--- title: "Purpose of governor and governing of Francis turbine" subject: "Hydro Power" chapter: 7 key: "semester_6/hydro_power:governing-francis-turbine" source: https://www.bctengineer.com/q/semester_6/hydro_power/governing-francis-turbine site: BCT Engineering --- # Purpose of governor and governing of Francis turbine Hydro Power · Chapter 7: Hydro-Electric Machines - Asked in: 2071 Magh, 2+4 marks - Video: [Governing of Francis Turbine](https://www.youtube.com/watch?v=CGzeYdTo6Ss) — BEST MECHANICAL ENGINEERING - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/hydro_power/governing-francis-turbine - Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-7 ## Question What is the purpose of governor? Write about the governing of Francis Turbine. ## Short answer The governor automatically maintains constant speed by adjusting guide vanes to match load. In a Francis turbine, a fly-ball sensor moves a control valve, sending pressure oil to a servomotor that rotates a regulating ring to open or close the guide vanes; feedback returns the valve to neutral to prevent hunting. A relief valve may bypass flow during rapid closure to avoid water hammer. ## Answer #### Purpose of a governor A **governor** automatically regulates the flow of water to the turbine so that the **speed stays constant** (synchronous speed, giving 50 Hz) whatever the load on the generator. It: - keeps the frequency constant when the load changes (voltage is held separately by the automatic voltage regulator); - prevents runaway on load rejection; - shares load among units in parallel; - uses water only in proportion to the power demanded. #### Governing of a Francis turbine In a Francis turbine the discharge is controlled by the **movable guide vanes (wicket gates)** arranged around the runner. All guide vanes are linked to a **regulating ring**, which is rotated by an **oil-pressure servomotor** controlled by the governor. ```text fly-ball/speed sensor | control (relay) valve <-- oil pump + accumulator | pressure oil servomotor piston | regulating ring --> guide vanes (open/close) | feedback linkage -> back to control valve ``` **Working (load decreases):** 1. Turbine speed rises above normal; fly-balls move out (or the electronic sensor detects rising frequency). 2. The control valve opens a port, sending pressure oil to one side of the servomotor piston. 3. The piston moves and rotates the regulating ring, **closing the guide vanes**. The flow area and discharge decrease, and the power input falls to match the load. 4. Speed returns to normal; feedback brings the control valve back to neutral to prevent hunting. When the load increases, the guide vanes open in the same way. **Relief (pressure regulating) valve:** a Francis turbine has no jet deflector, so rapid closure of guide vanes on sudden load rejection would cause high water hammer in the penstock. A **relief valve (synchronous bypass)** connected to the spiral casing opens at the same time as the guide vanes close, diverting water to the tailrace. It then closes slowly, so the penstock flow is reduced gradually. On long penstocks a surge tank also helps. Modern Francis units use **electro-hydraulic PID governors**, where an electronic controller senses frequency and drives the same oil servomotor. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the purpose of a governor? A. Keep water level constant B. Keep speed constant (synchronous speed) regardless of load by regulating flow C. Increase power with load D. Control the tailwater Answer: B. It holds frequency and voltage steady and prevents runaway. (Key point: Purpose of governor) 2. How is discharge controlled in a Francis turbine? A. Spear and deflector B. Movable guide vanes (wicket gates) rotated by a regulating ring driven by a servomotor C. Runner blade angle only D. Draft tube valve Answer: B. Guide vanes are linked to a regulating ring operated by an oil servomotor. (Key point: Flow control in Francis) 3. Why does a Francis turbine need a relief (pressure regulating) valve? A. It has no jet deflector, so rapid closure on load rejection would cause high water hammer; the valve opens to divert water B. To speed up the closing C. To increase the head D. To prime the runner Answer: A. The relief valve opens as vanes close and then closes slowly, reducing penstock flow gradually. (Key point: Relief valve) 4. When load decreases, the governor: A. Opens the guide vanes B. Closes the guide vanes to reduce discharge C. Rotates the runner D. Adds a jet Answer: B. Speed rises, the servomotor closes the vanes, and power input falls to match load. (Key point: Load decrease) ## Related in Hydro Power - [Purpose of governing hydraulic turbines](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aturbine-governing-purpose) — Hydro Power, chapter 7, asked 3× - [Powerhouse layout with Francis turbine](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Apowerhouse-layout-francis) — Hydro Power, chapter 5 - [Why draft tube is used in Francis turbine](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Adraft-tube-francis) — Hydro Power, chapter 7 - [Francis turbine design (55 m³/s, 25 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afrancis-design-55) — Hydro Power, chapter 7 - [Francis turbine design (45 m³/s, 150 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afrancis-design-45) — Hydro Power, chapter 7 - [Francis turbine design (140 m³/s, 120 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afrancis-design-140) — Hydro Power, chapter 7 ## Related in other subjects - [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× - [Turbine selection method and governing factors](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aturbine-selection-method-factors) — Power Plant Design, chapter 3, asked 3× - [Powerhouse layout with vertical axis Francis turbine](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apowerhouse-layout-vertical-axis-francis) — Hydropower Engineering, chapter 8, asked 3× - [Francis turbine in pumped storage plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Afrancis-turbine-pumped-storage) — Power Plant Equipment, chapter 1