Rand Water’s Filter House 3 upgrade

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randwaterVereeniging-based systems integrator, Autotronix, has just completed a multi-million rand upgrade of Filter House 3 at Rand Water’s Vereeniging facility. The upgrade consisted of removing a dated control system and replacing it with a state-of-the-art control and scada system consisting of the latest in communications, control hardware and instrumentation.
autotronixThe project management, engineering design, software, instrumentation network design (Profibus), installation and commissioning, the wiring and assembly of the PLC control panels, the design of the distribution boards was all performed by the Autotronix team.

General overview

Autotronix was tasked to supply a fully automated control system for water filtration, at Rand Water’s Vereeniging pumping station. This automated system operates 72 filters housed in the filter house, along with its associated wash plant.

The project comprised of refurbishing all valves (by Gunric), replacing valve actuators and replacing all pneumatic operated actuators with electric operated actuators with their corresponding control infrastructure.

The challenge was to keep part of the operation still in production, while refurbishing the selected galleries. The 72 filters were divided into six galleries (12 filters per gallery) with three washwater pumps and three air blowers.

Communications

Each filter has five electric actuators and two level transducers. All of these were on a Profibus DP copper bus to Siemens OLM. The Siemens OLMs (there are 14 per gallery) were configured in ring configuration on two separate network rings as shown in the figure. Fibre-optics was opted for the fibre ring for its higher immunity from lightening strikes and electrical interference. The entire bus runs at 1,2 MB.

rw_filterhseEach Gallery has a Schneider Quantum PLC which hosts two Profibus DP master modules, an Ethernet Communications module and input modules to keep track of its personal UPS health. A Magellis HMI was linked to the PLC via Ethernet. The PLCs were linked to the CCR via Ethernet again on optic fibre, for noise immunity.

The PLC in each gallery was linked to the CCR via fibre-optics also in a ring configuration. The CPU was programmed to execute the filter wash sequence, control the filter throughput and keep tabs on the water quality.

Continuous online monitoring of the water quality was introduced and should any filter turbidity exceed the threshold then the filter is promptly introduced to the FIFO queue where it waited its turn for a drain and a wash program. The filters can go into the drain or wash programme based on in-service time, turbidity or operator intervention.

There are a total of 377 actuators on the Profibus DP and the level measuring instruments amount to 79. This means that the total number of Profibus DP nodes is about 456 excluding the 13 master nodes. The PLC programming environment used was Schneider’s Concept and the entire program was written using IEC 61131 standard function blocks.

Supervisory system

The scada used was Wonderware’s Intouch with Archestra.

Key events, alarms and the overall system functionality were measured, logged (InSQL) and displayed on the scada which were situated in the control room. In addition, HMIs situated at each gallery DB also relayed this information.

The scada was a cinch as similar graphics were used on most of the mimics. Templates and scripting were used extensively to take advantage of the repetitive nature of the project. Archestra was used to model the entire plant. The repetitive nature of the plant lends itself well to Archestra. Just seven base templates were created from which over 500 objects were derived.

archestraWith Archestra, each primary object was modelled from a base template and then all objects in the plant like inlet valves, outlet valves, etc, were derived from the primary object. These objects are essentially children of the parent objects. This was advantageous as any modification to the parent object was propagated through to its children as required and very quickly – without any further effort required.

The main Intouch mimic was a single screen referenced to tags in Archestra. The scripting in Intouch allowed it to dynamically determine which filter was selected and the system would get the relevant data from Archestra. All tags are monitored and logged in InSql – Wonderware’s industrial proof historian and events database.

Techniques were introduced that would enable the implementation of similar upgrades to be more cost effective as new standards have been set with re-usable objects that have been tried and tested. The system has proven reliable even with the severe electric storms experienced in the past few months. This illustrates the quality of the installation and the reliability of the products used.

Article by: Collin Chetty of Autotronix and Pierre Zaayman of Rand Water
Source: SA Instrumentation & Control, April 2006