Hydraulic Turbine: Run Away Speed and Load Rejection

I have been in chemical process simulation modeling and development since 10 years.

My current assignment is on Modeling Hydraulic Turbine (HT).

I have modeled this HT using basic first principles.

The model is up and running fine.

Now i am onto, run away speed scenario modeling.
I have got Run away characteristics data from customer; Curves of Speed vs Wicket Gate Opening (WGO) and Discharge Flow vs WGO.

I am unable to link these characteristics to the basic modeled HT.

Please help in understanding Run Away characteristics.

Another one is Load Rejection, what is Load Rejection?

Appreciate your help