by
Michael J. Basler
With great assistance by the IEEE/PES
Excitation System Sub-Committee
Introduction
Excitation systems can be broken down into three basic types:
Type DC - dc commutator type exciters
Type AC - Alternator supplied rectifier excitation systems
Type ST - Static excitation systems
Control Techniques
Modern Control Techniques
Proportional, Integral and Derivative
PID for type DC and AC excitation systems
PI for type ST excitation systems
Rate Feedback
Control Techniques
Type DC
V
OEL
ALTERNATE
OEL INPUTS
V
UEL
V
S
V
C
V
REF
+
_
Σ
_
+
ALTERNATE
UEL INPUTS
V
UEL
V
RMAX
/K
A
K
P
+
K
I
sK
D
+ s 1+sT
D
V
RMIN
/K
A
HV
GATE
V
OEL
LV
GATE
V
T
Π
V
T
*V
RMAX
K
A
1+sT
A
V
R
+
-
Σ
V
T
*V
RMIN
Σ
+
+
V
X
V
1 sT
E
EMIN
K
E
V
X
=V
E
S
E
(E
FD
)
E
FD
V
F sK
F
(1 + sT
F
)
Control Techniques
Type AC
K
P
V
T
V
S
V
UEL
V
C
V
RMAX
+ +
-
+
Σ
-
K
PR
+
K s
IR + sK
+
DR
DR
V
RMIN
+
-
Σ K
PA
+
K
IA s
V
AMIN
V
AMAX
V
A π
-K
L
V
FE
+
Σ
V
EMIN
V
FEMAX
K
E
+ S
E
− K
D
I
FD
[ ]
1
1 + sT
E
V
E
V
Ref
+
Σ
+
K
F2
V
FE V
X
V
X
= V
E
S
E
[V
E
] sK
F3
1 + sT
F
+
Σ
+
+
Σ
+
K
E
π
F
EX
F
EX
= f [I
N
]
I
N
I
N
=
K
C
I
FD
V
E
K
D
I
FD
K
F1
E
FD
V
C
V
U E L
Control Techniques
Type ST
K
G
V
S
V
O E L
-
+
+
Σ
+
V
R m a x
K
P R
+
K
IR s
V
R 1
1 + s T
A
+
-
Σ
V
M m a x
K
P M
+
K
IM s V
M
L V
G a te
V
R m in
V
R E F
V
M m in
π
E fd
V
T
I
T
V
E
= | K
P
V
T
+ j(K
I
+ K
P
X
L
) I
T
|
V
E π
I
F D
I
N
= K c
I
F D
V
E
I
N
F
E X
= f(I
N
)
F
E X
V
B m a x
V
B
Control Techniques
Adaptive controls
Gain modification based on PSS status
Artificial Neural Networks
Fuzzy Logic
Optimal Control
Control Techniques
Intelligent Techniques
No known “production” excitation systems based on intelligent techniques
Controller gains typically tuned at no load, plant changes gain / time constant with load – non-optimal settings
Industry concerns about adaptive controls
Control Techniques
Power System Stabilizers
Single Input Stabilizers
Speed
Frequency
Power
Dual Input Stabilizers
Integral of Accelerating Power type PSS
Multi-band PSS
Adaptive PSS
Intelligent Techniques
Control Techniques
V
SI1MAX
V
SI1 sT
W1
1 + sT
W1
Power System Stabilizers sT
W2
1 + sT
W2
1
1 + sT
6
+
+
∑ 1 + sT
8
(1 + sT
9
) M
N +
-
∑
K
S1
1 + sT
1
1 + sT
2
V
SI1MIN
K
S3
V
SI2
V
SI2MAX sT
W3
1 + sT
W3 sT
W4
1 + sT
W4
K
S2
1 + sT
7
V
SI2MIN
1 + sT
3
1 + sT
4
1 + sT
10
1 + sT
11
V
STMAX
V
STMIN
Control Techniques
Supplemental Controls
Reactive Current Compensators
var/PF Controllers
Over / Under Excitation Limiters
V/Hz Limiters
Stator Current Limiters
Field Temperature Limiters
Limiter set points may be a function of cooling gas temperature / pressure
Redundancy
Manual Backup
Direct Control of Power Stage
Field Voltage / Current Regulator
Excitation Limiters
Auto-tracking
Auto-transfer
Redundancy
Redundant AVRs
Dual AVRs
Automatic Transfer
Watchdog
Autonomous External Module
Automatic Tracking
Best 2 of 3 voting
Redundancy
Redundancy
Power Converter Redundancy
Twin Excitation Systems
N+1 Redundancy
Current Sharing
Paralleling Inductors
Electronic Current Sharing Control
Redundancy
Dual Redundant
Power Bridges
Protection
Excitation System Protection
Converter temperature
Thyristor conduction monitoring
Converter fuse failure detection
Fan monitoring
Power potential transformer overload and fuse failure
Loss of sensing pt detection
Exciter phase unbalance
Protection
Generator Protection
Generator terminal over and under voltage
Field over voltage and over current
Volts per hertz
Field over temperature
Loss of excitation
Rotating diode monitoring
Field ground detection
Communications
Intra-unit Communications
Many digital excitation systems implement some form of communications within the controller
For information exchange among modules within the excitation system
Communications
Intra-unit Communications
Modern digital excitation systems use serial or parallel data format
Provide data exchange between the main processor and other circuits or modules in the excitation system
Communications channel is designed for a high degree of noise immunity
Fiber optics may be used to avoid influence from electrical noise
Communications protocols are typically proprietary to the equipment manufacturer
Communications
Inter-unit Communications
There are a number of situations where communications between separate excitation system controllers is necessary
Redundant controllers
To facilitate bumpless transfer
Sharing of reactive current among machines in parallel
To eliminate need for cross connection of CTs
Communications
External Communications
Most digital excitation systems provide a means to communicate to external devices
Various communications protocols used
USB
RS-232 / RS-485
Ethernet TCP/IP
Used to interface with
Overall plant control computer
Prime mover controls
User interface via a PC or PLC
Most external communications protocols include some form of password protection for security
Diagnostics
Self-Test
Most modern digital excitation systems provide some form of self-test
May include test of the memory elements and various power supply levels
Watchdog
Provided on most digital systems
Operates autonomous of the processor
Requires the processor to periodically service the watchdog function
If a problem exists, then the processor is reset and an alarm is issued
Diagnostics
Oscillographic Records
Many systems provide this feature
Records store many data points
Triggered by a variety of parameters
Variable number of data points per record
Variable time interval between data points
User specified amount of pre-trigger
Records may be stored in a non-volatile memory for recall and display at a later time
Diagnostics
Diagnostics
Diagnostics
Diagnostics
Event Logging
Parameters monitored by the excitation system can be set up to trigger an event log
Logs are typically date and time stamped and identifies what parameters changed when the event occurred
Time stamp may be synchronized with a system clock or using an IRIG-B signal
Input/output status changes, alarms and system status changes can be used to trigger an event log
These logs may also be stored in non-volatile memory for recall at a later time
Diagnostics
DECS-200 SEQUENCE OF EVENTS REPORT ( New Events ) Qty = 123
REPORT DATE : 24-05-06
REPORT TIME : 11:24A25
STATION ID : STATION ID
DEVICE ID : DECS 200
USER1 ID : USER 1 ID
USER2 ID : USER 2 ID
--DATE-- ----TIME---- --------POINT DESCRIPTION-------- --STATUS--
--------------------------------------------------------------------------------
24-05-06 11:07A53.973 STOP CONTACT DISABLED
24-05-06 11:07A52.822 SOFT START MODE STARTUP
24-05-06 11:07A52.772 ON/OFF RELAY DISABLED
24-05-06 11:07A52.672 UNDERFREQUENCY ALARM OFF
SYSTEM BELOW 10 HZ ALARM OFF
STOP/START STOP
24-05-06 11:07A52.622 STOP CONTACT ENABLED
24-05-06 11:07A52.221 SOFT START MODE OFF
24-05-06 11:07A47.617 START CONTACT DISABLED
24-05-06 11:07A47.266 ON/OFF RELAY ENABLED
24-05-06 11:07A47.216 SYSTEM BELOW 10 HZ ALARM ON
24-05-06 11:07A47.166 UNDERFREQUENCY ALARM ON
STOP/START START
24-05-06 11:07A47.066 START CONTACT ENABLED
Summary
Provide a general overview of the state of the art in excitation systems
Advent of digital-based excitation systems resulted in significant advancement in control and protective functions
Many more details available to the interested reader
Review the IEEE421 series of standards or
Contact the Excitation System Sub-Committee
Acknowledgements
The author would like to acknowledge the contribution of the members of the
IEEE/PES Excitation System Sub-
Committee, its chairman Om Malik, its working groups and task forces.
Questions?