hydroelectric power plant_overview.ppt

OVERVIEW
HYDROELECTRIC
POWER PLANT
1

Hydroelectricity is electricity generated by hydropower, i.e., the
production of power through use of the gravitational force of falling
or flowing water or by converting the potential energy of stored
water in a dam in to mechanical/ rotational/ electrical energy by
driving turbines and Generator. It is the most widely used form of
renewable energy. Once a hydroelectric complex is constructed, the
project produces no direct waste, and has a considerably lower
output level of the carbon dioxide (CO2).
Hydro power Plants are of the following types :
1. Surface Power House
2. Underground Power House
3. Pump Storage Power House
4. Small Hydro Power plants
INTRODUCTION
2

Common Terminology in a Hydro Power Plant
1. Reservoir
2. Main Dam
3. Spillway
4. Diversion Tunnel
5. Coffer dams
6. De-silting Chambers
7. Power Intake
8. Power Tunnels (Penstock)
9. Power Plant
10. Turbine
11. Main Inlet Valve
12. Generator
13. Tail Race Channel
14. Switch yard
INTRODUCTION
3

Generator Barrel & Turbine Pit
12

Turbine Runner (Francis Turbine)
15

Equipments Used in Hydro Power Plants
1. Main Inlet Valve
Type : - Rotary valve(Spherical Type)
Butter fly valve (Lattice Type)
Main Components
Valve body, Valve door, Seals, By-pass valve, servomotor,
Drain Valve, Air valve, Inlet/ outlet pipes.
Auxiliaries
Oil Pressure Unit, Oil Leakage unit, Control panel
2. Pressure Relief Valve
3.Turbine
Type : - Pelton, Kaplan, Francis, Bulb Reversible Turbines.
Main Components:
Runner, Shaft, Speed ring and Spiral, Draft Tube, pivot Ring, Guide
vanes, Top Cover, Servomotor, Regulating Ring, Shaft gland, bearing,
Air valve, Distributor, Pit linear, Spear Nozzle, Brake jet, Diffuser Nozzle,
Deflector and oil Header
Auxiliaries :
Governing system, Oil Pressure Unit, Oil leakage unit, GGLS, Top Cover
Drainage system
17

4. Common Auxiliaries
Synchronous condenser
H .P/LP air system
Cooling water system
Dewatering / Drainage system
5. Hydro Generator
Type : -
Conventional OR suspended rotor type.
Semi – umbrella
Umbrella
Main Equipments :
Shaft, Poles, field Coils, Rim, Spider, Stator Core, Stator Winding,
bottom / Top Brackets, Guide bearings,
Thrust bearing, Air coolers, fan & Ventilation.
Auxiliaries :
H. S lubrication, brake/Jack system, Oil purifier, brake/carbon
Dust collector, fire fighting system, Automatic voltage regulator
18

6. Control and Protection Panels
1. Unit control Boards
a) Metering, control & Indication panel.
b) Annunciation Panel, Relay Panel
c) Starter control panel
2. Electro Hydraulic Governor.
3. Excitation system
4. Gen. Tr. & Feeder Protection panel.
5. Synchronizing trolley
6. Control Desk.
7. L.T supply panel.
8. Battery & Charger Panel
7. Bus duct, LAVT & NG cubicle
8. Main Transformer
9. Excitation transformers
10.Unit Auxiliary Transformer
11.Station Transformer
12.Draft tube gates
19

Type : - Pelton, Kaplan, Francis, Bulb Reversible Turbines.
Based on Speed : -
Slow Speed machines : Speed less than 166.7 rpm
Medium Speed machines : Speed between 166.7 & 300 rpm
High Speed machines : Speed more than 300 rpm
Main Components:
Runner, Shaft, Stay ring and Spiral, Draft Tube,
pivot Ring, Guide vanes, Top Cover, Servomotor,
Regulating Ring, Shaft gland, bearing,
Air valve, Distributor, Pit linear, Spear Nozzle, Brake
jet, Deflector and oil Header
Auxiliaries :
Governing system, Oil Pressure Unit, Oil leakage unit,
CGLS, Top Cover, Drainage system
Hydro Turbine Overview
21

22
1. Rating and type of turbine
2. Head race & tail race levels
3. Max./Rated/min. Gross and net heads
4. Discharge in various seasons
5. Efficiency weightage factors at different loads
6. Speed rise and pressure rise
7. Water conductor system layout
8. Power house and tail race configuration
9. Setting of m/c w.r.t Minimum Tail Water Level.
10. Analysis of river water
Project Data Required For Optimum
Selection of Turbine

Francis Turbine
Kaplan Turbine
23

Pelton Wheel Turbine Bulb Turbine
24

Turbine shaft
Regulating Ring
Turbine Guide
Bearing
Levers
Guide Vanes
Stay Ring
Runner
Spiral Casing
Draft Tube
Hydro Turbine Main Components
25

Butterfly type MIV
Spherical type MIV
Main Inlet Valve Overview
26

TURBINE AUXILIARIES
(HYDRO POWER PLANT)
AUXILIARIES COMMONLY USED IN HYDRO POWER PLANTS FOR
TURBINE : -
1. Oil Pressure Unit
2. Oil Leakage Unit
3. H.P. Air Compressed system (Common)
4. Centralized grease lubrication system
5. Drainage system (Common)
6. Dewatering system of draft tube (Common)
7. Cooling Water System
8. Low Pressure compressed air System
9. Turbine Top Cover drainage system
10.Synchronous condenser operation system
11.Governing system
12.Turbine discharge measurement system.
27

TURBINE AUXILIARIES
(HYDRO POWER PLANT)- OPU
1. OIL PRESSURE SYSTEM (OPU)
The normal functioning of governor is depending upon a reliable source of oil
under pressure. This pressure is maintained constant within the desired limits. The
system consists of a pressure pumping set and pressure receiver.
1.1 PRESSURE PUMPING SET
The set consists of the following equipments:-
1. One sump tank
2. Two Idler valves
3. Two non return valve
4. Two pilot operated safety valve
5. Two screw pumps with motors
6. One Temperature Sensing device
7. Three oil level switch
8. One air breather
9. Oil Filter
10. Solenoid operated No-load start valve
Each unit is provided with its own pumping set and has to cater for the oil requirements of
governor and servomotors. The system has to operate as main and standby. In the ‘Main’ mode
one of the pumps operates continuously and the other pump as ‘Stand by’ operates intermittently
when the oil pressure is lower than the preset value. Pumping of oil into receiver is carried out by
main pump-motor under the control of idler valve. Switch over from main to stand by is
performed through control selector switch. 28

1.1.1 SUMP TANK
This tank is an electric welded steel tank and has two chambers separated by oil
strainer (360). One of the Chambers houses two screw type pumps with motors and
the other one is mounted with various devices, valves, piping etc. This tank stores
complete oil of governing system. The stored oil is supplied continuously to the
system and has a spare capacity of about 10% more than the normal oil requirement.
1.1.2 IDLER VLAVE
The idler valve is provided between oil pump and pressure receiver. This is
used to maintain pressure in the pressure receiver within maximum normal working
pressure to minimum normal working pressure.
LOADING: Oil pressure in the pressure receiver is supplied when the pressure drops
to minimum normal working pressure for building up the pressure to maximum normal working
range.
UNLOADING: when pressure in the pressure receiver reaches maximum normal
working pressure, the oil pressure diverted back to sump tank.
1.1.3 NON –RETURN VALVE
The non-return valve remains in closed condition when pump is in idling/ unloading
mode. When pressure falls in the pressure receive, the pump under closing action of
idler valve supplies oil to the receiver via this NRV, as the pressure on the pump side
is more than receiver. When the pressure reaches the maximum normal
working pressure idler valve opens and connects the oil from pump to drain. As a
result NRV closes due to the pressure on pump side being atmospheric.
TURBINE AUXILIARIES
29

1.1.4 SAFETY RELIEF VALVE
This is provided on each pump delivery. In case oil pressure increases
beyond normal working pressure (say 5% more), this device opens to
release oil of the pump back to sump tank. This avoids the possibility of
dangerous pressure in the Pr. Receiver.
1.1.5SCREW PUMP / MOTOR
These are mounted vertically on the sump tank. The suction line of the pump is
submerged in the oil. These are provided with one each suction catch on the
suction line making it all the time self priming to avoid any dry running. The
minimum oil level is maintained in the sump tank, after which the oil level alarm will
sound to avoid the dry running of the pumps. A 3 phase 415V ± 10%, 50 Hz AC
squirrel cage induction type totally enclosed fan cooled motor is mounted on the
stool of pump to drive the screw pump. Motor is suitable for direct on line starting.
1.1.6 TEMPERATURE SENSING DEVICE
A DTT type temperature sensing device is provided on the sump tank. In case of
undue rise in temperature of oil. This sounds an alarm for stopping the
pump and finding the fault in the system.
TURBINE AUXILIARIES
30

1.1.8 AIR BREATHER
Air breather has been provided on the sump tank so that oil space can be filled with
air against any vacuum formation due to oil being taken away from the sump and
also allows escape of air during the return of the oil to the sump.
1.1.9 OIL LEVEL SWITCH
The principle of operation of these switches is magnetic repulsion. A stainless steel
float having a magnetic operating arm, operates a magnetic operating lever which
operates the heavy duty potential free contacts provided in the outer casing. The float
and float arm are hinged in a fork welded to the flanges suitable for mounting on the
tanks horizontally.
1.1.10 OIL FILTER
This small filter is provided on the sump tank for supply of filtered oil to the idler valve
and no load start valve. It has a drain valve to flush the muck and foreign practices for
trouble free operation of idler valve and no load start valve.
1.1.11 SOLENOID OPERATED NO-LOAD START VALVE
A solenoid operated poppet valve is mounted on the idler valve to achieve the no-load
starting of the pump – motor set. This is connected in the control circuit of the pump –
motor starter with timer. When starting command goes to motor, first it operated the
S.V by energization of solenoid, in turn opens the idler valve and pump motor set
starts on no-load. After about 5 seconds when motor picks up full speed same solenoid
de-energized through timer in turn closes the idler valve and pump – motor gets
loaded.
TURBINE AUXILIARIES
31

TURBINE AUXILIARIES
1.2 PRESSURE RECEIVER
Each unit is provided with a pressure enough to meet all the requirement of the system
and it works as reservoir of energy for the control of servomotors. The oil in this
receiver is always kept under pressure with the help of compressed air within very
close range of operation. Normally the air-oil ratio is maintained as 2:1 at normal
working pressure. The following devices are mounted on the pressure receiver:
1. Oil level gauge
2. Pressure gauge
3. Pressure switches
4. Oil level switches
5. Non return valve
6. Solenoid operated valve
7. Air safety valve
8. Air trap valve.
1.2.1 OIL LEVEL GAUGE
Bi- colour magnetic roller type oil level gauge is provided. The type of level gauge is
very robust and reliable and is used for local indication of oil levels without liquid
contact & the Pt.receiver under pressure. The oil of Pr. Receiver is indicated as read
column of rollers with the floating position of S.S. float in main chamber, even in case
of power failure. In addition, level sensing element such as No. of reed switches are
fitted out side the main chamber to get the various pre-determined electrical contacts
for achieving auto control and alarm functions.
32

1.2.2 PRESSURE GAUGE
Borden tube type of pressure gauge for local indication of pressure in the Pr. Receiver
has been used.
1.2.3 PRESSURE SWITCHES
Six numbers pressure switches used in the complete oil pressure system. Their
functions are starting interlock, high pressure alarm, low pressure shut down, low
pressure alarm, automatic air replenishment, starting and stopping of stand by pump.
All these pressure switches are of rugged diaphragm sealed piston type and has got a
built in different.
1.2.4 OIL LEVEL SWITCHES
The principles of operation of these switches are magnetic repulsion and are mounted
on the S.S. body of the oil gauge. S.S float is floating in the main chamber of oil level
gauge is operating the reeds having 1 No ± 1 NC contacts at achieve required
functions.
1.2.5 NON RETURN VALVE
It is un directional flow valve having cast steel body, this does not allow any flow
opposite direction. This valve is provided on HP air supply line for pressure receiver.
TURBINE AUXILIARIES
33

1.2.6 SOLENOID OPERATED VALVE
This solenoid operated valve is provided for automatic air replenishment to the
pressure receiver from air receiver.
1.2.7 AIR SAFETY VALVE
Air safety valve of direct operated type has been used on the pressure receiver. This
is adjustable to set blow OFF at predetermined valve (approx.12- 15% above
normal working pressure). This avoids the possibility of dangerous pressure building up in
the pressure receiver due to failure of pilot operated oil safety valve.
1.2.8 AIR TRAP VALVE
It is provided at the bottom of oil/air receiver to prevent any air (Which may create
operational problem in the system) entry into the pipe line in case of excessive
demand /drawing of oil from the receiver. Whenever the oil level falls below the
predetermined minimum level the float comes down and the valves sits on its seat
maintaining minimum oil level and not allowing air to enter into the pipe line. The
counter weight is used for balancing the float – weight for buoyancy.
TURBINE AUXILIARIES
34

2. OIL LEAKAGE UNIT
The oil leakage unit is intended for the collection of oil leakage from the servomotors,
for draining of oil from the servomotors, controlling valves and oil pipe lines, and
periodic pumping from the tank of the oil leakage unit to the sump tank of oil pressure
unit. The oil leakage unit consisting a tank and mounted on it is a pump and motor. In
the tank a level relay is provided for automatic controlling of the pump and alarm in
case of high oil level.
3. H.P. COMPRESSOR PLANT
H.P. Air compressor system is common for all the units installed in the P.H. and is
used to supply high pressure compressed air to oil pressure accumulators of turbine
and MIV and their automatic refilling to maintain the required pressure. Two
compressors each of suitable capacity installed. The discharge of each compressor is
fed to an air receiver through suitable oil and water separator and non – return valves.
Each compressor can function as main and stand by and can be started and stopped
automatically through pressure switch connected to the air receiver. The receiver is
also provided with safety valve, pressure gauge and drain cock. Provision is also
made for supplying low pressure compressed air for generator braking. For this
purpose high pressure reducer is used. Low pressure receiver is provided with safety
valve, pressure gauge and drain cock.
TURBINE AUXILIARIES
(HYDRO POWER PLANT)
35

4. CENTRALISED GREASE LUBRICATION SYSTEM
Automatic grease lubrication unit serves both the turbine and main inlet valve. Once it
is switched ON, it feeds grease to all points. The back pressure switched OFF the
grease unit automatically. The CGLS serves for greasing of upper, middle and lower
bearings of guide apparatus and bearings of main inlet valve. Just after the lubrication
unit filters are installed on the lines which filter the grease before feeding to the main
line. Feeders have been used to distribute the required amount of grease of different
lubricating points. This unit consists the following equipments:
1. Greasing Tank
2. High Pr. Pump-Motor Set
3. Solenoid valves for different lines
4. Grease level limit switches
5. Dose feeders
6. End pressure switches
5. DRAINAGE SYSTEM
A sump collects all the station drainage through a channel running along the length of
power house. The bottom of the sump is at the sump is at the lowest level. Two
vertical turbines pump each of suitable capacity installed on the sump. The discharge
of both the pumps is combined through suitable valves and non-return valves and
goes to tail race. Level controller, control panels, pressure gauges are installed in the
system to start and stop the pumps depending upon the level in the sumps.
TURBINE AUXILIARIES
(HYDRO POWER PLANT)
36

TURBINE AUXILIARIES
(HYDRO POWER PLANT)
6. DEWATERING SYSTEM OF DRAFT TUBE
The water from draft tube is collected in a sump. Two or three vertical turbine
pumps are installed to dewater the sump. The discharge of both the pumps is
combined through suitable isolating valve and non-return valves and goes to tail race.
One isolating valve is provided for normal repairs before tail race. One gauge is also
provided in common discharge line. Level controllers are provided to control the
operation of motor-pump set. Each pump can function as main and stand by and can
be started and stopped automatically depending upon the level on the sump. The
system consists of a electrical control panel for each motor, level controller, pressure
gauges, non-return valve and motor pump set.
7. COOLING WATER SYSTEM
This system is used to supply cooling water to Generator Air Coolers, Guide bearings,
thrust bearing, Turbine guide bearing and transformer oil coolers. Turbine/Centrifugal
pumps – motor sets are provided for this purpose. The suction of each pump is taken
directly from the tail race through suitable strainers, foot valve and slide valve. The
discharge of pump is fed to various cooling points through suitable valves and non
return valves and simplex strainers. Duplex strainers are used to maintain continuity of
water supply in case one strainer gets choked. The discharges of all the sets are
collected in a common header to run any unit in emergency. The water through all the
coolers is discharged into the trail race above maximum tail water level. This has been
done to prevent any dust particles or foreign materials going inside the coolers.
Pressure gauge, motorized valves, Pr. Transmitters, flow relays, pump motor set,
control panels and isolating valves are provided in this system. 37

8. TOP COVER DRAINAGE SYSTEM
The water leakage from stationary and rotating parts is collected in the turbine top
cover. Leakage from G.V. link cup seals is also collected in the turbine top cover. To
prevent the top cover from flooding drainage system is used. Drainage system
consists the three systems.
1. Gravity Drain
2. Pump Motor Set
3. Ejector System
Capacitance type level relays is installed in the top cover for opening and closing of
ejector and also for starting and stopping of pump-motor set at pre determined level.
Capacitor type level relays gives the alarm /signal in the control room in case level
increases beyond set value.
9. LOW PRESSURE COMPRESSED AIR SYSTEM
This system is meant for running the unit in synchronous condenser made and is
capable of depressing the water level in the draft tube in succession and maintaining
that level during SCO. This system comprises the A.C. driven air cooled reciprocating
compressors each having free air discharge at 8 kg/cm² and two air receivers each of
suitable capacity. Hydro valve along with gate and non return valve is used to control
supply of air. Control of valve is through an electromagnet valve which is oil operated.
For constant monitoring of water level in the draft tube level controllers are provided
which control the operation of hydro valve.
TURBINE AUXILIARIES
(HYDRO POWER PLANT)
38

10. GOVERNING SYSTEM
It is the brain of the hydraulic Turbine frequency and Power regulator
PURPOSE
1. To Keep The Rotational Speed Of Turbine-Generator Unit Stable & Constant at any Grid
Load and prevailing conditions In the Water Conduit.
2. To close down the Turbine operation according to the acceptable limits of the rotational
speed rise of the unit and the pressure rise in the water conduit.
Governing System Consist of the following equipments:
1. High Pressure Compressed Air System
2. Pressure Pumping Unit
3. Oil Leakage Unit
4. Feedback Connection
5. Governor Hydro Mechanical And Electric/Electronic Cubicle
TURBINE AUXILIARIES
(HYDRO POWER PLANT)
39

Hydro Generator Overview
INTRODUCTION
Hydro Generator is a synchronous, slow speed electrical machine coupled with Hydro
Turbine to convert the Mechanical energy into electrical energy. Hydro generator
design is tailor made, Rating & speed of each hydro set depends upon the specific
hydraulic conditions i.e. head & discharge available at a particular place. BHEL has
built hydro generators rating up to 250 MW. Generator is built either with a horizontal
or vertical shaft axis.
Vertical hydro generators are divided into three types depending upon the location of Thrust
bearing & number of guide bearings:
Umbrella: - One Thrust bearing & one Guide bearing below the rotor. This type of layout is
adopted for slow & medium speed machines with large stator bore &small stator core
length. In Umbrella design, load / forces of Thrust bearing & lower guide bearing is
transmitted on foundation through lower bracket.
Semi –Umbrella: - In addition to above, one guide bearing above the rotor is also provided. This
type of generator is used for medium speed machines, when critical speed with one
guide bearing pads is more than the allowable limits.
Suspension: - One Thrust bearing, One Guide bearing above & one Guide bearing below the
rotor. Thrust & Guide bearings above the rotor may be combined or separate
depending upon critical speed of the unit. This type of generator is used for high –
speed machines.
41

Umbrella Type
Vertical Hydro Generator
Thrust
Bearing
Guide
Bearing
Rotor
Stator
42

Semi- Umbrella Type
Thrust
Bearing
Guide
Bearing
Guide
Bearing
43

Suspension Type
Guide
Bearing
Thrust
Bearing
44

Main Components of Hydro-Generator are the following:
1. Stator
a) Stator frame
b) Stator Core
c) Stator Windings
2. Rotor
a) Rotor Spider
b) Rotor Rim
c) Rotor Poles
d) Shaft
3. Thrust Bearing
4. Guide Bearing
5. Brackets (Lower & Upper)
6. Air Coolers
7. Oil Coolers
8. Instruments & Devices
46

Main Components of a Vertical Semi- Umbrella
Type Hydro Generator
47

Hydro Generator Stator
Generator Stator
It is the stationary part in the Hydro Generator housing the windings in
which EMF is induced during operation. Stator of Hydro-Generator is
designed to with stands the following forces, which are transmitted on
Generator Foundation through stator frame:
1. Weight of upper bracket assembly.
2. Forces on upper guide bearing assembly.
3. Various forces acting on stator frame during stator core pressing.
4. Vertical / Horizontal handling of assembled sectors.
5. Unbalanced magnetic pull exerted on the stator core building
short circuit of pole or stator winding or because of non uniform
air gap between Stator & Rotor.
6. Force acting on the stator core during transmits of electro
magnetic torque.
7. In addition to above stator frame is also used for Housing the
stator core, winding &Mounting the Air coolers.
48

Stator frame : The stator frame is of fabricated structure adequately designed to with stand
the forces acting on stator during operation. It consists of a number of horizontal shelves
joined together by means of number of vertical ribs & outer wall. Joints between the sectors
are made by means of thick joint plates & large number of studs. The sectors are joined
together at site with the help of these joint plates, studs & dowel pins. To accommodate large
diameter of Rotor, the inside diameter of stator frame is very large. Transportation problems
limit the size of a single package. Therefore stator is divided into sectors in such way that the
maximum package size does not exceed the transportation limits.
Stator Core :Stator core is made from hot rolled or cold rolled segment 0.5mm thick varnished
punching of low specific loss. These punching are held between pressing plates & pressing
pressure is applied by means of axial studs. The core is attached with the stator frame by
means of stator wedge & corner plates. Ventilating ducts are provided in between the core
packets by providing special profile steel section for circulation of cooling air.
Stator Windings : Each winding coil / bar is built from a number of insulation strands to
minimize eddy current losses and strands are transposed to reduced circulating current
losses. End winding is braced firmly together and lashed securely to with stand the forces
due to short circuit or other abnormal operation. The coils / bars are checked for dimensional
accuracy to ensure correct assembly of winding in the slots of stator core. For insulation
purpose Vacuum pressure impregnation (VPI), Epoxy resin type of insulation system
suitable for operation up to temperature class ‘F’ having temperature index 155 °C, allowable
temp. 130 °C is being used presently .
49

Stator Frame, Core & Winding Stator Winding
Stator Frame Stator Core
Stator
Windings
50

Stator Frame, Core & Windings Stator Frame & Stator Core
51

Complete Stator Frame Stator Core Intermediate Pressing
52

Hydro Generator Rotor
Generator Rotor
Rotor is the rotating part of the Hydro Generator housing the field windings poles and it
also provide the necessary moment of inertia for the rotational motion. Rotor of hydro
generator is designed to:
1. Accommodate large number of poles & its current carrying leads.
2. Provides required moment of inertia (GD ²).
3. With stand safely the stresses developed at run away speed. (SF = 1.5
recommended)
Shaft, Spider, Rim assembly, Current carrying leads, Poles, Slip ring & Fans are the
main assemblies of the rotor. Brief description of these assemblies is given below:
Rotor Shaft : Shaft is forged from high quality medium carbon steel. It is accurately machined
& has a large bore through out its length for inspection purposes. Generally for
umbrella machines, two piece shaft constructions is adopted, in which main shaft has a
flange coupling at the lower end & integrally forged Thrust collar at the upper end.
Rotor spider is coupled to the main shaft at Thrust bearing collar end. Other extension
shaft is bolted to the top flange of rotor spider. Slip ring, fans, over speed device etc
are mounted on this shaft. For suspended machines, single shaft is used. Thrust
bearing collar is integrally forged with shaft or separately forged collar is shrunk fitted
on shaft depending upon the bearing arrangement.
54

Rotor Spider : The rotor spider is of fabricated construction with arms radiating from central
hub. Central hub consists of two discs & vertical ribs welded to a thick cylinder or
bush. Heavy steel bars welded at the outer end of spider arms to support the rotor rim.
Rotor spider is either shrunk fitted to the shaft or bolted on the top of Thrust collar. The
driving torque is transmitted from the shaft to the spider by frictional force between
shaft & rotor bush or by radial or vertical dowels / keys in case of bolted spider. Brake
track segments are bolted below the lower disc of rotor spider to perform the braking &
jacking operations with hydraulic brakes.
Rotor Rim : Laminated rotor rim construction is used for medium & low speed machines. For
high speed machines, where the rotor diameter is less than 3 meter, Solid disc type
rotor rim design is used. Laminated rotor rim consists of high tensile thin sheet steel
laminations. The outer periphery of the segments has ‘T’ shaped slots for fixing the
poles. The joints in each subsequently layer are displaced to ensure adequate strength
of rim. Ventilating ducts are provided in rotor rim to flow air.
Rotor Poles : Pole assembly is designed to hold pole winding & withstand safely the stresses
developed at runway speed. The poles are fastened to the rim with T-tails. The pole
profile is chosen to ensure a suitable grading of the air gap to have sinusoidal flux. All
poles are connected in series with slip ring assembly. Direct current from static
excitation system is supplied to brush rocker / slip ring assembly. This is circulated in
the poles through current carrying leads to produce direct flux in the air gap. Pole
assembly consists of pole core, Pole winding & insulation between pole core & pole
winding etc.
55

Poles
Rim
Lower
Shaft
Spider
56

Rotor Spider Assembly Rotor Rim Assembly
57

Rotor Pole
Completed Rotor With Poles
Rotor Poles Rotor Pole Series
Connections 58

Lower Bracket
Lower & Upper Brackets : The bracket, which accommodates thrust bearing, is called load-
carrying bracket. In suspended type generator, upper bracket & in umbrella type
generator, lower bracket is a load carrying bracket. Bracket is made sufficiently rigid so
as to have deflection within permissible limits. The upper bracket rests on the top of
the stator frame. Upper bracket also holds guide bearing, Brush rocker, Oil cooler,
upper air baffle, and cover plate assemblies. Top of the upper bracket is used as
generator floor. In semi – umbrella & suspended type construction radial jacks are
provided at the end of the arms to transmit radial load to the concrete barrel. The lower
bracket rests directly on the generator foundation. Lower bracket holds guide bearing,
Braking & jacking system, lower air baffle, Oil cooler assemblies. In both types of
brackets, the central part is used as an oil tank for guide bearing & thrust bearing and
arms are extended to the foundations.
Upper Bracket 59

Lower Bracket Lower Bracket on
Foundation
60

Upper Bracket on Foundation
61

Thrust Bearing : Thrust bearing plays an important role in Hydro Generator. It is designed to
carry the complete vertical load of rotating parts of generator, Turbine & hydraulic thrust. This
load is transferred on generator foundations through oil film between surfaces. Top surface of
pad is babbited or Teflon coated depending on the design. In babitted pad system Hydro static
lubrication system is used to form forced oil film between thrust bearing pads & runner during
starting & stopping of machine.
Thrust bearing Springs Thrust bearing Spring & Pad Assembly
62

Thrust Bearing Assembly
Thrust Pads Springs
Thrust bearing Stand
63

Thrust
collar
Guide pad
Thrust pad
Lower
Bracket
64

Auxiliaries commonly used in Hydro Power Plants for Generator:
1. HS Lubrication system
2. Anti – Condensation (pit) Heaters
3. Brake jack system
4. Generator fire protection system
5. Brake / Carbon dust collector
6. Oil purifier
7. Excitation System
8. Automatic voltage regulator
9. Shaft voltage/ current monitors
10.On line vibration monitor
11.On line partial discharge monitors
12.Busduct, LAVT & NG Cubicle
Generator Auxiliaries
(Hydro Power Plant )
65

1. HYDROSTATIC LUBRICATION SYSTEM
A high pressure oil system i.e. H.S. lub is provided for the thrust bearing in order to
create a positive oil film over the pads at low speed during and stopping of the
generator. The component consists of a positive displacement pump with its motor,
control panel, filters, valves etc. mounted on a steel base. A pressure switch with
electrical contacts for starting interlock of the generator is also provided. The
system is arranged to come into operation automatically during starting & stopping.
Periodically check all the NRV’s being fitted JB pads to ensure for absence of oil
flow through them in reverse direction.
2. ANTI – CONDENSATION (PIT) HEATERS
Low temperature heaters to prevent condensation on the windings during periods of
shut down shall be mounted below the lower air baffles. They are of tubular type
construction consisting of a coiled resistance wire embedded in an electrically
insulated and heat conducting compound and protected with a metal sheath. They
are evenly distributed to form a balanced three phase load. These heaters are
switched on automatically when machine is under shut down and temperature of
generator barrel goes down below the set valve. This unit consists the following
equipments:
•Heaters
•Thermostat
•Control Panel
66

3. BRAKING AND JACKING SYSTEM
The generator has brakes mounted on lower on lower bracket. Each brake consists
of fiber based rigid molded friction material replaceable shoes, mounted on a
vertical piston moving in a cylinder and operates against a polished circular steel
brake track located on underside of the rotor rim.
To apply the brakes, air at 3-5 km/cm² is fed into the cylinders from the station
compressed air system. Provision has been made automatic brake application when
the speed of the machine reduces to a preset value, and it remains applied till the
machine stops completely. Brakes can also be applied manually. Limit switches have
been provided for each brake pad to prevent the machine from starting if any
brake paid is in raised position and also provide ‘ON’ and ‘OFF’ indication on the unit
control board.
The brakes also serve as a convenient means for jacking the rotor for maintenance
purposes. For jacking a unit has been provided. The arrangement of piping is such that
after the jacking system has been used, air under pressure can be applied to the
system to clear the pipes of oil. The braking system consists the following devices.
1. Solenoid operated air valves
2. Electrical contact pressure gauge / Pr. Switch
3. L.P. air system
4. High pressure oil pump
5. Air filter
67

Portable motor operated jacking pump is sued for jacking the rotor during
maintenance. The jacking pump consists of pump – motor with necessary filters
relief valve. Shut off valve, pressure gauges etc. These are mounted on the oil
tank which has enough capacity to pump out oil for fully jacking the rotor. Flexible
hose with swivel nuts for connection between jacking pump and brake jack pipe
line system also been provided.
4. FIRE PROTECTION SYSTEM
An automatic carbon – dioxide fire protection system, consisting of ring headers,
discharge nozzles, thermostatic temperature detectors (heat detectors), smoke
detectors, is provided in each generators.
The fire extinguishing equipment, which is of the carbon dioxide type, is initiated
by heat/smoke detectors or on operation of generator differential protection relay
and being effected by filling the generator air circuit with carbon dioxide at a
concentration sufficient to dilute the air content to a point where combustion
cannot continue.
Two carbon dioxide banks, one acting as main bank and other as standby bank,
consisting of an adequate number of cylinders have been provided in the power
house and one common for all the generators.
68

Fire Protection System Cont…..
Each bank of carbon dioxide cylinders is of sufficient capacity to provide the paid total
flooding of generator air circuit at high connection (initial; discharge)and slow release
of carbon dioxide to maintain the concentration during total period of (delayed
discharge) extension. The system consists high pressure pipe with pressure relieve
valves, directional valves, electrical release trips.
The electrical features of the CO₂ system such as relays, contactors, various
indications, showing status of the system and horns/gang bell is provided in a
separate main control panel. There is separate electrical solenoid cum trip assembly
for directional valve of each generator. The initiations of this solenoid open the
directional valve and further initiate the electrical solenoid – cum – trip assembly
provided for release of carbon dioxide gas.
The system can also be operated manually from remote.
Suitable fan with small ducting is provided and installed just outside the barrel for
evacuation of CO₂ out of barrel. Automatic weighing provision for each individual
cylinder of CO₂ with electrical contact is provided to indicate against any leakage of
CO₂
69

Excitation system :
In a synchronous generator the field winding has to be energized using DC voltage so
as to create magnetic poles in rotor. Excitation systems have a powerful impact on
generator dynamic performance and availability, it ensures quality of generator
voltage and reactive power, i.e. quality of delivered energy to consumers. Following
types are common:
a) Brushless excitation systems,
b) With rotating exciter machines and Automatic Voltage Regulator (AVR),
c) Static excitation systems (SES), feeding rotor directly from thyristor bridges
via brushes.
Main functions of excitation system are as follows :
1. It produces DC voltage (and power) to force current to flow in the field
windings of the generator.
2. to provide variable DC current with short time overload capability, controlling
terminal voltage with suitable accuracy.
3. It provides a means for regulating the terminal voltage of the generator to
match a desired set point and to provide damping for power system
oscillations. Varying the field excitation is an effect on power factor, armature
current, power angle, voltage and reactive power flow.
The supply required for excitation can be taken from following source :
1. Through the generator line itself using a step down excitation transformer.
2. Through some other AC source like grid.
3. Through DC battery bank (usually used for field flashing).
70

Generator Auxiliaries (Hydro Power Plant )
Static Excitation System
71

Automatic Voltage Controller :
Constant voltage at the generator terminals is essential for satisfactory main power
supply. The terminal voltage can be affected by various disturbing factors (speed,
load, power factor, and temperature rise), so that special regulating equipment is
required to keep the voltage constant, even when affected by these disturbing
factors. For this purpose Automatic voltage regulators are used which consist of
electronic (thyristor) based control circuitry. Voltage regulators for synchronous
generators must satisfy the following conditions:
1. Regulation to counter disturbances must take place as rapidly as possible
(high-speed regulators).
2. There should, as far as possible, be no derivation from the set voltage in
stationary installations.
3. In the event of the generator terminals being short circuited the excitation
must be controlled, so that the generator relay can act satisfactorily to
prevent any continuous feed into the short circuit.
4. The revolving field must be protected against overload by a limit device in
the regulator.
5. The rated voltage must be easily adjustable on the regulator.
6. Proper sharing of reactive load must be assured where several generators
are connected in parallel.
72

Online End Winding Vibration Monitor :
The purpose of such a system is to monitor the vibration in the overhung portion of
stator windings as :
1. Long unsupported portion of stator winding.
2. Overhangs are fixed with the help of bracings and support brackets / rings.
3. High vibrations can cause insulation failure due to rubbing of conductors
and fatigue
Online Partial Discharge Monitor :
Faults at incipient stage are often revealed by electric discharge before causing
serious short circuits. Discharge produces current pulses of Rf spectrum and can
be detected at generator neutral and phases using rf current probes, hv coupling
capacitors and a spectrum analyzer. Rf emission data gives the health of stator
insulation.
measuring methods :
1. Faults in generators get announced by pd bridging part of hv insulation
and are detectable due to Rf signal components.
2. Distribution of pd w.r.to phase angle of gen voltage is characteristic for
cause of discharge and allows for conclusion to further operation of
generator.
3. Rf couplers are installed at bus duct for 3 phases of generator to detect
discharges.
73

Busduct :
It is used to connect the Generator with generator transformers. The conductor is made of
aluminum alloy as it provides a good combination of electrical and mechanical properties. To
minimize skin effect and to achieve improved & better cooling hollow circular sections are
used. Conductors are supported on post insulators. Various sections of busbars are joined
by welding or bolting. Flexible connections are provided in the bus run to allow for expansion
under various bus bar temperatures. The connections consists of:
1. Main run between the generator line terminals and up to L.V. terminal of generator
transformer.
2. Neutral bus run between the generator terminals and the star points.
3. Tap-off bus from main bus run to surge protection and VT cubicle & Unit
transformers.
4. Connections between generator neutral star and N.G. cubicle.
NG Cubicle :
This cubicle is used for the grounding of the generator
neutral terminals and comprises of the following equipments :
1. N. G Transformer
2. Secondary Loading resistor
3. Space Heaters with thermostat
4. Fluorescent tube
5. Electrical connections and earthing arrangement
6. Marshalling box
74

LAVT cubicle :
This cubicle has voltage(potential) transformers and is used for taking out
connections for metering and protection systems and comprises of the following
equipments:
1. Voltage transformers for frequency transducers, metering, AVR,
Performance testing, Synchronizing & Relays.
2. H.T. Fuse
3. Surge capacitors
4. Lightening arrestors
5. HV connections, wiring connections, earthing terminals, marshalling box,
space heaters with thermostats/ florescent tubes
75

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