China's Water...

Danetta York

The seamless integration of Rockwell Automation and ProSoft Technology helps China realize its goal of enough clean, fresh water for all its citizens. 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.

Central Control

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.

Integration Solution

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."

Dual Redundancy

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.