07-02-2013, 09:42 AM
PENSTOCKS
PENSTOCKS.ppt (Size: 3.52 MB / Downloads: 180)
HYDRAULIC DESIGN OF PENSTOCKS
Penstocks: Pressure conduit or shaft, usually of short length to convey water from reservoir or Forebay to scroll case and thence to turbines.
The fabricated penstocks are tested for 1.5 times the design pressure. Radiographic and ultrasonic testing are done for detecting defects in the welded joints.
Gate is provided u/s of the Penstock and d/s of the gate air vent or stand pipe is provided, which connects the top of the Penstock to the open air. Air vent pipe facilitate proper escape of air from the Penstock while filling the Penstocks.
Air Valve is provided just before the powerhouse to discharge water when pressure increases on account of sudden closure.
Manholes are provided along the length of the Penstock at 120 m to 150 m to provide access to the pipe interior for inspection maintenance and repair.
A length of 5 to 10 times the diameter of the penstock should be horizontal from the centerline of the unit, so as to have a uniform distribution of water in the scroll or spiral case.
The radius of curvature in the Penstock profile should be three to five times the diameter of the Penstock.
Classification of Penstocks
(A) Based on Type of Installation
(i) Surface Penstocks – BSL in HP (Surface Penstock and Penstock in tunnel)
Advantages:
Easy and regular inspection
Less expensive installation
Maintenance and repairs easy
Safety against sliding may be ensured by properly designed anchorage
Disadvantages:
Prone to rusting and corrosion being exposed
Repeated painting of outer surface is needed
Supporting and anchoring on steep hill slope is difficult and costly.
Susceptible to damage by landslides, snowslides etc.
Expansion joint necessary
Chances of water conveyed being frozen in severe cold climates.