Braking jet in an impulse turbine is used to
- Abreak the jet of water.
- Bbring the runner to rest in a short time.Correct
- Cchange the direction of the runner.
- Dchange the direction of the flow
Solution
Concept
An impulse turbine like a Pelton wheel uses a high-speed water jet to rotate the runner. When we want to stop the turbine, a special small nozzle called a braking jet is used to throw a water jet in the opposite direction of the runner rotation.
Step-by-step solution
1. Understand what a Pelton turbine is. It is an impulse turbine where water strikes the buckets. 2. When the main nozzle is closed, the runner keeps rotating for a long time due to inertia because there is very little friction. 3. To bring the heavy runner to rest quickly, a small nozzle is opened. This directs a jet of water onto the back of the buckets. 4. This creates a braking force that slows down and stops the runner in a short time. Answer: (B) bring the runner to rest in a short time.
Explanation
The braking jet applies a reverse force on the turbine runner. This brings the heavy runner to rest quickly when shutting down the turbine.
Why the other options are wrong
A: It does not break the main jet of water. C: It does not change the direction of runner rotation. D: It is not meant to change the main flow direction of the turbine.
Shortcut
Remember 'Braking jet' means brake, which means to stop the runner quickly.
Common mistake
Students often think it breaks or damages the main water jet, but it is actually a mechanical brake using water.
Correct answer: B) bring the runner to rest in a short time.