Surge Tank Mass Oscillation & Thoma Stability Calculator
Determine critical surge tank area (A_Th), Franke/Thoma governor stability safety margin, and maximum water level excursion during full load rejection.
Head race Tunnel & Surge Shaft
Stability Margins & Upsurge Amplitude
Recommended Tools & Equipment
Tested hardware and components for high reliability
Surge Tank Hydraulic Stability & Oscillation
A surge tank installed at the junction between a low-pressure headrace tunnel and high-pressure penstocks isolates the long tunnel from rapid water hammer transients while providing water storage to damp U-tube mass oscillations between the reservoir and the tank shaft.
Thoma Stability Criterion
When an electrical turbine speed governor operates in constant-power control mode, any drop in net head causes the wicket gates to open further to sustain electrical output. If the surge tank cross-sectional area ($A_s$) is smaller than Thoma's critical area ($A_{Th}$), this feedback creates an unstable negative damping condition leading to runaway hydraulic oscillations. Modern guidelines require a safety factor $n = A_s / A_{Th} \ge 1.50$ to $1.80$.