---
title: "Control of water delivery to turbine"
subject: "Power Plant Equipment"
chapter: 1
key: "semester_7/power_plant_equipment:water-delivery-control"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/water-delivery-control
site: BCT Engineering
---

# Control of water delivery to turbine

Power Plant Equipment · Chapter 1: Hydro Power Plant

- Asked in: 2070 Chaitra, 8 marks
- Video: [Control of Water delivery to Turbine / Oil Pressure governer working principle](https://www.youtube.com/watch?v=QGRiytGPvXk) — ElectroTech Hub
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/water-delivery-control
- Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-1

## Question

Explain with neat diagram, how the delivery of the water to turbine is controlled in hydro generating station.

## Short answer

Water delivery is controlled by the governing system: a speed governor senses frequency, a pilot valve directs oil to a servomotor that moves wicket gates (reaction turbines) or a spear valve (Pelton). A restoring feedback link stabilizes gate position, matching water flow to load while limiting water hammer.

## Answer

In a hydro station, the water delivered to the turbine is controlled by the **governing system**. It keeps the speed (frequency) constant by adjusting the **wicket (guide) gates** in reaction turbines or the **spear (needle) valve** in Pelton turbines, so that water power matches the electrical load.

```text
     speed set point
          |
          v
 +-------------+   +---------+   +-------------+
 | speed       |-->| pilot / |-->| main servo  |
 | governor    |   | relay   |   | motor (oil  |
 | (fly-ball/  |   | valve   |   | piston)     |
 | electronic) |   +---------+   +-------------+
 +-------------+                     |  moves
      ^                              v
      |                     +------------------+
      |  speed signal       | wicket gates or  |
      |                     | needle/deflector |
      |                     +------------------+
      |                              | water
 +----------+       shaft     +-------------+
 | generator|<================| turbine     |
 +----------+                 +-------------+
      ^ restoring (feedback) link to relay valve
```

**Main components**
1. **Speed sensor / governor:** fly-ball (mechanical) or electronic (PID) unit that senses speed.
2. **Pilot (relay) valve:** directs pressurised oil to one side of the servomotor.
3. **Servomotor:** a double-acting oil piston that moves the gate ring or needle; provides the large force needed.
4. **Oil pressure unit:** pump, accumulator and sump.
5. **Restoring (feedback) mechanism:** a linkage from the servomotor back to the relay valve so that the gates stop at the correct position (gives droop).
6. **Wicket gates / needle valve and deflector**, plus the main inlet valve (butterfly or spherical) for shutdown.

**Working**
1. Suppose the load increases. Speed falls a little.
2. The fly-balls move inward (or the electronic governor detects the error) and move the pilot valve.
3. Oil flows to the servomotor, which opens the wicket gates (or withdraws the needle). More water enters the turbine and torque rises.
4. The feedback link closes the pilot valve when the gates reach the new position, so hunting is avoided. Speed settles at a value fixed by the droop; the load reference can then bring it back to 50 Hz.
5. On load decrease, the action is reversed and gates close. Closing is done slowly to avoid water hammer. In Pelton turbines the **deflector** first turns the jet away from the buckets, and the needle then closes slowly.

Thus water delivery is matched to load while keeping frequency within limits and penstock pressure safe.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which components regulate water delivered to the turbine?
   A. Surge tank only
   B. Wicket gates (reaction turbines) or needle/spear valve (Pelton) moved by the governing system
   C. Draft tube gates
   D. The tailrace level
   Answer: B. The governor moves the gates or needle to match water power to electrical load and hold speed constant. (Key point: What controls water delivery)

2. What is the role of the servomotor?
   A. It senses speed
   B. It stores oil
   C. It provides the large force to move the gate ring or needle, driven by pilot valve oil
   D. It measures voltage
   Answer: C. A double-acting oil piston supplies the large force needed to move gates. (Key point: Role of servomotor)

3. When load increases, what does the governor do?
   A. Speed falls, the pilot valve moves, the servomotor opens the gates and more water enters
   B. Speed rises and gates close
   C. Speed falls and gates close
   D. Speed stays constant so nothing happens
   Answer: A. A fall in speed makes the governor open the gates, raising flow and torque. (Key point: Load increase sequence)

4. Why is a restoring (feedback) link provided?
   A. To increase water hammer
   B. To stop the gates at the correct position and avoid hunting, giving droop
   C. To measure the head
   D. To start the oil pump
   Answer: B. The link closes the pilot valve when the gates reach the new position, preventing overshoot and hunting. (Key point: Restoring feedback)

## Related in Power Plant Equipment

- [Water turbine transfer function and characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Awater-turbine-tf-characteristics) — Power Plant Equipment, chapter 2, asked 2×
- [Water turbine response to step gate change](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Awater-turbine-step-gate) — Power Plant Equipment, chapter 2, asked 2×
- [Hydraulic turbine characteristics and water starting time](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Ahydraulic-turbine-water-starting) — Power Plant Equipment, chapter 2
- [Functional block diagram of excitation control](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aexcitation-control-block-diagram) — Power Plant Equipment, chapter 3
- [Transient response of turbine-generator with governor](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agovernor-transient-response) — Power Plant Equipment, chapter 2, asked 3×
- [Reactor to protect circuit breaker of small station](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactor-protect-circuit-breaker) — Power Plant Equipment, chapter 4

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- [Armature-controlled DC motor transfer function and block diagram](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Atf-armature-dc-motor) — Control Systems, chapter 2
- [Combined cycle gas turbine versus hydro](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Accgt-vs-hydro) — Power Plant Design, chapter 1
- [Impulse turbine blade work and diagram efficiency](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Aimpulse-turbine-diagram-efficiency) — Turbo Machines, chapter 2