As part of an ongoing Supervisory Control and Data Acquisition (SCADA) replacement project it was recognised that the physical transfer from the existing control system to the new system would require significant care and management. The difficulty of the task was significantly increased due to the requirement for the plant to remain operational during this transfer process. This process has to be carefully managed and the implications of the added complexity fully understood. To mitigate the risk in the transfer between the two SCADA systems, Tenet were contracted to evaluate the potential impact of removing the analogue / digital signals when each SCADA fan-card was swapped out as part of the changeover strategy. Through a great deal of collaborative working at the front end of the project, our team was responsible for identifying the potential problems from the outset and creating a risk reduction strategy for implementation.
The exiting SCADA system consisted of a number of outstations, with each outstation containing a varying amount of associated analogue and digital input fan-cards in a paired arrangement. Tenet were tasked with evaluating the impact on plant and process on the removal of each fan-card. This was achieved through inspection of each digital and analogue signal path to identify any associated Safety Mechanisms (SM) and Safety related Equipment (SRE). The purpose of this being to assess any inherent affect on the performance of each Safety Function. This information was captured in the form of Operator Worksheets. As part of this assessment, recommendations were made on how any impact on the safety case could be minimised by identifying substitution systems and allowable outage times for each Safety Mechanism and detailing what actions would be required prior to each outage. Additional to this, any instances where it was found that the SCADA system was responsible for delivering a safety function, a shortfall was raised and captured on the Operator Worksheets.
To aid the strip out and installation process, an Instillation Worksheet for each fan-card was produced to collate the existing signal and termination detail against the proposed modification detail for the replacement system. The Installation Worksheets would then be used to form part of the Commissioning Test Documentation.
A red line mark-up of each plant record Hook-Up was also produced to reflect the input signal connections to the new SCADA system, including new signal isolator or fuse and link details where required.
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