Researching water turbine designs.

by happy954 (student)

Investigation: Design of a Runner

Background:

Runner – Is a rotating part of Turbine consisting of curved vanes/blades or buckets on wheel that is turned by pressure of high veloctiy of water, thereby transforming falling water energy into rotating mechanical energy.

There are mainly 3 types of Runners:

1) Kaplan Runner: They are quite suitable for low heads and large discharge/ head variations ranging from 10M to 60M.

2) Francis Runner: Have widest range of application. They can operate under very different head ranging from 30M to 700M.

3) Pelton Runner: They can operate under a very large range of heads up to 1800M.

Aim: To Define Type of Runner to be used in Hydro Power Plant in order to generate Power based on the net head of water and flow rate.

Research question: How does the Water head and flow rate effect the type and size of Runner.

Introduction:

Types of turbines:

Impulse turbines

Pelton turbines

Pelton turbines are impulse turbines where one or more jets impinge on a wheel carrying on its periphery a large number of buckets. Each jet issues water through a nozzle with a needle valve to control the flow. They are only used for high heads from 60 m to more than 1 000 m. The axes of the nozzles are in the plan of the runner. In case of an emergency stop of the turbine (e.g. in case of load rejection), the jet may be diverted by a deflector so that it does not impinge on the buckets and the runner cannot reach runaway speed. In this way the needle valve can be closed very slowly, so that overpressure surge in the pipeline is kept to an acceptable level (max 1.15 static pressure).

As any kinetic energy leaving the runner is lost, the buckets are designed to keep exit velocities to a minimum.

One or two jet Pelton turbines can have horizontal or vertical axis, as shown in figure 6.5. Three or more nozzles turbines have vertical axis. The maximum number of nozzles is 6 (not usual in small hydro).

The turbine runner is usually directly coupled to the generator shaft and shall be above the downstream level. The turbine manufacturer can only give the clearance.

The efficiency of a Pelton is good from 30% to 100% of the maximum discharge for a one-jet turbine and from 10% to 100% for a multi-jet one.

Turgo turbines

The Turgo turbine can operate under a head in the range of 50-250 m. Like the Pelton, it is an impulse turbine, however its buckets are shaped differently and the jet of water strikes the plane of its runner at an angle of 20º. Water enters the runner through one side of the runner disk and emerges from the other. It can operate between 20% and 100% of the maximal design flow.

The efficiency is lower than for the Pelton and Francis turbines.

Compared to the Pelton, a Turgo turbine has a higher rotational speed for the same flow and head.

A Turgo can be an alternative to the Francis when the flow strongly varies or in case of long penstocks, as the deflector allows avoidance of runaway speed in the case of load rejection and the resulting water hammer that can occur with a Francis.

Cross-flow turbines

This impulse turbine, also known as Banki-Michell is used for a wide range of heads overlapping those of Kaplan, Francis and Pelton. It can operate with heads between 5 and 200 m.

Water enters the turbine, directed by one or more guide-vanes located upstream of the runner and crosses it two times before leaving the turbine.

This simple design makes it cheap and easy to repair in case of runner brakes due to the important mechanical stresses.

The Cross-flow turbines have low efficiency compared to other turbines and the important loss of head due to the ...