MCS was engaged by DCWW Welsh Water for the detailed design, supply, manufacture, modification of existing cabinets, PLC Migration (Hardware and Software), new HMI’s and SCADA, electrical installation, delivery and offloading of a complete control system to control the existing plant at Nash WwTW and associated satellite pumping stations
The existing site was at risk of plant and process failure due to hardware & software being end of life and obsolete. The Legacy replacement upgrades removed the risks replacing with current hardware and software.
All photographic images used in this post are currently stock awaiting image permissions by DCWW Welsh Water
MCS Onsite duties were prior to site commencement and beyond start date. Our Principal Contractors & Site Operatives attended site for 120 days, their duties including the following:
Carry out site inductions of contractors, DCWW personnel and visitors
Issue and monitor Permits to work on equipment that may become live
Carry out appraisals of submitted Risk Assessments, Method Statements, COSHH assessments, HAVS assessments, Noise assessments, Manual handling Assessments & lifting plans from site contractors.
Compile and maintained site activities Health and Safety Files. Carried out health and safety inspections and audits including toolbox talks for specialised task were being completed
Liaise with DCWW for access to site. Liaise with DCWW for isolation certificates and permits to work. Liaise with DCWW site operation staff on a daily basis
Request and compile information for the CDM Health and Safety file. Assisted in completion of any DCWW forms as required (CTRs, SAP forms etc)
Select each item to learn more
At the outset of the project MCS carried out a detailed site survey over a period of two weeks to investigate the best practice to carry out the migration of the PLC’s and to keep the plant running with minimum shutdowns. Whilst carrying out the site survey MCS also reviewed the existing PLC network and cable installation with a view to installing/modifying the existing installation without affecting site process. This work would be undertaken as part of enabling works.
MCS reconciled the existing FDS‘s with downloaded copies of the existing software and spoke with operations to ensure that the process operated as documented. This check exposed anomalies between the documents and the actual operation of the plant. MCS reflected these changes in the FDS and rewrote where required, with operations on functionality and possible risks to process. Forward planning of shutdowns was extremely important due to time of day and weather conditions as there was only 1 to 2hrs storage of sewage allowable while the migration of the existing Siemens/obsolete Mitsubishi PLC’s to new Mitsubishi PLC’s
The first stage of the PLC migration was to replace the existing Field terminals blocks with 3 way link terminals.
The advantage of these terminal blocks are they are the same width as existing. This allows the existing wiring to stay in situ while MCS connected looms from the new rack mounted PLC modules into the 3 way link terminals. This would allow the new PLC to be wired with a short loom ready for changing the links in the terminals to bring online the New PLC.
→This arrangement minimises risk if issues arise during commissioning as it’s simple to revert to control via the old PLC. Sometimes during these minimal shutdowns periods operations would assist by running the plant in hand.
The PLC’s that needed migration were
Each one of the above was controlled by an existing Mitsubishi ‘A’ series PLC, which was migrated to a new Mitsubishi ‘Q’ series PLC. The existing Centrifuge PLC was an old Siemens S7-300 PLC, the processor was changed to make this PLC remote IO and controlled by the Plant house PLC via Profibus to facilitate visibility onto the new SCADA.
As the site runs 24/7/365 continuously with only 1 – 2hrs storage facilities (inflow could be pumped to storage tanks) the modifications required an accelerated changeover which required MCS working closely with operations to achieve the PLC migration within the timeframe.
MCS designed portable frames for each of the 5 PLC’S that were due for migration. These wheeled frames enabled MCS to mount the new PLC’s onto them so they could be sited adjacent to the existing ICA/PLC cabinets.
Following successful commissioning of the works each of the old PLC’s needed to be removed from their location to allow the new PLC to be installed into the vacated space. MCS required a 1 hr shutdown to unscrew the existing I/O cables from the existing PLC and remove the hardware, ingress the new PLC from the frame into its final location and insert the new cables into the existing trunking and replace trunking lids.
A new Fibre ring network enclosure was installed for the SCADA, PLC and CC-Link (PLC to PLC comms) network and network node boxes were install into the Inlet, Aeration, RAS/SAS, FE and Plant House. These were was installed during normal daytime working hours as this could be carried out independently of the existing installation. This allowed MCS to setup all ethernet switches and test the network prior to changeover.
→The innovative approach, in depth planning and preparation prior to and during the successful migration allowed the treatment works to operate seamlessly without any issues with its customers.
Prior to going to site, MCS simulated the complete site and bench tested all the new PLC software along with the new standalone SCADA system against the agreed FDS before attempting any changeovers at site. A full Factory Acceptance Test was carried out in conjunction with the client with full simulation including SCADA.
At each stage of the Factory Acceptance Test, testing was carried out rigorously using a thorough proven testing process. Approximately 500+ test cases were performed to deliver a robust, error free system. By fully simulating the works MCS were confident that risk to the commissioning of each PLC after migration would be substantially reduced. To further minimise risk, MCS had a ‘fall back’ position of reverting to the existing PLC’s if anything untoward happened.
Our innovative approach, in depth planning and preparation prior to and during the successful migration allowed the treatment works to operate seamlessly without any issues with its customers.