Design turbo generator

Design turbo generator

1. Design , specification and operating principle of turbo generator M. G. Morshad , ADGM / Electrical TPS II ( 7 x 210MW) NLC India Ltd

2. Turbo Generator It is a synchronous machine It has the capacity to deliver active power with delivering of reactive power (lagging PF) and absorbing of reactive power (leading PF) Rotor is an electro magnet with S and N pole When it rotates at turbine speed , rotor flux cuts the stator coil and voltage is developed in the stator winding . The flux of the poles is controlled by supplying DC current in the rotor winding – this is know as excitation. When flux density in the pole is increased – it is called over excitation When flux density in the pole decreased – it is called under excitation Over excitation condition ( Lagging PF) - it delivers both active and reactive power Under excitation condition ( Leading PF) - it delivers active power but absorb reactive power Active power is controlled by steam input in Turbine Reactive power is controlled by excitation in Rotor winding ( Field) S N R DC source for excitation current Y B Stator axis Rotor axis Load angle (δ)

3. Total / Apparent Power (MVA) The current and voltage delivered by the machine is the total / apparent power of the machine . Total / apparent Power (MVA) = √3 x KV x Amps . Gen Total Power (MVA) Active Power (MW) Reactive Power (MVAR)

4. Active Power (MW) The power which can be converted to other forms is know as active power. Active Power (MW) = √3 x KV x Amps x Cos Φ . Gen Electric Motor (85%) Lighting (15%) Heating (5%) Active power is controlled by steam input in turbine Power = Torque x Speed ( Grid Frequency) Since machine operates at grid frequency, speed is constant Power is directly proportional to Torque or steam input to turbine

5. Reactive Power (MVAR ) The power which can not be converted to other forms but remains in the system in for maintaining voltage of the system. Reactive Power (MVAR) = √3 x KV x Amps x SinΦ . Gen Inductance Reactive power is controlled by - 1. Changing DC current in rotor field (excitation current ) 2. Tap changing in Generator Transformer) Magnetic Flux in motor Capacitance

6. Power Factor (Cos Φ ) Relation among – Total Power (MVA), Active Power (MW) & Reactive power (MVAR) MW M VA MVAR Φ PF = Cos Φ = MW / MVA PF indicates how much of the total power (MVA) is converted to active power (MW)

7. Generator parameters Values Stator Current 9500 Amps Terminal Voltage 15 KV Total Power (MVA) Power Factor (Cos Φ ) 0.85 Angle Φ 0.55 Deg Active Power (MW) Reactive Power (MVAR)

8. S N R DC source for excitation current Y B Stator axis Rotor axis Load angle (δ) To avoid falling down of rotor speed - mechanical torque has to be delivered by the prime movers. This process converts mechanical KE into electrical power by increasing load angle. As mechanical power (Pm) = Torque X speed, and electrical power ( Pe ) = Volt X Current are equivalent, torque input is directly proportional to load current . Therefore by increasing or decreasing torque in prime mover, electrical power out put in alternator is controlled When the machine is connected to Load, stator current create a opposite pole in the stator as per FARADAYS LAW . It creates an attraction force between stator & rotor causing falling down of rotor speed and decreasing of load angle. Operating principle

9. Types of Load Inductive load : It is due to coil configuration of the electrical machine It opposes the applied voltage causing reduction in applied It lags the current with respect to applied voltage ( i.e. current passes through the circuit after development of voltage) Capacitive Load : It is due to gap between the coil It absorb the charging current causing increment in applied voltage It leads the current with respect to applied voltage (i.e. current passes through the circuit before development of voltage) Resistive Load It is due to the material composition of the coil Current and voltage passes through the coil at the same time There is a I2R loss in the circuit. V EMF Flux I L V I C R AC Volt V I I V V I

10. Excitation system Controlled Rectifier (AC to DC) AVR Electronic / Digital type Set Terminal Voltage Exc Trans FB GENERATOR Grid voltage = 390KV GT voltage ratio = 15/400 Actual Terminal voltage = (15/400) X 390 = 14.62KV Set terminal voltage = 15 KV Error = 15 – 14.6 = 0.4 KV Automatic Voltage Regulator (AVR) sense the error and increase the field current for exporting reactive power (MVAR) to the grid (lagging PF operation). Grid voltage = 405KV GT voltage ratio = 15/400 Actual Terminal voltage = (15/400) X 405 = 15.19KV Set terminal voltage = 15 KV Error = 15 – 15.19 = - 0.19 KV Automatic Voltage Regulator (AVR) sense the error and decrease the field current for importing reactive power (MVAR) from the grid (leading PF operation). GT Voltage ratio 15/400 Grid

11. Over Excitation Stator flux Rotor flux or main flux Stator current When inductive load is predominate , reactive power required by the inductive load is supplied by machine. It increases the reactive current in the stator of the machine Reactive current creates higher flux in the stator which suppress the rotor main flux causing reduction in machine voltage Higher flux in stator increase the stator pole strength causing reduction in load angle. AVR come into action to maintain the machine voltage and load angle by increasing excitation current and the machine supply the reactive power with operating at lagging PF This situation occurs when grid voltage and frequency is lower than rated . Over excitation increase the excitation current which causes rotor heating . Therefore excitation current can be increased up to the rotor heating limit. Excitation current is reduced by reducing the set terminal voltage. Terminal voltage can not be reduced below 10% of the rated voltage.

12. Under Excitation Stator flux Rotor flux or main flux Stator current When capacitive load is predominate , reactive power required by the capacitive load is supplied by machine. It decrease the reactive current in the stator of the machine Due to decrease in stator flux , rotor main flux gets prominent and increase the machine voltage Due to decrease in stator current , stator pole strength gets reduce causing increase in load angle. AVR come into action to maintain the machine voltage and load angle by decreasing excitation current and the machine absorb the reactive power with operating at leading PF This situation occurs when grid voltage and frequency is higher than rated . Under excitation decrease the strength stator magnetic pole which causes pole slipping Therefore excitation current can be decrease up to the pole slipping limit. Excitation current is increased by increasing the set terminal voltage. Terminal voltage can not be increased above 10% of the rated voltage.

13. Capability curve MW MVAR (Lag) MVAR (Lead) Over excitation zone Under excitation zone Rotor current line Turbine Out put Limit Rotor Heating Limit Load Angle Limit Max lead MVAR Limit Operating point at boundary condition Stator current line

14. What is power & Energy The meaning of PF = 0.85 ,

15. Generator cooling

16. Generator Losses Losses in generator Core loss - 310 KW Copper loss - 498 KW Windage & Stray loss - 522 KW Mechanical Loss - 858KW Excitation Loss - 756 KW TOTAL LOSS - 2944 KW TURBOGENERATOR (Capacity 210MW / Efficiency 98.61%) Mechanical Input (210 / 0.9861) = 212.96 MW Electrical output 210 MW TYPES OF LOSS CAUSE DEPENDING FACTOR Core loss Hysteresis and eddy current Operating voltage and frequency Copper loss I 2 R Stator and rotor current Wind age loss Air friction loss in cooling fan mounted on the rotor shaft Gas density and speed of the machine Stray loss Undefined loss Geometry of the machine Mechanical loss Friction loss in bearings Viscosity of the bearing lubricant and speed of the machine Excitation loss I 2 R losses in excitation transformer and converters Excitation current

17. INSULATION TEMPERATURE CLASSIFICATION Insulation Temperature Classification for Machines Temperature Index Some Insulation Combinations Class O (Obsolete) 90°C Resinous , Cotton, Wood Class A 105°C Cotton, Vinyl Acetate Class E 120°C Phenolics , Alkyds, Leatheroid Class B 130°C Shellac/Bitumen, Silk, Mica, Polyesters Class F 155°C Epoxy/Polyesters, Silicone, Mica, Glass Class H 180°C Epoxy/ Polymides / Silicone/ Mica/ Glass Class C 220°C Glass/ Silicone/ Mica/ Nomex/ Silicates

18. DM Water Stator Iron Temp Rotor Temp Seal Oil Brg . Oil Stator copper temperature Stator current MW Loading Excitation current MVAR loading Hydrogen Gas cooler Seal Oil Cooler Brg oil cooler DM Water Cooler Brg . Metal Temp Heat generated by friction due to speed of the machine Auxiliary Cooling Water (ACW) Circulating water (CW) ACW Cooler Operating voltage & frequency Seal oil temp COOLING TOWER Source of Heat Effect Media Cooler Transporter

19. Design of turbo generator depending upon cooling method TARI THRI THDD THDW THWW TARI (4P) THWW (4P) MVA RATING T H R I Product name. T - turbo generator Cooling gas in the casing. A -air. H - hydrogen. Rotor Cooling . R - Direct radial. D - Direct axial Stator Cooling . I -Indirect gas. F /W - Direct water 45 290 412 880 1150 1560 1640

20. Vertical Cooler Cooled gas Stage - I generator : THRI (210MW)

21. Silica Gel Chamber Heater OFF Blower OFF Silica Gel Chamber Heater ON Blower ON H2 is returned back at low-pressure area H2 is taken out from high-pressure Moisture out Hydrogen Gas dryer

22. Hydrogen as a cooling media 210 3.7Ksc MW H2 Pressure (Kg /cm2 Hydrogen is a lighter gas (1/14 times of Air) Auto Ignition > 500 Deg Explosive limits: 4–76% (vol. % in air) Thermal conductivity : 0.186 W/m- C Low cost as it can be produce from water Heat transferring capacity increases with pressure. Loading (MW) of machine decrease with decrease of pressure Hydrogen pressure has to be maintained within the rated limit (3.5 to 4 Ksc ) High pressure - increase the windage loss, cause rupturing of gasket , increase the seal oil pressure Low pressure – decrease loading of machine, decrease stator cooling water pressure Hydrogen purity must be >97% ( free from moisture) to maintain rotor and stator free from moisture deposition. Number of cylinders to be charged = (Rated pressure – present pressure )/ 0.2

23. GAS COOLERS GAS COOLERS Hot gas temp at stator winding discharge (6 point) Hot gas temp at cooler inlet (4 point) Cold gas temp at cooler outlet (2 point) Cooling water in & out Cooling water in & out Monitoring – Gas temperature

24. Cold and hot gas temperature Depending upon the cooler arrangement (Vertical or horizontal) and circulating path of gas, temperature sensors are implanted in different location for accurate measuring of hot and cold gas temperature. Main locations for measuring gas temperature are - Hot gas temperature at stator winding discharge ( Below core temp , Max 65 Deg C) Hot gas temperature before cooler ( Below core temp , Max 65 Deg C) Cold gas temperature after cooler (2 to 3 Deg C above cooling water , Max 44 Deg C) Gas cooler inlet water temp ( Ambient temp) Gas cooler inlet water temp (Inlet Temp + 3 to 4 Deg C) 3) Gas temperature may go high because of the following reasons- High reactive loading (MVAR) of the machine High ambient temperature that increase the cooling water temperature Improper cooling of gas due to blocking of cooling water line (scale formation, air locking etc.)

25. Tube and shell type cooler Stator water Pump & Motor Expansion Tank ACW IN ACW OUT Stage - II generator : THW (210MW)

26. Extension Tank CW In Tube & shell type Cooler CW out Stator cooling water pump Flow controlling valve ET Vacuum Pump ACW tank (DM water) Stator water cooling system

27. Stator water flow & pressure Pressure is maintained below the hydrogen pressure so that in case of any puncture in line, water can not ingress into the winding rather hydrogen starts leaking through stator water and gets collected at gas trap. To maintain the pressure lower than operating hydrogen pressure, water flow is adjusted through flow controlling valve. Stator water conductivity Since water flows directly through the winding, conductivity of the water should be maintained as low as possible to avoid direct contact of winding through water. It is normally kept between 2.5 and 13.3 μmho /cm. Any physical or chemical contamination may increase the conductivity of water. ET vacuum pump is kept in service continuously used to remove the contamination Water-policing unit is to be commissioned as and when conductivity will be showing higher trends. Stator water inlet and out let temperature Inlet temperature ( Ambient temp) Out let temperature ( Inlet Temp + 8 to 10 Deg C) Effective cooling increase the difference between Out let and inlet temp Low difference means ineffective cooling may causes due to High ambient temp Low water flow Scale formation in the cooling tubes

28. Copper temperature sensor 2 RTD for each coil (Total number of coil 6) Core (Iron) temperature sensor 1 RTD for the core of one coil Monitoring – Core and copper temperature

29. Stator copper temperature Stator copper temperature increases proportionally with the square of current. High copper temperature damages the insulation of machine it must be restricted well below the temperature withstanding capacity of the insulation (Ambient temp 45 C + Temperature rise 135 C). Max allowable copper temperature 120 C. Temperature sensors (RTD) are implanted in the winding (two RTD for each six coils), for continuous monitoring the copper temperature through a 12 points recorder. Copper temperature may rise evenly for all 12 points . Uneven rising of copper temperature may cause due to blocking of cooling path of particular coil Stator iron (core) temperature Iron temperature increases due to Hysteresis and eddy current loss which is a function of frequency Core temperature should be well below the copper temperature (100 C). RTD is implanted uniformly throughout the core. It picks up the core temperature and records continuously through a 6-point record. It may rise due to any one of the following reasons - Failure of inter lamination insulation that causes development of hot spots. Blocking of ventilation duct for cooling Running of machine at higher voltage when frequency is low (V/f ratio ) d) Running machine in leading PF e) Core vibration due to looseness

30. Rotor temperature Because of rotating motion, rotor winding temperature cannot be measured directly through RTD, it is indirectly measured from rotor current. Rotor temperature = (Rotor current) 2 X (Rotor DC resistance) Normally maximum rotor temperature (110Deg) is limited to well below the temperature withstanding capacity of rotor insulation (180Deg for class F insulation). Rotor temperature may go high for any one of the following reasons - a) High lagging reactive loading (MVAR) b) Occurrence of first earth fault in rotor winding

31. What is grounding What is earthing

32. Whenever hydrogen comes in the contact with air, it forms explosive mixture, therefore it needs proper shaft sealing so that pressurized hydrogen gas cannot escape out from generator casing. The shaft sealing is done with high-pressure oil and the system, which supplies the high-pressure oil for that purpose, is known as seal oil system (SOS). Seal oil pressure and flow are very critical for maintaining the seal Higher than hydrogen pressure - Seal oil flows into the generator causing oil collection in generator casing Lower than hydrogen pressure - Seal oil flows out from the generator casing causing seal break and escaping of hydrogen Because of the above two reasons seal oil pressure is maintained slightly higher than hydrogen pressure so that neither oil ingression nor seal braking take place during normal operation of generator. Since the basic properties of any kind of oil are temperature dependent - high seal oil temperature (80 Deg C) leads to rapid liberation of oil vapour and low viscosity that may cause breaking of oil seals. Seal Oil System

33. Airside seal drain oil H2 side seal drain oil Seal oil flow Seal Oil tank Seal Oil Cooler ACW IN ACW OUT AC Seal oil pumps IOT Seal oil system vacuum pump Seal oil tank vacuum pump DC Seal oil pumps

34. DPRV Oil Flow Generator Hydrogen differential pressure relief valve (DPRV) Max hydrogen pressure = 4 Ksc Max ∆P = 1.5 Ksc DPRV position = Full open Seal oil flow = High Seal oil pressure = 4+1.5 = 5.5Ksc Min hydrogen pressure = 3 Ksc Min ∆P = 0.85 Ksc DPRV position = Partly open Seal oil flow = low Seal oil pressure = 3+0.85 = 3.85Ksc

35. Seal oil temperature before cooler - Seal oil is stored in a tank (Seal oil storage tank) from where it is sucked by pumps and pushed with high pressure (4 Ksc ) for circulation through cooler and seal rings. During traveling from tank to cooler, seal oil looses 8 to 10 Deg C due to natural process. Seal oil temperature before cooler may go high if - Seal oil tank and pipe lines are not exposed Pump generates more heat due to any mechanical failure Seal oil temperature after cooler – Optimum seal oil temp after cooler : Ambient temperature + 3 to 4 Deg C It may go high due to ineffectiveness of cooler caused by the following reasons - High ambient temperature Low flow of ACW cooling water Scale formation in cooler line Air & H2 sides seal oil drain temperature - Optimum drain temperature : Temperature after cooler + 25 to 30 Dec .C Airside drain oil temperature should be slightly higher (2 to 3 Deg C) than Hydrogen side drain oil temperature. It is because of partial carried away of H2 side seal oil heat by Hydrogen due to direct contact. Drained oil temperature may go high due to the following reasons - Low oil flow to seals due to chocking of line High seal oil temp after cooler due to ineffectiveness of cooler High active or reactive load on he machine

36. 1200 RPM 950 RPM 20000 RPM Ball brg Roller brg . Sleeve brg Max speed limit SPEED(RPM) 10 mm 300 mm Shaft ID Speed, shaft diameter and type of bearing used

37. End shields Journal Babbit metal Rotor shaft Oil film In sleeve bearing oil film instead of rolling element (ball / roller), is used between rolling parts (rotor) and stationary parts (journal fixed at end shields). To avoid accidental direct contact between rotor and journal that may damage the bearing race - a thin layer of low melting point (100 Deg Centigrade) BABBIT metal is provided over the inner race of the journal. Normally bearing metal temperature should be around 10 Deg. C higher than bearing drain oil temperature. Friction caused by direct contact between rotor and journal, generates sufficient heat to melt down BABBIT metal instantly and thereby damaging of inner race is avoided. Babbit metal temperature may go high if - a) Bearing oil temperature is high b) Direct contact between rotor and journal.

38. What is efficiency What is performance

39. Synchronization of generator with grid

40. GRID is an independent system of variable voltage and frequency GEN GEN is an independent system of control able voltage and frequency Generator breaker B RB Y R One cycle of sinusoidal voltage / current wave induced in R phase due to one rotation of generator pole Rotation of generator poles at 50 cycle / seconds S N Y B 120 120 R’ R‘ Y ' Y ' B' B ' R

41. A B A A B B Correct teeth angle Incorrect teeth angle Synchronization

42. Mechanical Electrical The direction of rotation of driving (B) and driven (A) wheel must be opposite Phase sequence The speed of both the wheel must be equal so that relative speed between two wheels becomes zero. Frequency The momentum (mass X velocity) of the driving wheel B must be equal to the momentum of the driven wheel A for making wheel B capable to transfer power. Voltage The teeth of driven wheel (A) must fall within the teeth angle of driving wheel (B). Phase angle

43. Connecting generator in right phase sequence - The out put RYB phases of generator are kept permanently connected to RYB phases of bus through generator breaker. Therefore phase sequence of generator and grid is maintained permanently.   Matching generator frequency with grid- To match the frequency of generator with grid, the generator has to be run at a particular speed, which can be calculated by the following formula Speed of the generator (RPM) = 60 X Present frequency of the grid Matching generator voltage with grid - After achieving required speed of the generator, field breaker is to be closed in manual mode of excitation for developing voltage in the generator. 48 49 50 51 52 Hz M/E BUS M/E BUS

44. Matching phase angle between generator and grid. The frequency of grid varies with time but the frequency of machine remains constant at a particular speed. Therefore with respect to grid voltage wave, machine voltage wave moves in forward or reverse direction depending upon the relative speed of machine - fast or slow. SYNCHROSCOPE provided at control desk indicates the relative speed of machine with respect to grid by rotating needle in FAST direction if the relative speed is higher and in SLOW direction if the relative speed is lower. +10 -10 Fast Slow SYNCHROSCOPE -10 +10 Fixed sinusoidal voltage wave of BUS FAST SLOW Moving voltage wave of MACHINE

45. Energy conservation and energy efficiency

46. Calculation of generation particulars

47. Location of energy meters GEN AC to DC Converter FIELD GB BRK BRK FB BRK EM GEN EM EXC EM UAT A EM UAT B EM ST

48. Rated MW Average MW Load curve 24 Hours Hours Generator load Gross generation (MU) = Area covered by load curve = (Final reading - initial reading) X MF Average load (MW)= Area covered by ABEF = (Total generation in MU / Running hours) Load factor (%) = (Area covered by ACDF / ABEF = (Average MW / Rated MW ) x100 Unit Auxiliary Consumption (MU) = Consumption (UAT A + UAT B + Excitation Transformer ) % Unit Auxiliary Consumption = UAC (MU) / Gross Generation (MU) Gross Generation for 210MW, 8 Hrs = 210 x 1000 x 8 /1000000 = 1.68 MU A B C D E F

49. Plant Load Factor (PLF)and availability factor (OPLF)

50. Switchyard Generator and it auxiliaries Turbine system Boiler system CLASS - C PROTECTION ZONE CLASS - A PROTECTION ZONE CLASS - B PROTECTION ZONE Generator Protection

51. CLASS - A PROTECTION This class of protection is intended to trip the generator instantly whenever faults occur in generator, generator transformer, UAT's, excitation system & generator breakers. Generator side - 1. Generator over voltage (59G) 2. Generator differential (87G) 3. Generator inter turn differential (87G1) 4. Stage II generator negative sequence (46G2) 5. Stage II generator back up impedance (21G2) 6. Generator thermal overload (51G) 7. Generator stator winding 100% earth fault (64G) 8. Generator stator winding 95% earth fault (64G1) 9. Generator stator winding stand by earth fault (51NG) Excitation side - 1. Rotor second earth fault 2. Loss of excitation (40G) 3. Rotor over voltage (+ ve or - ve ) 4. Thyristors bridge failure 5. Excitation transformer over current (Instantaneous) 6. Excitation transformer over current (Delayed) Generator Transformer side - 1. Generator transformer over flux (61GT2) 2. Generator transformer overall differential (87GX) 3. Generator transformer restricted earth fault (64RGT) 4. Generator transformer pressure relief 5. Generator transformer OLTC Buchholz 6. Generator transformer Buchholz Unit Auxiliary Transformer (UAT) side - 1. UAT (A / B) - LV side restricted earth fault (64RX1/ X2) 2. UAT (A / B) - differential (87X1/ X2) 3. UAT (A / B) - over current (50NX1/X2) 4. UAT (A / B) - HV side stand by earth fault (51X1/X2) Generator breaker side - 1. Generator breaker stuck up (50 LBB) 2. Transfer bus bar protection (96)

52. CLASS - B PROTECTION This class of protection is intended to trip the generator through reverse power protection whenever fault occurs in prime movers or generator auxiliary. 1. GT winding / oil temperature very high 2. UAT - A/B winding / oil temperature very high 3. Excitation transformer temperature very high 4. Excitation system regulation supply failure 5. Excitation system manual channel supply failure 6. Turbine trips due to fault or manual trips 7. Boiler trips due to fault or manual trips CLASS - C PROTECTION This class of protection is intended to trip the generator without tripping of prime movers whenever fault occurs in the grid of switchyard zone. 1. Generator back up impedance / stage I (21G2) 2. Bus bar protection (96BB) 3. Generator pole slip (78G) 4. GT stand by earth fault (51NGT) 5. Generator over voltage (51GT) 6. Generator - ve sequence / stage I (46 G1) 7. Under frequency (81G)

53. GEN GB RELAY CT PT Breaker Tripping Coil DC Supply Control Logic B U S B A R Basic principle of protection scheme

54. Class -B 86G2 Turbine trip Auto / MAN Turbine C&I Panel GRP DC Supply Turbine trip 32G 86T FB Class - A Class - C 86U 86G1 1) Trip FB 2) Bus change over 3) Trip GB 4) Initiate 50LBB 1) Trip GB 2) Initiate 50LBB 3) Limit excitation to O/C Generator protection logic

55. R CT 1 CT 2 I 1 I 2 X Y F S 1 S 2 S 1 S 2 Principle of differential protection

56. = + + IR IY IB IY1 IB1 IR1 IY2 IR2 IB2 IR0, IY0, IB0 Unbalance current vector Positive sequence current Negative sequence current Zero sequence current NGT Negative sequence filter 46G1 & 46G2 R Y B CT / Core 9 5000 / 5A Negative sequence protection

57. Back up impedance protection 21G1 21G2 N G T CT / Core 9 5000/5A CT / Core 1 5000/5A VT -3 200VA UAT

58. R X Z1 / 21G1 Z2 / 21G2 Operating point MHO relay continuously measure the impedance Z = √(R2 – X2) of the system

59. N G T 0% 95% 100% Stator earth fault

60. 0.5 Ohm Resistor 51 NG Stand By E/F 64 G ( 0 to 100%) 64 G1 0 to 95% F 250/1A NGT Injection Transformer VT Open delta Transfo

61. 64 RGT 51NGT Stand by E/F F2 E/F Current F1 CT core 4 500 / 4A GT 15.75 / 400KV GT Restricted and stand by earth fault

62. TE Side EE Side Shaft earth Field winding + - Slip rings SES DC BUS 64F1 Rotor earth fault 1st E/F 2nd E/F SES + S N

63. 50 LBB Line Isolator Generator Breaker GEN GT 86G Timer Switchyard DC Bus 220V supply Master trip relay contact at GRP Generator breaker struck up protection (50LBB)

64. Feeder I Feeder II Feeder III i1 i2 i3 i5 i4 i1+i2+i3 i4+i5 Differential Relay BUS I BUS II BUS COUPLAR Bus Bar Protection

65. Gross calorific value (GCV) and Net calorific value (NCV)

66. SPECIFICATION OF TURBOGENERATOR

67. Machine capacity in MVA MVA = √3 x Rated voltage X Rated current   Rated terminal voltage V = 4.44 X f X φ X Z X Kd X Kp f = Frequency φ = Flux Intensity of electromagnet directly proportional to excitation current. Z = Number of conductor per phase in stator winding. Kp & Kd = Design value depends on winding configuration] Since higher voltage increases the insulation level and decreases the size of conductor, standard machine voltage - 10.5 KV, 15.75KV and 21KV is selected for different MVA rating considering the cost factor. Rated current in Amps A = MVA / (√3 x KV) Rated power factor (PF) The power factor (PF) of any generator is defined to determine the field current rating. The field current of any generator decreases with the increase of PF. For example - an alternator designed to operate at 0.9 PF at rated load will take more field current when it is operated at 0.8 PF at rated load. PF is decided on the basis of stability of the system , length of transmission system and distance of load centre form the generator . Modern generator is manufactured with 0.85 Lag PF

68. MVA KV KA = MVA / (√3 x KV) PF MW = MVAXPF 62.5 10.5 3.43 0.8 50 125 10.5 6.87 0.8 100 156.25 10.5 8.59 0.8 125 247.05 15.75 9.05 0.85 210 294.11 15.75 10.78 0.85 250 555.55 21 15.27 0.9 500 888.88 26 19.73 0.9 800 Standard PF and terminal voltages for various capacity machines

69. Prime movers Alternator Speed Max. Capacity Diesel engine Diesel generator 750 to 1500 RPM 20MW Hydro turbine Hydro generator 750 to 1500 RPM 500 MW Gas turbine Turbo generator 1500 to 3000 RPM 1000 MW Steam turbine Turbo generator 3000 RPM 1000 MW Depending upon the types of prime movers - the size, capacity, & speed of any alternator is decided. Speed, pole and frequency Frequency (Hz) = [Numbers of pole X Speed (RPM)] / 120

70. Lagging MVAR capacity at full load (Rotor heating limit) MVAR (Lag) = MVA x Sin [Cos -1 (PF)] = (MW/PF) x Sin [Cos -1 (PF)]. If rated PF of 210MW machine is 0.85 lag, then lagging MVAR capacity of the machine at full load = (210/0.85) x Sin [Cos -1 (0.85)] = 130.14 MVAR   Leading MVAR capacity at full load (Line charging capacity) – MVAR (Lead) = MVA x Sin [Cos -1 (PF)] = (MW/PF) x Sin [Cos -1 (PF)]. If a 210MW machine is possible to operate safely at 0.95 lead PF without pole slipping - then leading MVAR capacity of the machine at full load = (210/0.85) x Sin [Cos -1 (0.95)] = 77.12 MVAR Efficiency - During the process of energy conversion machine cannot convert entire mechanical input power to electrical output but some part of the power is converted to heat, which is known as loss. Efficiency defines the losses in the machine and is calculated by the formula % Efficiency = [(Input power - output power) x 100] / Input power. Normal design efficiency : 98% . It gets reduced due to - 1) Higher Short-Circuit Ratio , 2) Higher GD 2 . Operating efficiency gets reduced by 2 to 3% at 50% loading.

71. Short circuit current ratio (SCR) Field current (I f ) required for developing rated voltage on open circuit SCR = Field current (If) required for circulating rated current on short circuit   SCR decides the following parameters of any generator a) Maximum field current on short circuit of stator b) Voltage regulation c) Stability limit d) Size, cost and efficiency LOW SCR 1) Wide variation of field current for small changes in terminal voltage (Poor voltage regulation) 2) Low stability limit 3) Low short circuit current 4) Higher field current capacity 4) Low air gap, smaller size of machine, higher efficiency, lower cost HIGH SCR 1) Low variation of field current for small changes in terminal voltage (good voltage regulation) 2) High stability limit 3) High short circuit current 4) Lower field current capacity 5) High air gap, larger size of machine, lower efficiency, higher cost Type of machine Value Synchronous condenser 0.4 Turbo generator 0.5 to 0.8 Hydro generator 1 to 1.4

72. Negative sequence current capability The power losses due to negative phase sequence stator current caused by single phase loads, unbalanced type line faults and open conductors, It appear primarily at the surface of the rotor. The negative phase sequence stator current generates double frequency currents in the surface of the rotor. This current flows axially over the length of the rotor and causes sufficient rotor heating. The standards require that the machine shall be capable of withstanding, without injury, unbalanced short circuits at its terminals of 30-seconds duration or less It is measured by I 2 2 t =K Type of synchronous machine Permissible I 2 2 t =K Salient pole generator 40 Synchronous condenser 30 Cylindrical rotor generator - Indirectly cooled 30 Cylindrical rotor generator - Directly cooled 8 - 10

73. Turbo generator type Cooling Media # Max capacity Rotor cooling Stator cooling TARI Air 150 MW Radial Indirect THRI H2 250 MW Radial Indirect THDD H2 ****** Direct H2 Direct H2 THDF H2 & water 500MW Direct H2 Direct water THWW Water ******* Direct water Direct water Type of cooling Depending upon the MVA rating of the machine following types of cooling systems are designed -

74. Type of excitation Depending upon the excitation power requirement and characteristic - following types of excitation system are provided for various capacity of generator Pilot exciter Low capacity, slow response, high maintenance, low reliability, mainly provided with TG manufactured in '60 &70 Static exciter High capacity, very fast response, low maintenance, high reliability, mainly provided with TG manufactured in '80 Brush less exciter Large capacity, very fast response, maintenance free, high reliability, mainly provided with large TG manufactured in '90

75. Full load torque The torque (twisting force) delivered by the prime mover to maintain rated speed of the generator at rated speed is the full load torque. Full Load Torque = (974 x rated KW / Rated RPM) Kg-m = (974 x 210000 / 3000) Kg-m = 68180 Kg-m = 68180 / 1000 = 68.18 Ton -m   Ratio of short circuit torque to full load torque The ratio of short circuit torque to rated torque is estimated by the following formula -   Te (Short circuit) (Excitation voltage in PU before short circuit) 2 = = (1.1) 2 / 0.2 = 6 Te (Rated) Sub transient reactance ( X"d )   In a large turbo generator - Maximum possible excitation voltage = 110% or 1.1PU Rated sub transient reactance = 0.2 PU It is seen from above that maximum value of torque after sudden 3 phase short circuit, is several times greater than its rated torque. In view of this the shaft and machine foundation must be suitably designed to withstand jerks caused by such large magnitude of sudden short circuit torque.

76. Centrifugal force mW 2 (D+E) Deflection (D+E) Counter force KD Rotational speed of shaft W RPM If the mass center of m is displaced by E from the center of rotation then centrifugal force exerted on the mass will be mW 2 E, where W is the angular velocity. This will cause a deflection D of the shaft, increasing the centrifugal force to mW 2 (D+E). The deflection is restricted by elastic shaft which develops a counter force equal to KD . For equilibrium KD = mW 2 (D+E). Or D = mW 2 E / (K - mW 2 ) At any angular speed W = √ (K/m) , when the defection is maximum , this peed is called critical speed. Turbo generators is designed to have critical speed much below its synchronous speed normally about 0.2 of syn speed. When the machine is started considerable vibration are experienced near the critical speed, which are avoided by quick starting through the region of critical speed. critical speed

77. Inertia constant This effect called fly wheel effect is expressed in terms of inertia constant H given by   Energy stored in joule (1/2) J w2 H = = Sec Machine VA rating VA     Type of machines Inertia constant (H) in MW-s / MVA Synchronous condensers 1.0 to 1.25 Hydro generator 2.0 to 4.0 Turbo generator 4.0 to 9.0