1. Main Turbine Generator & Exciter
Including:
Hydrogen, Stator Cooling Water, Generator Seal Oil, and Iso-Phase Bus & Duct Systems

2. Enabling Objectives STATE the function of the Main Generator.
LIST the three requirements for an electrical generator.
STATE the purpose of the four major components of the Main Generator.

3. Enabling Objectives (cont..)
LIST four main generator auxiliary systems and STATE the function of each.
STATE why Hydrogen gas is used for generator cooling and STATE a special precaution associated with its use.

4. Function of Generator
Converts the mechanical energy of the turbine into usable electrical energy

5. Picture of Generator

6. Generator Three phase, 4 pole AC generator
Frame pressurized with hydrogen gas for cooling and low windage losses
Stator windings cooled with circulating demineralized water
Full load rating of MVA (1354 MW at .9 pf, MW at .8 pf)

7. Basic Generator Theory
Requires three elements: conductor, magnetic field, and relative motion
Power output is proportional to the number of conductors, strength of the magnetic field, and speed of rotation (motion or shaft torque)

8. Basic Generator Theory

9. Basic Generator Theory (cont.)
Number of conductors in the generator is fixed
Speed (or shaft torque when paralleled) is controlled by the attached steam turbine
provides for power control - MWatts
Magnetic field strength is controlled by the rotor field current fed by the voltage regulator
provides for voltage control - MVars

10. Basic Generator Theory (cont.)
MWatts - megawatts- is actual power (dollar$)
MVAR - reactive power - represents the total current and voltage losses inherent with AC generation, transmission, and use.

11. Basic Generator Theory (cont.)
When the generator is paralleled to the grid:
power output (MW) is proportional to the torque (or push) of the turbine
reactive power output (MVAR) is proportional to the rotor field current

12. Main Generator

13. Generator Details
Enclosure Housing: Contains within its boundary the Rotor, Stator, and Hydrogen Cooler.
The Enclosure Housing is pressurized with hydrogen gas which is used as the cooling medium for the rotor and stator windings.

14. Generator Details
Stator : stationary winding through which electric current is induced by the rotating field windings
Function - collect the induced current and provide a circuit path to the output of the generator (output bushings)
Stator is cooled by Stator Cooling Water

15. Stator Bar

16. Generator Details (cont.)
Rotor : directly couple to the shaft of the Main Turbine and rotates at 1800 rpm synchronous speed (or 60hz)
Function - supply a regulated, rotating DC field to induce voltage, and resultant current flow in the generator stator windings
Rotor is cooled by the hydrogen gas

17. Picture of Rotor

18. Generator Details Stator Core - securely holds stator windings
Stator End-Turns - provides winding connections for a continuous circuit
Hydrogen Blower - circulates cooling hydrogen
Hydrogen Cooler - heat exchanger for hydrogen gas supplied by OLACW

19. Generator Details
Bearings : supports shaft and bears load of the generator weight and torque
Bushings : provides gas-tight electrical terminal for connection of output power to isolated-phase bus

20. Function of Exciter
Controls generator output voltage by varying the current to the generator rotating field windings

21. Exciter
Permanent Magnet Generator (PMG) supplies AC power to the Voltage Regulator
Voltage Regulator supplies DC field current to the Exciter
Exciter output is rectified and sent to the Rotor through leads in the shaft

22. Picture of Exciter

23. Exciter Diagram

24. Exciter Details
Self powered from attached Permanent Magnet Generator (PMG)
PMG consists of 24 permanent magnets located on the end of the exciter shaft. Produces : 120vac at 420hz
PMG also supplies power to the EH Governor Cab. and Turbine Supervisory Panels

25. Exciter Details
Power from PMG is rectified to DC, regulated by the voltage regulator, and applied to the exciter stationary field.
Larger AC power is produced in the exciter rotating windings and is rectified to DC by diodes mounted on the shaft
The DC is sent down the internal of the shaft to the attached rotor field

26. Exciter Details
Exciter Housing cooled by internal air circulation which includes a heat exchanger cooled by CLACW
Contains automatic rotor ground detection system, which provides for manual or automatic (once per 24hr) operation
Exciter bearing ungrounded to prevent circulating currents in the shaft which will attack the bearing seating surfaces

27. Picture of Exciter

28. Exciter Details
The output of the exciter is controlled by the Voltage Regulator
This controls the field current which controls the output voltage of the generator
While in parallel, the Voltage Regulator controls MVAR loading.

29. Voltage Regulator Diagram

30. Voltage Regulator Details
Two modes of operation:
Manual - regulator output set by rheostat, non-regulated or compensated. Sets base voltage output of generator
Automatic - regulator monitors output and regulates to a desired setting. Sets the MVAR loading of the generator

31. Voltage Regulator Cabinet

32. Generator Protection
Generator trips protect the Generator and Main Turbine in the event of a fault condition within the 25KV system
Protection is provided by coordination of:
Voltage Regulator Trips / Protective Actions
Field Breaker Trips
Generator Output Breaker Trips

33. Generator Support Systems
Generator Hydrogen Gas System
Generator Stator Cooling Water System
Generator Seal Oil System
Isolated-Phase Bus and Duct Cooling System
Closed Loop Auxiliary Cooling Water System

34. Hydrogen Gas System

35. Hydrogen Gas System
Provides filtered, pressurized (75 psig) hydrogen cooling medium for generator internals to aid in heat removal
Vital to obtaining full rated output of generator
Also provides for safe purging of hydrogen gas with carbon dioxide

36. Hydrogen Gas System
Besides cooling, the hydrogen gas system functions include
ability to purge to air using carbon dioxide
indication for pressure, temperature, moisture, and purity
ability to dry and remove impurities
pressurizes Stator Cooling Water system tank

37. Main Generator

38. Hydrogen Gas System Disadvantages of using Hydrogen
Explosive over wide range of concentration
Not detectable to senses
Advantages of using Hydrogen
High thermal conductivity
High specific heat capacity
Low density - low windage losses
Readily available - inexpensive
Does not contribute to corrosion

39. Stator Cooling Water System

40. Stator Cooling Water System
Uses filtered, demineralized water to remove heat from the stator coils.
Allows for obtaining more power from less copper in the coils
Also cools Main Lead Bushings, Neutral Bus and Bushings, and Current Transformers (CT’s)

41. Stator Cooling Water System

42. Stator Cooling Water System
Besides providing cooling water to the stator bars, the system also provides:
Cooling to the generator bushings
Cooling to the neutral bus segments
Cooling to current transformers (CTs)
Heat exchangers cooled by CLACW
Incorporates expansion tank which is maintained with hydrogen pressure (2 psig) for corrosion control

43. Stator Cooling Water System
Stator Cooling Water Skid (located beneath generator on 29’elev. east-side) contains:
2 full-capacity motor driven pumps (1 run, 1 backup)
2 heat exchangers
2 demineralizer beds
2 filter beds
2 heater banks
Instrumentation, and alarms
pressure, flow, core differential pressure
conductivity, oxygen concentration
tank level

44. Seal Oil System

45. Generator Seal Oil System
Provides lubrication to the generator gland seals and acts as a separating medium between internal hydrogen and outside air.
Two sub-systems
Air-Side Seal Oil – primary sealing oil against internal hydrogen pressure
Hydrogen Side Seal Oil – secondary sealing oil, increases efficiency of system to near 100%

46. Seal Oil System
Provides for maintaining full rated hydrogen pressure at shaft penetrations to generator frame
Each side has two seals; air-side and hydrogen-side
Oil pressure is maintained about 12 psig above generator gas pressure
Differential between oil and gas pressure must be maintained to prevent leakage
Pressure at both seals about the same for gas-tight seal

47. Seal Oil System
Air-side seal oil system shares oil with main lube oil system
Hydrogen-side seal oil is a closed loop system with provisions for removing entrained hydrogen gas from the oil
Each side has its own heat exchanger, supplied by CLACW

48. Seal Oil System

49. Seal Oil System
Seal Oil Skid (located beneath generator on 29’elev. west-side) contains:
3 seal oil pumps ; hydrogen-side, air-side, and air-side backup
2 oil coolers, 2 cuno-type filters
3 tanks ; hydrogen-side receiver, hydrogen-side drain regulator, air-side reservoir (includes heater)
4 regulating valves, 3 pressure relief valves
Instrumentation ; pressures, differential pressures, temperatures, tank levels, alarm

50. Isolated Phase Bus and Duct Cooling

51. Isolated-Phase Bus and Duct Cooling System
Connects the output of Main Generator (25kV) to the primary (input) windings of the main transformers.
Provides cooling of the enclosed circuit path bus conductors

52. Isolated Phase Bus and Duct Cooling
Consists of
Isolated Phase Bus Conductors
Tubular, all welded aluminum mounted on porcelain insulators
Isolated Phase Bus Enclosure Duct
Continuous weather and dust tight aluminum housing suitable for outside use
Bus and Duct Expansion Joints
Allows for expansion and contraction of bus and duct due to loading, temperature changes, and short circuit conditions
Disconnect Links
Stranded flexible connectors that make connection between the generator and the isolated phase bus

53. Isolated Phase Bus and Duct Cooling
Also:
Isolated Phase Bus Cooling
The busses between the main generator and the transformer are forced-air cooled
Consists of two full-capacity fans and heat exchangers
Surge Protection and Potential Transformer Cubicles
Contains the components that provide signals to instrumentation and protective relaying

54. Main Generator Output Breaker
Connects and disconnects generator output with the AC distribution system for protection of the generator
3 breakers poles – one per phase
Integral part of bus ducting
Operated by compressed air

55. Main Turbine Generator & Exciter
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