with remote sites often gets interrupted. After analysis, we found the main reasons were:

• Unstable quality of fiber optic lines
• Improper configuration of communication module parameters
• Network attack interference

Solutions:

1. Switch to dual-link communication
2. Optimize communication timeout parameters
3. Deploy industrial firewalls

5. Operational Effects and Summary of Experiences

5.1 Project Outcomes

• System reliability improved by 95%
• Energy consumption reduced by 30%
• Maintenance manpower reduced by 60%
• Achieved unattended operation

5.2 Lessons Learned

1. Thorough preliminary research is essential, especially to understand the real needs of users
2. System design should allow for expansion space
3. Documentation should be organized in a timely manner for future maintenance
4. Training for operation and maintenance personnel must be adequate to ensure normal system operation

6. Closing Remarks and Communication

After many years in automation, I deeply realize that even the best solutions need continuous improvement in practice. I hope these experiences can inspire everyone. If you encounter similar issues in your projects, feel free to leave a message for communication; I am happy to share more details.

Finally, I would like to share a saying: In engineering, one must both look up at the stars and keep their feet on the ground. Attitude determines height, and details determine success or failure.

Let us contribute our part to the development of industrial automation!

This concludes my experience sharing. If anyone is interested in certain technical details, I can discuss them in more depth later. I also welcome everyone to share their project experiences so we can learn from each other and progress together!