Electrical Systems in Power Plant - By energo engineering ETEs

7/31/2019 Electrical Systems in Power Plant - By energo engineering ETEs

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Electrical Systems in a

Thermal Power Plant

Presented

By:

Group B4


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Electrical SystemElectrical system one of the most important components of apower plant. With the help of this system the mechanical energyis converted to electrical energy and is distributed to variousconsumers according to their requirements.

Components:

Air Cooled generators

Digital voltage regulator Numerical protection relays for fastest response

Fault data recorder

SF6 circuit breaker for high voltage applications

Energy management system

Real time display of generation, dispatch and auxiliaryconsumption

SCADA (supervisory control and data acquisition) for remoteswitchyard operation and data transfer of load dispatch centre

Centralized monitoring of HT motor protection relays


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Contents

Boiler

Turbine

Generators

Transformers

Distributed Control System

Illumination

Fire Barriers Earthing


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Control System Operation of the power plant must be coordinated to meet the

electricity demand and the production process must be regulatedso that the cycle and the equipment are operated with design

limits

Control system provides integrated interface that is responsible

for monitoring and controlling its boiler and turbine-generator,and also for all other tasks as well, such as data management

and technical-service support.

Control system functions:

Acquisition & Processing of process data.

Open loop and closed loop control.

Open loop system is a non feedback type system relying only on the

current and the model of the system

Closed loop system gets feedback from the system and adjusts itself

accordingly

Calculation and optimization of the plant performance


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Control System

A distributed control system is one in which the controller

elements are not central in location but are distributed

throughout the system with each component sub-system

controlled by one or more controllers

Entire system of controllers is connected by networks for

communication and monitoring

The plant's information and control systems are determined

based on requirements of mechanical and electrical engineering

To ensure maximum operational surveillance and ease of

operation a basic system plan is created;

the system's configuration is drawn up;

the system's input output information is collected;

control logic diagrams are prepared;

logic of the plants automation systems is examined carefully.


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Operator Work Station

Alarm Monitoring

Mimic/graphic display

Trend Display

Operator guidancedisplay

System and diagnostic

display

Control Bar chart

Sequence display

Fault analysis display


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Types of Control Systems

On-Off control systems produces a controlaction that varies in discrete steps.

Motor driven rotating equipment such as pumps,

fans, compressors and conveyors;

Motor operated shutoff valves and dampers; and

Solenoid operated equipment such as pneumatic

shutoff valves.

Modulating control systems produces a control

output system that varies smoothly from one

value to another

Mainly found in the Boiler Regulation Control,

Steam Turbine Automation Control, and CCS

(Coordinated Control System)


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Data Acquisition System (DAS)

Main task is to acquire the data from any kind ofinputs such as sensors via amplifiers,

multiplexers, and any necessary analog-to-digital

converters

The data is used for

Plotting: Bar Chart, Curve plotting, etc.

Alarm Monitoring

Recording of SOE (Sequence of Event)

quick identification of the cause of faults.

Display Real-time or Historical Trends

Provides information and analysis of different

parameters.


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Boiler A Boiler or steam generator essentially is a container into

which water can be fed and steam can be taken out at desiredpressure, temperature and flow.

Boiler should have a facility to burn a fuel and release the heat.

Functions of a boiler:-

To convert chemical energy of the fuel into heat energy To transfer this heat energy to water for evaporation as well

to steam for superheating.

The basic components of Boiler are

Furnace and Burners, Steam and

Superheating Low temperature superheater

Platen superheater

Final superheater


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Boiler fittings and accessories

Safety valve: to relieve pressure and prevent possible

explosion of a boiler Water level indicators: show the operator the level of fluid in

the boiler

Bottom blow down valves: provide a means for removingsolid particulates that condense and lie on the bottom of a

boiler Continuous blow down valve: allows a small quantity of

water to escape continuously. Its purpose is to prevent thewater in the boiler becoming saturated with dissolved salts Saturation would lead to foaming and cause water droplets to

be carried over with the steam - a condition known as priming Flash Tank: High pressure blow down enters this vessel

where the steam can 'flash' safely and be used in a low-pressure system or be vented to atmosphere while the ambientpressure blow down flows to drain

Automatic Blow down/Continuous Heat Recovery System:This system allows the boiler to blow down only when makeup


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Hand holes: for inspections & installation of tubes and inspection ofinternal surfaces

Steam drum internals, A series of screen, scrubber & cans (cyclone

separators)

Low- water cutoff: It is a mechanical means (usually a float switch) that isused to turn off the burner or shut off fuel to the boiler to prevent it from

running once the water goes below a certain point

Surface blow down line: It provides a means for removing foam or otherlightweight non-condensible substances that tend to float on top of the

water inside the boiler

Circulating pump: It is designed to circulate water back to the boiler after ithas expelled some of its heat

Feedwater check valve : A non-return stop valve in the feedwater line. Desuperheater tubes: A series of tubes or bundles of tubes in the water

drum or the steam drum designed to cool superheated steam.

Chemical injection line: A connection to add chemicals for controllingfeedwater pH.


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Steam turbines Steam turbines have been used predominantly as prime

mover in all thermal power stations. The steam turbines aremainly divided into two groups: - Impulse turbine Impulse turbines change the velocity of a

water jet. The jet pushes on the turbine's curved blades which

changes the direction of the flow. The resulting change inmomentum (impulse) causes a force on the turbine blades.

Impulse-reaction turbine Reaction turbines are acted on bywater, which changes pressure as it moves through the turbineand gives up its energy.

The turbine generator consists of a series of steam turbinesinterconnected to each other and a generator on a commonshaft. There is a high pressure turbine at one end, followedby an intermediate pressure turbine, two low pressureturbines, and the generator.


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AC Generator

Alternating voltage may be

generated by rotating a coil in the

magnetic field or by rotating a

magnetic field within a stationary

coil.The value of the voltage generated

depends on-

the number of turns in the coil,

strength of the field,

the speed at which the coil ormagnetic field rotates


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Stator electrical faults

Overload Over Voltage

Unbalanced Loading

Over fluxing

Rotor Electrical faults Loss of excitation

Loss of Synchronization

Failure of prime mover

Lubrication Oil failure

Over-speeding Rotor Distortion

Difference in expansion between rotating and stationary parts

Excessive Vibration

Core Lamination faults

Problems faced with Generators


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Generator protection

Designed to run at a high load factor for a large number of

years

The generator circuit protection should be designed in such a

way that Damage is kept to a minimum,

Machine is not subjected to abnormal condition

The machine and its auxiliaries are supervised by monitoring

devices Electrical and mechanical faults may occur, therefore

generators may be provided with protective relays which in

case of faults, quickly initiate a disconnection of the machine

from the system and , if necessary, initiate a completeshutdown of the machine.


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Various methods of Generator ProtectionOver and Under Voltage Protection

The under voltage relays are mainly installed for the purpose ofidentifying loss of PT voltage

Overvoltage relays are also used as backup to the over excitationduring normal operation

Synchronizer and Sync-Check Relays

Unit can be brought up to speed automatically and synchronized to the

system Before doing so, the amplitude of the voltages of the system and

generator terminal must be within a narrow margin

frequency difference between the machine and the system, must belower than a given value

Generator Differential Protection

It protects generator winding against internal faults like excess currentflow

Short-Circuit Protection

Voltage control is provided to differentiate between a low-current fault


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Reverse Power Protection

This protective function trips the unit when power flows from the

system to the generator.

Voltage Balance Protection

The main function of the voltage balance relay is to avoid false

tripping of other protection relays due to a loss of secondary voltage

feed

Volts/Hertz Protection

when a severe over excitation occurs, the most probable

result is partial or complete destruction of the cores

insulation

over excitation occur during run-up, prior to synchronization


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Over/Under Frequency Protection

results from full or partial load rejection or overloading condition

Load rejection can be caused by a fault in the system or load shedding

Overload conditions may arise from tripping a large generator or a

transmission line

Loss-of-Field Protection

removal of the source of excitation to the generator can happen by

unplanned opening of the field breaker, a failure of the exciter and a

short-circuit in the field winding

in a loss-of-excitation condition its speed increases by some amount

of up to 3 to 5% of normal.

A fully loaded unit that loses its field may experience serious damage

every quickly under these conditions. Therefore the protection against loss-of-field occurrences is set to

alarm and trip the unit relatively quickly

Stator and Rotor Thermal Protection

Generators have a number of RTDs (resistance temperature detectors)


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Breaker Failure Protection

Most faults involving the generator require tripping the line breakers.

Failure of any such breaker to operate properly results in loss of

protection and other abnormal conditions, such as motoring

breaker failure scheme is carried out by a combination of triggering

signals from the generator protective relays, over current relays and

breaker auxiliary switches, via a timer

Loss of Synchronism Protection based on the fact that the apparent impedance at the

generators terminals changes in a predicted manner during an unstable

condition

To minimize any harmful effects, the protection should separate the

generator from the system as soon as possible


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TransformerAccording to winding it can be core type orshell type

According to cooling it can be classified as AN, ON, ONAN, ONAF, OFAF,OFWF

It can be liquid filled (oil), air cooled or resin cast type

Transformer core:

provides continuous path for electromagnetic flux

made of cold rolled grain oriented alloy steel(CRGO), which reducedhysteresis loss and enabled the core to operate at higher flux density

specific loss in watt/kg is lowest in the direction of rolling

Transformer oil:

protects the core assembly from chemical attack

provides dielectric strength of the transformer system

provides efficient cooling system of the transformer

Transformer oil is a pure hydrocarbon mineral oil and generally paraffin base

Oil temp. indicator:

Operates on the principle of expansion of liquid with temperature Fitted with max pointer and two mercury switches to provide alarm and trip


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Relief vent:

Terminal pressure may be built up to very high value by a severe fault

Diaphragm breaks open and relieves the pressure if the pressure is morethan 35 KN/m2

Circuit breakers:

capable of making and breaking of electric circuit under normal and abnorma

conditions

DG system:

Turbo generator sets takes about 20-25 min for coasting down to barring

speed

essential to provide emergency oil supply to the turbine and generated

bearings

DG sets gives oil supply to scanners in steam generators and power

generation


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Illumination SystemThe auxiliary building shall be provided with:

Main Lighting system for full illumination under normal power supply

conditions and shall operate from 415/ 240V AC Power supply tapped from

respective 415V switchgear

Emergency lighting system for reduced illumination operated by DG supply

feeders during failure of main power supply. It will cover only 20% of fixtures

in the building and associated area

Minimum emergency lighting system for reduced illumination during failure

of main power supply with the help of 220V DC batteries/ supply feeders

Suitable no. of Portable lighting units


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Luminous Performance Characteristics of commonly usedLuminaries


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Illumination Levels

Depending on the size of the area, no. of luminaries can becalculated.


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Design of Illumination System

Illumination Calculations

Lighting Layouts of Control

Room

Lighting layout of Switchyard.

Single Line Diagrams

Bill Of Materials


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Fire Barrier Envelope system installed around electrical componentsand cabling that are rated by test laboratories in hours of

fire resistance and are used to maintain safe-shutdownfunctions free of fire damage

Encase the components they are protecting to reduce thethermal exposure to the protected component during

elevated fire conditions. Fire barriers are often employed to ensure that the plant

can safely shut down in the event of a fire.

Barriers protect important equipment until the fire detectionand automatic fire suppression systems operate.

In the unlikely event that an automatic fire protectionsystem fails to operate, the barriers continue to providepassive fire protection.

Fire rating is defined as the endurance period of a firebarrier or structure, which relates to the period ofresistance to a standard fire exposure before the firstcritical point in behavior is observed


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Materials for fire barriers Insulation materials limit the exposure to the heat transfer rate by

reducing the conductive heat transfer rate to the protected

cable/circuits in accordance with Fouriers Law. Example :

A.B.S., ACETATE, CERAMIC, EPOXY/FIBERGLASS

Intumescences materials reduce the heat transfer rate to the

protected cable/circuits by chemically absorbing heat energy.

This endothermic reaction causes the material to swell,

increasing in volume and decreasing in density. Example:

Graphite, Sodium silicate

Ablation materials reduce the heat transferred to the protected

cable/circuits by sublimation. When heated, the ablation material

is consumed (sacrificed) through sublimation and mass loss

which provides cooling and forms a thermal shield. Example:

Silicone

Hydrate materials contain chemically bound water that is used

up during a fire exposure by an endothermic reaction, which

maintain temperatures near 100C until the hydrate (water) is

converted into steam. Example: Hydrated alkali metal silicate


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Swelling of Intumescences materials


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EARTHING SYSTEM

Following basic requirements are to be satisfied so as to ensure a properand sound earthing system.

The earth resistance for the switchyard area should be lower than a

certain_limiting value in order to ensure that a safe potential gradient

is maintained in the switchyard area

The grounding conductor material should be capable of carryingthe maximum earth fault current without-overheating and mechanical

damage.

The maximum fault level in the 400 kV system has been estimated to

be 40 kA and this value of fault current to used is the design of earth

mat for the 400 kv substation.


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REQUIREMENTS OF A GOOD

EARTHING SYSTEM

All metallic objects which do not carry current andinstalled the substation such as structures, parts

of electrical equipments, fences, armouring

and sheaths of the low voltage power and control

cables should be connected to the earthingelectrode system..

The design of the ground conductor should take

care of the effect of corrosion for the total life

span of the plant


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Material

The material of the earthing conductors shall be asfollows :

a) Conductors above ground level and in built up

trenches Galvanized steel

b) Conductors buried in earth Mild steel

c) Earth electrodes Mild steel rod

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Electrical Systems in Power Plant - By energo engineering ETEs