The face of China is changing...and so is its water. Water pollution, wastewater treatment and water resource protection have become a top priority for the Chinese government. Over the last ten years, the Chinese government has enacted a number of anti-pollution laws and has begun to educate their citizens on the importance of water resource management. China’s Ministry of Construction proposed last year that the central government allocate $2.4 billion USD to combat water pollution over the next five years.
“A decade ago, you could not see a single fish in any of China’s main rivers, especially the Suzhou River. ” said Alex Xu, Manager for Shanghai Yuandong Science & Technology Ltd., System Integrators for a number of water projects throughout China. “I was living by the river at that time and had to put up with the smell from the river over 200 days out of the year. But things are changing quickly in China. Now I regret that I moved away from the river because today it is clean and fish and crabs have reappeared.”
Numerous projects have been implemented throughout China to help regulate methods for optimizing water distribution. Many drinking water and wastewater facilities have been built or are in the planning stages along China’s many waterways. The coastal city of Shanghai, with a population of over 16 million, has positioned itself as a leader in this drive to revamp China’s water resources. Shanghai’s Mayor Xu Kuangdi stated at a conference on environmental protection that the “Shanghai government pledged to transform Shanghai into an ecological city.”
Shanghai Wastewater Treatment Plant
Under the City of Shanghai, ten huge pumping stations went on line recently pumping wastewater to the pre-treatment plant at Pudong for purification before being discharged into the East China Sea. At Pudong, the waste is purified before being discharged at a rate of 1.7 million cubic meters per day through a 41-kilometer pipeline. These pump stations are part of the latest phase of Shanghai’s Waste Water Treatment Project (SWWTP) under the auspices of the Shanghai Municiple Sewage Company.
In 1993, Shanghai Municipal Sewage Company conceived the development of a new wastewater treatment plant for the city. Plans were discussed and in 1998 the Shanghai Waste Water Treatment Project (SWWTP) was begun. The project is being implemented in stages and involves the installation of approximately 50 huge pumping stations throughout Shanghai.
In January of 1999, General Electric International began the construction of the central monitoring control system, which
included a centralized master control station and a total of 34 remote stations located throughout Shanghai, including Pudong.
The Master station, using Australian-developed Managed Information Technology Solutions (MITS) MOSAIC data acquisition and control technology, communicates to both Allen-Bradley and General Electric hardware. Many water control systems are PC-based and require a high level of manual intervention, but the MITS system is highly automated. While monitoring the passage of water, automatic adjustments can be made to make the most efficient use of energy and pumping equipment and pinpoint problems in emergencies.
DNP Protocol Specified
Immediately following the installation of the central control system, Rockwell Automation in Shanghai was contacted to bid on the installation of the SCADA system to control, collect and monitor data from the 10 pump stations, some of which are as far as 30 miles away from the Master station. In order to communicate with the end devices, the DNP protocol was specified.
DNP (Distributed Network Protocol) is an open communication protocol developed to achieve interoperability among systems specifically in the electric utility, oil & gas and water/wastewater industries. This non-proprietary protocol, available worldwide, was designed to optimize the transmission of data acquisition information and control commands. It is a highly efficient and reliable communications protocol between substation computers, RTUs, IEDs and master stations. DNP is also a layered protocol, featuring time stamping and True Report by Exception (TRBE).
Allen-Bradley hardware was the preferred choice, however, Allen-Bradley’s DH+ network contained Polled Report by Exception (PRBE). Polled Report by Exception only allows the slave to send its data when the master polls. With a system this large and complex, True Report by Exception (TRBE), which allows the slave to send its data whenever a change of status occurs, was needed. The DNP protocol was chosen because it contained TRBE as well as Date and Time Stamping.
Since both General Electric and Allen-Bradley equipment were used in the plant, a DNP interface was needed to allow them to communicate with all of the DNP compatible end devices. Shanghai Electrical Apparatus Research Institute (SEARI), the system integrator for the project approached Rockwell Automation Shanghai for an integration solution. Rockwell engineers demonstrated the ability of the Allen-Bradley PLC-5s to communicate with the DNP protocol through the use of a special communications module produced by Rockwell’s Encompass Partner, ProSoft Technology, Inc.
“Since ProSoft’s 3800-DNP module* has two communication ports, SWWTP were able to install a PLC5 backup system as well as a redundant communication system,” said Lenus Hong, Asian Regional Sales Manager for ProSoft Technology. “DNP Port 1 is connected to the Master Station via lease lines, while Port 2 allows a modem dial up connection. If communications should go down on Port 1, the Master still has dial up capabilities.”
Redundancy is a key issue in most wastewater system, a fact emphasized by Zhou Ping, Rockwell Automation Shanghai’s Senior Sales Engineer.
“When a pumping station has gone down, it can be very embarrassing for the client,” he says. “Potentially, there can be wastewater in the street. This means that the reliability of the entire control system is critical. It has to run all the time, with few maintenance or operations personnel.”
The pump stations are comprised of 6 to 8 pump sets each—4 to 6 for duty plus 2 stand-by pumps. The pumps range in size from 30 kW/760 cubic meter per hour to 145kW/2590 cubic meters per hour.
The control and data communications system contains a “hot backup” mode. It is comprised of two Allen-Bradley Remote I/O processors so that in the event of a failure in the primary controller, the system will automatically switch to the backup processor.
Flow and Level Control
Through a network of flow and level meters, level and flow data is relayed back to the central control station for monitoring and control. In order to ensure accurate control, Shanghai Municipal Sewage Company specified a quick feedback time between pump station PLCs and the central control station.
“Our client specified a system feedback time of better than 20 milliseconds,” said SEARI project engineer Zhou Zhiwei. “This is why we adopted the PLC-5 series processor coupled with the ProSoft DNP modules. It’s the first time the DNP module has been used in Mainland China and it’s been a great success.”
What the Customer Needs
When Rockwell Automation Shanghai contacted their Encompass Partner, ProSoft Technology, Inc., specializing in inter-network communication solutions regarding their 3800-DNP module, Rockwell knew it was exactly what they needed to allow their PLCs to communicate via the DNP protocol. Since the ProSoft module is designed to fit into Allen-Bradley PLC racks, it wasn’t a hard decision to make.
“The TRBE features of ProSoft’s DNP module was the major factor that convinced SWWTP to award this million dollar contract for this phase of the project to Allen-Bradley,” said Hong. “When RA-Shanghai contacted us we set up a demo and immediately sent it to Shanghai for testing.”
The Shanghai Wastewater Treatment Plant is now operational. Plans are now being made to expand this system to cover the areas surrounding Shanghai.
*Since this project was implemented, ProSoft’s 3800-DNP module has been upgraded and renamed to the MVI 71-DNP module. ProSoft also has DNP connectivity solutions for Allen-Bradley’s SLC, ControlLogix and FLEX platforms as well as DNP solutions for Schneider Electric and Siemens Automation processors.
Taihe Fresh Water Factory
Flowing from west to east, across the heart of China is the Yangzi River. It is the longest river in China and the third longest river in the world. Originating in Tibet, it flows past the construction site for the world’s largest dam, the Yangtzi River Three Gorges Dam, into the Pacific Ocean at the city of Shanghai. Raw water is collected from the Yangzi, filtered and purified and then sold to Tap Water Factories such as the Taihe Water Factory in Shanghai.
In 1995, Shanghai Taihe Tap Water Manufacture Ltd. began construction of the Taihe Water Factory. Phase I of the project established a SCADA system for the factory consisting of an ABB Modcell Multiloop Controller/Processor communicating with Modbus and ABB proprietary network, ICN. Clean water could then be pumped through a series of pipes to supply the daily tap water needs for over 43,000 Shanghai residents.
“When the factory was established,” said Alex Xu, Manager for Shanghai Yuandong Science & Technology Ltd., (SYST) the System Integrators. “It used a SCADA system only to supervise the working processes without any control functionality.”
In any water system, as complex as this one, the water flow can vary dramatically from hour-to-hour and day-to-day, depending on domestic demand cycles and the more unpredictable aspects such as rainfall and storms. This makes it essential that the Master Control System be equipped, not only with monitoring capabilities, but control as well.
“The second phase of the project planned to add control ability to the plant,” said Xu. “But they found it impossible since the substations were communicating as slaves, thus couldn’t exchange data and information between each other. The main problem was that data exchanged between the slaves needed to be accomplished through the master node. As long as a personal computer carried out the master task, we could not count on its performance, steadiness and security. Use of a PLC instead of the PC was preferred.”
In order to add the control needed Xu added an Allen-Bradley PLC5/20E with Ethernet capabilities. However, since the original SCADA system was ABB communicating with Modbus, an interface was needed to allow the Modbus end devices to communicate with the A-B processor. The solution Xu found was the Modbus Communication Module made by ProSoft Technology, Inc.
Designed to fit in an Allen-Bradley 1771 PLC rack, the module contains two active serial ports, each supporting RS-232, RS-422 and RS-485, supports full radio, modem and multi-drop and is configured using simple ladder logic. Since the module communicates over the backplane, needing only standard ladder programming, it provided highly configurable Modbus Master and Slave capability to the existing A-B PLC.
“It was the first time Shanghai Yuandong Science and Technology had used our 3100-MCM module,” said Lenus Hong, Regional Sales Manager for ProSoft Technology. “ But it certainly wasn’t the last. They also installed the module in the control system for the compressors in the Shanghai General Motors Plant. Since the MCM module fits directly into Allen-Bradley’s PLC5 racks, in both instances, it provided a seamless integration of technologies.”
“The 3100-MCM module played an important role in the second phase of this project,” said Xu. “Without the ProSoft module, this phase could not have been realized.”
When asked what the deciding factors were in choosing the ProSoft module for this project, Chen Zong-Liang, General Manager for SYST said, “Ease of operation, higher profits and ease of implementation...all of the above.”
The second phase was completed in May of 1999.
A Unique Partnership
This unique partnership of integrated technologies between Rockwell Automation and ProSoft Technology has enabled SCADA systems around the world to gather data and control operations in a multitude of plants just like the Shanghai Wastewater Plant and the Taihe Water Factory.
“The 3100-MCM Modbus module was also used at the Xin Ning Wastewater Plant in Suzhou, China,” said Hong. “According to Rockwell Automation-Shanghai, the customer needed to collect data from Diris Power Meters which have embedded Modbus communications. They elected to use the 3100-MCM module which allowed them to collect 30 parameters from the power meters instead of 3 parameters they would have gotten using Analog I/O. The bottom line is, our interface module made more data available for better control and monitoring.”
“We take great pride in our ability to help Rockwell Automation interface with alternate networks,” said Doug Sharratt, CEO for ProSoft Technology, Inc. “We have been able to provide a number of solutions for the water/wastewater industry in China. We are currently presenting SCADA solutions in conjunction with Rockwell on two other large water projects. One is a wastewater treatment plant involving ten pumping stations using our MVI56-101S module interfacing Allen-Bradley’s ControlLogix to the IEC870-5-101 protocol. The second is a water transportation project on China’s Yellow River, using one of our ProLinx Communication Gateways to interface Allen-Bradley’s PLC5 processors to DNPNET.”
The seamless integration of Rockwell Automation and ProSoft Technology is helping China realize its goal of enough clean, fresh water for all of its citizens.
“China has its problems,” said Xu. “ But it has faced these problems and is attempting to tackle them. Sometimes the progress may be a little slow and seem small, but it is steady and good willing. As the international community continues to give real help and useful advice, things will go better, smoother and expeditious.”