CAISO Presentation
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Sensitivity Studies
Northern California
Irina GreenCalifornia ISO
For Modeling and ValidationWorkshop, November 2006
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STUDY ASSUMPTIONS
• Operational case of July 29, 2003• Three-phase faults followed by opening of
the transmission lines in NorthernCalifornia
• Used BPA epcl. Added distribution
feeders and transformers• Load – 1 induction motor, resistive, and
constant power
• All loads throughout WECC modeled thesame way
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OUTAGES STUDIED
1. 230 kV line with a 6 cycle 3-phase fault at themost heavily loaded bus (Elk Grove-Rancho
Seco).2. Heavily loaded 230 kV line with a 6 cycle 3-
phase fault in an area that has an underline 60
kV system with long feeders (Tesla-Newark).3. The most heavily loaded 230 kV line with a 6
cycle three-phase fault (Newark-Ravenswood).
4. Heavily loaded 500 kV line with a 5 cyclethree-phase fault (Table Mountain-VacaDixon).
• Which outage is the worst?
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Induction Motor Parameters
Component Description XS XP TP H RS
Resid. Central Air Cond. or heat pump 2.476 0.135 0.136 0.28 0.033
Resid. Room Air Cond. 1.900 0.158 0.055 0.28 0.1
Resid. Refrigerator & Freezer 2.487 0.164 0.124 0.28 0.056
Resid. Dishwasher 2.940 0.199 0.069 0.28 0.11
Resid. Clothes Washer 2.120 0.242 0.051 0.69 0.11
Resid. Clothes Dryer 2.050 0.280 0.042 0.11 0.12
Comm. Central Air Cond. or heat pump 2.023 0.151 0.148 0.28 0.053
Comm. Pumps, Fans & other Motors 3.320 0.236 0.169 0.7 0.079
Ind. Heavy-Sm. Ind. Motors (5-200HP) 3.300 0.270 0.498 0.7 0.031
Ind. Heavy-Lg. Ind. Motors (200-UP HP) 3.867 0.230 1.170 1.5 0.013
Agricul. Pumping for Irrigation 3.288 0.249 0.559 0.8 0.025
Power Plant Auxiliaries 2.540 0.254 0.742 1.5 0.013
Res AC 2.476 0.135 0.136 0.28 0.033
1 ph motor 2.530 0.262 0.061 0.3 0.11
Comerc AC 2.023 0.151 0.148 0.28 0.0533ph motor 3.480 0.251 0.949 1 0.2
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Sensitivity to Percentage of Motor Load
a - 5% feeder voltage drop, 100% resistive loadb - 5% feeder voltage drop, 60% resistive load, 40% constant powerc- 5% feeder voltage drop, 30% motor load, other static
d- 5% feeder voltage drop, 60% motor load, other static worst casee- 3% feeder voltage drop, 60% motor load, other staticf-1% feeder voltage drop, 60% motor load, other static
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Sensitivity to Motor Inertia
Motor parameters in the original case.Ls = 3.1 L’ = 0.2 Ra = 0.025 T’0 = 0.33H = 0.3 D = 3Sensitivity to inertia constant.1) H= 0.1, 2) H=0.25, 3) H = 0.3, 4) H= 0.7, 5) H = 1.5
Case comparison (stalled motor)A – H=0.1, b- H = 0.25, c- H = 0.3, d – H = 0.7, e – H = 1.5
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Sensitivity to Motor Inertia
Motor parameters in the original case.Ls = 3.1 L’ = 0.2 Ra = 0.025 T’0 = 0.33H = 0.3 D = 3Sensitivity to inertia constant.1) H= 0.1, 2) H=0.25, 3) H = 0.3, 4) H= 0.7, 5) H = 1.5
Case comparison (recovered motor)A – H=0.1, b- H = 0.25, c- H = 0.3, d – H = 0.7, e – H = 1.5
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Sensitivity to Time Constant
Motor parameters as in the original case, but different time constants.
Ls = 3.1 L’ = 0.2 Ra = 0.025 T’0 = 0.33H = 0.3 D = 3
Case comparison
a)T’ = 0.1 b)T’ = 0.33 (base case) c)T’ = 0.4 d)T’ = 0.5 e)T’ = 1
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Sensitivity to Motor-Driven Load
IMPACT OF DAMPING
a) D= 0.5 b) D=1 c) D=2, d) D= 3 (base case) e) D=4
Case comparisona) D= 0.5 b) D=1 c) D=2, d) D= 3 (base case) e) D=4
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Sensitivity to Transient Reactance
Motor parameters as in the original case, but different L’:
Ls = 3.1 L’ = 0.2 Ra = 0.025 T’0 = 0.33H = 0.3 D = 3
Case comparisona) L’ = 0.1 b) L’= 0.2 (base case) c) L’ = 0.25 d) L’ = 0.3
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Sensitivity to Synchronous Reactance
Motor parameters as in the original case, but different Ls.
Ls = 3.1 L’ = 0.2 Ra = 0.025 T’0 = 0.33H = 0.3 D = 3
Case comparisona) Ls=1 b) Ls = 2 c) Ls = 2.5 d) Ls = 3.1 (base case) e) Ls = 4
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DO MOTORS RECOVER?H=0.1, Ls = 3.1, L’ = 0.2, Ra = 0.025
T’0 = 0.33 D = 3
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DO MOTORS RECOVER?H=0.3, Ls = 3.1, L’ = 0.2, Ra = 0.025
T’0 = 0.33 D = 1
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FREQUENCY WHEN MOTORS STALLH=0.3, Ls = 3.1, L’ = 0.2, Ra = 0.025
T’0 = 0.33 D = 1
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Conclusions
1. System dynamic stability performance appeared to be verysensitive to induction motor load parameters. Thissensitivity was especially critical for severe disturbances.The most critical parameters appeared to be percentage ofinduction motor load, damping coefficient, motor inertia androtor resistance.
2. The faults that were close to the load appeared to be more
critical than the faults on the 500 kV system and outages of500 kV lines. The system performance was worse for theoutages and faults in the area of long lower voltage linesand mesh networks.
3. Only motor-driven load (constant torque) showed the motorsthat completely stalled. Other critical parameters (lowinertia, low rotor resistance) showed significant slowing
down of the motors and depressed voltage, but the voltageand motor speed later recovered.
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Conclusions– cont’d
4. Mix of commercial and industrial motors appeared to be moreprone to stall than other motors due to their low rotorresistance and low inertia.
5. The study showed that the system frequency might go upwhen induction motors stall, even if some generators that
go-out-of-step are tripped, because the motor loadbecomes very low.
6. It is important to obtain accurate load models because thesystem dynamic stability performance is extremely sensitiveto the motor parameters.