Demands of Future Elektricity Market on Surge Tank Design

Ever since hydro power plants have been planned and erected the surge tank design is of prior importance for transient behaviour and flexibility of these plants. In the beginning simple shaft surge tanks were designed for single load rejection only, e.g. by Thoma. Later the design developed further to chamber surge tanks due to increasing demands on plant operation flexibility until nowadays highly sophisticated throttled executions – so called differential surge tanks – have come up with multiple water surfaces in different chambers under atmospheric pressure.
Especially for the demands of power regulation, the ability of completely free operation of HPP is usually requested at least for new plants. However, in order to improve revenues also with their existing plants an increasing number of operators is interested in providing power regulation mode, i.e. highly flexible operation, to the electricity market also with these plants - although they were not designed for this purpose. In these cases, it is of major importance to know the consequences of these operation modes on the waterway as the opening and closing speed of the guide vanes is in general sufficiently high.
But it is still an open question whether the capability of a completely free operation is really needed as there are more economic ways to fit the electricity markets purposes, e.g. such as a digital surge tank protection. Based on different case studies the demands on the waterway hydraulics are shown which result from primary power regulation. Long-term experience shows that multiple plant switching in the natural frequencies and thus the excitation of water level oscillations is very seldom. Thus, if it should happen accidentally, digital surge tank protection systems are shown to be an appropriate means to protect plants from unsecure conditions - also in the case of power plants which originally were not designed for this operation mode.