Controlling the power needle is critical to any hydroelectric plant with an impulse turbine configuration. Operating head ranges are between 20-2000 meters where the water is converted to a high velocity jet stream when released from the nozzle’s orifice. As part of the nozzle for an impulse turbine, the power needle controls the water jet that impinges on a series of buckets rotating the runner.
There are two types of impulse turbines – Pelton and Turgo. A Pelton turbine power needle is in-line with the buckets of the runner that splits the water jet in half for maximum efficiency. The water impinges on the buckets from an incline, releasing it to the other side of the buckets with a Turgo turbine. Orientation can either be vertical or horizontal. Single and multi-jet power needles can also be utilized for a system. A deflector or other method of redirecting the water jet can be used as both for more control and safety. The use of either turbines and configuration can vary depending on plant strategy.