Generators What its all about
How do we make a generator?
Synchronous Operation
Rotor Magnetic Field
Stator Magnetic Field
Forces and Magnetic Fields
Force Between Fields
Motoring Generators & motors are the same thing Generators motor if they are synchronized and the governor is closed Power flows in from the grid
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
Generator Simplified Equivalent Circuit
Phasor Diagram
Increasing Steam Flow
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
Generator Prior to Synchronization
Magnetic Core Heating
Conditions for Synchronization Phase sequence Voltage magnitude Frequency I a =0 Phase angle E V T
I a =0 + + E V T V V V Grid Generato r being paralleled to Grid - - Grid
Machine slower than system Generator Grid
Phase Angle Generator Grid
Properly Synchronized Generator Grid
Synchronizing Equipment Grid System Generator being paralleled to the grid V System Slow Fast V Generator
Armature Reaction N Rotor S N S Stator
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
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
AVR
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
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
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
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
Governor Control I L Turbine V T Steam No Load Setpoint Gov. Valve Speed Governor Shaft Speed Variable Load Droop Setting
Speed Droop Electrical word for proportional control Speed Drop NL to FL Droop = 100% Rated Speed Isochronous - proportional + integral
Isochronous Freq. % Speed Change 62.4 +4% 61.8 +3% 61.2 +2% Isochronous Governor 60.6 +1% 60Hz 0 Constant Frequency 59.4 58.8 58.2-1% -2% -3% 25% 50% 75% 100% 200 400 600 800 % Rated Load or MW 57.6-4%
4% Droop Freq. % Speed Change 62.4 61.8 +4% +3% E D Governor Speed Droop 61.2 60.6 60Hz 59.4 +2% +1% 0-1% C B A Loading Un-Loading 25% 50% 75% 100% 200 400 600 800 % Rated Load or MW 58.8-2% 58.2-3% 57.6-4%
Effect of Adding Load
Generator Synchronized
Increasing Load 0.3 Hz{ 0.3 Hz{ 61.5 61.2 61 60.9 60.5 60 59.5 50 MW Frequency (Hz) 59 58.5 50 MW 300 200 100 0 100 200 300 Load Generator G1 (MW) Load Generator G2 (MW)
Freq. 62.4 Unequal Speed Droops 61.8 B 61.2 60.6 60Hz A 59.4 58.8 600 400 200 200 400 600 Load MW G1 G2
Finite Bus 61.2 61 60.5 }0.6 Hz 60 0.6 Hz{ 59.4 Frequency (Hz) 59 58.5 300 200 100 0 100 200 300 Load Generator G1 (MW) Load Generator G2 (MW)
Frequency Restoration 0.6 Hz{ 61.8 61.2 61 60.5 60 }0.6 Hz 59.4 Frequency (Hz) 59 58.5 300 200 100 0 100 200 300 Load Generator G1 (MW) Load Generator G2 (MW)
Adjusting Steam Flow Steam Flow Armature Current Active Power Re active Po we r 1.0 Power Factor (Lagging).6 Time
Adjusting Excitation Field Current Armature Current Active Power Re active Po we r 1.0 Power Factor (Lagging).6 Time
Stability P V T X Transmisson Line V s Large System P = V T V s sin X
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 1 0 0 Load Angle δ 180 0 t 3
Out of Step Angular + Velocity Pole slipping commences here (90 ) Rapid acceleration during pole slip (90-360 ) 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)
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
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
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
H 2 Pressure
Cooling
For You To Do