PSI - Issue 48

Aleksandar Šotić et al. / Procedia Structural Integrity 48 (2023) 266 – 273 Šotić et al / Structural Integrity Procedia 00 (2023) 000 – 000

272

7

After defining this structure, in the following, as the analysis progresses, additional details of the control structure are determined: responsibilities and process models for each controller, control actions and feedback loops. Also, it is necessary to consider the communication between individual controllers. The analysis of potentially unsafe control actions is carried out by (i) placing the control action in contexts/process analysis tables and (ii) defining safety constraints for un-safe control actions. Identification of potential causes/scenarios of hazardous control actions (preliminary) yielded the following results: A. Inadequate control algorithm (control actions are missing or flawed, or not followed) A.1 Inappropriate control actions (safety constraints); for example: A.1.1 By looking at several Environmental Impact Assessment (EIA) studies regarding HPP, the following can also be read: 'All measures prescribed by law should be taken' (paraphrased), which is one of the confirmations that the EIA is often just a bureaucratic addition, not an essential act. A.1.2 For the minimum sustainable flow as the flow that must be provided downstream of the water intake in the watercourse for the survival and development of downstream biocenoses and meeting the needs of downstream users, the Ministry of Environmental Protection did not prescribe the method and criteria for calculation (Law on Waters). A.2 Control actions are not applied, for example, A.2.1 In the case of HPP Pirot, compensation basins are not used in HPP operation, as designed. A.2.2 The designed operation mode is not followed; in 2018, the annual electricity production plan was achieved already at the beginning of April. A.3 Missing of control actions; for example: A .3.1 Ristić and colleagues further state that the Environmental Impact Assessment Studies, as one of the elements of the technical documentation, mainly support the investor's intention, i.e., almost all of them show "that there are no negative impacts on the environment and biodiversity", which, as they say, is not true. A.3.2 Protection of fish stocks, for example, is nowhere mentioned. B. Missing of feedback B.1 Not all system variables are measured; and the controller is not reported on a possible violation of safety restrictions in regard with that. B.2 As the activities of state inspection, partly in the role of a sensor, monitoring the implementation of control actions B.2.2 Insufficient supervision according to prescribed checklists; for example, which enables the operation of HPP Pirot even without using the planned compensation basins and/or other measures to limit the discharge of water into Nišava River. C. Control algorithm flaws C.1 If one compensating pool has changed its purpose (it has become a swimming pool), and the other is not used as intended, it is necessary to change the process model and the control algorithm that will adapt the working mode of HPP Pirot to those changes. D. Process model flaws D.1 Without measuring key system variables (flows, levels, etc.), the actual state of the system cannot be obtained, nor can the model of the controlled process be obtained. D.2 There is an evident change in designed mode of operation, the importance and role of HPP Pirot in the energy system, due to all the changes that occurred during the transition, from planned work, on a weekly, less often daily, level, to (perhaps) hourly changes, D.3 The change of the process model certainly refers to climate changes, that is, to the updating of hydrological models accordingly. Conditions in the catchment have also changed significantly in terms of urbanization, changes in land use, new users, etc. The method has applications in the safety arrangements of existing systems, applications in the development of new designs, or investigations of adverse events that have already occurred, which are briefly demonstrated in this paper.