Power Plant Guruji

[Hindi] Power Plant Exam | NSPCL , IOCL , NTPC , TATA STEEL Experience ...

2019-10-02T17:01:00.001+05:30

Power Plant Exam | NSPCL , IOCL , NTPC , TATA STEEL Experience Basis Po...

2019-10-01T14:25:00.001+05:30

Centrifugal Pump | Difference Between Pump Head And Pressure

2019-09-30T18:05:00.001+05:30

Power Plant Exam | NSPCL , IOCL , NTPC , TATA STEEL Experience Basis Po...

2019-09-29T16:28:00.001+05:30

Power Plant Departmental Exam | IOCL , NTPC , TATA STEEL Experience Basi...

2019-09-28T18:04:00.001+05:30

Thermal power plant performance || Specific coal consumption of power plant

2019-09-26T21:42:00.001+05:30

Need for Pre-commissioning Checks in Boilers | Boiler - Power Plant Guruji

2019-08-16T17:49:00.000+05:30

Pre-commissioning Checks in Boilers

Pre–commissioning check up are done to identify the fault points so that corrective actions can be taken in time which can helps the commissioning programme can be carried out without unnecessary delays .

Different Activities During Pre-commissioning Of Boiler

Trial run of equipments
Pre –commissioning Tests
Alkali boil out
Thermal flow tests
Chemical Cleaning
Steam Blowing
Safety Valve Setting

Trial run of equipments

Running the equipment for some time with all the interlocks and protections, indications etc.

Check freeness of movements, full travel and full closure of like dampers, gates, valves, etc.

Pre –commissioning Tests

Gas tightness , air pressure and hydraulic test on the boiler pressure parts are carried out to identify and rectify leakage points in the systems.

Alkali boil out

It is carried out to remove oil grease and

impurities adhering to the interior of the pressure parts after erection of the boiler has been completed.

Alkali boil out operation is performed

at 40 kg/ cm2 gauge pressure with 1000 ppm tri-sodium phosphate for 24 hours, the boiler is fired for the process.

Steam Blowing

In steam blowing process purging of super heaters and steam pipe lines is carried out with the help steam .

Puffing method of steam blowing is used .

Re heater safety valves are floated during steam blowing

Thermal flow tests

To detect possible chocking in the boiler
tubes thermal flow test is carried out.

The water wall tubes, economisers and superheaters tubes are normally checked by means of this test.

Safety Valve Setting

The drum and super heater safety valves are required to be set to operate at the desired pressure after steam blowing operations is completed.

Commissioning of the Boiler

After completion of the pre commissioning

activities the unit is made ready and the boiler is under going commissioning and

reliability run.

P.C.Nayak

Power Plant Operation

Steam Turbine Eccentricity - Turbine Supervisory System

2019-08-16T00:06:00.000+05:30

Steam Turbine Eccentricity

What is eccentricity

Eccentricity is the very important parameters to monitor the conditions of turbine.

Every machine, is built up with certain amount of eccentricity on account of the deficiency in machining, sag due to its weight and the clearance at the bearings.

This eccentricity level starts increasing temporarily during its starting, normal running and shut down periods due to following causes

Temperature causes
Mechanical causes

Tempreature Causes Eccentricity

If non-uniform heating and cooling of turbine rotor during turbine start-up, load changes and casting down period take place.
when the steam leakages are uneven or the sealing steam temperature is abnormal then uneven temperature gradient increases the eccentricity level temporarily.
Uneven cooling due to improper lagging or water splashes causes the eccentricity to increase.

Mechanical Causes Eccentricity

Mechanical causes such as rubbing, faulty couplings, wearing of bearings etc. also increases the eccentricity level .
All these causes increase the eccentricity level, though temporarily, they get settled to a permanent eccentricity if corrective measures are not taken.

Unit To Measure Eccentricity

Eccentricity is measured in microns or millimeters.

How To Measure Eccentricity

Eccentricity measured as a deviation of the mass centre from the geometrical centre of the bearing journal.
This is simply proportional to the maximum rotor deflection occurring at the middle of shaft.
The rotor deflection shifts the centre of gravity of the rotor thus creating an unbalance in the rotating mass which in turn generates excessive vibrations when the machine is running at normal speeds.
Thus eccentricity measurements provide information on the onset of vibration even when the machine is at bearing gear speed or at low speeds.

P.C.Nayak

Power Plant Operation

Steam Turbine - Working Principle And Basic Parts Of Steam Turbine

2019-08-15T10:20:00.000+05:30

Steam Turbine

Basic Parts Of Steam Turbine

A steam turbine's two main parts are the cylinder and the rotor.
The cylinder (stator) is a steel or cast iron housing usually divided at the horizontal centerline.
Its halves are bolted together for easy access.
The cylinder contains fixed blades, vanes, and nozzles that direct steam into the moving blades carried by the rotor.
Each fixed blade set is mounted in diaphragms located in front of each disc on the rotor, or directly in the casing.
A disc and diaphragm pair a turbine stage. Steam turbines can have many stages.
The rotor is a rotating shaft that carries the moving blades on the outer edges of either discs or drums.
The blades rotate as the rotor revolves.
The rotor of a large steam turbine consists of high, intermediate, and low-pressure sections.

Working Principle Of Steam Turbine

In a steam turbine, steam at a high pressure and high temperature enters the first row of fixed blades or nozzles through an inlet valve or valves. As the steam passes through the fixed blades or nozzles it expands and its velocity increases.

The high-velocity jet of steam strikes the first set of moving blades. The kinetic energy of the steam changes into mechanical energy, causing the shaft to rotate. The steam then enters the next set of fixed blades and strikes the next row of moving blades.

As the steam flows through the turbine, its pressure and temperature decreases, while

its volume increases. The decrease in pressure and temperature occurs as the steam transmits energy to the shaft and performs work. After passing through the last turbine stage, the steam exhausts into the condenser or process steam system.

Impluse Turbine Working Principle

The kinetic energy of the steam changes into mechanical energy through the impact (impulse) .
An impulse turbine uses the impact force of the steam jet on the blades to turn the shaft.
Steam expands as it passes through the nozzles, where its pressure drops and its velocity increases.
As the steam flows through the moving blades, its pressure remains the same, but its velocity decreases.
The steam does not expand as it flows through the moving blades.
Another type of impulse turbine is a pressure-compounded turbine .
It consists of two or more simple impulse stages contained in one casing.
The casing contains diaphragms that connect to nozzles.
The nozzles make efficient use of the steam pressure that remains after the steam flows through the previous stage.
The pressure drops in each stage as steam expands through the nozzles.

Reaction Turbine Working Principle

A reaction turbine uses the "kickback" force of the steam as it leaves the moving blades and fixed blades have the same shape and act like nozzles .
Thus, steam expands, loses pressure and increases in velocity as it passes through both sets of blades.
All reaction turbines are pressure compounded turbines

Impulse And Reaction Turbine

Many large turbines use both impulse and reaction blading.
These combination turbines usually have impulse blading at the high-pressure end, and reaction blading at the low pressure end.
The blade length and size increases throughout the turbine to use the expanding steam efficiently.
Blade rows require seals to prevent steam leakage where the pressure drops.
Seals for impulse blading are located between the rotor thediaphragm to stop leakage past the nozzle.
Seals for reaction blading are located at the tips of both the fixed and moving blades.

P.C.Nayak

Power Plant Operation

What is acidity and alkalinity? | Power plant interview question

2019-08-14T07:54:00.001+05:30

Alkalinity and Acidity

Alkalinity

The property of a solution that causes the presence of free hydroxyl ion has been referred to as basicity or alkalinity. But alkalinity has a specific meaning in water chemistry, the ability to neutralize acidity.

Measure Unit

Alkalinity is measured in some specific unit of concentration, commonly parts per million (ppm).

Acidity

Acidity is the ability to neutralize alkalinity.

Acids form free hydrogen ions (H+) .

Measure Unit

Acidity is measured in ppm.

Why Alkalinity and Acidity are measured

Alkalinity and acidity are invariably measured when characterizing the quality of a water. Knowing these properties helps to predict the behaviour of any water in

service, practically whether it will form scale or be corrosive.

Alkalinity and Acidity are consists

The alkalinity and acidity in natural waters always consists of free carbon dioxide,

carbonate ions, bicarbonate ions, hydroxyl ions, or some combination of these

components. In rare instances raw water will contain some other alkaline or acid

ion as well, but this situation is so unusual that it is generally ignored.

P.C.Nayak

Power Plant Operation

Conductive Level Measurement Working Principle

2019-08-14T00:30:00.000+05:30

Measurement principle

The system consists of number of conductors of different lengths connected together by a series of resistors. As the level increases more and more conductors are shorted together, so
shorting out the resistors joining them, thus the overall resistance will decrease.

If a constant voltage is applied across the terminals, then as level increase, resistance

decrease, hence the current flowing in the circuit will increase. Therefore current will be proportional to the level. If an ammeter is placed in series with the circuit, then it will indicate the
current flowing in the circuit. Since the current is proportional to level the ammeter can be
calibrated directly in terms of level.

Applications

For switching off pumps when running dry and indicating an empty tank to avoid wear and tear and production stoppage
For maintaining a constant level to avoid material wastage

Advantages

Multi-point detection with one process connection
Simple, cost-effective measuring principle

P.C.Nayak

Power Plant Operation

Hydra Step Drum Level Indicator Working Principle

2019-08-13T23:44:00.001+05:30

Hydrastep System

Basic Principle of the Hydrastep System

The principle upon which the Hydrastep is based is that of the differing electrical resistivities of water and steam.

This difference exists, the vertical arrangement of electrodes in the vessel, each of which is connected to a separate detector vessel, each of which is connected to a separate detector circuit, enables the level to be determined at which the transition occurs between water and steam values.

How to Work

Each electrode, with its associated portion of the vessel, forms a cell in which the resistance measured is a function of the contents of the cell. Except at the interface, each cell is filled either with steam, (high resistance) or with water (low resistance); at the interface for a continually falling water level (gradually increasing cell resistance) the corresponding channel of

the detector follows the curve shown. As the output voltage reaches about +4.5 VDC, the corresponding logic circuit changes to indicate steam. A small amount of hysteresis is built in so that in the reverse direction the change back to water occurs at about +3.5 V DC, to avoid excessive operation due to insignificance level fluctuations.

Resistivities of water and steam at Elevated Tempreature

At the time that the use of a direct electrical measurement was first considered for the

determination of drum level, little was known of the resistivities of water and steam at elevated temperatures as exhibited in a dynamic system with continuous condensate flow through a side-arm vessel from the boiler drum. A series of measurements was made, therefore, using the vessels designed for the field trial equipments, on boiler in the 110 and 183 bar groups. These measurements are presented and show that up to 360 deg.C

Adequate Differential

An adequate differential for Hydrastep exist between the resistivities of the water and the stream in a side arm–gauge at boiler pressures up to about 216.5 bar &

, Tsat 372.8 deg.c

Electronic Circuit

To ensure absolute safety to personal the maximum voltage which appears at an electronic terminal is 10v rms, and its maximum short circuit current is 10 uA, 50 Hz. Each electrode circuit therefore meets the requirements for intrinsically safe apparatus with a margin of safety of five

orders of magnitude in respect of current. At 10 uA, the maximum electrode current is only one-fortieth of the 0.55% human perception current at 50 Hz.

The potential on each electrode is applied to its own individual discriminator channel to control an output electromagnetic relay carrying six sets of changeover contacts.

One set of contacts is used for display purpose in the control room of either water or steam, as appropriate, for each channel or the electronics, each display module being arraigned in the order corresponding to the disposition of the associated electrodes in the vessel. Two further

sets of contacts on each relay are used in a logic matric to raise an alarm should a fault. Occur such that any channel is ‘out-of-step’, i.e. that it gives an indication which is physical impossibility such as “water above steam” or “steam below water”. The three remaining contact sets are available for high or low level alarm purposes, or for

additional logic configurations to provide validated control signals, alarms and / or emergency tripping of the generator and its auxiliaries.

P.C.Nayak

Power Plant Operation

Steam Jet Air Ejector Theory- How Steam Jet Ejector Work & Its different Application

2019-08-11T23:21:00.000+05:30

How Does a Steam Jet Air Ejector Work ?

A steam jet air ejector (SJAE) is a device which uses steam motion to carry another fluid called suction fluid(steam,non condensable gases)

Air Ejector Working Principle

The air ejector works on the basic principle of convergent / divergent nozzle which creat venturi effects & helps to draw suction fluid.

Convergent Nozzle

In convergent nozzle the steam velocity increase where as its pressure decrease.

Divergent Nozzle(Diffuzer)

In divergent nozzle the steam pressure increase where as its velocity decrease.

How to workh

A steam is used as the motive fluid to withdraw air and dissolved gases from the condenser by the ejector action. In each stage of the steam jet ejector, high pressure steam is expanded in a convergent /divergent nozzle. The steam leaves the nozzle at a very high velocity in the order of 1220 m/s and a proportion of the kinetic energy in the steam jet transferred by interchange of momentum to the body of air which entrained and passes along with the operating steam through a diffuser in which the kinetic energy of combined steam is re-converted to pressure energy.

Appliction of Air Ejectors:

The following are the given field where ejector are used.

1.Steam Jet Air Ejector

2 .Fresh Water Generator

3 .Self Priming of Centifual Pumps

Writer

P.C Nayak

Temperature Measuring Instruments In Power Plant | Power plant interview question

2019-08-11T20:13:00.000+05:30

TEMPERATURE MEASURING INSTRUMENTS

Why Measuring Instruments are Important

Accurate measurement of temperature is required to assess the material fatigue, heat balance, heat transfer etc.

Measuring Medias

Temperature measurement is to made in many medias such as water/stream, oil (fuel oil and lubricating oil), air fuel gases,

hydrogen gas, metal temperatures of bearing babbits, turbine top and bottom, generator winding and cores, S.H. tube metal etc.

Selection of Tempreature Measuring Instruments

The selection of thermometer depends upon the range of the temperatures to be measured. These instruments are available with electrical contacts for setting up annunciation and protection system wherever required.

For local indication mercury in glass, mercury in steel, vapour filled or gas filled

are used

Remote Tempreature Measuring Instruments

Resistance thermometer or thermocouples are used as primary sensors in remote

measurement of temperatures depending upon the range.

Resistance Thermometer

Resistance thermometer are of platinum and copper resistance type.
Platinum resistance thermometers are calibrated to have46 ohms or 100 ohms at 0 deg.C.
The secondary instruments used in conjunction are cross coil indicators or electronic bridges.
These instruments indicate temperature by measuring the nature of resistance which changes with the change in temperature.
Resistance thermometers are generally used up to 300 deg. C

Thermocouples

Above 300 deg. C, thermocouples are used as primary sensor.
The common type of thermocouples used in thermal power station are chromel-alumel or chromel-copel depending upon the temperature.
Iron constantan is another thermocouple in use.
The secondary instruments for thermocouple sensor are pyrometriv millivolt meters or electronic potentiometers.
Null balance method is used for the very accurate measurement of millivolts generated by thermocouples sensing the process temperatures.

P.C.Nayak

Power Plant Operation

Primary cause of scale formation in Boilers

2019-08-11T10:46:00.000+05:30

Scale Formation

The process of deposition of mineral constituents in boiler on metal

surfaces is called scale formation.

Primary Cause

The primary cause of scale formation is

the fact that the solubilities of scale forming salts decrease with increase

in temp. Consequently, the higher the temp. and pressure of boiler

operation, the more insoluble the encrusting salt become and may tend to

form strong adherent scale on the evaporation surfaces. Amongst the

natural substances found in water are salts of calcium and magnesium,

which may give rise to scale formation. It is this particular salt which give

water its “Hardness”.

How to prevented Scale formation

Scale in boiler can be prevented by removing hardness salts from make

up water, so that no calcium and magnesium enter the boiler from this

source and by internal chemical treatment of boiler water to deal with any

trace which may enter the system.

In modern boiler, all the impurities forming scale is removed before the water enters the boiler.

What happen due to scale formation

Scale formation provides over-heating of tubes, less heat transfer and finally leads to tube leakages.

P.C.Nayak
Power Plant Operation

What will be happen if cfbc boiler bed height is too low

2019-08-10T01:06:00.000+05:30

What will be happen if cfbc boiler bed height is too low

Problem due to bed height is very low

1.Bed tempreature will be very high i.e beyond the desire limit

2.Due to very high bed tempreature there will be chance of clinker formation

in furnace bed

3. Bed nozzle will be chock due to clinker formation on bed

4.At very high tempreature coal will be fuse which result clinker formation in bed

Reason of bed height very low

1.Due to very high quality coal i.e high GCV coal

2. Due to ash percentage very low in coal there will be very low bed inventory produce in furnace

3. Due to Cyclone chock there is no return of bed matterial through cyclone

4. If loop seal air pressure not ok there will be chance of cyclone return path chockage

Action taken to solve bed height very low

1.Maintain bed height by taking sand or bottom ash in furnace through sand silo passes

2.Clear cyclone chockage

3.Check loop seal air pressure if not ok then supply the air with proper pressure

P.C.Nayak

Power Plant Operation

What will be happen if cfbc boiler bed height is too heigh ??

2019-08-09T08:12:00.001+05:30

What will be happen if cfbc boiler bed height is too heigh ??

Reason of bed height high

1.Due to very low quality coal i.e very low GCV Coal

2. Due to ash percentage high in coal

3. If ash evacution system failure or not properly work

4. Due to wind box tempreature low

5. Due to bed nozzle chock

6. Malfunction of wind box tempreature transmitter

Problem due to bed height high

1.Bed tempreature will be low

2.Furnace draft will be towards positive due to which boiler explosion situation arise

3.Due to too much bed height not proper combustion of coal inside the furnace which causes large amount of unburnt formation

4.Both PA & ID fan taking high amps due to which there will be chance of both pa & id due to over load

5. Evaporation ratio will be low

P. C. Nayak

Power Plant Operation

Power Plant performance analysis

2018-12-22T23:52:00.000+05:30

Power Plant performance analysis at various steps help in improving the power generation capacity. The points that are mainly responsible for the unit/station performance are described below

1. Planned Maintenance loss.

2. Thermal efficiency factors.

3. Plant load factor.

4. Forced outages.

5. Plant Availability factor.

Principles of Combustion

2017-10-05T23:00:00.001+05:30

The primary function of oil and coal burning systems in the process of steam
generation is to provide controlled efficient conversation of the chemical energy of the
fuel into heat energy which is then transferred to the heat absorbing surfaces of the
steam generator. The combustion elements of a fuel consists of carbon, hydrogen and
usually a small amount of sulphur. When combustion is properly completed the exhaust
gases will contain, carbon dioxide, water vapour, sulphur dioxide and a large volume of
Nitrogen, Combustion is brought about by combining carbon and hydrogen or
hydrocarbons with the oxygen in air. When carbon burns completely, it results in the
formation of a gas known as carbon dioxide. When carbon bums incompletely it forms
carbon monoxide.

Composition of air: the supply of oxygen for combustion is obtained from air. This is as
important as the supply of fuel. The average composition of air is
79% nitrogen and 21% oxygen by volume
77% nitrogen and 23% oxygen by weight
Nitrogen does not bum but passes through the combustion chamber to the chimney
unchanged excepting its temperature.

Ignition: Fuel must be ignited before it can burn. Combustion is brought about by
raising the temperature of the fuel to its ignition temperature. This temperature varies
with different fuels.

Excess air: The amount of air required to burn any fuel can be calculated if the amount
of the elements present in the fuel are known. This amount of air is known as the
theoretical air. In practice this quantity is not sufficient to ensure complete combustion
and extra air has to be supplied. This extra air is known as excess air.

The loss of combustibles and unburnt gas loss reduces as excess air is added reaches
a maximum and any further additions of excess air beyond this stage, the boiler losses
increase. Thus there is one and only one quantity of excess air, which will give the
lowest combustion loss. The value of excess air needed depends upon the fuel used,
the type of firing etc.

Combustion process

The following factors in efficient combustion are usually referred to as "The three T's.

Time: It will take a definite time to heat the fuel to its ignition temperature and having

ignited, it will also take time to bum. Consequently sufficient time must be allowed for

complete combustion of the fuel to take place in the chamber.

Temperature: A fuel will not burn until it has reached its ignition temperature. The

speed at which this Temperature will be reached is increased by preheating the

combustion air. The temperature of the flame of the burning fuel may vary with the

quantity of air used. Too much combustion air will lower the flame temperature and

may cause unstable ignition.

Turbulence: Turbulence is introduced to achieve a rapid relative motion between the air

and the fuel particles. It is found that this produces a quick propagation of the flame

and its rapid spread throughout the fuel/air mixture in the combustion chamber.

Combustion efficiency: It varies with individual different grades of fuel within each

boiler. The idea to be aimed at, is the correct quantity of air together with good mixing

of fuel and air to obtain the maximum heat release. Maximum combustion efficiency depends on

• Design of the boiler

• Fuel used

• Skill in obtaining combustion with the minimum amount of excess air.

Thermal efficiency of a boiler is measured by the amount of heat transferred to the

water in the boiler by each Kg of fuel used and is expressed as a percentage of the

total heat energy in one Kg. of fuel. The thermal efficiency is dependent on the factors governing efficient combustion.

Author

Power Plant Guruji

Know About Turbine Protection System

2017-10-02T19:51:00.000+05:30

Now-a-days, steam turbine stands as a most important prime mover for large scale

energy production in thermal and nuclear power stations. A steam turbine consists of

regulated quantity of steam flowing over an alternate series of fixed and moving blades.

In a turbine, the heat energy of steam is converted into mechanical energy in terms of

torque at a certain rpm and thin in turn is converted into electrical energy in generator.

When a generating unit is in operation, equipment or operation error can result in

dangerous conditions effecting equipment and/or operator safety. In a small generating

unit with few auxiliary equipment, the operator can take action in time to any failures

and can ensure safe conditions. However, with large units, the no. of auxiliary

equipment has increased and the operation has to be remote from centrally located

control room. So in order to provide safety the remote control system is equipped with

protection and interlocks.

An interlock can be stated to be a condition or state that is a prerequisite to a

subsequent stage in operation or control. A motor with a journal bearing should be

started only after ensuring that the bearings have an established film of lubricating oil

and an assured supply of lub oil is established. Thus the starting of the motor is

interlocked with lub oil pressure or flow. This starting interlock is introduced in the motor

starting circuit in such a way that the motor .can be started only if the tub oil pressure is

adequate and the condition is called a permissive.

In this example continued running of the motor with the absence of lub oil flow is

harmful to the bearings and consequently to the motor. This is a failure and the motor is

required to be provided with protection against such a failure. Thus the protection of

protective interlock in this case is to automatically disconnect the motor when the lub oil system drops below a certain value. In both the above operations the permissive and

protection interlock are set to operate at a particular set value.

Turbine Protection System Overview

The modern steam turbines are generally provided with the following protections to trip

the turbines:

1. Lubrication oil pressure dropping to impermissible value.

2. Vacuum in condenser dropping to impermissible value.

3. Speed rise upto 111 to 112%.

4. Speed rise upto 114 & 115%.

5. Impermissible axial shift.

6. Main steam and reheat steam temperature dropping to impermissible values.

7. Condensate level in H.P. heater rising to impermissible level.

8. Operation of generator protection

9. Manual tripping

10. Governing oil pr. falling to inadmissible value.

There will be a number of such interlocks and protections that are required with the

large number of auxiliary equipment of both boiler and turbine generator units.

Thank's

Power Plant Guruji

PRINCIPLES OF RELAYS

2017-10-02T17:37:00.000+05:30

Every electrical equipment is designed to work under specified normal conditions. In
case of short Circuits, earth faults etc., an excessive current will flow through the
windings of the connected equipment and cause abnormal temperature rise, which will
damage the winding. In a power station, nonavailability of on auxiliary, at times,
may cause total shut down of the unit, which will result in heavy loss of revenue.

So, in a modern power system, to minimise damage to equipment two alternatives are
open to the designer, one is to design the system so that the faults cannot occur and
other is to accept the possibility of faulty and take steps to guard against the effect of
these faults. Although it is possible to eliminate faults to a large degree, by careful
system design, careful insulation coordination, efficient operation and maintenance, it
is obviously not possible to ensure cent percent reliability and theretofore possibility of
faults must be accepted; and the equipment are to be protected against the faults. To
protect the equipment, it is necessary to detect the fault condition, so that the
equipment can be isolated from the fault without any damage. This function is
performed by a relay. In other words, protective relays are devices that detect
abnormal conditions in electrical circuits by constantly measuring the electrical
quantities, which are different under normal and faulty conditions. The basic
quantities, which may change during faulty conditions, are voltage, current, frequency,
phase angle etc. Having detected the fault relay operates to complete the trip circuit
which results in the opening of the circuit breaker there by isolating the equipment
from the fault. The basic relay circuit can be seen in fig.

Basic Relay Circuit

Thank's

Power Plant Guruji

Losses In Steam Turbines

2017-10-01T07:29:00.000+05:30

Steam Turbine

Steam Turbine Losses

Stage Losses

One of the main cause of inefficiency of a stage is friction and eddies on the

blade surface. Other factors that affect the stage efficiency are

Windage Loss

Windage, disc friction, or rotational losses occur because the rotors are

revolving in an atmosphere of steam. The windage loss basically comes from

the drag of steam on revolving blades in the steam atmosphere. The drag

depends on viscosity of fluid (density increases viscosity) and linear velocity of a

stage. Both HP and LP blades do suffer to the same extent owing to the fact that

the latter have high linear velocity though the viscosity of atmosphere is much

less. The windage loss on LP stages increases at low load thus increasing the

exhaust hood temperature.

Blade Length

Short blades are less efficient than long blades because of interference caused

by roots and tips. This is an advantage for high rating turbines at HP stages.

Partial Admission Loss

Steam regulation at turbine inlet are done in two ways. Throttle governing, where

all control valves operate simultaneously and nozzle governing where control

valves operate in a sequence. Blades directly opposite to the nozzle block are

running full of steam but the blades away from nozzles will produce eddies and

extra losses. This loss which is found in nozzle controlled turbines due to steam

being admitted around part of the periphery only is known as partial admission

loss.

Interstage Gland and Tip Clearance Loss

The reaction stages there is a pressure drop across the moving blades and the

clearance between them and the casing is sealed by providing radial or axial

seals. Inter stage seals are also provided between root diaphragms and the rotor.

If gland leakage annulus area is 1% of blade area the steam flow through gland

will be 0.2 to 0.5%. Loss of efficiency due to this leakage 0.3 to 0.75% (i.e. 50%

greater than actual leakage because of turbulence and disturbance in main steam

path). This loss depends on shaft and blade sizes and type of labrinth used.

Normal value for modern turbines is between 1/3 to 1%. One bad start with

eccentric shaft causing rub could easily increase clearance to large extent

incurring heavy efficiency Joss.

External Gland Loss

External gland leak off also causes of available energy but this loss is not 1% for

every 1% leakage because same heat value of leak off is utilized in Gland steam

coolers with and without ejectors. Low-pressure gland leak off is sucked by gland

steam cooler with ejector which* also forms a part of regenerative feed heating

system.

Wetness Loss

Wet steam causes a loss of stage efficiency of 1% for every 1% water because of the water droplets lagging behind the steam and thus reducing the efficiency with

which energy conversion takes place. This is one of the important cause of

erosion which permit to restrict moisture to 12% in last rows of LP.

Leaving Loss

The KE of steam represented by residual velocity of steam leaving the stage is

known as leaving loss. It is the energy which cannot be practically converted into

mechanical work.

Turn Up Loss and Exhaust Hood Pressure Drop

These two also constitute the part of exhaust losses of which leaving loss is pre

measure factor. Turn up loss occurs at low steam flows. It is because of the fact

that last stages become progressively less efficient as steam flow fall below 30%

MCR. This exhaust overheating may require hood sprays.

Exhaust hood pressure drop is also a loss of available energy amounting to the

difference between the energy level (enthalpies) at condenser and IP turbine

exhaust.

Mechanical Losses

Mechanical losses are bearing losses plus power required to drive oil pump and

governors. They are constant irrespective of load.

Thank's
Power Plant Guruji

Types of Relay used in power plant for protection

2017-10-01T04:08:00.001+05:30

Types Of Relay images

Types Of Electrical Relay

Every electrical equipment is designed to work under specified normal conditions. In

case of short Circuits, earth faults etc., an excessive current will flow through the

windings of the connected equipment and cause abnormal temperature rise, which will

damage the winding. In a power station, nonavailability of on auxiliary, at times,

may cause total shut down of the unit, which will result in heavy loss of revenue.

So, in a modern power system, to minimise damage to equipment two alternatives are

open to the designer, one is to design the system so that the faults cannot occur and

other is to accept the possibility of faulty and take steps to guard against the effect of

these faults.

To protect the equipment, it is necessary to detect the fault condition, so that the

equipment can be isolated from the fault without any damage. This function is

performed by a relay. In other words, protective relays are devices that detect

abnormal conditions in electrical circuits by constantly measuring the electrical

quantities, which are different under normal and faulty conditions. The basic

quantities, which may change during faulty conditions, are voltage, current, frequency,

phase angle etc. Having detected the fault relay operates to complete the trip circuit

which results in the opening of the circuit breaker there by isolating the equipment.

Classification of Relays

Depending upon their principle of operation they are classified as:

Electromagnetic attraction type relays:

These relays operate by virtue of a plunger

being drawn into a solenoid or an armature being attracted towards the poles of an

electromagnet.

Induction type relays: In this type of relay a metal is allowed to relate between two

electro-magnets. The fields produced by the two magnets are displaced in space &

phase. The torque is developed by interaction of the flux of one of the magnets and the

eddy current induced with disc by the other.

Thermal relays: They operate due to the action of heat generated by the passage of

current through the relay element. The strip consists of two metals having different

coefficients of expansions and firmly Fixer) together throughout the length so that

different rates of thermal expansion of two layers of metal cause the strip to bend

when current is passed through it. This principle is used in these relays.

Static relays; Employ integrated circuits, transistors, comparators etc. too obtain the

operating characteristic.

Moving coil relays: In this relay a coil is free to rotate with magnetic field of a

permanent magnet. The actuating current flows through the coil. The torque is

produced by the interaction between the field of the permanent magnet and the field of the coil.

Relays can be classified depending upon their application also:

- Overvoltage, over current and overpower relays, in which operation takes place

when the voltage, current or power rises above a specified value.

- Under voltage, under current under frequencies low power relays, in which

operation takes place when the voltage, current frequency or power fall below a

specified value.

- Directional or reverse current relays: In which operation occurs when the

directional of the applied current changes.

- Distance relays: In this type, the relay operates when the ratio of the voltage &

current change beyond a specified Limit.

- Differential relays: Operation takes place at some specific phase or magnitude

difference between two or more electrical quantities.

Relays can also be classified according to their time of operation.

- Instantaneous relay: In which operation takes place after negligibly small

interval of time from the incidence of the current or other quantity causing

operation.

- Definite time lag relay: This operator after a set time lag, during which the

threshold quantity of the parameter maintained.

- Inverse time lag relays: In which the- time of operation is approximately

inversely proportional to the magnitude of the parameter causing operation; the

philosophy behind it is when more fault current flows the protection should

operate faster and vice-versa.

Thank's

Power Plant Guruji

Measurement PH of feed water used in Thermal power plant BoilerMeasurement PH of feed water used in Thermal power plant Boiler

2017-09-27T01:03:00.000+05:30

Measurement PH of feed water used in Thermal power plant Boiler....?

Defination of PH

Relationship is used to express relative degree of acidity or basicity in terms of the hydrogen ion concentration. This

relationship has been given the name pH.

It is defined mathematically in terms of the logarithm of the hydrogen ion concentration

Range Of pH Values

A neutral solution has a pH of 7.
An acid solution has a pH less than 7.

3. A basic solution has a pH greater than 7.

Measurement Of pH

The pH of a solution can be determine directly by measuring the

voltage developed across a cell composed of two electrodes and

the solution to be tested. The pH meter is a sensitive voltmeter

whose output is calibrated in pH units. One of the two electrodes is

a reference electrode, and the other is an electrode made of a pH-

sensitive glass. As the H+ concentration of the solution changes, the

voltage developed between the reference electrode and the glass

electrode also changes. The pH meter measures the voltage

developed in pH units.

Since the electrodes are sensitive to temperature, the temperature

of the test solution must be measured, and a compensating dial on

the pH meter must be adjusted. Some pH measuring systems

measure the temperature and adjust the meter automatically.

These automatic systems are generally used for the on-line pH

meters that are installed in plants.

A pH meter is always calibrated with a solution of known pH to

ensure that it operates properly. The solutions used are called

Buffer Solutions, because they maintain constant pH over a range

of concentrations and in the presence of small amounts of acidic or

basic impurities.

Author

P.C.Nayak

Power Plant Operation