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L&T- Power
Basics of Engineering Basics of Engineering ElectricalElectrical
L&T- Power
Electrical System for a Power Station can be broadly classified as:
Main Power SystemThe Main power system deals with Generation of Power and stepping it up to a Extra High Voltage (EHV) level. It also deals with Unit start-up power.
Plant Auxiliary Distribution SystemThe Auxiliary distribution system deals with supply and distribution of power to various auxiliaries (e.g. boiler feed pump, Cooling water pumps etc) within the station boundary, necessary for keeping the Unit up and running.
Power Evacuation SystemPower evacuation system deals with receipt of power from Station at EHV level, Export/Import of Power to the Grid and Deriving Unit start-up power.
Electrical System for Power Plants
L&T- Power Typical Main Power System for Large Thermal Power Plant
Unit AuxiliariesStation Auxiliaries
Main Power System
L&T- Power Overview – Main Power System
Main Power System deals with Generation of Power and stepping-up this generated power to the evacuation voltage
For a 800MW Unit, power generated at 24kV and transmitted to the Generator Transformer (GT) thru Isolated Phase Bus Duct (IPBD)
Main route of IPBD is provided with taps to feed the plant unit auxiliaries thru Unit transformers (UTs)
Main Power system also deals with Unit start-up
For this mainly two schemes exists, Station transformer scheme and Generator Circuit Breaker (GCB) Scheme.
L&T- Power
Start-up power derived from Grid thru Station transformer.
Unit is started by supplying power to the necessary Turbine & Boiler auxiliaries thru Station to Unit interconnector
After start-up, unit is synchronized to the grid at EHV breaker in switchyard. Synchronization achieved thru automatic synchronizing equipment – normally a part of turbine control equipment
After synchronization with grid, unit load are transferred to the UT by paralleling via 11 kV interconnector
Unit supplies power to unit auxiliaries through UTs. Power is evacuated through GT.
HV side of ST – 132 kV, 220 kV, 400 kV LV side of ST – 11 kV On load Tap Changer is required
Station Transformer (ST) scheme
L&T- Power Station Transformer scheme
L&T- Power Generator Circuit Breaker (GCB) scheme
L&T- Power
• A switching device (GCB) introduced between generator and GT
• Start-up power is derived from Grid by back charging GT and UT and keeping GCB open
• Unit is started by supplying power to the necessary Turbine & Boiler auxiliaries
• After start-up, generator is synchronized with the grid thru GCB
• Once synchronized, unit supplies power to auxiliaries through UTs. Power is evacuated through GT.
HV side of UT – 24 kV LV side of ST – 11 kV
This scheme is not widely used for large thermal power plants, However this scheme is very popular for Combined cycle plants
Generator Circuit Breaker (GCB) scheme
L&T- Power
Major Constituents of Main Power System are:
• Generator with Excitation System
• Station Transformer
• Generator Circuit Breaker (GCB) (As applicable)
• Isolated Phase Bus Duct
• Generator Transformer
Main Power System
L&T- Power
Mainly comprises of:
• Generator with Excitation System
• Generator Control Protection & Monitoring System
• Neutral Earthing Equipment
• Above are in scope of Original Equipment Manufacturer (OEM) for Turbine Generator Package
• Generator stator and rotor - some of the heaviest equipment to be transported and handled at site, with stator weighing approx. 370 MT and rotor 80 MT for 800MW generator
• Major domestic suppliers - BHEL• Major international suppliers - MELCO, GE, ALSTOM, SIEMENS, HITACHI,
ABB, Toshiba• Major Chinese suppliers are Don fang Electric (DEC), Sanghai Electric, Harbin
Generator
L&T- Power
ROTOR
COIL END SUPPORT STRUCTUREWITH RESIN CONE
STATOR COIL
TURBINE SIDE
EXCITER SIDE
GAS COOLER
LARGE DIAMETER ROTOR
BLOWER
H2 GAS
STATOR CORE
BEARINGBEARING
COOLING SYSTEMSTATOR COIL: WATER COOLEDROTOR COIL: HYDROGEN INNER COOLED
BUSHING
Major Parts of a Large Water Cooled Generator
L&T- Power Picture of a 990MVA 3000rpm MHI Generator
Static Excitation System
Turbine
Generator
L&T- Power Picture of a 1,310MVA 1,800rpm MHI Generator
Brushless type Excitation system
L&T- Power Picture of a 1,600MVA 1,800rpm MHI Generator
L&T- Power Generator Excitation System
Function:
1. SUPPLY AND CONTROL THE DIRECT CURRENT FOR THE FIELD WINDING (FIELD CURRENT) OF THE GENERATOR.
2. CONTROL THE VOLTAGE AND REACTIVE VOLT- AMPERE OF THE MAIN GENERATOR BY CONTROLLING ITS EXCITATION.
Types of Excitation System:
1. STATIC EXCITATION SYSTEM
POWER ELECTRONICS BASEDMORE ADVANCED TECHNOLOGY
2. BRUSHLESS EXCITATION SYSTEM
ROTATING ELECTRICAL MACHINECONVENTIONAL TECHNOLOGY
THYRISTOR EXCITER
BRUSHLESS EXCITER
L&T- Power
MAJOR COMPONENTS:
- EXCITER & AVR CUBICLES
- EXCITER TRANSFORMER
- AC BUS DUCT
- DC BUS DUCT
- SLIP RING & BRUSH GEAR
MAJOR COMPONENTS:
- EXCITER & AVR CUBICLES
- EXCITER TRANSFORMER
- AC BUS DUCT
- DC BUS DUCT
- SLIP RING & BRUSH GEAR
EX PMGG
CT
PT
AVR
Field Breaker
BRUSHLESS EXCITATION SYSTEM
BRUSHLESS EXCITATION SYSTEM
STATIC (THYRISTOR) EXCITATION SYSTEM
STATIC (THYRISTOR) EXCITATION SYSTEM
AVR
Exciter Transformer
PT
CT
G
Thyristor Rectifier
Field Breaker
AC Bus Duct
DC BusDuct
Slip Ring & Brush Gear
MAJOR COMPONENTS:
- BRUSHLESS EXCITER
- AVR CUBICLE
MAJOR COMPONENTS:
- BRUSHLESS EXCITER
- AVR CUBICLE
System Configuration of Excitation System
L&T- Power
• Special type of breaker, capable of withstanding the short circuit level at Generator terminal
• Requires breaking capability of a very large amount of short circuit current, being very close to Generator
• Enables power to unit auxiliaries by back charging of Generator Transformer (as explained earlier)
Suppliers - ABB, Areva and Hitachi
ABB HEC-7 & HEC-8 more suitable for large thermal power units
Generator Circuit Breaker (GCB)
L&T- Power
GeneratorTransformer sideGenerator
side
Generator Circuit Breaker
L&T- Power
• Also known as Isolated Phase type Bus Duct.
• Main run connects Generator to GCB and GCB to Generator Transformer.
• Tap-off run connects main run to Unit Transformers, Excitation transformer etc
• For a 800MW unit, continuous rating of the Main run is in the range of 25,000 A and short-circuit rating of around 165 kA
• Major domestic suppliers - C&S, Powergear• Major International suppliers – ALFA Standard, EGE, Simelectro
from Europe, Delta Unibus from USA, Hyosung from Korea• Major Chinese suppliers - DAQO, Beijing Power Electric
Isolated Phase Bus Duct
L&T- Power Typical IPBD Layout and connection scheme, and internal details
Tubular (hollow) conductor
Enclosure
L&T- Power GE 7FA Gas Turbines – Part of a 500 MW Combined Cycle Power Plant
IPBD
GCB
Generator Transformer
L&T- Power
• Step up the generation voltage to evacuation voltage
• Available in three phase bank (Single unit) up to 315 MVA rating
• Single Phase banks (One transformer per phase) employed in large thermal power plants for
a) 3-Phase transformer impose transport weight and height limitations beyond 315 MVAb) Failure in one bank does not affect others
• Typical rating: 3 x 333 MVA for a 800 MW Unit and 3 x 260 MVA for a 660 MW Unit
• One of the heaviest and largest equipment to be transported to site
• Major domestic suppliers are AREVA, ABB, CGL, BHEL• Major International suppliers are GE Prolec, Fortune Electric, SPECO
(Shandong Power Equipment Company)
Generator Transformer
L&T- Power
FirewallTo restrict fire to a limited area
IPBDTransformerCooler banks
View of a 290 MVA Generator Transformer
Connection with the overhead lines
L&T- Power
Plant Auxiliary Distribution is broadly divided in to following sub-systems :
• Normal AC System
• Emergency AC System
• DC System
• UPS System
Plant Auxiliary Distribution System
L&T- Power Typical Unit & Station System for a 660MW Generator
Motors <160 kW
1500kW > Motors > 160 kW
Motors > 1500 kW
BFP largest motor, rating around 19 MW typically for a 800 MW Unit
L&T- Power
• Medium Voltage levels generally used are - 3.3 kV, 6.6 kV and 11 kV
• MV switchgears comprises of SF6/VCB breakers & protective relays.
• MV switchgears are used to feed HT motors and auxiliary / service transformers.
• Major Manufacturers – ABB, Siemens, L&T has entered in this field with a joint venture with TAMCO, Malayasia.
• Low Voltage levels generally used are - 415 V, 240 V and 110 V
• LV switchgears comprises of Air Circuit Breakers & protective relays.
• LV switchgears are used to feed LV loads, MCC and DB.
• L&T make switchgears are used in L&T projects.
Medium Voltage (MV) and Low Voltage (LV) Switchgear
L&T- Power Diesel Generator backed Emergency Power Supply
• Diesel Generator provide start-up or shut-down power
• In the event of total power failure, DG set provides power required for safe shutdown of the plant like AC lube oil pumps, turning gear, cooling water pumps/fans (as required), back-up to UPS and DC system
• DG sets also provide start-up power for combined cycle power plants (CCPP).
• Rating in the range of 1500 KVA for a 250 to 500 MW CCPP. Normally provided at LV (415V) level.
• For large thermal power plants, DG not adequate for huge start-up power supply requirements. Hence Gas turbines may be provided.
L&T- Power Diesel Generator (DG) room pictures
Auto Mains Failure (AMF) Panel
DG Set inside acoustic enclosure
L&T- Power
DC system
Supply power DC Emergency Oil Pumps, Control Supply to Switchgears & Panels, Emergency Lighting
DC system mainly comprises of :
• Batteries (Lead acid tubular/plante, Ni Cd type)• Battery chargers (float and float cum boost chargers)• DC distribution boards
Major local suppliers for Batteries: Exide, HBLNIFEMajor local supplier for Battery Chargers: Chhabi, Caldyne
Plant DC Supply System
L&T- Power Battery Room Picture
Battery Rack
Operation & Maintenance Space
Cable Trays
L&T- Power
UPS System
Provides uninterrupted AC power to:
• DCS• Various control panels• Instrumentation System
• Mainly comprises of : Battery charger, Battery, Static Inverter, Static Switches, Isolation Transformer, UPS DB.
• Major local suppliers for UPS: DB power, HIREL, Emerson, Gutor, HiRel
Uninterrupted Power Supply (UPS) System
L&T- Power
• Large thermal power plants are generally located away from the load centers
• Generated power is stepped up to a suitable high voltage in step-up substation / switchyard at generating end to minimize the transmission losses.
• Evacuation system receives power from the generating station at high voltage level, interconnects generating station with the regional / National grid.
• Provides power to generating station to feed plant auxiliaries during start up, and to feed station-load during running condition.
Overview - Power Evacuation System
L&T- Power
Generator Transformer
IPBD
Connection with the Switchyard
Connection of Generating Station with a Switchyard
L&T- Power Outdoor (AIS) type Switchyard
Switchyard Control Building
Transmission Tower& Lines
L&T- Power
Current
Transformer (CT) Centre rotating
double break isolator
Circuit
Breaker (CB)
Major equipment of a Outdoor type Switchyard
L&T- Power
400 kV Circuit breaker &Lighting tower
Wave trap, Capacitive Voltage Transformer (CVT), Lightning Arrestor,Double circuit Transmission tower
LA
Wave Trap
Major equipment of a Outdoor type Switchyard
CVT
TransmissionTower
CB
LightingTower
L&T- Power
Front View
Rear View
33 kV Gas Insulated Switchgear (GIS)
L&T- Power 132 kV GIS
CB MODULE
BUS BAR MODULE
VT MODULE
CT MODULE
L&T- Power Comparison between Outdoor AIS and GIS type Switchyard
Parameters Outdoor AIS Indoor GIS
Layout Occupies large space.
Hence suitable for plants in remote areas.
Occupies less than 40% space as compared to AIS. Hence suitable for urban area where land is at premium.
Civil & Structural aspects
Involves construction of large number of small foundations over a vast area, and vast length of small cable trenches
Involves construction of a GIS building
Environmental Considerations
Noise and electromagnetic radiation emanating from EHV lines is a cause of concern
Not a concern, as all the EHV conductors are enclosed
Overall Economics Excluding land cost, Initial capital cost is substantially less as compared to GIS.
Approximately 2.5 to 3 times costlier than AIS of similar capacity, for 220kV and 400kV level
L&T- Power
Load flow for the study of voltage regulation
Motor Starting Analysis - for the study of voltage regulation during motor starting, constraints on motor starting current
Short Circuit / Fault Studies - for selection / verification of % impedance of transformers, fault rating for Switchgear / MCC, assigning short circuit rating for equipment / system
Relay co-ordination / Settings for protection co-ordination, designing primary protections, ensuring system safety and maximum availability
Power System Studies
L&T- Power Switchgear Room Picture – Showing HV Switchgear
L&T- Power Switchgear Room Picture – Showing LV Switchgear
L&T- Power Model View of Cable Trays on Pipe rack
L&T- Power Picture of Cable Trays on Pipe rack
L&T- Power Picture of Cable Trays on Pipe rack
L&T- Power Picture showing Under ground cable trench
L&T- Power Underground Duct bank pictures
L&T- Power
