1. Generation of Electrical Energy: Sources and Generators
References:
Schavemaker, P. & van der Sluis, L., Electrical Power Systems Essentials, 2nd Ed, Wiley, 2017, pp. 53 et seq.
Hitachi Review Vol. 56 (2007), No. 4 pp. 99 et seq. at

2. Energy Sources by Fuel Type
Europe in 2006 – Bracketing Practices
Source
France
Germany
Thermal
22%
57%
Nuclear
55%
17%
Hydroelectric
21% 7%
Wind/PV 3%
19%
Total Installed Capacity
115 GW
124 GW
New England in 2009 – In-state Generation
Fuel Source
Rhode Island
Massachusetts
Coal
25%
Oil
15%
Natural Gas
99%
43%
Nuclear (U235)
12%
Biomass combustion 3%
Hydroelectric
< .01 1%
Wind/PV
<.01 2%

3. Thermal to Mechanical Energy Conversion
Temperature 450 to 650 deg. C
Superheater
Temperature 900 to 1450 deg. C
Nuclear and old coal plants use only Rankine cycle because combustion temperature is too low.

4. Efficiency – Endoreversible Thermodynamics
Carnot Cycle:
Endoreversible:
See: for an introduction to this subject. The endoreversible result is the same as the Carnot efficiency between a source at the geometric mean of T_H and T_C and the low temperature T_C.

5. Smooth and Salient Rotors with Stator Windings for Three-Phase Generation

6. Exciter

7. Exciting Wiring Customer Demand Generator Output
Turbine Fuel Valve Control and Rankine Exciter Control
Generator Output

8. The Unexciting Way – Slip Rings

9. Generator with Single Slot-Pair on Both Stator and Rotor
B, Flux, Voltage
Bad Idea Three Ways

10. Designing Rotor Windings to Give a Sine Wave
Spread the slots with the rotor wires unevenly around the rotor to form a stepwise approximation to a magnetic field that is sinusoidal around the circumference.

11. General Electric Smooth-rotor Generator Fully Assembled

12. Why so Big? Size, Power, Mechanical Design Constraints
Power is product of torque and angular velocity
Torque is force times radius at which it is applied. Force on circumference is proportional to product of B of the rotor with NISTAT of the stator and the length of the stator/rotor assembly
Let , called the “Electric loading,” be the ratio of NISTAT to the circumference of the rotor, then:
This expression is the product of the rotor volume, the operating frequency, the rotor peak field and the ampere turns per meter of rotor circumference. The frequency is fixed, the B field has practical limits from materials, and the electric loading also has practical limits from heat transfer and the properties of copper. As a result, the rotor volume is the simplest and principal design parameter to determine generator capacity.

13. Threading a Four-pole Cylindrical Rotor into the Stator of a 1525 MVA Generator

14. Schematic Representation of a Stator Structure – Provides Return Flux Path, Winding Retention and Ventilation Slots

15. Rotor with Bearings, End Caps, Winding and Ventilation Slots….

16. Structure of a Rotor with Slip-ring Excitation and Axial Fans for Cooling Windings

17. Poor Picture – Cross-section of Gas Cooling System: Gas Enters Through Rotor Shaft and Gap – Exits Through Slots in Stator

18. Cooling Stator and Rotor:
Water used to cool stator coils – copper tubing among wires or bar with pipe through it. High purity water (deionized) to avoid shorting output.
Gas cooling is required for the rotor and either gas or water cools the stator magnetic structure.
Hydrogen is used as coolant for generators over 100 MW
Advantages of hydrogen:
Density is 1/14 th that of air which implies the velocity of flow is times faster for a given pressure difference.
Specific heat by volume is the same for air and hydrogen, so if heat transfer is similar, hydrogen is more than 3 times as efficient
Filling above atmospheric pressure trades off viscosity and specific heat. Higher density pressurization improves heat transfer, that is, watts per deg. temperature difference is but at an increase in viscous drag.
Speed of sound is inversely proportional to the square root of molecular mass so speed of sound is 1270 m/sec vs. 330 m/sec for air
Disadvantages of hydrogen:
Flammability and explosive potential
Need to seal the generator and to reinforce its structure to withstand the pressure