FUNCTIONAL
DESCRIPTION
In Thermal Power
Station fuel burns & use the resultant to make the steam, which derives the
turbo generator. The Fuel i.e. coal is burnt in pulverized from. The pressure
energy of the steam produce is converted into mechanical energy with the help
of turbine. The mechanical energy is fed to the generator where the magnet
rotate inside a set of stator winding & thus electricity is produced in India 65% of
total power is generated by thermal power stations. To understand the working
of the Thermal Power Station plant, we can divide the whole process into
following parts.
1. COAL FLOW
In coal fired
plants, raw material are air & water in PTPS, coal is transported through
Railway wagons from M/s Coal India & is kept reserved on a buffer stock.
The brought out to the station is unloaded with the help of wagon tippler.
After unloading, the coal is sent to crusher house with the help of conveyor
belts. The coal which is now reduced to very small pieces is sent to the coal
bunkers with the help of conveyor belt.
The raw coal is fed to coal mills through raw coal feeders raw coal
feeders basically regulate raw coal to pulverized coal pipes. A position of the
primary air is heated utilizing the heat of the fuel gases & then mixed
with the cold air as per requirement by the pulverized coal. Normally the
temperature is maintained at 60 to 70 degrees. The coal is now burnt in the furnace
using oil in the beginning showered through the nozzles at different elevations
in the furnace. To provide air for combustion, the heat of the flue gases also
heat it the heat produced due to combustion is utilized for the conversion of
water into steam. This water is stored in the boiler drum. There are two sets
of pipes attached to the drum, one called riser & other known as down
corner through which the water comes to the ring header & steam moves up
due to the density difference of water & steam. Its steam is super heated
using super heaters & meanwhile the flue gases are through out in the
atmosphere through chimney.
2. STEAM
FLOW
The super heated
steam is sent to the turbine through pipelines there are three turbines in the
units, using this steam at different temperature & pressures. After passing
through high pressure turbine the steam is send to the reheater for rising the
temperature of the steam. After reheating the steam is sent to the intermediate
pressure turbine through reheated line. Here it losses most of its temperature
& pressure & finally sent to low pressure turbine. The uses of three
different turbines help in increasing the efficiency of the plant. The turbine
in turn connecting with a generator produces electricity. Then this electricity
is stepped upto 220 KV with the help of step up transformer & supplied to
various sub-stations grids.
Meanwhile, the
steam through low pressure (L.P.) Turbine is condensed and the condensed water
is stored in hot well.
3. WATER
FLOW
The condensed
water is extracted from the hot well through condensate extraction pumps &
sent to the boiler drum with the help of BOILER FEED PUMP (B.F.P.) before
passing through low pressure heater and dearater. While loss in water is make
up from C.S. Tank, which have D.M. Moor in it. The C.S. Tank is directly
connected to hot well.
The water used
in condenser is sent to cooling tower for cooling. After cooling this water is
again sent to condenser with the help of circulating water pump. The loss is making
from raw water pump house through clarifier pump house.
COMPONENTS DESCRIPTION
1. WAGON
TIPPLER:
It
is the machine which is used to tip the coal from the wagon. The coal tipped is
directly feed to conveyor belt. Its capacity is 12 wagon per hour.
2. CRUSHER:
It crushes the coal into small
pieces.
3. COAL
MILLS:
In
it small pieces of coal are converted into pulverized from. They are 6 in
number.
4. FURNACE:
It is the chamber in which fuel
burns & fire blows.
5. BOILER
DRUM:
It contains water for boiling.
6. ELECTROSTATIC
PRECIPITATOR:
In
this we have electrodes which attract fly ash and extract it from flue gases so
that it cannot enter atmosphere.
7. CHIMENY:
It is used to release flue
gases into the atmosphere.
8. TURBINE:
Turbine
is the part which revolves due to steam pressure. It is of three types.
a) High pressure turbine.
b) Intermediate pressure turbine.
c) Low pressure turbine.
9. TURBO
GENERATOR:
It
is the main machine which produces 250 MW electricity .It is (H2O)
water and H2 (Hydrogen) gas cooled therefore it is contained in
cylindrical chamber.
10. CONDENSER:
It condenses steam coming from low pressure turbine
(L.P.T.) to hot water. By removing air and other non-condensable gases from steam
while passing through them.
11. COOLING
WATER (C.W.) PUMP:
This pump send water from
cooling tower to condenser.
12. COOLING
TOWER:
It
is used to coal the water its height is near about 143.5 mtrs. The hot water is
led to the tower top and falls down through the tower and is broken into small
particles while passing over the baffing devices. Air enters the tower from the bottom and flow
upwards. The air vaporizes a small percentage of water, thereby cooling water
falls down into tank below the tower from where it is pumped to the condenser
and cycle is repeated.
13. RAW
WATER PUMP HOUSE:
It supplies raw water to the
boiler.
14. CLARIFIER
PUMP HOUSE:
The
water from raw is clear at clarifier by putting alum in it & filtering it
& then supplied to the condenser.
15. CONDENSATE
EXTRACTION PUMP:
C.E.P.
pump is used to extract the condense water from the hot well and supply to the
deaerator after passing through L.P. heater & Economizer, so that high
pressure steam in the cylinder can be created.
16. LOW
PRESSURE HEATER:
It
is used to increase the temperature of water, in this way efficiency of system
increases.
17. DEAREATER:
It
is used to remove air from water which is entrapped in the water molecules. It
is very important part because the entrapped air effect air drum badly.
18. BOILER
FEED PUM (B.F.P.):
It
is the heaviest drive in the plant & supply water to boiler drum from dearator.
19. HIGH
PRESSURE HEATER (H.P.):
In
this temperature of water increases. Thus efficiency further increases.
20. ECONOMISER:
In
this flue gases exchange heat to the water to increase system efficiency, causes saving in fuel consumption
(5 to 10%). Economizer tubes are made up of steel either smooth or covered with
fins to increase the heat transfer surface area.
CURRENT TRANSFORMER (C.T.)
SPECIFICATIONS REQUIRED FOR CTS ARE:
1.
Class
2.
Burden
3.
Ratio
4.
Resistance
5.
Knee Point Voltage/Saturation
CTs can be broadly divided into two categories:-
1. Metering CTs:
Metering
CTs are of very accurate for design of material having nickel iron alloys to
reduce losses and having low flux density. The accuracy class of these CTs is
0/2%, 0.5% & 1.0%. Saturation level of these CTs is low i.e. 100 to 120% of
In (CR secondary current) are thermal protection of meters.
Metering CTs are
also known as Measuring CTs. These CTs cannot be used for protection purpose.
The can only measure the current.
2. Protection CTs:
Protection
CTs are less accurate than metering CTs having high flux density. Saturation
level of these CTs is high. Protection CTs are of two class i.e. 5P 10 &
PS. 5P 10 is generally used for simple o/c & E/F protection where PS
(purchaser specified) class is used for differential protection. These CTs are
also used to measure current but up to specified limit.
GENERATOR
SPECIFICATION OF GENERATOR
KW/MW -210
|
P.F. -0.85
|
KVA -247000
|
KV -15.75
|
Amp -9050
|
Rotor volt -310
|
EPM -3000
|
Rotor amp -2600
|
Hz -50
|
Phas -3
|
Connection-star star
|
Gas pressure -3.5kg/cm2
|
Insulation class-B
|
SPEC- IE C34.1834.3 IS.5423
|
DIVIN-HARIDWAR
|
Coolants- H2O & H2
|
Supervision of
cooling gas & cooling water temperature
The
adjustment or setting of cooling water flow should be made only by changing the
adjustment f cooling water outlet valves. The inlet valve at header or valve at
individual cooler section should be opened fully. The pressure of water at
inlet of each cooler should be so adjusted as to keep the valve to 0.2kg/cm2
below the pressure of H2 in casing.
Operating value
|
MAX. SETTING
|
||
1. Stator
water inlet temp. to stator winding
|
40oC
60oC
|
45oC
85oC
|
|
ALARM HIGH
|
VERY HIGH
|
||
3. Cold gas temp.
|
25o-44oC
|
44oC
|
55oC
|
4. Hot gas temp.
|
40o-75oC
|
75oC
|
-
|
5. Stator core temp.
|
<95oC
|
95oC
|
-
|
6. Stator slot temp.
|
50o-75oC
|
75oC
|
-
|
7. Rotor winding temp.
|
<115oC
|
115oC
|
120oC
|
8. Humidity monitor dew point
|
<10oC
|
<-3oC
|
-
|
HYDROGEN COOLERS
The turbo generator has been
provided with four nos. gas coolers mounted longitudinally in side stator body
for cooling of hot gas, thus taking away the heat losses generated by rotor
winding, stator core and windage losses.
The gas cooler is a shell
and tube heat exchanger consisting of cooling tubes with coiled copper wire
around them to increase the surface area of cooling. Cooling water flow through
the tubes while hydrogen flowing across coolers comes into contact with external
surface of cooling tubes. Heat remove from hydrogen is dissipated through
cooling water.
On both ends of coolers, water
chambers are bolted to two plates. The outside flange of water chamber on
slipping end is elastically fixed to stator body with the help of molded rubber
gasket to allow free expansion of cooler where as on the turbine end; it is
fixed rigidly to the stator. At turbine end, inlet and outlet water pipes are
connected to water flange. In order to remove air from cooler while filling
them with water, wind pipes are provided on slip ring end. Shut off valves are
installed in pipe line at inlet and outlet of each cooler.
GENERATOR DESCRIPTION
210 MW GENERATOR
The generator is two pole
type with cylindrical rotor using direct water cooling of stator winding,
including phase connecting bus bar, terminal bushing and direct hydrogen
cooling of rotor winding using gap pick up method. The losses in other parts of
generator such as stator iron losses, friction & windage losses are removed
by hydrogen circulating in casing.
The generator stator frame
is of pressure-resistant and gas tight construction with four horizontal
coolers in the frame itself forming part of ventilation and closed cooling
circuit.
The generator
consists of the following components as shown:
STATOR:
Ø Stator
body
Ø Stator
core
Ø Stator
winding
Ø Gas
coolers
ROTOR:
Ø Rotor
shaft
Ø Rotor
winding
Ø Rotor
retaining ring and other fittings
Ø Field
connections.
BEARING WITH BRUSH GEAR:
Ø Bearing
Ø Brush
gear
STATOR
1. Stator Body:
The stator body is a totally enclosed gas tight
fabricated structure, suitable ribbed internally to ensure high rigidity, it is
designed mechanically to withstand internal pressure and forces as a result of
unlikely event o explosion of hydrogen, air mixture without any residual
deformation, Hydrogen gas coolers are housed longitudinally inside the stator
body.
2. Stator
Core:
The stator core is made up
of segmental, varnish insulated punching of Electro technical sheet with low
loss factor. The stampings are assembled in an inter leaved manner on dove
tailed core bars in order to damp out the oscillations so that magnetic
vibration of stator core are not transferred to foundation through stator
frame.
3. Stator
Winding:
Stator bars, bus bars and terminal bushing are
designed for direct water cooling. In order to minimize the eddy losses, the
bars are composed of separately insulated strands, solid as well as hollow. The
high voltage insulation is provided by thermosetting insulation using epoxy
mica paper tape. With this insulating system, several layers of this tape are
applied to the formed bars continuously and half over lapped. The no. of layers
i.e. the thickness of the insulation depends on the machine voltage. The
insulation is also water proof and oil resistant. For protection of the stator
winding against the effects of current forces in slots sides fillers, bottom spacers
and top spacer below the slot wedge ensure permanently firm seating of the bars
in the slot during operation. The water headers are insulated from stator body
which permits measurement of insulation resistance of winding. The stator
winding is connected inside the machine by connecting bus bars and brought out
to nine bushing located in box of welded non magnetic steel below the generator
at exciter end.
ROTOR
1. ROTOR SHAFT:
The rotor shaft is single piece
forging manufacturing from ingots which are cast by vacuum degassing process.
The longitudinal slots for insertion of the field winding are milled into
barrel portion. The slots are distributed over the circumstances so that two
solid poles are obtained. To ensure that only high quality and defect free
forging is used, strength test, chemical analysis and ultra sonic test are
carried out during manufacturing. After completion of rotor assembly the rotor
is balanced at different sped in various planes and then subjected to an over
sped test at 120% of rated sped for 2 minutes.
2. ROTOR WINDING AND
RETAINING RINGS:
The rotor winding comprises
several coils which are inserted into the slots and series connected in such a
way that two coil groups enclosing one pole each are obtained. The centrifugal
forces of the rotor overhauling windings are taken up by single piece retaining
ring. The retaining rings consist of non-magnetic high strength steel in order
to reduce stray losses.
3. FIELD LEAD CONNECTIONS:
a). SLIP RINGS:
The slip rings consist
of helically grooved alloy steel ring shrunk on the rotor body shaft and
insulated from it. For convenience in assembly both rings are mounted on a
single common steel bush which has an insulating jacket premoulded on it. The
complete bush with slip rings is shrunk on the rotor shaft.
The
slip rings are provided with inclined holes for self ventilation. The helical
grooves cut on the outer surface of the slip rings improve brush performance by
breaking the pressurized air pockets that would otherwise get formed between
the brush and slip ring surface.
b). FIELD
LEAD:
The slip
rings are connected to the field winding through semi flexible copper leads and
current carrying bolts placed radially in the shaft semi-flexible o thin copper
sheets silver plated and copper leads are made up insulated by glass cloth
impregnated with epoxy resin for low resistance and ease of assembly. The
connection between current carrying bolt and field winding is done by a filed
lead bar which has similar construction as that of semi-flexible copper lead.
BEARING AND BRUSH GEAR
a). BEARING:
The generator bearings are pedestal type with
spherical seating to allow self alignment and are supported on a separate
pedestal on slip ring side and in L.P. casing on the turbine side. The bearings
have provision of hydraulic shaft lifting during start up and turning gear
operation. To eliminate shaft current, exciter side bearing and its pipes are
insulated from earth. The bearing temperature detectors embedded in the Babbitt
of lower half bearing liner. Vibrations on the bearing in horizontal and
vertical direction are measured by vibration pickups mounted on the bearing
pedestal.
b). BRUSH
GEAR:
The
rotor winding is solidity connected to slip rings by means of field lead bars,
current carrying bolts, field lead core bars and flexible leads. The filed
current to the rotor winding is provided through the brush gear.
The
current carrying brush gear assembly is rigidly fixed on the extended part of
bearing pedestal on the exciter side. There are two brush gear stands, each
made up of two symmetrical silicon brass casting half rings, which are bottled
at the top to make one stand assembly, kept vertically. These rings stands are
designed as helical from one end to the other to achieve uniform wear of slip
rings as well as carbon brushes and smooth removal of carbon dust all along the
width of slip rings. The design of brush gear permits replacement of the
brushes during normal operation condition. This complete gear stand assembly is
rigid fitted in position on brush gear support which as a whole unit is to be
fixed on to bearing.
c). SHAFT
SEALS:
In order to prevent the
escape of hydrogen from the generator casing along the rotor shaft, shaft seals
supplied with oil under pressure are used. To ensure perfect sealing, the oil
pressure in the annular gap is maintained at a higher level than the gas
pressure in the generator cas8ng. As long as the seal oil pressure in the
annular gap between the shaft seal and the rotor exceeds the gas pressure in
the generator. No hydrogen will escape from the generator housing. The shaft
seal is provided with seal oil by a separate closed circuit system.
For the operation of
generator the following auxiliary system are required.
d). STATOR WATER COOLING
SYSTEM:
1.
Seal oil supply system
2.
Gas system.
3.
Stator water cooling system.
SEAL OIL SUPPLY SYSTEM:
The
shaft seals are supplied with seal oil from a separate circuit which consists
of following principle components:
Ø
Vacuum tank
Ø
AC seal oil pump 1 & 2
Ø
DC seal oil pump
Ø
Vacuum pump
Ø
Oil coolers
Ø
Sea; oil filters
Ø
Intermediate oil tank
Ø
Constant pressure regulating valve-1
Ø
Constant pressure regulating valve-2
Ø
Constant pressure regulating valve-3
Ø
Differential pressure regulating valve-1
Ø
Differential pressure regulating valve-2
GAS SUPPLY SYSTEM:
The
gas system essentially consists of the following equipment:
Ø
H2 & CO2 cylinders
Ø
Pressure reducers
Ø
CO2 vaporizer
Ø
Pressure gauges
Ø
Gas drier
Ø
Humidity monitors
Ø
Purity measuring instruments
STATOR WATER COOLING SYSTEM:
The
stator water supply system essentially comprises the following components:
Ø
Expansion tank
Ø
Stator water pump-A
Ø
Stator water pump-B
Ø
Stator water cooler-A
Ø
Stator water cooler-B
Ø
Stator water filter-A
Ø
Stator water filter-B
GENERATOR PROTECTION:
An
AC generator forms the electromechanical stage of an overall energy conversion
process that results in the production of electrical power. A reciprocating
engine, or one of many forms of turbine, acts as a prime mover to provide the
rotary mechanical input to the alternator. There are many forms of generating
plant that utilize a variety of sources of energy available, e.g. Combustion of
fossil fuels, hydro dams and nuclear fission. Generation schemes may be
provided for base-load production, peak lopping or for providing standby power.
Electrical
protection shall quickly detect the initiate shut down for major electrical
faults associated with the generating plant and less urgently to abnormal
operating conditions which may lead to plant damage.
Abnormal
electrical conditions can arise as a result of a failure within the generating
plant itself, but can also be extremely imposed on the generator. Common
categories of faults and abnormal conditions which can be detected electrically
are listed as follows:
Major Electrical Faults:
Ø
Insulation failure of stator windings or
connections.
Secondary Electrical Faults:
Ø
Insulation failure of excitation system.
Ø
Failure of excitation system.
Ø
Unsynchronized over voltage
Abnormal Prime Mover or Control Conditions:
Ø
Failure of prime mover
Ø
Over frequency
Ø
Over fluxing
Ø
Dead machine energisation
Ø
Breaker flashover
System Related:
Ø
Feeding on un-cleared fault
Ø
Prolonged or heavy unbalance loading
Ø
Prolonged or heavy overload
Ø
Loss of synchronism
Ø
Over frequency
Ø
Under frequency
Ø
Synchronized over voltage
Ø
Over fluxing
Ø
Under voltage
In
addition various types of mechanical protection may be necessary, such as
vibration detection lubricant and coolant monitoring, temperature detection
etc.
The
action required following response of an electrical or mechanical protection is
often categorized as follows:
Ø
Urgent
shutdown
Ø
Non-urgent
shutdown
Ø
Alarm
only
An
urgent shutdown would be required for example, if a phase to phase “Fault
occurred within the generator electrical connection. A non-urgent shutdown
right to sequential, where the prime mover may be shutdown prior to
electrically unloading the generator, in order to avoid over sped. A non-urgent
shutdown may be initiated in the case of continued” unbalanced loading. In this
case, it is desirable that an alarm should be given before shutdown becomes
necessary, in order to allow for operator intervention to remedy the situation.
For
urgent tripping, it may be desirable to electrically maintain the shutdown
condition with latching protection output contact, which would require manual
resetting. For a non-urgent shutdown, it may be required that the output contacts are self-reset, so that production of
power can be re-started as soon as possible. Accordingly generator protection
has been divided into three categories:
1. Class
A Protection:- Urgent shutdown /tripping without any time delay
causing tripping of GCB, FB, UATs & Turbine simultaneously.
(a) GT
REF Protection (64 GT)
(b)
Generator differential Protection (87G)
(c)
Generator interterm fault (87G1)
(d)
Generator Reserve Power Protection (32G1)
Loss of Excitation (40G)
(e)
Backup impedance Protection 21G)
(f)
UAT Differential protection (87UAT)
(g)
GT/UAT Turbine (63 PTXG, 63 PTX)
(h)
Over voltage protection (59 G1)
(i)
Generator 100% stator E/F Protection (64G3)
(j)
Over fluxing Protection (99G)
(k)
AVR Trouble
(l)
Over Current for UAT (50UAR)
(m) Rotor
E/F Protection (64F)
(n)
GT Overall differential protection (87 OA)
(o)
Generator 95%
stator E/F Protection (64G2)
2. Class
B Protection:- Urgent
shutdown /tripping delay of turbine first and tripping of GCB, FB, UATs & Turbine on class A
protection through LEP/RP protection (0.5% to 210 MW).
(a) Under Frequency Protection (81 G)
(b) GT Trouble relays
(c) Loss of Excitation Protection
(40 G1)
(d) Negative Phase flow seq.
Protection (46 G)
(e) Stator water flow low and
Conductivity high
(f) UAT Trouble
3. Class
C Protection:- Only GCB trip and unit can be run on house load.
(a) Generator Backup impedance protection
(21 G)
(b) GT Over current Protection (51 GT)
(c) Negative Phase seq, Protection.
(d) U/F Protection
(e) GT Natural O/C Protection (51 NGT)
(f) Generator Pole Slipping Protection (78 G)
Generator Differential Protection
Failure of stator
windings, or connection isolation, can result in severe damage to the windings
and state core. The extent of the damage will depend, upon the fault current
level and the duration of the fault. Protection should be applied to limit the
degree of damage in order to disconnection of the plant from the power
generating plant, high –speed maintain system stability.
Two
methods are commonly used. A biasing technique, where the relay setting is
raised as through current increases. Alternatively, a high impedance technique,
where the relay impedance is such element is insufficient for the relay to
operate.
Biased differential protection
In
a biased differential relay, through the current is used to increase the
setting of the differential element or heavy through faults, it is
unlikely that the CT outputs at each
zone end will be identical, due to the effects of CT saturation. In this case a
differential current can be produced. However, the biasing will increase the
relay setting, such that the differential spill current is insufficient to
operate the relay. Through the current is calculated as the average of the
scalar sum of the current entering and leaving the zone of protection. This
calculated through current
is then used to apply percentage bias to increase the differential setting.
Setting Guidelines For
Biased Differential Protection
The
differential current setting, should be set to a low setting to protect as much
of the machine winding as possible. A setting of 5% of rated current of machine
is generally considered to be adequate. The threshold, above which the second
bias setting is applied, should be set to 120% of the machine rated current.
The initial bias slope
setting should be set to 0% to provide optimum sensitivity for internal faults.
The second bias slope may typically be set to 150% to provide adequate
stability for external faults. These settings may be increased where low
accuracy class CTs is used to protection.
High impedance differential
Protection
The
high impedance principle is best explained by considering a differential scheme
where one CT is saturated for an external fault, as shown in Figurer.
If
the relay circuit is considered to be very high impedance, the secondary
current produced by the healthy CT will flow through the saturated CT. If the
magnetizing impedance of the saturated CT is considered to be negligible, the
maximum voltage across the relay circuit will be equal to the secondary fault
current multiplied by the connected impedance, (RL3+R14+RCT12)
The
relay can be made stable for this maximum applied voltage by increasing the
overall impedance of the relay circuit, such that the resulting current through
the relay is less than its current setting. As the impedance of the relay input
alone is relatively low, a series connected external resistor is required. The
value of this resistor, RST, is calculated by the formula shown in
Figure 3. An additional on linear resistor, Metrosil, may be required to limit
the peak secondary circuit voltage during internal fault conditions.
To
ensure that the protection will operate quickly during an internal fault the
CTs used to operate the protection must have a knee point voltage of at least
4Vs.
USE OF “METROSIL” NON –LINEAR
RESISTORS
Metrosils
are used to limit the peak voltage
developed by the below the insulation level of the current transformer, relay
and interconnecting leads, which are normally able: to withstand 30000V peak.
The
following formulae should be used to estimate the peak transient voltage that
could be produced for an internal fault will be a function of the current
transformer knee point voltage and the prospective voltage that would be
produced for an internal fault if current transformer saturation did not occur.
This prospective voltage will be a function of maximum internal fault secondary
current, the current transformer ratio, the current transformer led resistance
to the common point, the relay lead resistance and the stabilizing resistor
value.
Vp=2V2
Vk (Vf-Vk)
V,=1(RCT+2RL+RST)where
Vp=peak
voltage developed by the CT under internal fault conditions.
Vk=
current transformer knee-point voltage
V=
Maximum voltage that would be produced if CT saturation did not occur.
Setting guidelines for Stator earth fault protection function (51N)
·
Current operated from a CT in the neutral earth
path.
·
Two independent tripping stages.
·
First stage tripping can incorporate either a
definite time or standard inverse type IDMT delay.
·
Second stage tripping can be instantaneous or
definite time delayed.
·
Immune to third harmonics.
Applied to
directly connection generators.
The
protection must be time graded with other earth fault protection; the setting
employed should be less than 33% of the earth fault level.
In
case of direct generator connection, it is common that only one generator of a
parallel set is earthed at any one time, with the arth connections of other machines left open, if the generating plant can also be run
directly in parallel with a medium voltage public supply, it is a common requirement
that all generator earth connections are left open during parallel operation.
In such circumstances, the main earth fault protection element (le>) will
only be operational for an earthed machine, It will provide primary earth fault
protection for other machines and the rest of the power system and thermal
protection for the earthing resistor.
For
indirectly connected applications, the time-delayed earth fault protection
function may be employed in one of two ways.
1. To measure earth fault current indirectly, via a CT in
the secondary circuit of a distribution transformer earthing arrangement.
2. To measure earth fault directly, via a CT in the
generator winding earth connection.
With
the first mode of application, the current operated protection function (51N)
may be used in conjunction with voltage operated protection function (59N),
measuring the distribution transformer secondary voltage. This is a
complementary arrangement, where the voltage operated protection function (59N)
is able to operate in the event of an open –circuited loading resistor and the
current operated protection function (51N) is able to operate in the event of a
short circuited resistor.
The
second mode of application would be used for cases of direct resistive
earthing. For distribution transformer earthing, this mode offers the advantage
of being able to respond to an earth fault condition that leads to a flashover
of the distribution transformer primary connections. Such a primary short
circuit would render protection on the secondary side of the transformer
inoperative and it would also result in a very high and damaging primary earth
fault current.
In
either mode of application, the main stator earth fault current operated
protection element (le>) should be sent to have a primary sensitivity of
around 5% of the maximum earth fault current as limited by the earthing
impedance. Such a setting would provide protection for upto 95% of the
generator stator windings. The probability of an earth fault occurring in the
lower 5% of the generator ‘winding would be extremely low, due to the fact that
the winding voltage with respect to earth is low in this region.
The
time characteristic and setting of the main current operated protection element
(le>) should be set to prevent false operation during HV system earth fault
clearance, where a transient generator earth connection current may appear as
–result of the inter-winding capacitance of the generator step-up transformer.
The protection element should also co0operate with operation of generator VT primary
fuses, for a VT primary earth fault, and with VT secondary fuses for a
secondary earth fault on a VT that has its primary windings earthed. Depending
on the VT fuse characteristics, and on HV system earth fault protection
clearance times, a definite time delay anywhere between 0.5s and 3.0s would be
appropriate.
In machines with complex winding connection
arrangements, e.g. some hydro generators, the probability of a fault occurring
in the stator winding star-end region (first 5% of the winding) might be
higher. For a higher rated, expensive machine such increased probability may
prompt operators to apply 100% stator earth fault protection. A suitable 100%
stator earth fault protection scheme can be applied in these cases.
A
setting of 5% of the earth fault level should be applied for applications where
the differential protection provides less than 95% coverage of the stator
winding.
Applied to in-directly connected
generators
(With the generator earthed via a
distribution transformer)
Can
be supplied from a CT in either the primary or secondary circuit of the
Distribution transformer.
With
a CT in the primary circuit, the protection has the advantage of being able to
detect an earth fault which causes flashover of the primary winding of the
distribution transformer. With the CT in the secondary circuit the protection
has the advantage of detecting a short circuit across the loading resistor. A
sensitive 5% setting can be applied to the first tripping stage, a short time
delay can be applied to stabilize the protection against small earth current
due to VT failures or earth leakage during HV system faults.
The
second tripping stage can be utilized as a high set a 10% setting and
instantaneous operation ensures fast clearance of generator earth faults.
100% stator Earth Fault Protection:
The
conventional unit type generator has the neutral earthed through a resistance
loaded distribution type transformer. For a single ground fault near the
neutral end of the winding, there will be proportionately less voltage
available to drive the current through the ground, resulting in a lower fault
current and a lower neutral bus voltage.
6.6 K.V. CIRCUIT BREAKER
A circuit
breaker is device which:-
- Makes or breaks a circuit either manually or by remote control under normal conditions.
- Breaks a circuit automatically under fault conditions.
Thus
a circuit breaker is just a switch which can be operated under normal &
abnormal conditions both automatic or manually to perform this operation, a circuit
breaker is essential consisting of fixed and moving contacts called electrodes.
When a fault occurs on power system, the trip coil of circuit breakers
energized which pulls apart moving contacts. Thus open the circuit dc supply is
used for the operation of circuit breaker on the basis of medium used for
extinction the circuit breakers are classified as:
- OIL CIRCUIT BREAKERS
- AIR BLAST CIRCUIT BREAKER
- SULPHER HEXAFLURID CIRCUIT BREAKER
1. OIL
CIRCUIT BREAKER: -
It is well known
that when a circuit carrying a large current is broken, an arc occur at that
point where the contacts are separate, the arching is specially served when
high voltages are involved and if a short circuit occur on a high voltage cable
which is supplied from large power station. The arc would be powerful to bridge
the contacts of the switch and destroy it by burning the device is employed as
a oil circuit breaker. Oil breaker posses the property of always breaker an
alternative current at its zero value.
These switches are suitable for a maximum
voltage of 6.6kv the contact of these switches, which break high tension
circuit are put in a box in which we have create a vacuum .to ensure rapid
& effective rupture of the circuit. When the arc occurs, there is no medium
in the box and the arc slow down easily, as it is difficult to maintain high
value of vacuum under the condition of commercial manufacture and operation.
Oil is the best
voltage insulator with stress level upto 107v/cm limited only by emission from
the electrode surface. This decreases to less then 105v/cm for gaps for
coverall centimeters. The dielectric constant of all dialectical gases is very
nearly hinting.
SPECIFICATION
OF OIL BREAKER:-
TYPE – BIBARE.T,
BKRT TYPE.
VOLTAGE – 7.2KV
FREQUENCY – 50Hz
SHORT TIME CURRENT
– 40A
DURATION – 15
MAKING CAPACITY –
100 KAP
POWER FECTOR WITH
STAND – 27KV
IMPULSE WITH STAND
– 60KVP
SHUNT TRIP COIL –
220V
SPRING RELEASE COIL
– 220V
2. AIR
BLAST CIRCUIT BREAKER:
3.
SULPHER HEXAFLURID CIRCUIT BREAKER:
6.6 KV UNIT
SWBD # 8CA
1) BFP#8C 4600KW
2) ACWP#8A 550KW
3) CWP#8A 1965KW
4) CEP#8A 325KW
5) SPARE
MOTOR FEEDER 2400KW
6) BFP#8A 4600KW
7) MILL#8AB 2400KW
8) PAFAN#8A 1550KW
9) FDFAN#8A 790KW
10)
IDFAN#8A 1800KW
11) 2500KVA 6.6/0.433KV
OIL
FILLED SPARE TRANSFORMER FEEDER.
12) 2000KVA 6.6/0.433KV
DRY TYPE UNIT SERVICE TRANSFORMER #
8DAT01
13) 2500KVA 6.6/0.433KV
OIL FILLED ESP SERVICE TRANSFORMER #
8DBT01
14) FEEDER
PT
15) INCOMER
FROM UAT#8A
16) BUS PT
17) TIF
FROM 6.6KV STATION SWBD#OCC
6.6KV
STATION SWBD # OCC
1) TIE TO 6.6KV UNIT SWITCH BOARD # 8CA
2) O/G FEEDER TO 6.6KV COAL HANDLING SWBD # OCE
3) 1000KVA
6.6/0.433KV
OIL FILLED SPARE TRANSFORMER CP #8C
4) TIE TO 6.6KV STATION SWBD#OCA.
5)
1000KVA
6.6/0.433KV
OIL FILLED CHP. TRANSFORMER # ODHT02.
6) 2000KVA
6.6/0.433KV
OIL FILLED
SWITCHYARD TRANSFORMER#02.
7) 2000KVA
6.6/0.433KV
DRY TYPE UNIT SERVICE TRANSFORMER#ODATO2.
8)1250KVA
6.6/0.433KV
OIL
FILLED RAW WATERTRANSFORMER # ODGT02.
9) AIR COMPRESSOR # C 400KW
10)
CEP # 8C 325KW
11)
MILL#8EF 2400KW
12)
SPARE MOTOR FEEDER 2400KW
13)
BUS PT.
14)
FEEDER PT.
15)
INCOMER FROM STATION TRANSFORMER#B.
6.6KV
STATION SWBD#OCD
1)
INCOMER FROM
STATION TRANSFORMER#B.
2)
FEEDER PT.
3)
BUS PT.
4)
SPARE MOTOR FEEDER 1800KW.
5)
PAFAN # 8C
1550KW.
6)
AIR COMPRESSOR #D
400KW.
7)
ID FAN # 8C
1800KW.
8)
1600KVA 6.6/0.433KV
OIL FILLED SPARE
TRANSFORMER FEEDER.
9)
1250KVA
6.6/0.433KV
OIL FILLED WATER TREATEMENT #ODBTO2.
10)
2000KVA 6.6/0.433KV
DRY TYPE STATION SERVICE TRANSFORMER # ODBT02.
11) 630 KVA 6.6/0.433
KV
OIL FILLED ASH SILD TRANSFORMER
#ODTT02.
12) 1600KVA
6.6/0.433KV
OIL FILLED FIRE FIGHTING TRANSFORMER
#ODCT02.
13) TIE TO 6.6KV
STATION, SWBD#OCB.
14) O/G FEEDER TO 6.6KV ASH HANDLING SWBD #
OCF.
15) TIE TO 6.6KV UNIT SWITCH BOARD # 8CB.
6.6 KV UNIT SWBD#8CB
1)
TIE
FROM 6.6KV STATION SWBD#OCD.
2)
BUS
PT.
3)
INCOMER
FROM UAT # 8B.
4)
FEEDER
PT.
5)
2500
KVA
6.6/0.433 KV
OIL FILLED ESP SERVICE
TRANSFORMER # 8DBT02.
6)
2000
KVA
6.6/0.433KV
DRY TYPE UNIT SERVICE
TRANSFORMER # 8DAT02.
7)
2500KVA 6.6/0.433KV
OIL
FILLED SPARE TRANSFORMER FEEDER.
8)
ID FAN# 8B 1800KW.
9)
FDFAN# 8B 790KW.
10)
PAFAN# 8B 1550KW.
11)
MILL 8CD 2400KW.
12)
BFP# 8B 4600KW.
13)
SPARE MOTOR FEEDER 1800KW.
14)
CEP# 8B 325KW.
15)
CWP# 8B 1965KW.
16)
ACWP# 8B 550KW.
17) BFP# 8C 4600KW.
MOTOR
HIGH TENSION MOTOR
HIGH TANSION MOTORS OPERATED AT HIGH
VOLTAGES
IN PANIPAT
THERMAL POWER STATION, THESE MOTORS ARE OPERATED AT 6.6kv SOME OF THESE MOTORS
ARE AS FOLLOWS:-
1. CIRCULATING WATER
(C.W.) PUMP MOTERS:-
A). SPACIFICATIONS:-
I. MAKER – B.H.E.L
II. CAPACITY (K.W.)-1265KW
iii.
RATED VOLTAGE(VOLTS)-6600V
iv.
RATED R.P.M.-493
v.
RATED CURRENT-140A
vi.
CONNECTINS-STAR
vii.
DUTY-CONTINUOUS
viii.
INSULATION CLASS-F
ix.
INSTALATION POSITION-VERTICAL
x.
PHASE-3
b).
FUNCTION:-
C.W PUMP IS USED TO CIRCULATE COOLING WATER TO THE CONDENSER;
SO THAT HIGH PRESSURE LEFT OUT STEAM IN THE L.P. CYLINDER CAN BE CONVERTED INTO
WATER.
2. C.E.P. MOTOR:-
a) SPECIFICATIONS:-
i. MAKE-B.H.E.L.
ii. CAPACITY-500KW
iii. RATED VOLTAGE-6600V
iv.
RATED R.P.M.-1482
v.
RATED CURRENT-52.8A
vi.
CONNECTIONS-STAR
vii.
DUTY-(2WRKING, 1 STANDBY) CONTINUOUS
viii.
INSULATION CLASS-F
ix.
INSTALATION POSITION-VERTICA
x.
PHASE-3
b). FUNCTION:-
C.E.P. PUMP IS USED TO EXTRACT THE CONDENSATE WATER FROM THE
HOT WELL AND SUPPLY TO THE DEAREATOR AFTER PASSING THROUGH L.P. HEATER AND
ECONOMIZER, SO THAT HIGH PRESSURE STEAM IN THE CYLINDER CAN BE CREATED.
3. BOILER FEED PUMP(B.F.P.)
MOTOR:-
No. of motor used = 3(6A, 6B, 6C)
a). SPECIFICATION:-
i. MAKE B.H.E.L.
ii.
CAPACITY-3500KW
iii.
STATOR VOLTAGE-6600V
iv.
RATED R.P.M.-1481
v.
RATED CURRENT-360A
vi.
CONNECTION-STAR
vii.
DUTY-(2WRKING, 1 STANDBY) CONTINUOUS
viii.
INSULATION CLASS-F
Xi PHASE-3
b). FUNCTION:-
ITS FUNCTION IS TO SUPPLY THE WATER TO WATER TO THE BOILER
DRUM. IT TAKES THE WATER FROM THE
DELINEATOR BY CREATING A STRONG SUCTION.
4. COAL MILL MOTOR:-
No. of motor used = 3(6A, 6B, 6C)
a). SPECIFICATION:-
i.
MAKE B.H.E.L.
ii.
CAPACITY-2400KW
iii.
STATOR VOLTAGE-6600V
iv.
RATED R.P.M.-992
v.
RATEDCURRENT-40.7A
vi.
CONNECTION-STAR
vii.
DUTY- CONTINUOUS
viii.
INSULATION CLASS-F
ix.
INSULATION POSITION-HORIZONTAL
x.
PHASE-3
b). FUNCTION: -
THE
FUNCTION OF THE COAL MILL IS TO GRIND THE COAL PIECES OF THE FINE POWDER
(PULVERIZED FORM) i.e. UPTO TO SIZE OF 25 MICRON.
5. COAL CRUSHER:-
No. of motor used = 2(6A, 6B)
a). SPECIFICATION:-
i.
MAKE – N.G.F.E
ii.
CAPACITY-600KW
iii.
RATED VOLTAGE-6600V
iv.
RATED R.P.M.-747
v.
RATED CURRENT-72A
vi.
CONNECTION-STAR
vii.
DUTY- CONTINUOUS
viii.
INSULATION CLASS-F
ix.
PHASE-3
b). FUNCTION:-
IT’S FUNCTIONED TO CRUSH THE BIG SIZE COAL PIECES TO A SIZE
OF 25 MM SQ. WHICH ARE THEN CARRIED TO THE BANKERS ON THE CONVEYOR BELT.
6. PRIMARY AIR FAN (P.A.
FAN) MOTOR:-
No. of motor used = 3(8A, 8B, 8C)
a). SPECIFICATION:-
i.
MAKE B.H.E.L.
ii.
CAPACITY-1250KW
iii.
RATED VOLTAGE-6600V
iv.
RATED R.P.M.-1487
v.
RATED CURRENT-132A
vi.
CONNECTION-STAR
vii.
DUTY- CONTINUOUS
viii.
INSULATION CLASS-F
ix.
PHASE-3
b). FUNCTION:-
ITS FUNCTION IS TO CARRY PULVERIZED COAL FROM THE COAL MILL
TO THE FURNACE FOR ITS IGNITION. IT
CREATES A STROP IT CREATES A STRONG DRAFT OF AIR THAT CARRIES THE POWDERED
COAL.
7). FORCE DRAUGHT (F.D.)
FAN MOTOR:-
a). SPECIFICATION:-
i.
MAKE B.H.E.L.
ii.
CAPACITY-750KW
iii.
RATED VOLTAGE-6600V
iv.
RATED R.P.M.-1490
v.
RATED CURRENT-80.2A
vi.
CONNECTION-STAR
vii.
DUTY- CONTINOUS
viii.
INSULATION CLASS-F
ix.
PHASE-3
b). FUNCTION:-
ITS FUNCTION IS TO SUPPLY FRESH AIR TO THE FURNACE FOR THE
PROPER IGNITION OF COAL IN SIDE THE FURNACE.
8. INDUCED DRAFT (I.D.)
FAN MOTOR:-
a). SPECIFICATION:-
i.
MAKE B.H.E.L.
ii.
CAPACITY-1300KW
iii.
RATED VOLTAGE-6600V
iv.
RATED R.P.M.-750
v.
RATED CURRENT-147.5A
vi.
CONNECTION-STAR
vii.
DUTY- CONTINOUS
viii.
INSULATION CLASS-F
ix PHASE -3
b). FUNCTION:-
ITS FUNCTION IS TO DISCHARGE THE FLUE GASSES TO THE ATMOSPHERE
THROUGH
THE CHIMNEY AFTER PASSING THROUGH THE PRECIPITATOR.
9. BEARING COOLING WATER PUMP MOTOR:-
a). SPECIFICATION:-
i.
MAKE CROMPTON CREAVESES.
ii.
CAPACITY-335KW
iii.
RATED VOLTAGE-6600V
iv.
RATED R.P.M.-980
v.
CONNECTION-STAR
vi.
DUTY- CONTINOUS
vii.
INSULATION CLASS-F
viii.
INSTALTION POSITION-HORIZONTAL
ix.
PHASE-3
b). FUNCTION:-
IT
SUPPLIES COOLING WATER TO THE MOTOR & OTHER AUXILLARY FOR
COOLING PURPOS.
LOW TENSION MOTOR
LOW TENSION MOTORS ARE THOSE WHICH ARE OF 415V. THEY ARE
MAINLY USED IN
H.T MOTOR AUXXILLARY.
1. B.C.W.DRAIN MOTOR
(BEARING COOLING WATER):-
A) SPECIFICATION:-
i).
CAPACITY-136KW
ii). RATED R.P.M-987
iii).RATED
CURRENT-43A
iv).FREQUENCY-50HZ
v). MAKE –KRILOSKER
vi).INSULATION
CLASS-B
B) FUNCTION:-
IT
PUMP THE D.C WATER TO THE BEARING OF HT MOTER FOR THE PURPOSE OF COOLING.
2. SEAL WATER PUMP
MOTER:-
A) SPECIFICATION:-
i). CAPACITY-25KW
ii). RATED R.P.M-1479
iii).RATED CURRENT-43A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE –NGEF
vii).INSULATION
CLASS-B
B) FUNCTION:-
IT
PROVIDES A LAYER OF WATER TO THE LOWER POSITION OF BOILER IN ORDER TO SEAL IT
FROM THE ENTERY OF ATMOSPHERIC AIR.
3. SEAL WATER VAPOUR
EXHAUST FAN:-
A) SPECIFICATION:-
i). CAPACITY-1.5KW
ii). RATED R.P.M-6205
iii).RATED
CURRENT-3.1A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE –KILOSKER
vii).INSULATION
CLASS-B
B) FUNCTION:-
IT PREVENTS THE ENTERY
OF AIR BUBBLES IN THE TURBINE CYLINDER BY PROVIDING THE OPPOSITE PUSH.
4. CENTIFUGE PUMP MOTOR :-
A) SPECIFICATION:-
i). CAPACITY-7.5KW
ii). RATED R.P.M-1440
iii).RATED CURRENT-14.2A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE –CROMPTION
GREAVES
vii).INSULATION
CLASS-B
B) FUNCTION:-
TO CENTRIFUGE
THE VAPOUR THAT ENTERS BY CHANGE IN
TURBINE AN REMOVE THEM.
5. ASH SULLRY PUMP MOTOR:-
A) SPECIFICATION:-
i). CAPACITY-100KW
ii). RATED R.P.M-1485
iii).RATED
CURRENT-176A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE –NGEF
vii).INSULATION
CLASS-B
B) FUNCTION:-
IT PUMP ASH SLURRY
TO THE ASH DISPOSAL AREA .IT PUMPS THE SLURRY WITH GREAT PRESSUR TO THE OUT
SIDE ,IT IS KNOWN OF THE HIGH PRESSUR OF HANDLING FAN AND IT MAKES SLURRY OF
ASH AND WATER.
6. EMERGENCY OIL PUMP:-
A) SPECIFICATION:-
i). CAPACITY-15KW
ii). RATED
R.P.M-1425
iii).RATED
CURRENT-125A
iv).FREQUENCY-NA
(DC)
B)FUNCTION:-
TO PROVIDE OIL THE
SHAFT AND BEARING OF THE TURBINE IF
SEAL OIL PUMP AND TAKING OIL PUMP FAILS.
7. RAW WATER MOTOR PUMP:-
A) SPECIFICATION:-
i). CAPACITY-90KW
ii). RATED R.P.M-1450
iii).RATED
CURRENT-154A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE –KILOSKER
vii).INSULATION
CLASS-B
B) FUNCTION:-
IT
IS USE TO PUMP RAW WATER FROM THE
LAKE TO THE PLANT.
8. INSTRUMENT AIR COMPRESSOR :-
A) SPECIFICATION:-
i). CAPACITY-105KW
ii). RATED R.P.M-1485
iii).RATED CURRENT-184A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE –KILOSKER
vii).INSULATION
CLASS-B
B)
FUNCTION:-
IT IS USED TO
COMPRESS THE AIR USED THE AIR USED TO CANTROL PNEUMATIC CANTROLLED INSTRUMENTS
AT A PRESSUR 6 TO 7 KG/CM CUBE.
9. SERVICE AIR
COMPRESSOR:-
A) SPECIFICATION:-
i). CAPACITY-30KW
ii). RATED R.P.M-1485
iii).RATED CURRENT-184A
iv).FREQUENCY-50HZ
v). PHASE-3
vi). MAKE- NGEF
vii).INSULATION CLASS-B
B) FUNCTION:-
ITS FUNCTION IS SIMILER TO INSTRUMENT
AIR- COMPRESSOR .
10. CLARIFIER WATER PUMP MOTOR:-
A) SPECIFICATION:-
i). CAPACITY-30KW
ii). RATED R.P.M-1470
iii).RATED
CURRENT-43A
iv).FREQUENCY-50HZ
v).
PHASE-3
vi).
MAKE- CROMPTON
vii).INSULATION
CLASS-B
B) FUNCTION:-
IT
PUMP THE FILTERED WATER FROM CLERIFIER TO D.M. WATER TREATEMWNT PLANT.
TRANSFORMERS
The
Transformer is the most convenient & economical device for transfer of
power from one
voltage to another voltage at the same frequency. It works on
the principle of
electromagnetic induction. There is hardly any installation
without a transformer. Due to this
equipment it has been possible to transmit
bulk power to load centers from far off power
houses and to various machineries
and switchgears of the power plant. Transformers are of
two types:-
STEP-UP TRANSFORMER –
Which step-up
the voltage at secondary side called step up transformer.
STEP-DOWN TRANSFORMER –
Which step-down
the voltage at secondary side are called step-down transformer.
MAIN PARTS OF POWER TRANSFORMERS
# Primary
winding
# Secondary
winding
# Oil tank
# Drain coke
# Conservator
# Breather
# Tubes for
cooling
# Transformer
oil
# Earth point
# Explosion vent
# Temperature gauge
# Buchholz relay
# Primary terminals
# Secondary terminals
SOME ACCESSORIES OF
TRANSFORMERS ARE DESCRIBES BELOW:-
1. Oil conservator: - Oil
conservator is a short of dump mounted on the top of transformer. A level
indicator is fixed to it, which gives alarm at low level. Conservator is
connected through a pipe to the transformer tank containing oil. This oil
produced & so the oil level in conservator is left open to the atmosphere
through a breather so that the extra air may go out or come in.
2. Breather:- The
breather is a box containing calcium chloride or silica gel to absorb moisture
of our entering the conservator as it is well known fact that the insulating
property of the transformer oil is lost if a small amount of moisture enter in
it. So dry air is allowed to pass though the breather. When oil level in oil
conservator changes, air moves in & out of the conservator. This action is
known as breathing. Dry silica gel is of the blue color it turns pale pink as
it absorbs moistures. The wet silica gel can be regenerated by drying.
3. Buchholz
relay:- This relay is a gas- actuated relay which is meant
for the protecting of oil immersed transformer from insulation failure, core
heating or any type of internal fault which may cause the heating of oil beyond
the specified temp. due to any internal fault, oil is heated-up & oil
vapour so formed causes either the alarm circuit (for less fault) or trip the
circuit (for server fault).
4. Explosion
vent: - It is also a safety device of the transformer
which protects the transformer tank from gases induced by & any type of
short circuit in the transformer. This consists of a vertical pipe closed by a
diaphragm of thin bakelite sheet. This diaphragm burst or slides out is case of
abnormal pressure inside the tank. A diverter plate is used at the bottom of
the explosion vent to ensure that gases produced inside the transformer are
directed toward the buchholz relay & don’t get collected inside the
ventilation and equalize the pressure on each side of the diverter plate.
5. Tem.
Indicator: - It is also a protective device fitted to the
transformer to indicate temp. of transformer oil. For measuring temp. of the
oil, bulb of the vapor pressure type transformer is placed in the hot oil &
dial of the transformer is mounted outside the tank. Two indicating pointers
black and red are provided. Alarm contacts are predetermined permissible higher
temperature is reached under abnormal operating conditions.
6. Bushing: - The serve as
supports and insulation of the bus bars and transformer thermal. The bushing
consists of porcelain shell body. Upper and lower locating washer used for
fixing the position of bus bar and mounting flange with the hole drilled for
fixing bolt and it is supplied with an earthing bolt.
7. Magnetic
oil gauge: - The magnetic oil level gauge supervises the
level of oil in the conservator tank. The oil level gauge is provided on the
transformer are of dial type with minimum and maximum level marking and a
pointer which indicate the level of oil in the conservator sometime the scale
is also graduated for oil temperature o the basis of its level.
8. Tap
changer: - The voltage control of transmission and distribution
system is obtained by Tap Changer tap changer are either on load or off load
tap changer, tap changer is fitted with the transformer for adjusting secondary
voltage.
SWITCHYARD COMPONENTS
1. SWITCH-GEAR: - Switch
gear is a control switch that controls the operation of a power circuit. The
two function of a switch in power systems are:-
i) To permit
the transmission lines to be convenient put into and taken out from service.
ii) To disable
the some plant and lines when these become faulty. To be rapidly and safety
isolated by automatic means.
The
first of these can be served by relatively simple switches the second however require circuit breakers, which are more robust & capable of breaking the
largevalue of fault power that results in faults on major power system since
all plants and lines are liable to develop faults as a results of mechanical
damage, electrical breakdown, errors in operation etc. The simple isolators
switch in favour of automatic circuit breakers even for switching function. The
whole switchgear assembly consists of two parts:
1. PANEL:
Panel consists of
protective relays. Mounting of potential transformer, current transformer,
ammeter, voltmeter & energy meter. The potential transformer is mounted on
the panel. The primary is connected to 11KV & the reduce voltage from the
secondary is given to energy meter as line voltages & for protective purposes.
2. TROLLEY:
The trolley
consists of current carrying contracts called electrodes. These are normally
engaged but in predetermined conditions. Separate to interrupt the circuit,when the contact are made.
BUS BAR
ARRANGEMNT
Conductors
to which a number of circuits are connected called bus-Bars. In power plants,
shut down results disconnection of supply to a large are. Hence to avoid shut down the major plants should have elaborate bus bar arrangement with duplicat buses. Alternative supply arrangement section etc. The extra high voltage
equipments such as isolators circuit breaker are generally costly hence
unnecessary equipment should not be provided.
1. SINGLE BUS BAR ARRANGEMENT: -
The
single arrangement consists of a single (three phase) Bus Bar to which various feeders are connected. In case of fault or maintenance of Bus. The entire bus
bar has to be de-energized and the total shutdown results. This scheme is most
economical and simple.
2. DOUBLE BUS BAR ARRANGEMENT: -
The
double bus systems provide additional flexibility, continuity of supply and
permit
periodic maintenance. In the event of fault on the bust bar the other
can be used. The
figure shows to the bus bar arrangement. There are two buses
called main bus and
reserve bus. The two buses can be closed so as to connect
two buses while
transferring the power to the reserve bus
i)
Closed bus coupler the two buses are now at same
potential.
ii)
Closed isolator on reserve bus.
iii)
Open isolator on main bus.
LIGHTING ARRESTER
A lighting
arrester is device, which proves low impedance path for the flow of currentbetween the line and earth when the systems voltage increases more than the
desire valueand regains its original properties of an insulator at normal
voltage. It is connected betweenline and earth at the switchyard near the
transformer.
The lighting
arresters are extensively used for protection of transformers, switch gears andelectrical equipments of over head lines, power houses and sub-station. There
are also use toprotect the line and equipments from sky lighting.
Following are
the main type of lighting arresters.
i)
Horn gap lighting arrester.
ii)
Expulsion type lighting arresters.
iii)
Oxide film lighting arrester.
iv)
Pellet lighting arrester.
v)
Thyrite lighting arrester.
vi)
Auto value lighting arrester.
EXPULSION
TYPE LIGHTING ARRESTER
IT CONSISTS OF:-
i)
A tube made of fibre which is very effective gas
evolving materials.
ii)
An isolating spark gap (or external series gap)
iii)
An interrupting spark gap inside the fibre tube.
During operational, ARC due to impulse spark or inside. The fibrous tube
causes some fibre material of the tube volatize in form of gas, which is
expelled through a vent from the bottom of the tube. Thus extinguishing the ARC
just like in circuit breaker since the gases generated have to be expelled one
of the Electrode is hollow and diverter is open at its lower end.
THYRITE LIGHTING ARRESTER:-
This type of lighting arrester consists of number of discs of inorganic
ceramic compound. These discs are placed in a series having some gap in between
them and are sealed in a porcelain tube. This tube has metallic cap and
electrodes at its end.
The compound used for disc serves as an insulator but changes to a good
conductor when voltages across it rise to a certain predetermined value. It is
used upto 220 KV systems.
210 MW
TURBO GENERATOR
GENERAL: -
Modern features of direct cooling by
water & hydrogen are incorporated in the 210 mwturbo generator, thus
evolve an economical & reliabledesign. The machine is provided with a fast
acting excitation system & dependableauxiliary service to give prolonged trouble free operation over the years. All the material that goes into the
manufacture of this machine subjected to various test as per national &
international standards. Each component undergoes series of stage wise tests.
Description of various parts is given below:-
1.
STATOR
WINDING AND INSULATION: - The
stator has a three phase, double layer, short chorded, bar type winding, having
two parallel parts. Each coil side consists of glass insulated solid and hollow
conductors with cooling water passing through the patter. The elementary
conductors are rebel transposed in the slot position of winding to minimize
eddy current losses.
Adequate
protection is provided to avoid corona & other discharges in the slots, the
sides are firmly held in the position by fibrous slot wages, which are
mechanically strong and have high dielectric properties. The overhang portion
of the coil is securely lashed with glass chord to bondage rings & special
brackets of non magnetic steel, which are in turn, fixed to the core press
rings. On short circuits the process between the conductors tends to open the
cone formed by overhang portion of the coils, but the movement is effectively
presented by supports & lashings.
2.
DISTILLATE
HEADERS OR STATOR WATER HEADER: - Ring type water heads, made of copper are provided
separately for distillate inlet & outlet in the stator on turbine side. The
headers are supported on insulators and isolated from stator body. The winding
ends are than ultrasonically tested. Individual bars provided with water
inlet/outlet connections made of P.T.F.E. houses. The bar heads are insulated
by fiber moulded corners. The winding scheme along pneumatic tests at various
stages to ensure water tightness and to detect blocking of the flows paths.
3.
TERMINALS
BUSHINGS: - Water
cooled terminal bushings are housed in the lower part of the stator on the slip
ring side. Porcelain insulators are provided to insulate the terminal bars from
the stator body. Effective sealing is provided between the terminal bushing are
housed inside a chamber made of non magnetic steel plates. Three phase
terminals are brought out to facilitate external connections. The terminal
bushings can be replaced without removing the stator from foundation. Provision
is made for fixing the external bus ducts with the terminal plate.
4.
ROTOR: - The rotor is of cylindrical
type shaft and body being forged in one piece from chromium, nickel, molybdenum
& vanadium steel. Prior to matching, a series of comprehensive ultrasonic
examination and other tests are carried out on rotor body and shaft portion to
ensure of any internal defects. The rotor with all the details assembled,
dynamically balanced to a high degree of accuracy and subjected to 20% over
speeding for 2 minutes ensuring mechanical strength.
5.
FIELD
WINDING: - The
field winding is made from hard drawn silver bearing copper. Rotor winding is
held in position against centrifugal forces by duralium forces wedges in the
slot portion & by non magnetic steel retaining rings in the over hang
portion. Gap pick up system is employed for direct hydrogen cooling of rotor
winding. Several groups of ventilation ducts are mulled on the sides of the rotor
coil for gas passage. The rotor slot wedges are of special profiles with
elliptical holes rolled in to match the ventilation ducts on the windings
stacks. The end windings are insulated from rings with the help of glass epoxy
molded segments. Copper segmental type damper winding is provided in the end
zone of rotor morrows to prevent over heating of returning rings during
asymmetrical & asynchronous operation.
6.
SHAFT
MOUNTED FANS: - For
circulating the cooling gas inside the generator, two propeller type fans are
shaft mounted on this & of rotor body fan hubs are made from alloy forging
and are hot fitted on the Rotor shaft with sufficient interference. The steel
cast fan blades are machined in the tail portion to suit the fan hub and held
in position with the help of conical pins. The blades can be easily removed
from or assembled in the fan hub. Fan shields fixed to the end shields. Guide
the flow of Gas through the fan sections.
7. SLIP RINGS: -
The slip ring consists of helically grooved Allow steel rings shrunk on
the rotor shaft & insulated from it. For convenience in assembly both the
rings are mounted on a single common steel bush, which has an insulated jacket
pre moulded on it. The complete bush with slip ring is shrunk on the rotor
shafts. The slip rings are provided with inclined holes for self- ventilation.
The slip rings improve brush performance.
REFERENCES:-
- www.wikipedia.org/wiki/Panipat_Thermal_Power_Station_I
- www.hpgcl.gov.in
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