SWITCHYARD, NTPC SIPAT Training report

A Report on Power Plant Familiarization & SWITCHYARD

Submitted to:

HR department Submitted by: Katakam venkataramesh Electrical Engineering 2nd year, 4th sem National Institute of Technology, Raipur

CONTENTS Part A - Power Plant Familiarization  About NTPC Limited  About NTPC SIPAT  Introduction of Thermal Power Plant  Evolution of Thermal Power Plant  Typical Diagram of a Coal-Fired Thermal Power Station  Main component of Thermal power plant

Part B – Switchyard  Salient features of NTPC switchyard  Switchyard levels  Transformers and ratings  Equipment ratings  Line parameters  Circuit breaker ratings  Protection concept

ABOUT NTPC LIMITED

 NTPC, a public sector company, was in cooperated in 1975 to accelerate power development in the country as a wholly owned company of the government of India.  In the last 33 years, it has grown into the largest power utility of India.  NTPC is the sixth largest thermal power generator in the World.  It is the second largest in utilizing the capacity.  It delivers power at minimal environment cost and minimizes environmental impact.  Its core business is engineering, construction and operation of power generating plants. As on date the installed capacity of NTPC is 34,000 MW through its 15 coal based (23,395 MW), 7 gas based (3,955 MW) and 4 Joint Venture Projects (1,794 MW).  Recognizing its excellent performance and vast potential, Government of the India has identified NTPC as one of the jewels of Public Sector 'Maharatnas'- a potential global giant.  Source CoalGasOilTotal Thermal

Installed Capacity (MW) 85,193.38 17,055.85 1,199.75 103448.98

Percentage 53.3 10.5 0.9 64.7

ABOUT NTPC SIPAT NTPC SIPAT being located in Bilaspur district of Chhattisgarh state is a coal Fired project of NTPC with capacity of  3*660 MW (Stage I project) based on “SUPERCRITICAL BOILER TECHNOLOGY”  2*500 MW (Stage II project) based on “SUBCRITICAL BOILER TECHNOLOGY”

 NTPC Sipat accomplishes its water resource requirements from Hasdeo Right Bank Canal, which is 22 kilometres away from the thermal project and coal from Dipika mines of SECL.

 NTPC Sipat has a 765 kV transmission system, which is also the first time in India. This is the largest Transmission-system of its kind.  This thermal project has a submerged ash dyke, situated around 12 kilometres from the main plant accompanied by an Ash Water Recirculating Plant.  High efficiency electrostatic precipitators(ESP)s  It is the first implementation of super critical technology in India.  An ash water recirculation system, effulent treatment plant and central mointering basin.  A circulating water system with induced draft cooling towers  2*275 m high twin flue emission stacks, 1*275m high single flue stack.

INTRODUCTION TO THERMAL POWER PLANT  A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle.

BASIC POWER PLANT CYCLE

 The thermal power plant uses a dual (vapor + liquid) phase cycle in a closed way to enable the working fluid (waterfluid (water) to be used again and again. The cycle used is RANKINE CYCLE modified to include super heating of sheating of steam, regenerative feed water heating and reheating of steam.  On large turbines, it becomes economical to increase the cycle efficiency by using reheat, which is a way of partially overcoming temperature limitations. By returning partially expanded steam to reheater, the average temperature at which the heat is added is increased.

Advantages of thermal power stations:

 The fuel used is quite cheap.  Less initial cost as compared to other generating plants.  It can be installed at any place irrespective of the existence of coal. The coal can be transported to the site of the site of the plant by rail or road.  It requires less space as compared to Hydro power plants.  Cost of generation is less than that of diesel power plants.

Disadvantages

 1. It pollutes the atmosphere due to production of large amount of smoke and fumes.  2.

It is costlier in running cost as compared to Hydro electric plants.

 3.

Vital usage of natural resources (coal).

EVOLUTION OF THERMAL POWER PLANT & ENHANCES IN EFFICIENCY  The “efficiency” of the thermodynamic process depends on how much of the energy fed into the cycle is converted into electrical energy. If the energy input to the cycle is kept constant, selecting elevated pressures and temperatures for the water-steam cycle can increase the output.  Based on the operating parameters of steam, Power plants are of generally three types -

1) SUB CRITICAL POWER PLANT  Up to an operating pressure of around 190 bar in the evaporator part of the boiler, the cycle is sub-critical. This means, that there is a nonhomogeneous mixture of water and steam in the evaporator part of the boiler. In this case a drum-type boiler is used because the steam needs to be separated from water in the drum of the boiler before it is superheated and led into the turbine.  Sub-critical fossil fuel power plants can achieve 36–40% efficiency.

2) SUPER CRITICAL POWER PLANT  Supercritical is a thermodynamic expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase. Water reaches this state at a pressure above 221above 221 bar (22.1 Mpa) and temperature above 374°C. Fluid is heated in super critical state undergoes a continuous transition from a liquid-like

state to a vapor-like state. There is no distinct temperature such as a boiling point in the supercritical state.  Super critical designs have efficiencies in the low to mid 40% range,

3) ULTRA SUPER CRITICAL POWER PLANT  The steam parameters in this case are higher and exceed 600° C with pressure of 300 bar (30MPa). There are few power plants operating at such high temperature/ pressure and are referred to as Ultra Supercritical (USC) plants. In future further efficiency increase is expected to be achieved principally through the use of USC parameters by achieving live steam conditions of 760°C and 350 bar (35MPa).  Ultra Critical designs using pressures of 30.3 MPa and dual stage reheat reaching about 48%

Typical diagram of a coal-fired thermal power station

1. Cooling tower 2. Cooling water pump 3. transmission line (3-phase) 4. Step-up transformer (3-phase) 5. Electrical generator (3-phase) 6. Low pressure steam turbine 7. Condensate pump 8. Surface condenser

10. Steam Control valve 19. Superheater 11. High pressure steam 20. Forced draught (draft) turbine fan 12. Deaerator 21. Reheater 13. Feed water heater 22. Combustion air intake 14. Coal conveyor 23. Economiser 15. Coal hopper 24. Air preheater 16. Coal pulveriser 25. Precipitator 26. Induced draught (draft) 17. Boiler steam drum fan

9. Intermediate pressure steam 18. Bottom ash hopper turbine

27. Flue gas stack

MAIN COMPONENTS OF POWER PLANT Boiler (steam generator):

It is a closed vessel in which water,under

pressure is converted into steam. A boiler is always designed to absorb maximum amount of heat released in the process of combustion. This heat is transferred to the boiler by all three modes of heat transfer i.e, conduction,convection and radiation.

Types of boilers: 

Fire-Tube Boilers-

The fire, or hot flue gases from the burner, is

channelled through tubes that are surrounded by the fluid to be heated. The body of the boiler is the pressure vessel and contains the fluid. In most cases this fluid is water that will be circulated for heating purposes or converted to steam for process use.

Fire tube boiler



Water Tube Boiler - Here the heat source is outside the tubes and the water to be heated is inside. Most high-pressure and large boilers are of this type. In the water-tube boiler, gases flow over water-filled tubes. These water-filled tubes are in turn connected to large containers called drums. This type of boiler is being used at SIPAT in both the stages.

Water tube boiler

Components of Boiler 

Economiser : Section of boiler in which feed water is first introduced into the boiler and flue gas is used to raise the temperature of water.



Steam drum:

Steam drum separates steam from steam water

mixture and keeps separated steam dry. 

Super heaters: Bundles of boiler tubing located in the flow path of the hot flue gases. Heat is transferred from flue gases to the steam in super heater tubes.



Re-heater: Bundles of boiler tubes exposed to combustion gases in the same manner as super heater



Burners:

These may be coal burners / oil burners arranged in a

fashioned manner in different elevations either in all corners of furnace or in front & rear wall of the furnace. In Sipat we have corner located –  Coal burners in 10 different elevations and Oil guns in 5 different elevations. Arrangement of Boiler Auxiliaries –

 Coal Bunker ( 10 nos) – These are used for storing crushed coal from coal handling plant. These are 10 in nos for 500 MW / 660 MW units.  Coal Feeders (10 nos) – These are conveyor belt driven devices which fed coal in controlled way to Pulveriser  Pulveriser (10 nos) – These are located at zero meter adjacent to boiler and pulverise coal in to fine powder form for proper combustion

 Primary air (PA)fans: These are used to transfer the pulverized coal to the boiler  Secondary air(SA)fans: These are used to supply the air required for the combustion of coal. The velocity of primary and secondary air creates the necessary turbulence and combustion takes place with fuel in the suspension 

DRAFT SYSTEM: The circulation of air is caused by the difference in pressure known as Draft. Thus draft is a differential in pressure between the two points i.e, atmosphere and inside the boiler. A differential in draft is needed to cause flow of gases through the boiler setting. This required differential is proportional to square of rate of flow. In a draft system the movement of air is due to the action of fans. These fans have high efficiency, aerofoil blades inclined backward to the direction of rotation.  Forced draft (FD) fans: This fan is installed near the base of the boiler. This fan forces air through the furnace, economizer, air preheater and chimney. The pressure of air through the system is above atmospheric and air is forced to flow through the system.  Induced draft(ID) fans: This fan is installed near the base of the chimney. The burnt gases are sucked out of the boiler, thus reducing the pressure inside the boiler to less than atmospheric.

 Primary / secondary Air Pre Heaters ( 2 nos each) – This equipment transfers heat from flue gases (from boiler ) to cold primary / secondary air by means of rotating heating surface elements.  Electro Static Precipitator – These are are generally two plate type located between boiler and the chimney. These are arranged for horizontal gas flow where Fly ash get precipitated.

TURBINE –  A steam turbine is a mechanical device that extracts thermal energy from pressurized steam and converts it into mechanical work.  Steam is made to pass through three stages in the turbine.  These are High pressure, Intermediate Pressure, Low Pressure i.e. HP, IP and LP turbines respectively.  Steam through the boiler first enters the Hp turbine. The parameters of the steam are 540°C and 172 kg/cm2.  After coming through the final row, the steam temperature and pressure decreases due to throttling. Hence the steam that comes out from the HP turbine is at 120°C and 40 Kg/cm2.  It is sent to re-heater in order to increase its temperature and pressure.  It is then fed to IP and LP turbines respectively. The steam that enters the IP turbine is at 365.9°C and 44.9 Kg/cm2.  After undergoing its operation in the IP and LP turbines the mixture of steam and water is at a temperature of 40°C and at less pressure.  But the heat content in it is very high. This heat cannot be utilized and hence has to be dissipated. The mixture of steam and vapor comes into the condenser and into the hot well.  From the hot well the mixture is cooled into water using the cooling tubes which supply a continuous flow of water at normal temperature and it absorbs the heat from the steam water mixture.  The water in the cooling tubes which have absorbed maximum heat is then sent to the cooling towers to remove its heat content.

Generator: In 1831,Michael faraday discovered that if a conductor is moved through a magnetic field, an electrical voltage is induced in the conductor. The magnitude of the generated voltage is directly proportional to the strength of magnetic field and rate at which the conductor crosses the magnetic field. The induced voltage has a polarity that will oppose the change causing the induction-LENZS LAW. Synchronous generators are used because they offer precise control of voltage, frequency, VARs and watts. This control is achieved through the use of voltage regulators and governors. Exciter is the back bone of generator control system. It is the power source that supplies the dc magnetising current to the field windings of a synchronous generator there by ultimately inducing voltage or current in the generator armature. The amount of excition required to maintain the output voltage constant is a function of generator load.  As the generator load increases the amount of excitation increases.  Reactive lagging pf loads require more excition than unity pf loads  Reactive leading pf loads require less excition than unity pf loads

BRUSHLESS EXCITATION SYSTEM: They do not require slip-rings, commutators, brushes and are practically maintenance free.  Main exciter:  Field winding on stator and armature winding on rotor  Having 6 poles and produce AC at 150Hz  Field is fed power from pilot exciter( controlled by ECS)  Pilot exciter:  It is a Permanent magnet alternator  Having 16 poles and produce AC at 400 Hz  It has armature winding on stator

SWITCHYARD Switchyard It is a switching station which has the following credits :

 Main link between generating plant and Transmission system, which has a large influence on the security of the supply.  Step-up and/or Step-down the voltage levels depending upon the Network Node.  Switching ON/OFF Reactive Power Control devices, which has effect on Quality of power.

Salient Features of SIPAT Switchyard  First switchyard in INDIA at 765 Kv level.  First switchyard in NTPC with total substation automation and numerical relays.  First switchyard in INDIA with a highest rating EHV Interconnecting transformer of 1000MVA.  Various voltage levels such as 765Kv, 400Kv and132Kv.  Two 765 kv lines to SEONI , two 400 kv lines to Raipur, two 400 kv lines to Ranchi. One LILO from LANCO patadi to Raipur.

Switchyard details and notations  765 kv switchyard is having sectionalized double main bus with one and half breaker system . It has 26 bays  400 kv switchyard is having double main bus and one and half breaker scheme with 24 bays  132 kv switchyard is having double bus with bus coupler and has 13 bays  Nomenclature for identifying a particular equipment : Ex:-400 kv Raipur line-3 tie breaker code is 4-552 in which 4represents the first digit of

voltage level 400kv 5represents the bay no. 52represents standard code of breaker and 89 represents isolator. Levels ( all in meters ) Equipment Level Bus level Stringer level Earth wire level (shield wire) P- P Clearance (min) P- E Clearance (min) Bay width

132KV 4.6 8.5 12.2 17.4 1.587 14.8 12

400KV 8 8 16 24.5 4 3.5 27

765KV 14 26 38 46 7.6 4.9 51.5

Comp ariso n of switc hyard levels

Transmission line details Line Seoni-1& 2 Raipur 1,2 & 3 Ranchi 1 &2 Lanco Patadi Muph 1&2

Voltage 765Kv 400Kv 400Kv 400Kv 132Kv

Distance 344Km 157Km 440Km 60Km 28Km

Current 2800 A 1400 A 1400 A 1400 A 550 A

MW 3338.95 872.93 872.93 872.93 113.17

 MAXIMUM THERMAL LOAD LIMIT AT 0.95 POWER FACTOR

Switchyard equipments Switchyard consists of the following main equipments  Power transformers  Circuit breakers  Isolators  Earth switches  Bus bars  Lightning arrestors  Current transformers(C.T’s)  Capacitance voltage transformers(CVT’s)  PLCC equipments ( Wave traps)  Protective Relays, metering equipments, control units.

Functions of various equipment : Transformers : Transforms the voltage levels from higher to lower level or vice versa, keeping the power constant.

Circuit breakers :

A circuit breaker is an automatically operated

electrical switch designed to protect an electrical circuit from damage caused by overload or short-circuit. Its basic function is to detect a fault condition and by interrupting continuity to immediately discontinue an electrical flow unlike a fuse which operates ones and then must be replaced, a circuit breaker can be reset(either manually or automatically) to resume normal operation.

Circuit breakers are made in varying sizes from small devices that protect household appliances upto large switchgear design to protect high voltage circuits feeding an entire city.

TYPES OF CIRCUIT BREAKERS: i.

Miniature CB

ii.

Air break CB

iii.

Air blast CB

iv.

Oil CB

v.

SF6 CB

vi.

Vaccum CB

SF6 circuit breaker 1. Op mechanism 2. Interrupter

3. Support 4. Op rod 5. Linkage 6. Terminals 7. Filters 8. Puffer cylinder 9. Nozzle 10. Fixed position. 11. Fixed contact 12.. Moving contact. 13. Gas inlet

One and half CB system: The power stations have 400/765 kv outgoing line arranged in a one and half scheme breakers meaning there are 3breakers per 2 outgoing lines i.e, 1.5 breaker per line. These breakers are connected on to buses main bus 1 and 2. When one of the line is tripped breakers 1-52CB and 2-52CB trips then line isolated i.e, isolator 1-89, 1-89A,2-89A and 1-89L is opened, that side becomes dead(are known as stub). Isolator 2-89B is not opened as line 2 is in service. Now the area between (3-52CB and T/F-1 and 2-52CB i.e,stub or dead end) is protected by stub protection on 3-52CB side which gives bus over current trip if the line isolator is opened and current exceeds preset value.

Systematic diagram of one and half breaker CB

Isolators :  Opens or closes the electrical circuits under No-load conditions  Interlocked with breakers and earthswitces.  Isolates sections for maintenance.  Used to select bus bars and CT switching for bus bar protection  Should withstand extreme wind pressures  Motor driven and handdriven systems.

Systematic diagram showing isolators

Instrument transformers

:

Used mainly for stepping-down the

electrical parameters (Voltage or Current) to a lower Metering and Protection logics. 

Current transformers(CT): To

and safe value for

step down high values of current

to a safe value to incorporate Measuring and Protection Logics. It is also used for instrumentation, protection or measuring of power systems. 

Voltage transformers(PT):

To step down high values of voltage

to a safe value to incorporate Measuring and Protection Logics. They serve a number of functions in a power system. They are required for the operation of many type of instrumentation and relay protective systems. They measure voltage and in conjunction with CT they measure power.

Earth switch :  It is a safety device used to ground sections required for maintenance by grounding the induction voltages  Interlocked with isolators and breakers  Motor driven or hand driven

Lightning arrestors: Safe guards the equipment by discharging the high currents or high voltage surges in power system due to Lightning.

Overhead earth wire: Protects the O/H transmission line from Lightning strokes.

Bus bar: Conductors to which a number of circuits are connected. WaveTraps/Line traps:  Used in PLCC circuits for protection of transmission line and communication between substations.  VHF signal is transmitted from one end to other through the same power line.  Sends inter-trip signal to the other end circuit breaker(CB)s so that the faults can be isolated at the earliest time.

Systematic diagram showing wavetraps/line traps

Reactive Power control devices:

Controls the reactive power

imbalance in the grid by switching ON/OFF the Shunt Reactors, Shunt Capacitors etc.,

Current Limiting Reactors: Limits the Short circuit currents in case of faulty conditions.

Power transformers at Sipat Transformer

Type

IBT- 1,2,3

GT-4,5

Auto T/f (3 ph unit) Auto T/f (3X1 single ph units) 2 winding t/f (3X1 single ph units) 2 winding t/f (3X1 single ph units)

ST-1,2,3

3 winding T/f

ST-4,5

3 winding T/f

MST-1,2

2 winding t/f

ICT-1,2 GT-1,2,3

Rating 400/132Kv 200MVA 765/400Kv 3X333 MVA 24/765Kv 3x 260 MVA 21/765Kv 3x 260 MVA 132/11Kv 90/45/45 MVA 132/11Kv 80/40/40 MVA 132/11Kv 16 MVA

Reactors at sipat Bus reactor Line reactor Line reactor

765Kv 80 MVAR 765Kv line Seoni 1 and 2 80 MVAR 400Kv line ranchi 1 and 2 63 MVAR

Circuit breaker ratings All circuit breakers are SF6 breakers

Parameter

132 KV

Make Rated Voltage Rated Current Type of interrupter Number of breaks Closing Time Opening Time

Alstom,India 145Kv 1250 A SF6 1 < 150mSec 65 ms

400 KV

765 KV Areva, Alstom,India T&D,France 420Kv 800Kv 2000 A 3150 A SF6 SF6 2 4 120mSec 120mSec Max 18 to 24mSec 20 to 24mSec

Protection concept 

 Protective relays and relaying systems constantly measure and monitor the electrical parameters under all conditions.  Abnormal conditions are detected by the changes in theelectrical parameters such as Current, Voltage, Impedance frequency and phase angle.  After fault detection the relay operates & opens the circuit breaker thereby isolating the faulty part of the equipment  Any protective relaying requires the basic characteristics Sensitivity, Selectivity, Reliability, Operating speed, Economy and Simplicity

Types of relays Electromechanical type: operates on electro mechanical principles and has moving parts

Static relays:

contain no moving parts, uses static components such as diodes, transistors and level detectors.

Digital relays:

measured quantities are manipulated in analog form and subsequently converted into binary Voltages (square wave). logic circuits & microprocessors compare the Phase relationships of the square waves to make a trip decision.

Numerical relays: Numerical relays are those in which the measured a.c quantities are sequentially sampled and converted into numeric data form. A microprocessor performs mathematical and /or logical operations on the data to make trip decisions.

Advantages of numerical relays  

 Analogue circuits are replaced with microprocessors to implement relay functions.  Microprocessor uses protection algorithms & other computational functions for characteristic generation.  Programmable function setting  Multiple functions by the same relay.  Internal fault diagnosis. (self checking)  High operating speed.  Flexibility in wide parameter adjustment  Built in event logger and disturbance recording options (Post trip analysis)  Digital communication facility  Control through personal computers and remote control is possible.  Low failure rate & less no. of spare cards

400 KV line protections  Duplicate primary protections named as Main-1 and Main-2 with individual D.C source for each main protection and Carrier protection through PLCC  Distance Protection  Directional Phase O/C and E/F  Over Voltage and Open Jumper  Power swing blocking  TEE Differential-1  Under voltage protection  VT supervision  CT supervision  Circuit breaker failure detection

765KVline protections All protections same as 400 kv line and in addition 765 kv seoni lines have acompensated over voltage protection

IBT/ICT protections Transformer protection comprises of main and backup protections

Main protection      

Pressure relief valve trip Buchholz relay alarm and trip Differential Tee-1 Over flux protection Winding temperature alarm and trip Diffrential

Back-up protection      

Pressure relief valve trip OLTC trip Oil temperature alarm and trip Directional Over current & Earth fault on HV & LV sides REF protection on both HV & LV sides. Differential Tee-2 protection.

Bus-bar protection  Bus-bar protection system primarily protects bus-bars and associated equipments of transmission or distribution network substations/switchyards from phase to phase or phase to earth faults  Bus-bar protection operating speed should be very high for internal faults and it should not operate for external fault.  MUST be very stable during normal operating conditions  Bus-bar protection is based on KCL  Sum of incoming currents and out-going currents =0 during healthy condition  Implemented by using biased differential protection  Decentralized protection has Peripheral units attached to each bay and a central unit for scheme logic, and has many zones