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The assessment of the real penstock safety margin during transient operation

Overload Detection Module (ODM)

The diagnostic of over pressure is performed by the overload detection module, ODM. The  ODM uses proprietary algorithms based on the behaviour of a simple hydro acoustic system. This allows to continuously diagnose the class of any pressure fluctuation phenomena. And finally to detect the risk of exceeding the admissible maximum pressure over each section of the penstock.

  • ODM assesses the impact of the transient on each point along the penstock. This assessment is carried out in real-time by using the pressure measured on the downstream section of the penstock. Thus allowing the detection of potential security risks in each section.

The diagnostic of over pressure is carried out for all potentially damaging phenomena

  • ODM detects any Mass Water Hammer phenomena to determine if the measured pressure on the penstock does not exceed the  admissible maximum pressure profile,
  • ODM detects any Wave Water Hammer phenomena (or rapid water hammer) to determine if the speed of the transient flow drop will not create a propagating pressure surge. This wave could exceed the admissible maximum pressure level over upstream sections of the penstock and damaging its structure.
  • ODM detects any risks of Water Column Separation phenomena to determine if the speed of a sudden increase in flow rate leads to a propagating pressure drop wave. The depressurization could lead to cavitation over the upstream sections of the penstock and finally a large void cavity. This cavity that collapses when the pressure recovers cause strong over pressure in upstream sections of the penstock.
  • ODM detects any risks of resonance by checking if the cyclical levels of the pressure are properly amortized. If not, these cycles drive to self-sustained pressure fluctuations and dangerous structural fatigue damage.
  • Maximum penstock pressure profile caused by Mass Water Hammer

Mass Water Hammer

The mass water hammer phenomenon is only related to the inertia of the water column located upstream of the component which cuts the flow. Closure time is longer than the return time of the reflected wave from the top of the penstock.

The affected area is meanly the downstream part of the water system:  penstock sections, manifolds, unit casings.

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  • Maximum penstock pressure profile caused by Wave Water Hammer

    Wave Water Hammer

    The wave Water Hammer phenomenon results from a quick drop in the flow. The closure time is shorter than the return time of the reflected wave. Because of the wave propagation, the affected area is meanly the upstream sections of the penstock. This phenomenon is related to the overall compressibility of the water in the penstock. Thus, safety requires to quantify the maximum pressure profile reached along the penstock for each transient event.

    HYDROSURGE is designed to detect warning signs of Wave Water Hammer phenomena.

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    • The collapse of the cavity caused by Water column separation

    Water column separation

    Water Column Separation phenomenon resulting from a rapid increase in the flow. The opening time is shorter than the return time of the reflected wave. The affected area is meanly the upstream sections of penstocks. Thus, hydro safety requires to quantify the minimum pressure profile reached along the penstock for each transient event.

     HYDROSURGE is designed to detect warning signs of Water Column Separation phenomena.

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    • Cyclical penstock pressure profile caused by hydro-acoustic Resonancehydro-acoustic Resonance

    Self-sustained cyclical pressure fluctuations may cause low-cycle fatigue damages of penstocks. The whole sections of the penstock are affected.

    HYDROSURGE is designed to detect warning signs of self-sustained cyclical pressure fluctuations for each transient event.

    • See a visual of a known case of hydro acoustic penstocks resonance

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