The document discusses governing systems for hydro turbines. Governing systems are feedback control systems that maintain constant turbine speed despite varying load. They work by sensing speed and adjusting the water flow via mechanisms like spear regulation or guide vane positioning. Modern digital governors provide more precise control than early mechanical governors. Proper governing requires balancing sensitivity, response time, stability, reliability and other factors to prevent issues like water hammering.

3. BASIC DEFINITION OF GOVERNING OF A TURBINE
Governing of a turbine is the operation by virtue of which the rotational
speed of the turbine is kept constant irrespective of varying load.

4. DETAILED DESCRIPTION
OF THE GOVERNING
SYSTEM AND ITS
COMPONENTS

5. Governor control system for Hydro Turbines is basically a feed back control system
which senses the speed and power of the generating unit or the water level of the fore
bay of the hydroelectric installation etc.
Governing system comprises of following sections.
a) Control section: The control section may be mechanical, analogue, electronic or
digital.
b) Mechanical hydraulic Actuating section: Actuator can be hydraulic controlled,
mechanical (motor) or load actuator . Hydro actuators are mostly used.
Fig-:Digital Electro-hydraulic governor.

6. Mechanical Controller: By the middle of 20th century, mechanical
governors(1st generation) directly driven by prime movers through belt were
used for small machines. The speed of rotation was sensed by fly-ball type
pendulum(2nd generation).In second-generation mechanical governors,
permanent magnet generator and pendulum motor were utilized for sensing
the speed of the machine.
Analogue Controller: Next came the third generation Electro-Hydraulic
Governors (3rd generation) where speed sensing , speed/output setting and
stabilizing parameters were controlled electrically and the use of mechanical
components was reduced considerably.
Digital Controller: Present day trend is to use digital governing control
system in hydroelectric units(4th generation).

7. Set Points
Speed of unit
Operational
feedback
Speed
Power
Water level
Turbine
control
actuator
Governor
controller
Turbine control
gate, Blades,
Needles,
Deflector,
Relief valve etc
Hydraulic
Pressure
(Oil)
Mechanical
motors
Load
Fig: Schematic representation of a basic control system for a
turbine

8. Turbine Control Actuator System
Pressure oil system with oil servomotor is most commonly used actuator .
Actuator system compares the desired turbine actuator position command
with the actual actuator position.
Fig-:Control valve and actuator
system

9. Governor
(Flyball
Actuator)
Oil supply
system
Control
valve
SERVOMOTOR
To spear valve of
pelton turbine
To regulate lever
mechanism of
reaction turbine
Or
Fig: Schematic representation of 2G mechanical governor of a
turbine
Movement of
piston rod of
servomotor

10. Impulse turbine(Pelton wheel turbine) governing
In order to regulate the quantity of water rejected from the turbine nozzle and
from striking the buckets one of the following methods of regulation may be
adapted:
 Spear regulation
 Deflector regulation
 Combined spear and deflector regulation
Spear regulation:
 In this method the rate of flow is regulated by altering
the cross-sectional area of stream by moving the spear
to and from inside nozzle.
 This method of speed regulation is suitable when the
fluctuation of load is small and a relatively large penstock
feeds a small turbine.
 The disadvantages of this method is that when the
load falls all of sudden, the turbine nozzle has to close suddenly which may
cause water hammer in the
penstock.

11. Deflector regulation
 The deflector is generally a plate connected to the oil pressure
governor by means of levers.
 When necessity arises to deflect the jet, the plate can be brought in
between the nozzle and buckets, thereby diverting the water away
from the runner and directing into the tail race.
 The use of deflector regulation is restored to when the supply of water
is constant but the load fluctuates.
 The position of spear can be adjusted by hand. As the nozzle has
always a constant opening, it results in wastage of water and can be
employed only when there is an abundant water supply.

12. Combined spear and deflector regulation
The before-mentioned methods have some disadvantages. So, the modern
turbines make use of combined spear and deflector regulation; the spear
regulates the speed and the deflector arrangement regulates the pressure.
WORKING PRINCIPLE:
 Works on the principle of a centrifugal governor. When the speed changes
the governor senses it and closes or opens the valves accordingly.
 To set the closing rate of the needle control of the nozzles to a value which
satisfies the prescribed pressure rise .
 To bend the jet flow temporarily away from the runner by a deflector so the
speed rise does not exceed the accepted level.
This process has two different cases of workings.

14. Combined spear and deflector regulation
CASE 1 :WHEN ELECTRICAL LOAD DECREASES
Steps-:
 When the electrical load decreases the resisting torque will also be reduced
,the load on the governor decreases which increases the speed of governor
as well as the speed of the turbine.
 This causes the centrifugal governor to rotate with a larger speed. So speed
of the fly ball increases and it moves up which causes the sleeve to move
upwards.
 When the sleeve moves upward a lever about the fulcrum turns.
 The turning of the lever causes the piston rod of the control valve to move
down valve V1 closes and calve V2 opens.
 The oil pumped from the oil pump to the control valve under pressure will
flow through the valve V2 to the servomotor and will exert force on the face
A of the piston of the relay cylinder.
 Piston along with piston rod and spear will move towards the right. This
will decrease the area of flow of water at the outlet of the nozzle and it will
reduce the rate of flow to the turbine which consequently reduces the speed
of the turbine.
 Meanwhile, the bell crank lever moves downward, the jet deflector will
operate and divert the whole or part of the jet away from the buckets.
 As soon as speed becomes normal, the fly balls, sleeves, lever and piston
rod come to its normal position

15.  Combined spear and deflector regulation
CASE 2 : WHEN ELECTRICAL LOAD INCREASES
Steps-:
 When the electrical load increases the resisting torque will also be
increased ,the load on the governor increases which decreases the speed of
governor as well as the speed of the turbine
 This causes the centrifugal governor to rotate with a smaller speed.so
speed of the fly ball decreases and it moves down which causes the sleeve
to move downwards
 When the sleeve moves down a lever about the fulcrum turns
 The turning of the lever causes the piston rod of the control valve to move
up valve V2 closes and calve V1 opens
 The oil pumped from the oil pump to the control valve under pressure will
flow through the valve V1 to the servomotor and will exert force on the face
B of the piston of the relay cylinder.
 Piston along with piston rod and spear will move towards the left. This will
increase the area of flow of water at the outlet of the nozzle and it will
increase the rate of flow to the turbine which consequently increases the
speed of the turbine.
 Meanwhile, the bell crank lever moves downward, the jet deflector will
operate and divert the whole or part of the jet away from the buckets.
 As soon as speed becomes normal, the fly balls, sleeves, lever and piston
rod come to its normal position.

16. Reaction turbine (Francis turbine) governing
In a reaction turbine the discharge is controlled by varying the area of flow
between adjacent guide vanes.
Working principle:-
 works on the principle of a centrifugal governor. When the speed changes the
governor senses it and closes or opens the valves accordingly.
 To set the closing rate of the guide vane opening to a value, which satisfies
the rotational speed, rise limits.
 To divert as much of the discharge through a controlled by-pass valve that
the pressure rise in the conduit is kept below the prescribed level.
Construction:-
-The guide blades of the Francis turbine are connected to the regulating ring by
means of levers and links.
-The regulating ring is connected to two regulating rods which are connected to
the regulating lever.
-The regulating lever is connected to the regulating shaft.
-The regulating lever is controlled by the piston of servomotor.
This process has two different cases of workings.

17. Reaction turbine (Francis turbine) governing
CASE 1
 When the load on the turbine decreases, speed tends to increase, which
moves fly balls upwards and thus raises sleeves. The main lever on the other
side of the fulcrum pushes down the control valve rod and opens port V1. Oil
under pressure enters the servomotor from right and pushes the piston to
moves towards left.
 When the piston of the servomotor moves towards the left, regulating the
ring is rotated to decrease the passage between the guide vanes by changing
guide vane angles. Thus the quantity of water reaching the runner blades
decreases and speed decreases to the normal speed.
 Sudden reduction in passage between the guide blades may cause a water
hammer which can be prevented by providing a relief valve known as
“pressure regulator” near the turbine which diverts the water directly to the
tailrace. When the guide vanes have to be suddenly closed then the relief
valve opens and directs the water into the tail race thus preventing water
hammer. Thus it functions similar to that of jet deflector as in the Pelton
wheel. Thus double regulation is also well performed in Francis turbine.

18. Reaction turbine (Francis turbine) governing
CASE 2
 When the load on the turbine increases, speed tends to decrease, which
moves fly balls downwards and thus lowers sleeves. The main lever on the
other side of the fulcrum pushes the control valve rod and opens port V2. Oil
under pressure enters the servomotor from left and pushes the piston to
moves towards right
 When the piston of the servomotor moves towards the right, regulating the
ring is rotated to increase the passage between the guide vanes by changing
guide vane angles. Thus the quantity of water reaching the runner blades
increases and speed increases to normal speed.
 Water hammer is prevented by
the presence of relief valve.

19. SENSITIVITY: It is the measure of a smallest change in parameter that can be
detected and corrected.
RESPONSE TIME: Very quick response may set up Water-hammering
problems whereas a very slow response may endanger the performance and
operation of the electrical system. This may be termed as a conflicting
requirement.
STABILITY: The governing system must stable and return to the stable
equilibrium after each episode of deviation from normal conditions.
RELIABILITY: The governing system should be reliable and safety devices
should be incorporated for unforeseen events of emergencies. Safety shut-off
overrides should be available in the turbine governing system.
 STRENGTH : Governor used in hydraulic turbine should be very strong as it
has to deal with large quantity of water flowing with a large force.
WEAR RESISTANCE : Governor should be mad up of wear resistant material.
DESIREABLE QUALITIES IN A GOVERNING SYSTEM.

20. Regarding governing conditions there are three different modes of operation:
 Steady state operations when the unit is operating at constant load, head
and command input.
The total system is subject to small changes caused by fluctuations in load or
command input. In this mode none of the governor elements will reach the
limit of closing or opening speed. The stability guarantees are always referred
to this mode.
 The total system is subject to changes, which is resulting in speed limits,
closing and opening movements of parts of the governor system. This is the
situation during load ejections when the main servomotors are operating at
maximum closing speed.

21.  Governing system used in India
 Micro Hydro (up to 100 kW) :- Digital speed control system will load
actuator is used.
 Small Hydro (Up to 3 MW) :- Flow control governing system with
hydraulic actuator and digital PID speed and power control system.
Mechanical motor type actuator have also been used up to 1000 kW unit
size with microprocessor based level control PI Controller.
 Small Hydro (Above 3 MW) :- Flow control PID governor with hydraulic
actuator.

22. CONCLUSION
 Governing process in hydro-turbines are very essential. Without it,
disaster may happen in hydro powerplants.
 Governing processes helps in maintaining constant frequency of
electrical power output and in maintaining quantity of water flow of
turbine.
 While using governing systems, components need to be frequently
replaced due to wear.
 Also, there is high possibility of water hammering if precautions are not
taken.
 Wastage of water may take place in deflector regulation method as nozzle
remains open for long period of time.
 So, with certain precautions, governing systems should be embraced in
case of hydraulic turbines. Since these are the days of PID controlling
governing system, thee possibilities of accidents are too less.

23.  BIBLIOGRAPHY
BOOKS:
 A Textbook of Fluid Mechanics & Hydraulic Machines By R K Rajput
 A Textbook of Fluid Mechanics & Hydraulic Machines By R K Bansal
 Introduction to Fluid Mechanics and Fluid Machines By S.K. Som & G.
Biswas
 Hydraulic Machines By K. Subramanya
JOURNALS
 HYDROPOWER IN NORWAY Mechanical Equipment: A survey By Arne
Kjølle, Professor Emeritus, Norwegian University of Science and
Technology [Trondheim, December 2001]
 HYDRO-TURBINE GOVERNING SYSTEM; Reviewed by Dr. R. Thapar
 GUIDELINES FOR SELECTION OF TURBINE AND GOVERNING
SYSTEM FOR HYDROELECTRIC PROJECT By Alternative Hydro
Energy Center, IIT ROORKEE
LINKS:
https://learnmech.com/governing-of-hydraulic-turbines-pelton-francis-
turbine/
https://www.engineeringenotes.com/electrical-engineering/turbines/water-
turbines-characteristics-governing-and-selection-electricity/29450