Reaction Turbines
The figure below is a schematic of a typical reaction turbine. A volute casing and a ring of guide vanes (or wicket gate around the circumference) deliver water to the turbine runner. The wicket gate controls the flow passing through the turbine and the power it generates. A mechanical and/or electrical governor senses gradual load variations on the generator and opens or closes the wicket gates to stabilize the system (by matching electrical output to grid load).
Hammer currently models hydraulic transients that result from changes in variables controlled by the governor: it does not explicitly model the governor's internal operation or dynamics. Depending on the Operating Case being simulated, HAMMER either assumes the governor is `disconnected' or `perfect'.
The governor is an electro or mechanical control system that may not be active - or may not react fast enough - during the emergency conditions of primary interest to modelers: instant load rejection or (rapid) load rejection. Instant load rejection assumes the governor is disconnected.
At other times, the governor will strive to match electrical output at the synchronous or `no-load' speed: e.g. during load acceptance or load variation. Given the fact that no two governors are the same, it is useful to assume the governor is `perfect' in those cases and that it can match the synchronous speed exactly.
Each of these categories corresponds to a range of specific speeds that can be calculated from the turbine's rated power, rotational (synchronous) speed and head.
Note that there is no option in HAMMER to change the runner blade angle of a Kaplan turbine, so it is assumed the runner blade angle is constant during the transient analysis. Engineering judgment should be used to determine if this approximation is satisfactory in each case.
The primary hydraulic variables used to describe a turbine in the above schematic are: