Generators. What its all about

Transcription

1 Generators What its all about

2 How do we make a generator?

3 Synchronous Operation

4 Rotor Magnetic Field

5 Stator Magnetic Field

6 Forces and Magnetic Fields

7 Force Between Fields

8 Motoring Generators & motors are the same thing Generators motor if they are synchronized and the governor is closed Power flows in from the grid

9 Limits Under steady state conditions the load angle must be less than 90 Exceeding 90 leads to pole slipping Tremendous current and torque pulsations Can lead to catastrophic failures

10 Generator Simplified Equivalent Circuit

11 Phasor Diagram

12 Increasing Steam Flow

13

14 Synchronizing Machine is run up to speed 1800 rpm (4 pole machine) Field is applied Machine is adjust so E g = V t in magnitude and phase Breaker is closed to connect generator to the system

15 Generator Prior to Synchronization

16 Magnetic Core Heating

17 Conditions for Synchronization Phase sequence Voltage magnitude Frequency I a =0 Phase angle E V T

18 I a =0 + + E V T V V V Grid Generato r being paralleled to Grid - - Grid

19 Machine slower than system Generator Grid

20 Phase Angle Generator Grid

21 Properly Synchronized Generator Grid

22 Synchronizing Equipment Grid System Generator being paralleled to the grid V System Slow Fast V Generator

23 Armature Reaction N Rotor S N S Stator

24 Closing onto a dead bus Leading PF AVR will reduce excitation Lagging PF Terminal voltage will drop AVR increases excitation Faulted Bus High currents flow No load Nothing happens

25 Finite or Infinite Operation of the generator is apparently different Changes in steam valve position have no effect on speed (infinite) Changes in excitation only affect voltages locally Generator >5% gives finite characteristics

26 AVR

27 Resistive Load I R (Unity pf) R G X G V R V X = 0 E V T R Load V x E g V t I

28 Lagging Load I L (Lagging pf) R G X G V R V X E V T L Load E g -V x V t I

29 Capacitive Load I C (Leading pf) R G X G V R V X E V T C Load V t -V x E g I

30 V-curves Load MW (V Curve) 0.85 pf Lagging Load Load MVA 0.95 pf Leading Load (Under Excited) (AVR Bucking) Unity pf Load (Over Excited) (AVR Boosting) Decrease Increase Excitation Current

31 Governor Control I L Turbine V T Steam No Load Setpoint Gov. Valve Speed Governor Shaft Speed Variable Load Droop Setting

32 Speed Droop Electrical word for proportional control Speed Drop NL to FL Droop = 100% Rated Speed Isochronous - proportional + integral

33 Isochronous Freq. % Speed Change % % % Isochronous Governor % 60Hz 0 Constant Frequency % -2% -3% 25% 50% 75% 100% % Rated Load or MW %

34 4% Droop Freq. % Speed Change % +3% E D Governor Speed Droop Hz % +1% 0-1% C B A Loading Un-Loading 25% 50% 75% 100% % Rated Load or MW % % %

35 Effect of Adding Load

36 Generator Synchronized

37 Increasing Load 0.3 Hz{ 0.3 Hz{ MW Frequency (Hz) MW Load Generator G1 (MW) Load Generator G2 (MW)

38 Freq Unequal Speed Droops 61.8 B Hz A Load MW G1 G2

39 Finite Bus }0.6 Hz Hz{ 59.4 Frequency (Hz) Load Generator G1 (MW) Load Generator G2 (MW)

40 Frequency Restoration 0.6 Hz{ }0.6 Hz 59.4 Frequency (Hz) Load Generator G1 (MW) Load Generator G2 (MW)

41 Adjusting Steam Flow Steam Flow Armature Current Active Power Re active Po we r 1.0 Power Factor (Lagging).6 Time

42 Adjusting Excitation Field Current Armature Current Active Power Re active Po we r 1.0 Power Factor (Lagging).6 Time

43 Stability P V T X Transmisson Line V s Large System P = V T V s sin X

44 Power Transfer Curve Power Power Delivered to Load α V 2 V Before Fault P Steam t 0 Area B After Fault t 2 Area A During Fault t Load Angle δ t 3

45 Out of Step Angular + Velocity Pole slipping commences here (90 ) Rapid acceleration during pole slip ( ) Synchronism Speed Normal Operation (360-0 position) Generator tries to regain synchronism (a) Time MW Output Normal MW Output Surges in output power Time (b)

46 Generator Heating Q MVAR Reactive Power Lag Motoring U 2 = P 2 + Q 2 (Circle) U MVA Total Power Generating P MW Active Power Lead

47 Limits Q MVAR Reactive Power Lag A U 2 = P 2 + Q 2 (Circle) B 0.85 pf Lag U MVA Total Power < Motoring Generating > P MW Active Power Lead D C 0.95 pf Lead A-B Field Heating B-C Stator Heating C-D Stator Core End Heating

48 Stability Limits Q MVAR Reactive Power U 2 = P 2 + Q 2 (Circle) Lag A B 0.85 pf Lag U MVA Total Power < Motoring Generating > P MW Active Power Lead A-B Field Heating B-C Stator Heating C-D Stator Core End Heating Limit with No AVR Limit with Fast AVR

49 H 2 Pressure

50 Cooling

51 For You To Do