Synchronous generator and Static Excitation system
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Full description
Excitation System
y Susobhan Patra
5/8/2014
Excitation Excitation System • General Conception • Different Types of Excitation systems • Operational Operational characteristics characteristics • Case studiesstudies- sharing sharing ideas ideas
Ef
j XsI t
s acos
δ
Vt
Ø Ia
Phasor diagram
Xs IasinØ
Excitation Excitation System • General Conception • Different Types of Excitation systems • Operational Operational characteristics characteristics • Case studiesstudies- sharing sharing ideas ideas
Ef
j XsI t
s acos
δ
Vt
Ø Ia
Phasor diagram
Xs IasinØ
Basic dynamo principle Φ
= B cos Ø A = BA cos ωt
Change of magnetic flux = d Φ / dt
Rate of change of magnetic flux i.e.
dΦ / dt = -BA ω sin ωt e = NBA ω sin ωt e0 = NBA ω e = e0 sin ωt
Generator When a closed coil is rotated rapidly in a strong magnetic field, the number of magnetic flux lines passing through the coil changes continuously. continuously. Hence, an emf is induced in the coil and a current current flows in it in a direction given by FRH FRH Rule
Motor When a current is passed through a coil placed in a magnetic field, the coil experiences a torque in a direction given by FLH Rule. Rule. The torque gives a continuous rotary motion to the coil in the magnetic field.
AVR- Automatic voltage control s ystem
If
Synchronous Machine
Excitation System Controller
Ug
Specification
5/8/2014
• • • • • • •
Apparent power in air 70.59 MVA Active power 60 MW Phase Current 3881 amps No of phases 3 No of poles 2 Terminal Voltage 10.5 ± 5 KV Speed 3000 rpm
• • •
Power factor 0.85 (lagging) Field current for rated output Field voltage 202 V
833 amps
(TGS)
CONNVENTIONAL EXCITATION SYSTEM FOR ALTERNATOR
ALTERNATOR OUTPUT
PILOT EXCITE R ALTERNATOR FIELD
MAIN EXCITE R FIELD
PILOT EXCITER
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MAIN EXCITER
3-Ph
ALTERNATOR
From
Pulse from Auto channel control
AUTI Channel Thyristor bridge
PMG
MANUAL Channel Thyristor bridge
Pulse from Manual channel control
Field Breaker
Gen
Gen. Rotor
Rotating Diode Bridge
Main Exciter
Schematic Diagram for Brush Less excitation System 5/8/2014
Main Exciter Rotating Diode Bridge
PMG
• • • •
Brush Less excitation System 5/8/2014
Case studies: Failure of PMG Failure of fuse Failure of Magnet Rise in PMG Temp
BRUSHLESS EXCITATION SUSTEM ROTATING RECTIFIER UNIT
Main Exciter Maxm continuous rating 207 KW Rated terminal voltage (at 225 VDC Rectifier DC terminals) Rated current (at rectifier 920 ADC DC terminal Frequency 150 Hz Rated speed 3000 rpm No of phases 3 No of poles 6 Rotating Rectifier Diodes (Positive) type IR GB 490 / U Diodes (Negative) type IR GB 491 / UR No of rings 2 No. of + ve diodes per ring 9 No. of - ve diodes per ring 9 Peak inverse voltage of diodes 2200 V repetitive peak volts Connections Full wave, 3 arm bridge with 3 parallel paths per arm Fuse type EE GSA 250 No of fuses 18 Fuse current rating 250 A rms Fuse voltage rating 240 A rms Neon indicators 18 (one per parallel path)
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PILOT EXCITER
SOLID SHAFT
PERMANENT MAGNET FIELD ON ROTOR, ARMATURE ON STATOR
MAIN EXCITER
ROTATING RECIFIER HOLLOW SHAFT
ARMATURE ON ROTOR, FIELD WINDING ON STATOR
SILICON DIODE BRIDGE ON SHAFT 3-Ph (3-ph 150 Hz at TGS)
3-ph power (1-Ph 200Hz at TGS)
Alternator terminal Controlled dc to field on stator
THYRISTOR CONTORLLED BRIDGE
C.T
AVR
REGULATOR
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Alternator field
P.T
Rotating Rectifier Ring -VE
Carbon Brush on slip rings for measurement of Rotor Voltage & protection 5/8/2014
Rotating Rectifier Ring +VE
Terminal block
ROTATING RECTIFIER ASSEMBLY OF BRUSHLESS EXCITATION SYSTEM NEON LAMP DIODE
FUSE AUX. SLIP RING
POSITIVE DIODE CARRING RING
1P
A2
1
2P
B2
2
1N
3P
C2
2N
3
4P
A2
3N
4
5P
B2
4N
5
6P
C2
5N
NEGATIVE DIODE CARRING RING
6
7P
A2
6N
7
8P
B2
7N
9P
8
C2
8N
R O T O R W I N D I N G
9
9N
AUX. SLIP RING
1P, 2P, 3P, 4P………….9P : DIODE & FUSE ASSEMBLY ON POSITIVE RING 1N, 2N, 3N, 4N………..9P : DIODE & FUSE ASSEMBLY ON NEGATIVE RING
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TO ROTOR VOLT METER AND ROTOR E/F RELAY
Lamp
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Diode
Fuse
Brushless Excitation • No use of any brush • PMG output is fed to the AVR • AVR output is the field for the main exciter • Main exciter output is directly coupled with the rotating rectifier • rotor • Carbon brushes are used for voltage measurement & rotor protection system- rotor E/F • There are two channels for operation control
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AUTO Mode • It is built as a voltage regulator and is ON during normal operation & the reference point is set through manual switch • Various limiters and corrective control circuits are used for stable operation up to operating limits. • In case of any malfunction the AVR will change over to manual mode
MANUAL Mode: • It is built as a simple field current regulator • It serves as a back up channel in case of failure of the AUTO channel. • Operations in this channel require expert adjustment and continuous monitoring of the parameters as there is no automatic limiter action. 5/8/2014
Digital AVR with BL Excitation
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3.2.3 UN6080 Control HW n
Power INterface UNITROL 6080 Hardware Devices (D1..D4)
PIN608 0 CCM6080
PIN608 0 CCM6080
PIN608 0 CCM6080
Communication Control Measuring Combined IO
3.2.3 UN6080 Control HW n
Communication Control Measuring CCM6080 (UC D240)
CCM6080
CCM6080
CCM 6080
PIN – 6080 X12
X113
X14
AO
X14
D5
PIN – 51
CCM 6080 X12
X12
X13
X13
GDI X113
DCS800 Box
D1…D4
X12
X113
CCM6080
X113
UG
IG
Optical Li nks
Ethernet
• • • • • •
Excitation Control Terminal • Display of actual values • Local operation of the excitation system • Parameter settings • Transient recorder • Event/Fault recorder
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Providing variable DC current with short time overload capability Control terminal voltage on preset value with required accuracy Ensure stable operation with network and/ or other machines Keep machine within permissible operating range. Contribution to transient stability subsequent to a fault. Communicate with the power plant control system
Rotating Diode Failure
Band pass filter
Ripple Diode failur e detection Ie
t
Rotating rectifier Diode failure 5/8/2014
Set point V/Hz Limiter
Setting r ange V/Hz
UG set point UG max setpoint UG nominal UG min set point Allo wed ran ge of oper ati on
f nominal
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f
Static Excitation ( Digital Voltage regulator) •
The DVR regulates the voltage of the synchronous machine by direct control of the rotor current using thyristor converter.
•
Redundancy in the regulator section is ensured by means of two fully separate channels with independent measuring inputs, control and monitoring
Thyristor Converter for Excitation Control •
3 Phase fully controlled thyristor bridges, each bridge consisting of 6 thyristors, arm fuses & snubber circuit.
•
Cooling fan for keeping the junction temperature rise of every device within safe limits.
•
Pulse transformers for electrical isolation between power & control circuits and coupling the firing pulses to the gates.
•
Fuse monitoring Unit
•
Air Flow Monitoring Unit
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SEE
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Regulation
Field Flushing
Field Flashing Circuit Ug 100%
Softstart Field flashing off
U>70% Field flashing characteristic
Usyn
Thyristor bridge U>10% starts to conduct
AVR
Ug
Thyristor bridge
Generator
Sequence:
t 5s 10s Field flashing OFF Field flashing failed FCB Trip
• Field br eaker CLOSE • Excitation ON • Pulses to the thyri stors are released
Field flashing b reaker Diode Bridge
• Field Flashing b reaker clo ses if start up with residual machine voltage is to low • Stator volt age raises • Field flashing br eaker opens
Aux il iar y Sources
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~
+
• The softstart function raises the generator voltage smoothly up to its nominal value.
SEE
Complete Thyristor cubicle- 3 Channels One Thyristor panel 5/8/2014
SEE- Case study
Damaged holder
CB-32x32x64
Slip Ring & Carbon Brush Holder
5/8/2014
Channel 1 (The AUTO): •
It is built as a voltage regulator and is ON during normal operation.
•
Various limiters and corrective control circuits are used for stable operation up to operating limits.
•
In case of any malfunction the DVR will change over to Channel 2.
•
It is built as a simple field current regulator
•
It serves as a back up channel in case of failure of the AUTO channel.
•
No special limiters.
•
Operations in this channel require expert adjustment and continuous monitoring of the operating parameters.
•
In case of any malfunction of channel 2 it will lead to excitation failure.
