Excitation
System
By
Susobhan Patra
5/8/2014
Excitation System
General Conception
Different Types of Excitation systems
Operational characteristics
Case studies- sharing ideas
Ef
j XsI t
Xs Iacos
Vt
Ia
Phasor diagram
Xs Iasin
Basic dynamo principle
= B cos A
= BA cos t
Change of magnetic flux = d/ dt
Rate of change of magnetic flux d/ dt = -BA sin t
i.e. e = NBA sin t
e0 = NBA
e = e0 sin t
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. Hence, an emf is
induced in the coil and a current flows in it in a direction given by 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. The torque gives a
continuous rotary motion to the coil in the magnetic field.
AVR- Automatic voltage control system
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
Frequency
50 Hz
Power factor 0.85 (lagging)
Field current for rated output
833 amps
Field voltage 202 V
(TGS)
CONNVENTIONAL EXCITATION SYSTEM FOR ALTERNATOR
ALTERNATOR
OUTPUT
PILOT
EXCITE
R
ALTERNATOR
FIELD
MAIN
EXCITE
R FIELD
PILOT EXCITER
5/8/2014
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
GENERATOR
EXCITER
AUXILIARY SLIPRINGS
..
Y
B
..
.
.
..
.
.
..
.
.
.
.
.
.
P.M.G. SINGLE PHASE
PILOT EXCITER
500/5A
C.T.
5/1 A
C.T.
EXCITER TERMINAL BOARD
J1 J2
A AXCITER/ GEN. FIELD
V31 CURRENT AMMETER
X XX 1 2 3 4 5 6 7 8 9 10 11 12
FOR TEST ONLY
A.V.R. CUBICLE
5/8/2014
Slip Ring
for rotor
voltage
FB &
protection
5/8/2014
Rotating
Rectifier
Main
Exciter
Armature
PMG
Excitation System: Specification
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)
5/8/2014
PILOT EXCITER
MAIN EXCITER
SOLID
SHAFT
PERMANENT
MAGNET FIELD
ON ROTOR,
ARMATURE ON
STATOR
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
5/8/2014
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
B2
1N
3P
C2
2N
4P
A2
3N
5P
B2
4N
6P
C2
5N
NEGATIVE DIODE CARRING RING
7P
A2
6N
8P
B2
7N
9P
C2
8N
ROTOR WINDING
A2
2P
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
5/8/2014
TO ROTOR VOLT METER
AND ROTOR E/F RELAY
Lamp
5/8/2014
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
The output from rectifier is directly connected to the generator
rotor
Carbon brushes are used for voltage measurement & rotor
protection system- rotor E/F
There are two channels for operation control
5/8/2014
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
5/8/2014
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
X12
X113
X113
X14
X14
X12
PIN 51
X12
X13
X13
CCM 6080
X113
DCS800 Box
D1D4
AO
D5
GDI
X113
CCM6080
UG
IG
Optical Links
Ethernet
Excitation Control Terminal
Display of actual values
Local operation of the excitation system
Parameter settings
Transient recorder
Event/Fault recorder
5/8/2014
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 failure
detection
Ie
Rotating rectifier
Diode failure
5/8/2014
Set point V/Hz Limiter
Setting range V/Hz
UG set point
UG max setpoint
UG nominal
UG min set point
Allowed range of operation
f nominal
5/8/2014
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
5/8/2014
SEE
5/8/2014
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
U>70%
Generator
Thyristor
bridge
Sequence:
5s
10s
Field flashing OFF Field flashing failed
FCB Trip
Field breaker CLOSE
Excitation ON
Pulses to the thyristors are released
Field flashing breaker
Diode
Bridge
Field Flashing breaker closes if start up
with residual machine voltage is to low
Stator voltage raises
Field flashing breaker opens
Auxiliary
Sources
5/8/2014
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.
Channel 2 (The MANUAL):
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.
5/8/2014
E.T.
THYRISTOR
BRIDGE
3 CHANNELS
PT
Pulse Trafo
AVR
Pulse Trafo
Pulse Trafo
CT
BACK
Q1
G
ROTOR
Q2
5/8/2014
SCHEMATIC DIAGRAM FOR STATIC EXCITATION SYSTEM
FIELD FLASHING SUPPLY
5/8/2014
Q&A
Thank you very much
Save Energy
5/8/2014
