2. PURPOSE OF EXCITATION SYSTEM
• REGULATE TERMINAL VOLTAGE OF THE MACHINE.
• MEET EXCITATION POWER REQMTS UNDER ALL NORMAL
OPERATING CONDITIONS.
• ENABLE MAXIMUM UTILISATION OF MACHINE CAPABILITY.
• GUARD THE MACHINE AGAINST INADVERTANT TRIPPING
DURING TRANSIENTS.
• IMPROVE DYNAMIC & TRNSIENT STABILITY THEREBY
INCREASING AVAILABILITY.
3. PERFORMANCE SPECIFICATION OF
EXCITATION SYSTEM
• ACCURACY OF VOLT. REGLN. : +/- 0. 5 %
• RANGE OF AUTO CONTROL : 90 TO 110 % OF UGN
• RANGE OF MANL CONTROL :75 %NL TO 110 % FL If
• RANGE OF DROOP/DROP COMPSN : 0 TO 15 %
• FREQ. RANGE OF OPERATION : 47 TO 52 HZ
• FIELD FORCING FACTOR : 1.6 TO 2.0/2.2
• FIELD FORCING TIME : MAX 10 SECONDS
• RESPONSE RATIO & TIME : 2 TO 4 & < 20 mSEC
• VOLT.RISE ON FL THROW-OFF : < 15 %
• CHANGE OF GEN. VOLT : <= +/- 1 %
WITH CHL. CHANGE OVER
4. TYPES OF EXCITATION SYSTEM:
1.INDIRECT EXCITATION (BRUSHLESS EXCITATION)
2.DIRECT EXCITATION (STATIC EXCITATION)
• INDIRECT EXCITATION (Brushless Excitation)
• APPLICATION IN SYN MACHINE (THERMAL/GAS)
• EXCITATION POWER TO EXCITER FIELD WINDING
• THE EXCITER ARMATURE RECTIFIED OUTPUT TO MAIN FIELD
WINDING ( ON THE ROTOR)
• ROTATING DIODES MOUNTED ON THE ROTOR
• INPUT POWER TO EXCITATION FROM PMG/AUX SUPPLY
5. AUTO MANUAL CONTROLS
POWER
SUPPLY
POWER
SUPPLY
POWER
SUPPLY
POWER
SUPPLY
INTERFACE
USYN1
MICROPROCESSOR BASED H/W
GATE
CONTROL
GATE
CONTROL
USYN2
LOGIC
CONTROL
FIELD CURRENT
REGULATOR
AVR
WITH LIMITERS
PULSE
AMPLIFIER
AUTO. CHL
PULSE
AMPLIFIER
MAN. CHL
FCB
FDR
.
G
GRID
*
LCD
CT
PT
REF
MICRO TERMINAL
STN. AUX. SUPPLY (FOR TESTING)
.
FROM PMG/PE O/P
STN. BAT. SUPPLY
AUTOMATIC VOLTAGE REGULATOR
ALARM
A M C/O
TRIP
If
GEN. O/P
STN. AUX. SUP.
THYRISTOR
BRIDGES
USYN1
USYN2
P
E
V
AVR CUBICLE
CT
PT
REF
7. MICROTERMINA
L
KEYBOARD
DISPLAY
READ AND WRITE
READ ONLY
PARAMETER
SETTINGS
REFERENCE
VALUES
INTERMEDIATE
VALUES
K - FLAGS
PARAMETER
SETTINGS &
REFERENCE
VALUES
SPARE
K - FLAGS
SUBPROGRAMS
R
A
M
E
E
P
R
O
M
E
P
R
O
M
E
P
R
O
M
V
I
II
III
IV
COMPUTER UNIT UN 0660
MEMEORY STRUCTURE FOR AVR APPLICATION
8. AVR channel 1 Software version HIER 452555R2 in AA49
FUNCTION ELEMENT DE-
FLT
FACTORY
SETTING
OK.BY
TEST/COMMN
K-Flags (factory settings to be
altered temporarily only) KDVR
0000= OFF
1111= ON
Active current compensation F710 X 0000 OK / ______
Reactive current compensation F712 X 1111 OK / ______
V/Hz limiter F714 X 1111 OK / ______
Softstart F716 X 1111 OK / ______
Reactive load discharge F718 X 0000 OK / ______
Set point preset to bus voltage F71A X 0000 OK / ______
Follow up of cos phi reference
value F71C X 0000 OK / ______
Follow up of reactive power ref.
value
F71E X 0000 OK / ______
Actual value for superimpimposed
CTRL from external X-ducer
F720 X 0000 OK / ______
Tie line power factor regulator F722 X 0000 OK / ______
Additional analog input F724 X 0000 OK / ______
Rotor current reduction due to
overtemp.
F726 X 0000 OK / ______
9. List of Parameters for Auto channel-1:
FUNCTION ELEM
ENT
ADJUST
MENT RANGE
FACTORY
SETTING
OK.BY
TEST/COMMN
2. Voltage reference value
Preset C250 50....120% 100 % OK / ______
Maximum value C252 100...142% 110 % OK / ______
Minimum value 1 C254 0.....100% 90 % OK / ______
Minimum value 2 C256 0.....100% 90 % OK / ______
Fullrange traveltime 1 C258 0.1...120s 60 s OK / ______
Fullrange traveltime 2 C25A 0,1...120s 60 s OK / ______
Softstart traveltime C290 0.1...65,5s 5 s OK / ______
3. Reactive load discarge
Pulsetime C260 0.1...10s 1 s OK / ______
Pausetime C262 0.1...60s 1 s OK / ______
Sensitivity C264 0.....100% 5 % OK / ______
4. V/Hz limiter
Max. overvoltage
U-p.u/f-p.u C280 0.9..1,3p.u. 115 % OK / ______
Time delay C28E 0....65,5s 0s OK / ______
5. Reactive / active current influence
Reactive current Influence C282 0....20% 0 % OK / ______
Polarity ( 0000=DROOP;
FFFF = COMP) C284 see left FFFF OK / ______
Active current influence C286 0....20% 0% OK / ______
Polarity (0000=DROOP
FFFF=COMP) C288 see left 0000 OK / ______
10. S-
SIGNAL FLOW OF MANUAL CHANNEL UP TO THY GATE
I from CT
f
R+
DEVICE
PULSE
TRANS-
FORMER
FROM/TO
UN0662 OF PLC FUNCTION
ANALOG
I/P
MODULE
UNC4660
BINARY
SIGNALS
PI
REGULATION
REF
FOR
FLD
CURRENT
REG
U R,S,T 110VAC
sync 22V AC
3V DC
AT RATED
ANALOG
SIGNALS
FOLLOW
UP
PULSE
GENERATION
GATE CONTROL
UNIT UN0663
UN0096
PULSE
INTERM
STAGE
DC
SHORT
CKT
PROTECTION
UN0809/UN0097
PULSE
FNL
STAGE
R+
T-
S+
R-
T+
CHNL BLOCK
BRIDGE BLOCK
12. PID PARAMETERS
V∞ is the gain at high frequencies, as this will come into picture for a very small
time and when the frequency is very high (as t->0, ν ->∞)
Vo is the steady state gain (static amplification).
Vp is the proportional amplification.
Ta is the integration time constant.
Tb is the differential time constant.
t1 in the PID response is determined by the factor Vp/V∞*Tb.
t2 in the PID response is determined by the factor Vo/Vp*Ta.
13.
14. Over (Maximum)-Excitation Limiter: OEL
Under this classification we have:
• Maximum Field Current Limiter
• Stator current inductive limiter
• V/Hz limiter
Maximum Field Current limiter:
It protects the rotor from over-currents occurring
in steady state due to improper raising of the voltage set point
by the operating staff, or
during transient operation caused by sharp drop in system
voltage due to increased reactive power requirements from
switching of large motors or from faults near the generator
OEL detects the field-over current condition and acts with time
delay to ramp down the excitation to a preset value ( typically
100-110% of rated field current).
16. 9. Field current Limiter
Thermal reference value 1 C400 0...300%Ifn 105 % OK / ______
Thermal reference value 2 C402 0...300%Ifn 71 % OK / ______
Ceiling reference value 1 C406 0...300%Ifn 160 % OK / ______
Ceiling reference value 2 -HIER
452542 C40E 0...300%Ifn 120 % OK / ______
Ceiling time C408 0...32,7s 10 s OK / ______
Attenuation factor of limiter
output
C40A 0...100% 50 % OK / ______
du/dt setting for Iceiling release C40C 0...3000%/s 400 % OK / ______
Back integr. time Ifdn , dim.
s/p.u.
-
C414 0,02..600 s 9,6 s OK / ______
" I
2
*t -ITIf C416 0...500 p.u. 6,0* p.u. OK / ______
Ceiling release (IFmx
0000=AUS; 1111=EIN C418 0000/1111 1111 OK / ______
* matching with o/c monitoring.
17. 9. Field current Limiter
Inversetime(ROTI 0000=AUS;
1111=EIN
C41A 0000/1111 1111 OK / ______
10. Minimum field current limiter
Reference value C410 0...100% 5 % OK / ______
11. Inductive stator current limiter
Thermal reference value C430 0...142% 105 % OK / ______
C432 not used 105 % OK / ______
Maximum reference value -
200%=inactive C434 0...142% 200 % OK / ______
Overcurrent time C436 0...32,7s 10 s OK / ______
Attenuation factor of limiter
output C438 0...100% 50 % OK / ______
du/dt setting for Iceiling release C43A 1...3000%/s 400 % OK / ______
Minimum reactive current
limitaion C43C 0...30% 2 % OK / ______
Back integration time -IGdn C440 0,02..600 /p.s. 8,3 /p.s OK / ______
I
2
*t -IT/IF C442 0...500p.u.*s 21,6 p.u. OK / ______
Ceiling relase (IGmx
0000=AUS; 1111=EIN C444 0000/1111 1111 OK / ______
Inversetime (GENI
0000=AUS; 1111=EIN C446 0000/1111 1111 OK / ______
IG signal (IGrn 0000=3V; -
1111=7V C448 0000/1111 1111 OK / ______
18. Over (Maximum)-Excitation Limiter: OEL
V/Hz Limiter:
This limiter is activated if ‘V/Hz ratio’ exceeds 1.15 pu on the
generator base. This is an over-excitation condition that can
cause saturation of the magnetic core of the generator and/or
the connected transformer. Damage can occur within seconds.
V/Hz protection is provided for generator & transformer from
these excessive magnetic flux density levels.
This limiter comes in to operation for the cases when,
m/c connected to grid & frequency dips to a value to enhance
V/Hz ratio more than 1.15.
Generator in under-excited mode and terminal voltage rises to
make V/Hz ratio > 1.15
Under the above conditions AVR reduces excitation to restore
V/Hz ratio.
19. Minimum (Under)-Excitation Limiter: MEL
Generators may operate in an under-excited condition due to
power system condition or equipment failure :
• power system condition:
during light system loads, transmission lines behave as
reactive power sources; therefore the generators are required to
draw excessive reactive power to prevent high-voltage system
conditions.
• equipment failure:
an AVR failure in a generator ( in the grid) could drive this
unit to an over-excited condition and create an excess of
reactive power that needs to be absorbed by the nearby
generators. These nearby generators may reach under-excited
operating conditions.
20. Minimum (Under)-Excitation Limiter: MEL
Under this classification we have:
• Capacitive Stator Current limiter
• Load Angle limiter
Capacitive stator current limiter:
When the drive output from turbine is very high for the operating
voltage, stator current may exceed permissible limits. This limiter
holds the stator current Ig within permissible limits- while the
generator is in the under-excited operating region- by increasing the
field current as required. Thus excitation is increased because for
reducing leading generator current (Ix) the generator calls for increase
in the field current.
When the capacitive loading of the machine is low, this limiter is
prevented from influencing the field current, or else the control circuit
will oscillate back & forth between the Inductive stator current limiter
( de-exciting) and the Capacitive stator current limiter ( exciting)
21. Minimum (Under)-Excitation Limiter: MEL
Load Angle limiter:
This limiter prevents the synchronous machine from slipping
out of phase due to slippage of the rotor.
The load angle ‘delta’, the difference in phase between the
rotor & the stator rotating field, results mainly from the driving
torque ( active power P) acting on the generator and the level
of rotor current (excitation). If the driving torque remains
constant, an increase in the excitation reduces load angle
‘delta’.
The set point is the permissible rotor angle delta, definable by
the leading reactive power region of the capability diagram of
the generator. It can be a straight line or a multiple segment
representation on the capability diagram.
22. Ig
LOAD ANGLE COMPUTATION
E : Induced EMF in the air gap
Ug : Gen. terminal voltage
Unet : Grid voltage
Ig : Gen. current
Xq : Quadrature axis reactance
Xe : External reactance
ɗ : Load angle
Ig. Xq
Ig. Xe
Ug
E
Unet
ɗ2
ɗ1
ɸ
Xe = (change in voltage
Ug/ Ugn) / (change in
MVAR/ S)
Ug = Generator terminal
Voltage
Ugn= rated generator
terminal voltage.
S= Rated MVA capacity of
generator.
23. 12. Stator current limiter under excited
Reference value C460 0...142% 105 % OK / ______
Attenuation factor C462 0...100% 25 % OK / ______
13. Ixmin/Ir limiter underexcited
Reference value C480 - 0...-100% -100 % OK / ______
Active current influence C482 0....100% 20 % OK / ______
Attenuation factor C484 0....100% 30 % OK / ______
14. Load angle limiter
- Reference value C4A0 0....179 75el OK / ______
Attenuation factor of limiter
output C4A2 0....100% 30 % OK / ______
Quadrature reactance xq C4A4 0....3p.u. 2 p.u. OK / ______
- External reactance C4A6 0....2p.u. 0.2 p.u. OK / ______
15. Additional analog input
Attenuation factor C520 - 0....100% 100 % OK / ______
16. Superimposed regulator
Running time for cos phi ref.
value C504 1....120s 120 s OK / ______
Running time for Q-reference
value C506 1....120s 120 s OK / ______
Preset for cos phi reference
value
C508 -0..1..+0 1 OK / ______
Preset for Q-reference value C50A 0... 100% 0 % OK / ______
Pausetime for pulseregulator C50C 1....60s 1 s OK / ______
28. CONFIGURATION OF PLC FUNCTION
BINARY CONTROLS
OUTPUT INTERFACE
UNC 4662
INPUT/OUTPUT
UN0662
SIGNALING
UN0665
INPUT INTERFACE
UNC 4661
OUTPUT SIGNALS INPUT SIGNALS
CRU IN
CRU OUT
SERIES
BUS
PROCESSOR
UN 0660
MICRO TERMINAL
DATA TRANSFER
TO THE DIGITAL
VOLTAGE
REGULATOR
ADRESS BUS
31. THYRISTOR BRIDGE( AVR)
• One bridge is provided for each of the
channels (AUTO & MANUAL)
• The bridges are natural air cooled and
fully controlled with RC snubber ckt.
• Final pulse stage for each bridge
• Line or arm fuses (with monitoring)
• One of the bridges conduct depending
on the active channel
• Conduction monitoring(optional)
32. PULSE SEQUENCE
0° 60° 360°
60° 120°
120° 180°
180° 240°
240° 300°
300° 360° / 0°
1R+
2T-
3S+
4R-
5T+
6S-
DOUBLE PULSES ARE REQUIRED FOR SIMULTANEOUS FIRING OF
ONE POSITIVE ARM AND ONE NEGATIVE ARM OF THYRISTOR
BRIDGE DURING STARTING
24V
0V
36. FUNCTIONAL TEST AT
STAND STILL
• Periodical functional test increases
reliability (best of all during overhaul of TG
group)
The main activities involved are :
• Checking the connections (cables, wires,
connectors )
• Checking for wear on the mechanical parts
(e.g : relays, switches)
• Testing the electronics equipment
• Testing the power supplies and measurement
Circuits
• Testing pulse generation and amplification.
• Testing the monitors.
38. 1. Schematic diagram number
2. Name of the functional group
3. Page Number
4. Designation of Location
5. Assignment of connection for the signal
6. Processing priority
7. Internal address
8. Output address to UN0665 (without an “Assignment of connection” )
9. Output address, binary/analog ( with an “Assignment of connection” )
10. Designation for the signal
11. Signal plain reference
12. Plain text
SIGNAL OUTPUT FROM THE BINARY CONTROLS
39. 1. Plain text
2. Signal designation
3. Signal cross-reference
4. Input address, binary/analog ( with an “Assignment of connection” )
5. Internal address
6. Input address, binary or analog (without an “Assignment of connection” )
SIGNAL INPUT FOR THE BINARY CONTROLS
40. 1. Location of the module
2. Wire-Wrap connection
DIRECT HARDWARE SIGNALS ON MODULES
