unit 02a- elec equip in power station.ppt

8/10/2019 Unit 02A- Elec equip in power station.ppt

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Major

Electrical Equipments

in Power Stations


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ajor omponents o a

Power Station

Alternators- Hydro turbo generators, Steam turbine generators. Exciter and Excitation System Power Transformers Bus Bars

Voltage Regulators Lighting Arrestor Switches Air Break Switches, Isolators Circuit Breakers Protective Relays Reactors Power Line Carrier Current Equipments Metering Equipment-CTs and PTs, Energy Meters, Frequency

meters Control Room Equipments


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Alternators

The generator employed in power plants are threephase synchronous generators, called as alternators

Main types are Hydro-generators and Turbo Generators Used to generate electricity

Input to Hydro-generator is velocity or pressure ofwater and output is electrical power

Input to turbo generators is pressurized steam andoutput is electric power

Turbine used for hydro generators are Kaplan turbine,

Francis turbine Turbine used for turbo generators are impulse and

reaction turbines


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Alternators

Hydro Generators

Salient pole type alternator is used. Field winding is wound on rotors and

stator is used as armature. The frequency of supply is depends on

f=NP/120. As the speed of hydro turbine is lower, to

get required frequency, number of polesis high.

To provide large number of poles, thediameter of pole is large as compared toaxial length.

For impulse turbine the alternator is

horizontally mounted (for speed 100-1000 rpm) and for Francis and Kaplanturbine it is vertically mounted (forspeed 50-500 rpm)

Machines are usually air cooled and sizesvaries from 0.5MW to 1000MW.

SHAFT

Exciter

Altenator

Slip

Rings

Roto

r

3 Phoutput

Stato

r


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Alternators

Steam Generators

Cylindrical rotor (non-salient)typesynchronous generator is used

Field winding is wound on rotors andstator is used as armature.

Rotor construction is cylindrical. The frequency of supply is depends on

f=NP/120. As the speed of steam turbine is large

(3000 rpm or 1500 rpm), to get requiredfrequency, number of poles is 2 or 4.

To reduce peripheral speed, the diameterof rotor is small and axial length is

increased. Nearly sinusoidal flux distribution in air

gap Machines are usually air cooled, hydrogen

cooled or oil cooled and sizes varies from10MW to over 1500MW

SHAFT

Exciter

Altenator

Slip

Rings

Rotor

3Ph

output

Stator


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Alternators

Specifications

The following specifications are given for alternator

Rated Capacity in MVA Rated Over load capacity Rated voltage Rated current Rated speed or frequency Excitation voltage and current Cooling system Maximum allowable temperature Bore diameter, frame diameter, core length, shaft

diameter Rotor weight, stator weight
http://localhost/var/www/apps/conversion/sw-bkup/Technical/10.LIR/Gen-Data.xls


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Excitation Systems

It required to provide the necessary field current to the rotorwinding of synchronous generator

Should available for all time. Loss of excitation is serious than drop of a generator from

line. Unexcited alternator will draw large reactive power fromline.

Main requirements areReliability, easy to control, ease tomaintenance, stable for higher transients

The amount of excitation depends onLoad current, Loadpower factor, speed of machines. More load current, large p.fand lower speed will require more excitation.

Exciter is normally a small ac or dc generator provided on

same shaft of machine (centralise or separate one) Types of Excitation Systems are:

--DC excitation system--AC excitation system--Static excitation system


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Excitation Systems

DC Excitation System

Having two exciter Main exciter-to provide field current to alternator

--a separately excited dc generator- Pilot exciter-To provide field current to main exciter

--a compound wound self excited generator

Directly coupled exciter are used for small turboalternators Directly coupled gear driven exciter of large and

medium alternators Large time constant (response time is about 3sec) and

commutation difficulty are the drawbacks

Main ExciterAlternator

Pilot

Exciter

Main Field

Main Excitor

Field


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Excitation Systems

AC Excitation System

Consists ac exciter and rotating thyristor system Main ac exciter-to provide ac input to rectifier

--small ac alternator with fixed field and rotating armature Rotating rectifier- provide field current to alternator The field of ac exciter may be fed from a rectifier unit As commutator is not required, it eliminates the problem of

commutation Short time constant (response time is less than 0.1 sec)

Main ExciterAlternator

Main FieldMain Excitor

Field

Rotating Rectifier


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Excitation Systems

Static Excitation System

Supply for excitation is taken from alternator itself Output of alternator is connected to three phase star delta oil

immersed force air cooled step down transformer Star connected primary is connected to alternator output and delta

connected secondary to three phase controlled rectifier The output of this controlled rectifier unit is fed to field winding of

alternator Response time is 20msec and excellent dynamic performance. Eliminate the exciter winding loss possibility and reduced operating

costs

Alternator

Main Field

Three Phase

Transformer

Star-Primary

Delta-SecondaryThree phase

rectifier
http://localhost/var/www/apps/conversion/sw-bkup/Technical/11.Generator/Generators%20-%201%20.PDF


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Power Transformers

Used for step up voltage at generating stationand step down voltage at main distributionsubstation

Upto 10MVA-Naturally cooled, oil immersed(ON type).

Above 10MVA-Blast cool For higher ratings-Forced oil, water cooing orair blast cooling

To regulate the voltage the on load tap changeris used on hv winding of the transformer

It is generally operated at full load so it isdesigned to have maximum efficiency at fullload.

Flux density of 1.5 to 1.77 % impedance ranging from 6-18% % regulation is 6-10%


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Power Transformers


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Power Transformers


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Power Transformers

Specifications of power transformers

kVA Rating Rated voltage HV and LV Number of phases Rated frequency

Connection type (star or delta for both windings) Tapping Type of core Cooling system Permissible temperature rise above ambient temperature of oil and

windings Voltage regulation

% impedance Efficiency in % at full load, load, load at unity and 0.8 p.f.

lagging Covered under IS 2026-1962
http://localhost/var/www/apps/conversion/sw-bkup/Technical/10.LIR/Transformers%20-%20PG.xls


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Instrument Transformers

Potential or voltage transformer (PT or VT) isused to reduce the higher voltage level tomeasurable voltage (generally above 440V isconverted to 110V)

Current transformer (CT) is to reduce thehigher current level to measurable current

(generally above 50A is converted to 1A or 5A) Having two types 1) measuring instrument

transformer 2) protection instrumenttransformer

Specification of PT and CT

Rated primary voltage/current

Rated secondary voltage/current Accuracy class Burden Rated frequency Insulation systems Tapping
http://localhost/var/www/apps/conversion/sw-bkup/Technical/17.PT/VT.ppthttp://localhost/var/www/apps/conversion/sw-bkup/Technical/16.CT/A%20-%20%20MAIN%20%20CT%20LECT.ppt


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Power Switches

A Switch is used in electric circuit for makingand braking the electric circuit by simplemotion of knob

Switches may classified as air break switchesand oil switches

Air Break Switches

Horn gap type contact for quenching the arc May opened singly or in gang Mounted such that it opens in downward

direction

Isolators

Not equipped with arc quenching devices so cannot be used on load If opened on load arc flashover may take place

between contact and earth and causes accidentto operator


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rotective quipments

Circuit Breakers

A circuit breaker is a mechanical devicedesigned to close or open contact members,thus closing or opening an electrical circuitunder normal or abnormal conditions.

Can be operated manually or remote controlledunder normal conditions and automatically inabnormal condition.

Must carry normal load currents withoutoverheating and damage

Must quickly open short circuit current withoutserious damage with minimum burning contact

Types- Air circuit breaker, oil circuit breaker,SF6 circuit breaker, vacuum circuit breaker

Function: i) to carry full load current

continuously ii) to open or close the circuit onno load iii) to make and break the short circuitcurrents of magnitude which it is designed for.


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rotective quipments

Circuit Breakers

Specifications

Type of construction : No. of Poles : Nominal System voltage :

Highest System voltage : Rated Frequency : Rated Continuous current : Rated short circuit breaking current : Rated short circuit making current : Rated short time current : Rated duration of short time current : 1 Sec Rated operating duty : O 0.3 Sec- CO-3 Min

CO


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rotective quipments

Relays

The protective relay is an device which isinterposed between the main circuit and thebreaker in a such manner that anyabnormalities in the circuit acts on the relay.

The protective relay ensures the safely of thecircuit equipment from any damage from the

fault. Fundamental items of relay

--Sensing Element: sometimes it is measuringequipment. Responds to change in actuatingquantity--Comparing Element: serves to compare theaction of the actuating quantity on the relay

with pre selected setting.--Control element: on pick up it opens the maincircuit

Over current Relay, Over voltage, underfrequency, distance relay, differential relay

SensingElement

ComparingElement

Control

Element

To trip or signalcircuit


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Power line carrier

communication PLCC

It is installed in an power system forcommunication, relaying, tele-metering orfor supervisory control.

The power itself is used forcommunication

LC type of filter is used to convert carriersignal to audible vice or commands

Series connected L acts as the low passfilter (blocks high frequency signal) andprotect substation equipment from carriersignal

Shunt connected C acts as high pass filterto transfer carrier signal to control room.

Reliable, fast operating, need not separateline to transfer signal

Substation A

Substation B

ControlRoom


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Control Panel and Room

The various controls are performed suchas voltage adjustment, load control,emergency control.

It consists voltage regulators, relays,ammeters, voltmeters, energy meters,

temperature gauges, water level metersetc.

Well equipped with suitable display andalarms which shows the current status ofthe station.

It should be neat, clean, away from noise,well ventilated and illuminated, good fire

handling facility etc. All the meters should be clearly visible to

operator and it should be calibrated.


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Other Equipments

Battery room: used to supply allrelays and CB for operation

Lightning arrestor and SurgeAbsorber: to provide protectionagainst lightning and overvoltages

Earthing and earthing mat: toprovide protection against earthfault and prevent from shocks.

Instruments: used to measureelectrical and mechanical

quantities.


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unit 02a- elec equip in power station.ppt

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