August 6, 2008
Expedited System Impact Assessment Report
Abitibi Consolidated Company of Canada
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
1.0
CAA ID Number: 2007-EX345
General Description
Abitibi-Consolidated Company of Canada have replaced the original pilot exciter on the gas turbine (G1) at their
Fort Frances (West Coast GS) site with a new Brush model A30 digital pilot exciter in May 2007. G1 is rated at
69.4 MVA @ 0.85 pF.
Abitibi-Consolidated have also replaced the original pilot exciter on the steam turbine (G2) with an identical
Brush model A30 digital pilot exciter. This replacement was completed in May 2008. The steam turbine (G2) is
rated at 54.9 MVA @ 0.85 pF.
While the main excitation systems on G1 and G2 were not modified, the installation of the new digital pilot
exciters will enable the automatic voltage regulator (AVR) and limiter functions. .
2.0
Models and Parameters
2.1
AVR and Exciter Model and Parameters for G1 and G2
The appropriate simulation model for both excitation systems is the IEEE type AC8B. The block diagram of
these excitation systems is shown in Figure 1. The parameters of the excitation systems for both G1 and G2 are
shown in Table 1.
Figure 1 - Block Diagram of Brush Exciter A30 - IEEE Type AC8B
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
(CAA ID Number: 2007-EX345)
Excitation system parameters for IEEE model type AC8B
Updated to reflect new pilot exciters
Description
Voltage transducer time constant
AVR proportional gain
AVR integral gain
AVR derivative gain
AVR derivative time constant
PID maximum limit
PID minimum limit
AVR power stage gain
AVR power stage time constant
AVR positive ceiling voltage
AVR negative ceiling voltage
Rectifier regulation
Demagnetizing constant
Exciter field proportional constant
Exciter time constant
Exciter field current limit
Exciter field proportional constant
Saturation coefficient
Saturation coefficient
Saturation coefficient
Saturation coefficient
CONs
Parameter
J
J+1
J+2
J+3
J+4
J+5
J+6
J+7
J+8
J+9
J+10
J+11
J+12
J+13
J+14
J+15
J+16
J+17
J+18
J+19
J+20
Tr
Kpr
Kir
Kdr
Tdr
Vpidmax
Vpidmin
Ka
Ta
Vrmax
Vrmin
Kc
Kd
Ke
Te
Vfemax
Vemin
E1
S(E1)
E2
S(E2)
Values
G1
G2
0.01
58
7
32
0.07
999
-999
1.04
0.01
10
0
0.15
1.57
1
1.2
8.8
0
11.5
0.54
13.4
2.03
0.01
173
16
36
0.1
999
-999
1.04
0.01
53
0
0.15
1.98
1
1.2
8.8
0
7
0.18
13
1.52
Table 1: AC8B Model Parameters for G1 and G2
2
Units
sec
sec
sec
sec
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
2.2
(CAA ID Number: 2007-EX345)
Generator Model
For completeness, the generator model parameters for G1 and G2 are shown in Table 2.
GENROU: Round Rotor Generator Model
Values
Description
D-Axis O.C. Transient Time Constant
D-Axis O.C. Sub-Transient Time Constant
Q-Axis O.C. Transient Time Constant
Q-Axis O.C. Sub-Transient Time Constant
Inertia
Speed Damping
D-Axis Synchronous Reactance
Q-Axis Synchronous Reactance
D-Axis Transient Reactance
Q-Axis Transient Reactance
D-Axis/Q-Axis Sub-Transient Reactance
Leakage Reactance
Open Circuit Saturation factor
Open Circuit Saturation factor
Cons
J
J+1
J+2
J+3
J+4
J+5
J+6
J+7
J+8
J+9
J+10
J+11
J+12
J+13
Parameter
T'do (>0)
T"do (>0)
T'qo (>0)
T"qo (>0)
H
D
Xd
Xq
X'd
X'q
X"d= X"q
Xl
S(1.0)
S(1.2)
Units
G1
G2
10.9
0.05
3.3
0.05
1.04
0
2.59
2.37
0.2
0.24
0.15
0.1
0.152
0.537
10.6
0.05
3.2
0.05
1.04
0
1.99
1.82
0.157
0.19
0.12
0.1
0.152
0.537
sec
sec
sec
sec
pu
pu
pu
pu
pu
pu
pu
pu
pu
pu
Table 2: IEEE GENROU Round Rotor Generator Model Parameters for G1 and G2
3.0
Assessment
G1 and G2 had been operating in power factor mode prior to the replacement of the pilot exciters. The pilot
exciters were replaced in order to have the ability to operate in voltage control mode, as required by the IESO
3.1
Excitation System Performance Testing
For situations where the main exciter is not replaced, appendix 4.2 of the Market Rules states that the original
excitation system design capabilities must be preserved. These design capabilities are determined by performing
excitation system performance tests.
In addition to the excitation system performance tests, dynamic simulations were performed to determine the
transient response of the excitation systems using the models and parameters determined during commissioning
of the new pilot excitation systems.
3
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
3.1.1
(CAA ID Number: 2007-EX345)
Open Circuit Tests
Open circuit tests for G1 and for G2 (figures 2 and 3) were used to evaluate the voltage response time to a 5%
step change in reference voltage.
Figure 2: Open Circuit Response Test Results for G1
The replacement of the pilot exciter on G1 results in a longer open circuit response time of 270 msec as
compared to the original open circuit response time of 160 msec.
4
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
(CAA ID Number: 2007-EX345)
Figure 3: Open Circuit Response Test Results for G2
The replacement of the pilot exciter on G2 results in a longer open circuit response time of 313 msec as
compared to the original open circuit response time of 139 msec.
5
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
3.1.2
(CAA ID Number: 2007-EX345)
Response Ratio Tests
The results of the excitation system response ratio test (Figure 4) indicate that the exciter positive ceiling voltage
exceeds the Market Rules requirements for both G1 and G2.
Figure 4: Response Ratio Test Results for G1 and G2
The test results show that the ratio of ceiling voltage to exciter rated field voltage for G1 is 2.8 pu, which is more
than twice the rated field voltage. The ratio for G2 is 2.6 pu, which is also more than twice the rated field
voltage.
The nominal response for each generator was calculated as follows:
Nominal Response for G1 =
Nominal Response for G2 =
9.37 − 3.24
3.24 × 0.5
4.53 − 2.90
2.90 × 0.5
= 3.78
= 1.12
6
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
3.1.3
(CAA ID Number: 2007-EX345)
Discussion
The results summarized in section 3.1.1 indicate that G1 and G2 exciters equipped with new pilot exciters
perform slower than the old systems and neither the new or the old systems meet the excitation systems time
response requirements.
The response ratio test results presented in section 3.1.2 meet the 2 p.u. exciter ceiling voltage requirement, as
listed in Reference 12 of Appendix 4.2 in the market rules.
These results indicate that the West Coast GS exciter systems do not meet the high level performance
requirements of Appendix 4.2 of the market rules. However, further analysis of the response ratio test results
shown in figure 4 indicates that the nominal response for G1 (gas turbine) is 3.78 and for G2 (steam turbine) is
1.12. Hence the two generators meet the lesser exciter system performance requirements in the market rules.
The performance of equipment that was in service at the opening of the electricity market was grandfathered.
The market rules only become applicable in cases where entire facilities, in this case the excitation systems,
would be replaced.
It can be concluded that the replacement pilot exciters result in a slightly slower time response of the exciters but
the exciters’ performance exceeds the lesser market rules requirements. To determine if the impact on system
reliability of the slower exciter behaviour is acceptable, transient stability analysis was carried out and the results
are discussed in the next section.
3.2
Contingency Analysis
Transient stability analysis was performed for a L-L-G fault on 115 kV circuit F1B at Fort Frances TS with
normal clearing time of 116 msec.
The excitation voltage, rotor angles, transient voltages and power flows for G1 and G2 at Abitibi's West Coast
Fort Frances facility were investigated. An example of plots of rotor angles for 10 seconds is shown in Figure 5.
7
Fort Frances West Coast G1 and G2 Pilot Exciter Replacements
(CAA ID Number: 2007-EX345)
Figure 5: Simulation Results for a LLG Fault on G1 and G2
The results show that G1 and G2 at Abitibi's West Coast Fort Frances facility display well damped and stable
performance for an L-L-G fault at Fort Frances TS. Although not shown in this report, simulated L-L-G faults
were also studied on circuits K24F, F25A and F3M with similar results.
It can be concluded that the replacement of the pilot excitation systems do not have a material adverse impact on
the dynamic performance of the system and hence on system reliability.
4.0
Conclusions
Although the replacement pilot exciters result in a slightly slower exciter time response, the exciters’
performance exceeds the lesser market rules requirements.
Although the exciter response appears to be slower, the 10 second simulation shows that for both the old and the
new pilot excitation equipment, the oscillations settle down within 4 seconds.
Furthermore, transient analysis for a severe fault close to the location of this facility (at Ft. Frances TS) show
well damped oscillations that settle down in approximately 6 seconds.
Based on these results it is concluded that system reliability is not materially affected and the replacement
equipment meets IESO requirements.
8