When modeling a turbine under the load rejection operating case, why do I see a change in the transient results before the operating rule is set to close the wicket gate?
For the Load Rejection operating case, an electrical torque vs. time curve is supplied in the turbine properties. If the hydraulic torque from the initial conditions multiplied by the turbine efficiency does not equal the electrical torque at time zero from this electrical torque curve, the turbine will either speed up or down, causing results to not be steady, even before the wicket gate moves.
To fix this and stop the initial surge at the beginning of the transient simulation, you will need to adjust the electrical torque value at the beginning of the electrical torque curve, so that it is equal to the hydraulic torque multiplied by the efficiency. For more on how to do this, see the link below.
Calculating initial electrical torque for use with the Load Rejection turbine Operating Case
Using Turbines in Bentley HAMMER