DEH Means "Digital Electro-hydraulic Control System" mostly for steam turbine

turbine is considered there as a prime mover.this turbine will be driven bt STEAM OR HYDRAULIC OIL OR ELECTRICALLY so that when it is coupled with a pump it works creating a pressure or vaccum enough to pump the fluid.

The runaway speed of a hydraulic turbine is the speed at which the turbine coupled to the generator runs at the maximum possible speed due to loss of load and this happens until the shut off valves completely closes the discharge from the penstock.

the runaway speed of the turbine is determined by the turbine designer and is influenced by the maximum discharge of water from the penstock, the combined inertia of the turbine runner and the generator and the flywheel.

this factor can vary from 1.5 up to 3 times the nominal speed of the turbine and is determined by the turbine designer considering all the load parameters.

F. O. Ruud has written:

'Stress analysis of hydraulic turbine parts' -- subject(s): Hydraulic turbines

The runaway speed of a water turbine is its speed at full flow, and no shaft load. The turbine will be designed to survive the mechanical forces of this speed. The manufacturer will supply the runaway speed rating.