---
title: "Purpose of governing hydraulic turbines"
subject: "Hydro Power"
chapter: 7
key: "semester_6/hydro_power:turbine-governing-purpose"
source: https://www.bctengineer.com/q/semester_6/hydro_power/turbine-governing-purpose
site: BCT Engineering
---

# Purpose of governing hydraulic turbines

Hydro Power · Chapter 7: Hydro-Electric Machines

- Asked in: 2081 Chaitra, 3 marks; 2073 Bhadra, 4 marks; 2071 Bhadra, 3 marks (asked 3 times)
- Video: [Governing of hydraulic turbine](https://www.youtube.com/watch?v=Um6qchq3jMg) — Sampurna Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/turbine-governing-purpose
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-7

## Question

Explain why governing of hydraulic turbines is necessary.

## Answer

**Governing** of a hydraulic turbine is the automatic regulation of the flow of water to the turbine (by guide vanes, nozzle spear or runner blades) so that its **speed remains constant** when the load on the generator changes.

#### Why governing is necessary
1. **Constant frequency:** the generator is coupled directly to the turbine, and frequency $f = \dfrac{PN}{120}$. Electrical loads (motors, clocks, electronics) need constant frequency (50 Hz in Nepal), so the speed must stay at synchronous speed.
2. **Load changes all the time:** consumer demand varies through the day. If the load falls and water input stays the same, the extra energy accelerates the runner; if the load increases, the turbine slows down. Water input must follow the load.
3. **Prevent runaway:** on sudden full-load rejection (e.g. a line trip), an ungoverned turbine speeds up to runaway speed (1.8–2.5 times normal), causing dangerous centrifugal stresses and damage to generator and runner.
4. **Constant voltage and stable parallel operation:** speed variation affects voltage and the synchronism of machines running in parallel on the grid; governors share load among units in proportion to their droop settings.
5. **Economy of water:** water is used only in proportion to the power demanded, which saves stored water.
6. **Safety against water hammer:** governors close guide vanes or nozzles at a controlled rate, and use deflectors/relief valves, so that pressure rise in the penstock stays within limits.

```text
 load drops -> speed rises -> governor senses ->
 closes guide vanes/spear -> less Q -> speed normal
```

## Check yourself

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

1. What is the aim of governing a hydraulic turbine?
   A. Keep power output constant at all loads
   B. Keep speed constant when load changes by regulating water flow
   C. Keep head constant
   D. Keep efficiency at 100%
   Answer: B. Governing automatically adjusts water flow so speed stays constant as load varies. (Key point: What governing does)

2. Why must turbine speed be constant for a directly coupled generator?
   A. Frequency f = PN/120 depends on speed, and loads need constant frequency (50 Hz)
   B. Voltage is independent of speed
   C. Water consumption depends on speed only
   D. Penstock pressure depends on speed
   Answer: A. Since frequency is proportional to speed N, constant frequency needs synchronous speed. (Key point: Constant frequency)

3. What happens to an ungoverned turbine on sudden full-load rejection?
   A. It stops immediately
   B. Its speed falls to half
   C. It speeds up to runaway speed (about 1.8-2.5 times normal), stressing runner and generator
   D. Nothing changes
   Answer: C. Water input continues with no load, so the runner accelerates to dangerous runaway speed. (Key point: Load rejection)

4. If load falls and water input stays the same, what happens?
   A. Speed falls
   B. Speed rises, because the extra energy accelerates the runner
   C. Speed stays constant
   D. Head increases
   Answer: B. Surplus energy goes into accelerating the runner, so the governor must reduce flow. (Key point: Load change response)

## Related in Hydro Power

- [Purpose of governor and governing of Francis turbine](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Agoverning-francis-turbine) — Hydro Power, chapter 7
- [Selection criteria of hydraulic turbines](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aturbine-selection-criteria) — Hydro Power, chapter 7, asked 2×

## Related in other subjects

- [Governing of hydraulic turbines](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Aturbine-governing) — Fluid Machines, chapter 3
- [Factors governing illumination level](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aillumination-factors-lighting-schemes) — Industrial Power Distribution and Illumination, chapter 7
- [Compounding of impulse steam turbines](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Asteam-turbine-compounding) — Fluid Machines, chapter 5