What are Impulse turbine types? | An-Overview
Impulse turbine has the following basic types:
Pelton Turbine
The Pelton turbine has three main components: the nozzle, the runner, and the deflector. These turbine types use for high headwater. The water head is converted to high-speed current by one or more nozzles (up to 6). The flow of water and as a result, the power of the turbine is controlled by the spear, which controls the flow of water.
A series of symmetrical buckets are arranged around the cylindrical runner of the turbine. Due to the special shape of these buckets, the water jet bounces in the center (splitter) and comes out from both sides. This exhaust means that the water coming out of the bucket does not touch the next one and the brake does not apply. The Pelton wheel turbine axis can place vertically or horizontally. For high forces and a large number of nozzles, the shaft is always vertical and installed above the generator turbine.
There is a deflector between the rafter and the nozzle, and its function is to prevent water from spraying from the nozzle into the buckets when a sudden load is removed from the turbine and its rotational speed increases. Then, with the help of a slow spear, the flow of water stops. As water hammer is likely to occur, the velocity of water in the nozzle cannot be reduced quickly and the discharge may be cut off.
Here are some other hydraulic and physical features:
- It can release heads between 20 meters and hundreds of meters and release between 5 and 1000 liters per second.
- Pelton turbine installation is generally easier than a combined reaction turbine, with equal power because the piping requirements are lower due to the lower flow rate.
- Due to the operation of the Pelton turbine at high water pressure, the equipment required for penstock in these turbines is complex and expensive.
- Pelton turbines can achieve up to 95% efficiency; Micro-level hydropower plants have a maximum efficiency of 90%.
Turgo Turbine
The turgo turbine is another type of induction turbine that works similarly to the Pelton; The difference is that in these turbines, the water jet touches the buckets exclusively (approximately 20 degrees). Due to the complex shape of the bucket, the bucket is more difficult to build. These impulse turbine types have a certain speed than the Pelton. The advantage compared to the Pelton for equal power is the larger jet and smaller machine size. This type of induction turbine is used in small hydropower plants.
Crossflow Turbine
This impulse turbine is a modified type of turbine used in small hydropower plants. Like other types of induction turbines, the rotor moves in the air and does not sink completely like a reaction turbine. One of the important advantages and features of this turbine is that it can operate a wide range of flow rates, heads and consequently. In addition, it adapts well to changes in flow while saving capacity. A special control system adjusts the active part of the turbine according to the amount of water flow.
The various parts of this turbine are shown in the figure below. The runner is in the shape of a drum. In cases where the head is low, the runner is long and, conversely, high head, short runner. After passing through the inlet adapter and guide vans the water enters the turbine, which plays a guiding role by directing the flow to hit the rotor at the appropriate angle to achieve the best efficiency. After passing through the runner twice the water leaves the turbine through the outlet pipe; It first flows to the upper rotor blade and then returns through the middle and lower blade of the rotor, producing torque in both processes. Hence the name crossflow for these turbines.
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