Drilling rig drawworks hook load overspeed preventing system

Abstract

The method and apparatus for preventing runaway lowering of a hook block in an oil drilling rig characterized by monitoring the instantaneous values of hook load and speed and using these values together with parameters associated with the rig drawworks to calculate an energy value which must be dissipated during a braking stop by the drawworks brake. The brake or an emergency brake associated with the drawworks is automatically actuated when the calculated energy value reaches a predetermined value representative of the maximum energy absorbing capability of the brake. The brake may also be automatically activated when the position of the hook block reaches predetermined upper and lower limits. The processor associated with the system also calculates a hoist value representative of the normal energy dissipating rating of the brake and activates an alarm if this value is matched by the calculated energy value for a particular load and speed, and a second value representative of the maximum energy dissipating capacity of the brake for emergency stopping, and activates the brake if the second value is matched by the calculated energy value for a particular load and speed.

Dependencies are inferred from the claim text.