A key component of the above presented three phase approach is the assessment of a hydropower plant during the DIAGNOSIS phase. It is an important tool providing the basis for the development of possible modernization or upgrading scenarios in an early planning phase. In the following, four major activities with focus on the safety and life cycle aspects will be discussed.
1. General Inspection and Data Collection
This activity forms the basis for the following steps in a hydropower plant assessment. On the one side, many data can be analysed in form of a desktop review of available information provided by the hydropower plant owner.
Items for a desktop review can be:
– Studies of the hydrological scheme, drawings
– Inspections and maintenance reports
– Operation logs, Commissioning and site test reports
– Operation and maintenance manuals
It has to be kept in mind that data from existing drawings or records are not always reliable since changes in operation conditions or design modifications might have been implemented in the past.
It is also the task of a site visit or inspection on the other side to identify such deviations. The assessing engineers who undertake this work are generalists with a broad level of knowledge covering all aspects of the plant. An in-house developed inspection matrix helps to define the assessment scope before the inspection which can help together with hydropower plant owner to find the most suitable timing for the assessment. During the site visit
systematic check lists & questionnaires support in the communication during the close dialogue with owner and the very important site personnel. Mainly visual inspections and simple measurements are undertaken in this phase to achieve an overview of the original und current physical condition & performance of the units. An inspection report summarizes the results of this first inspection phase which is presented to the power plant owner who can decide according the report‘s recommendations (e.g. further test and measurements, detailed inspection which require are partly dismantling of the unit) about the further proceeding.
2 Detailed Inspections and Material Tests
The outcome of the first general inspection as described in 6.1 might indicate to perform a more detailed analysis for certain parts or systems. This can include a further collection of geometric or operational data. Verifications of actual dimensions, clearances, wears and checks of temperatures and flow rates, e.g. in the cooling system, are standing in the foreground. Also non-destructive testing (i.e. hardness test, surface roughness, magnetic particle test, dye penetrate test, ultrasonic test) are common tools used in this assessment step to check material properties and damages. In most of the cases partly dismantling of the unit is required to get access to the objects of interest.
In relation to the safety and life cycle aspects the main measurements for the mechanical part are already mentioned. The mechanical integrity check can be extended by hydraulic measurements (relative and absolute efficiency test) which will show the actual performance of the unit and delivers important input parameters (flow rate, component losses) for the new hydraulic design. Transient tests (pressure fluctuation tests) are relevant in case of planned changes in operating conditions or general changes in the hydraulic system (increased flow, installation of additional units).
In case of unavailable dimensions or geometry of key parts which will be kept for the planned modernization or upgrading scenario an instrumented site measurement of the prototype dimensions can be performed. The resulting geometry models are used to perform hydraulic (CFD) as well as mechanical calculations (FEM) which are described in the following chapter.