generator overview
TRANSCRIPT
-
8/20/2019 Generator Overview
1/66
1/29/20
th -
School
Generation Track
Overview Lecture
Generator Design, Connections, and
Grounding
-
8/20/2019 Generator Overview
2/66
1/29/20
Generator Main Components
• Stator
– Core lamination
– Winding
• Rotor
– Shaft
– Poles
– Slip rings
Stator Core
Source: www.alstom.com/power/fossil/gas/
-
8/20/2019 Generator Overview
3/66
1/29/20
Stator (Core + Winding)
Core Lamination
Winding Connections
Winding (Roebel bars)
Typical Types of Generator Windings
Stator Winding: Random-Wound Coils
-
8/20/2019 Generator Overview
4/66
1/29/20
Typical Types of Generator WindingsStator Winding: Form-Wound Coils
Typical Types of Generator Windings
Stator Winding: Roebel Bars
-
8/20/2019 Generator Overview
5/66
1/29/20
Roebel Bars Inside Stator Slot
Source: Maughan, Clyde. V., Maintenance of Turbine Driven Generators, Maughan Engineering Consultants
Stator Winding Combinations
Typical for Two- and Four-Pole Machines
-
8/20/2019 Generator Overview
6/66
1/29/20
Series Connection of Roebel Bars
Source:www.ansaldoenergia.com/Hydro_Gallery.asp
Rotor
-
8/20/2019 Generator Overview
7/66
1/29/20
Classification of Synchronous
Generators
Rotor designCylindrical rotor
Salient-pole rotor
Cooling: Stator and
rotor
Direct
Indirect
connection to dc
source
Brushless
Rotor Design
Salient-Pole Rotor
-
8/20/2019 Generator Overview
8/66
1/29/20
Two-Pole Round Rotor
Source: www.alstom.com
Salient Pole Rotor
Source:www.ansaldoenergia.com/Hydro_Gallery.asp
-
8/20/2019 Generator Overview
9/66
1/29/20
Stator Winding Cooling
Directly CooledIndirectly Cooled
Cooling Ducts,
Water Cooled Bar
Rotor Winding Cooling
Directly CooledIndirectly Cooled
-
8/20/2019 Generator Overview
10/66
1/29/20
Field Winding Connection to DC Source
Brush Type
Field Winding Connection to DC Source
Brushless
-
8/20/2019 Generator Overview
11/66
1/29/20
Generator Station Arrangements
Generator-Transformer Unit
Generating Station Arrangements
Directly Connected Generator
-
8/20/2019 Generator Overview
12/66
1/29/20
• Resonant roundin Petersen Coil
IEEE C62.92.2-1989
Synchronous Generator Grounding
• Ungrounded neutral
• High-resistance grounding
• Low-resistance grounding
• Low-reactance grounding
• Effective groundingIncreasing Ground
Fault Current
Why Ground the Neutral?
• Minimize damage for internal ground faults
• Limit mechanical stress for external ground faults
• Allow for ground fault detection
• Ability to coordinate generator protection withother equipment requirements
-
8/20/2019 Generator Overview
13/66
1/29/20
Ungrounded Neutral
• No intentional connection to round
• Maximum ground fault current higher than forresonant grounding
• Excessive transient overvoltages may result
High-Resistance Grounding
distribution transformer
• Resistor value selected to limit transient overvoltages
• Maximum single-phase-to-ground fault current: 5–15 A
-
8/20/2019 Generator Overview
14/66
1/29/20
Low-Resistance Grounding
• Limit ground fault current to hundreds of
amperes to allow operation of selective
(differential) relays
• Low temporary/transient overvoltages
Effective Grounding
• A low-impedance ground connectionwhere: X0 / X1 3 and R0 / X1 1
• roun au curren s g
• Low temporary overvoltages during phase-to-ground faults
-
8/20/2019 Generator Overview
15/66
1/29/20
Generator Capability Curves
Defining Generator Capability• Curve provided by the generator manufacturer
• Defines the generator operating limits during steadys a e con ons
• Assumes generator is connected to an infinite bus
• Limits are influenced by:
– Terminal voltage
– Coolant
– Generator construction
-
8/20/2019 Generator Overview
16/66
1/29/20
Generator Capability Curve for a
Round Rotor Generator
Generator
Capability
Curve for a
Salient Pole
Generator
-
8/20/2019 Generator Overview
17/66
1/29/20
Capability Curve Construction
Phasor Diagram – Round Rotor Generator
)cos()sin(
)cos(
0
V
I Xd E
I V P
0 E
Xd
I
V
)cos()(
coss n0
I V BC Xd
V
Xd
)sin( I V Q
φ
C
0 E
P
)sin()(
)sin()))cos(((
s ncos
0
0
I V AB Xd
V
I V V E Xd
V
A B
V
I Xd
Q I
-
8/20/2019 Generator Overview
18/66
1/29/20
Power Angle Characteristic
P
Operation with Constant Active Power
and Variable Excitation
C
I Xd
C’C’’
A B
0 E
V
Q
I 0 E 0 E
I Xd I Xd
B’B’’
P
I
I
Q
Q
4513.1
606.1
87.361
00.1
6.1
I
I
I
V
Xd
5.7831.1
7.21466.3
15.3334.2
0
0
0
E
E
E
-
8/20/2019 Generator Overview
19/66
1/29/20
Power Angle Characteristic
5.7831.1
7.21466.315.3334.2
0
0
0
E
E E P
V-Curves
).( u p I
(p.u.)0 E
CurrentExcitation
inductivecos cap.cos
-
8/20/2019 Generator Overview
20/66
1/29/20
Operation with Constant Apparent
Power and Variable Excitation
0 E
I Xd
A B
I
87.361
00.1
6.1
I
V
Xd
Operation with Constant Excitation
and Variable Active Power
0 E
C
0 E
I Xd
I T h e o r .
S t a b i l i t y
L i m i t
A B
V
I Xd
I
-
8/20/2019 Generator Overview
21/66
1/29/20
Capability Curve – Round Rotor
E
I V V E Xd
V
-
0
)sin()))cos(((
0
0
t a b i l i t y
L i m
i t
0P
0
)cos()sin(
0
0
E
I V E Xd
V
Xd Q
T h e o r .
S
P ( R e a
l P o w e r )
max.
625.0VV-
Q
Xd
0.1
6.1
V
Xd
Q (Reactive Power)
Generator Fault Protection
-
8/20/2019 Generator Overview
22/66
1/29/20
Generator Fault Protection
• Stator phase faults
• Stator ground faults
• Field ground faults
• External faults (backup protection)
Stator Phase Fault Protection
• Phase fault protection
– Percentage differential
– High-impedance differential
– Self-balancing differential
• Turn-to-turn fault protection
– Split-phase differential
– Split-phase self-balancing
-
8/20/2019 Generator Overview
23/66
1/29/20
Phase Fault Protection
Percentage Differential
Dual-Slope Characteristic
-
8/20/2019 Generator Overview
24/66
1/29/20
Phase Fault Protection
High-Impedance Differential
O O O
Phase Fault Protection
Self-Balancing Differential
http://www.polycastinternational.com/old_cat/pdfs/Section4/Section4-Part2.pdf
-
8/20/2019 Generator Overview
25/66
1/29/20
Stator Winding Coils with Mult iple Turns
Turn-to-Turn Fault Protection
Split-Phase Self-Balancing
-
8/20/2019 Generator Overview
26/66
1/29/20
Turn-to-Turn Fault Protection
Split-Phase Percentage Differential
Stator Ground Fault Protection
• High-impedance-grounded generators
– Neutral fundamental-frequency overvoltage
– Third-harmonic undervoltage or differential
– Low-frequency injection
• Low-impedance-grounded generators
– Ground overcurrent
– Ground directional overcurrent
– Restricted earth fault (REF) protection
-
8/20/2019 Generator Overview
27/66
1/29/20
Ground Fault in a Unit-Connected
Generator
High-Impedance Grounded Generator
Neutral Fundamental Overvol tage
Fault Location/
% of Winding
Voltage V
F1 / 3%
F2 / 85%
3%•3
Vnom
85%•3
Vnom
-
8/20/2019 Generator Overview
28/66
1/29/20
Generator – Flux Distribution in Air Gap
Total Flux
Fundamental
Harmonics
Generator – Flux Distribution in Air Gap
Neutral Third-Harmonic Undervoltage
F1
GSU
High-Impedance Grounded Generator
59GNRV(3) OR (2)
27TN
Full Load
No LoadVN3
No Fault
VP3
No Load
VP3
VN3
Fault at F1
-
8/20/2019 Generator Overview
29/66
1/29/20
Third-Harmonic DifferentialGSU
High-Impedance Grounded Generator
59GNRV
(3)
(3)
–+
Pickup Setting
• 3 3k VP VN
Third-Harmonic Differential Element
Generator Winding Analysis
• Generator data
–
– 216 slots
• Winding pitch
– Full pitch = 216/18 = 12 slots
– Actual pitch = 128 – 120 = 8 slots
– Actual pitch / full pitch = 8/12 = 2/3
-
8/20/2019 Generator Overview
30/66
1/29/20
Full-Pitch Winding
2/3 Pitch Winding
Removes Third Harmonic
-
8/20/2019 Generator Overview
31/66
1/29/20
Low-Frequency InjectionGSU
High-Impedance Grounded Generator
(3) OR (2)
I
59GNR V
64S
Coupling
Filter
Low-Frequency
Voltage Injector
Protection
Measurements
100% Stator Ground Fault Protection
Elements Coverage
-
8/20/2019 Generator Overview
32/66
1/29/20
Low-Impedance-Grounded Generator Ground Overcurrent and Directional Overcurrent
Low-Impedance-Grounded Generator
Ground Differential
-
8/20/2019 Generator Overview
33/66
1/29/20
Low-Impedance-Grounded Generator
Self-Balancing Ground Differential
Zero-Sequence CTs
5 / $ f i l e / 1 v a p
4 2 8 5 6 1 - d
b_
b y z . p
d f
r i t y d i s p
l a y
/ b e a a e
b 0 1 2 3 3 7 6 5 4 1 8 3 2 5 7 3 4 6 0 0 6 2 a
7 6
h t t p : /
/ w w w
0 5
. a b b
. c o m
/ g l o b a
l / s c o
t / s c o
t 2 3 5
. n s
f / v
Zero-sequence CT
-
8/20/2019 Generator Overview
34/66
1/29/20
Field Ground Protection
Field Ground Protection
• Types of rotors
• Winding failure mechanisms
• Importance of field ground protection
• Field ground detection methods
• Switched-DC injection principle of operation
• Shaft grounding brushes
-
8/20/2019 Generator Overview
35/66
1/29/20
Salient Pole Rotor
Source:www.ansaldoenergia.com/Hydro_Gallery.asp
A Round Rotor Being Milled
Source: Maughan, Clyde. V., Maintenance of Turbine Driven
Generators, MaughanEngineering Consultants
-
8/20/2019 Generator Overview
36/66
1/29/20
Round Rotor – End Turns
Source: Main Generator Rotor Maintenance – Lessons Learned - EPRI
Source: Main Generator Rotor Maintenance – Lessons Learned - EPRI
Two-Pole Round Rotor
Source: www.alstom.com
-
8/20/2019 Generator Overview
37/66
1/29/20
Two-Pole Round Rotor
Source: www.alstom.com
Two-Pole Round Rotor
Source: www.alstom.com
-
8/20/2019 Generator Overview
38/66
1/29/20
Round Rotor Slot — Cross Section
Coil Slot
Wedge
Copper Winding
Creepage BlockRetaining Ringe a n ng ng
Insulation
Winding Short
Slot Armor
Turn InsulationEnd Windings
Winding GroundWinding Ground
Field Winding Failure Mechanisms inRound Rotors
• Thermal deterioration
• Thermal cycling
• Abrasion
• Pollution
•
-
8/20/2019 Generator Overview
39/66
1/29/20
Salient Pole Cross Section
Pole Body
Turn Insulation
Winding Turn
Winding Ground
Windin Short
Insulation
Pole Collar
* Strip-On-Edge
Field Winding Failure Mechanisms inSalient Pole Rotors
• Thermal deterioration
• Abrasive particles
• Pollution
• Repetitive voltage surges
•
-
8/20/2019 Generator Overview
40/66
1/29/20
Importance of Field Ground
Detection
• Presence of a single point-to-ground in fieldwinding circuit does not affect the operation ofthe generator
• Second point-to-ground can cause severedamage to machine
– Excessive vibration
– Rotor steel and / or copper melting
Rotor Ground Detection Methods
• Voltage divider
• DC injection
• AC injection
• Switched-DC injection
-
8/20/2019 Generator Overview
41/66
1/29/20
Voltage Divider
Field Breaker Rotor and Field Winding
+
–
Exciter BrushesR1
R2
R3
Grounding BrushSensitive Detector
DC Injection
+
Field Breaker Rotor and Field Winding
–
Exciter Brushes
Sensitive Detector
roun ngBrush
DC Supply
+
–
-
8/20/2019 Generator Overview
42/66
1/29/20
AC Injection
+
Field Breaker Rotor and Field Winding
–
Exciter Brushes
Sensitive Detector roun ng
Brush
AC Supply
Switched-DC Injection Method
+
Field Breaker Rotor and Field Winding
–
Exciter
Grounding
BrushR1
Brushes
Measured Voltage
R2
Rs
-
8/20/2019 Generator Overview
43/66
1/29/20
Switched DC Injection Princ iple of Operation
VDC
Voscp
R
R
Cfg
Rx
+
–Vrs
Voscn
Vosc
Measured Voltage (Vrs)
Rs
V
Vrs
Shaft Grounding with Carbon Brush
-
8/20/2019 Generator Overview
44/66
1/29/20
Shaft Grounding with Wire Bristle Brush
Source: SOHRE Turbomachinery, Inc. (www.sohreturbo.com)
Generator Abnormal Operation
Protection
-
8/20/2019 Generator Overview
45/66
1/29/20
Generator Abnormal Operation
Protection
• Thermal • Overvoltage
• Current
unbalance
• Loss-of-field
• Abnormalfrequency
• Out-of-step
•• Motoring
• Overexcitation
energization
• Backup
Stator Thermal Protection
Generators With Temperature Sensors
-
8/20/2019 Generator Overview
46/66
1/29/20
Stator Thermal Protection
Generators Without Temperature Sensors
2 2 I I
22
ln NOM
T I k I
Current Unbalance Causes
• Single-phase transformers
• Untransposed transmission lines
• Unbalanced loads
• Unbalanced system faults
• Open phases
-
8/20/2019 Generator Overview
47/66
1/29/20
Generator Current Unbalance
Produces negative-sequence currents that:
– Cause magnetic flux that rotates in opposition to rotor
– Induce double-frequency currents in the rotor
Rotor-Induced Currents
-
8/20/2019 Generator Overview
48/66
1/29/20
Negative-Sequence Current Damage
Negative-Sequence Current Capabil ity
Continuous
Type of Generator I2 Max %
Salient pole (C50.12-2005)
Connected amortisseur windings 10
Unconnected amortisseur windings 5
Cylindrical rotor (C50.13-2005)
Indirectly cooled 10
Directly cooled, to 350 MVA 8
351 to 1250 MVA 8 – (MVA – 350) / 300
1251 to 1600 MVA 5
-
8/20/2019 Generator Overview
49/66
1/29/20
Short Time
22 2 I t K
Negative-Sequence Current Capabil ity
Type of Generator I22t Max %
Salient pole (C37.102-2006) 40
Synchronous condenser (C37.102-2006) 30
Cylindrical rotor (C50.13-2005)
Indirectl cooled 30
Directly cooled, to 800 MVA 10
Directly cooled, 801 to 1600 MVA →
Short Time
Negative-Sequence Current Capabil ity
-
8/20/2019 Generator Overview
50/66
1/29/20
Negative-
Sequence
Overcurrent
22
2
K T
I
NOM
Common Causes of Loss of Field
• Accidental field breaker tripping
• Field open circuit
• Field short circuit
• Voltage regulator failure
• Loss of field to the main exciter
• Loss of ac supply to the excitation system
-
8/20/2019 Generator Overview
51/66
1/29/20
Effects of Loss of Field
• Rotor temperature increases because of
edd currents
• Stator temperature increases because of
high reactive power draw
• Pulsating torques may occur
• Power system may experience voltage
collapse or lose steady-state stability
Negative-Sequence Current Caused
Damper Winding Damage
Damper
Windings
-
8/20/2019 Generator Overview
52/66
1/29/20
LOF Protection Using a Mho Element
LOF Protection Using Negative-
Offset Mho Elements
-
8/20/2019 Generator Overview
53/66
1/29/20
LOF Protection Using Negative- and
Positive-Offset Mho Elements
Zone 2 Setting Considerations
-
8/20/2019 Generator Overview
54/66
1/29/20
Possible Prime Mover Damage
From Generator Motoring
•
• Hydraulic turbine blade cavitation
• Gas turbine gear damage
unburned fuel
T ical values of reverse ower re uired to
Small Reverse Power Flow
Can Cause Damage
spin a generator at synchronous speed
Steam turbines 0.5–3%
Hydro turbines 0.2–2+%
Diesel engines 5–25%Gas turbines 50+%
-
8/20/2019 Generator Overview
55/66
1/29/20
Directional Power Element
Q
P
32P1
32P2
P1
P2
Overexcitation Protection
• NOM f V
• Overexcitation occurs when V/f exceeds
1.05
• Causes enerator heatin
NOM
• Volts/hertz (24) protection should trip
generator
-
8/20/2019 Generator Overview
56/66
1/29/20
Core Damaged due to Overexcitation
Source: Maughan, Clyde. V., Maintenance of Turbine Driven Generators, Maughan Engineering Consultants
Core Damaged due to Overexcitation
Source: Maughan, Clyde. V., Maintenance of Turbine Driven Generators, Maughan Engineering Consultants
-
8/20/2019 Generator Overview
57/66
1/29/20
Overexcitation Protection
Dual-Level, Definite Time Characteristic
Overexcitation Protection
Inverse- and Defini te Time Characterist ics
-
8/20/2019 Generator Overview
58/66
1/29/20
Overvoltage Protection
• Overvoltage most frequently occurs iny roe ec r c genera ors
• Overvoltage protection (59):
– Instantaneous element set at 130–150percent of rated voltage
– Time-delayed element set at approximately
110 percent of rated voltage
Abnormal Frequency Protection
-
8/20/2019 Generator Overview
59/66
1/29/20
Possible Damage From
Out-of-Step Generator Operation
•
• Damage to shaft resulting from pulsating
torques
• High stator core temperatures
• Thermal stress in the step-up transformer
Single-Blinder Out-of-Step Scheme
-
8/20/2019 Generator Overview
60/66
1/29/20
Double-Blinder Out-of-Step Scheme
Generator Inadvertent Energization
• Common causes: human errors, control,
• The generator starts as an induction motor
• High currents induced in the rotor causerapid heating
• High stator current
-
8/20/2019 Generator Overview
61/66
1/29/20
Inadvertent Energization Protection
Logic
Logic for Combined Breaker-Failure
and Breaker-Flashover Protection
-
8/20/2019 Generator Overview
62/66
1/29/20
Backup Protection
Directly Connected Generator
Generator With Step-Up Transformer
Voltage-Restrained Overcurrent
Element Pickup Current
-
8/20/2019 Generator Overview
63/66
1/29/20
Mho Distance Element Characteristic
Synchronism-Check Element
-
8/20/2019 Generator Overview
64/66
1/29/20
Power System Disturbance Caused
by an Out-of-Synchronism Close
Nominal Current: 10560 A
Voltage: 6.5 kV
Possible Damaging Effects
During Synchronizing
• Bearing damage
• Loosened stator windings
• Loosened stator laminations
-
8/20/2019 Generator Overview
65/66
1/29/20
IEEE Generator Synchronizing
Limits
rea er c os ng ang e –
Generator-side voltage
relative to system
100% to 105%
Source: IEEE Std. C50.12 and C50.13
Frequency difference +/–0.067 Hz
Issues Affecting Generator
Synchronizing
• Voltage ratio differences
• Voltage angle differences
• Voltage, angle, and slip limits
Synchronism
Check relay
Synchronism
Check relay
-
8/20/2019 Generator Overview
66/66
1/29/20
Synchronism-Check Logic Overview