Assessment of power swing blocking functions of line protective ...
Transcript of Assessment of power swing blocking functions of line protective ...
2008 IEEE T&D LA Conference, Aug. 2008
Assessment of power swing blocking functions
of line protective relays for a near scenario of the Uruguayan system
C. Sena, R. Franco, A. Giusto. Instituto de Ingeniería Eléctrica
Facultad de Ingeniería Universidad de la República - Uruguay
Grant PDT 47/05 Ministerio de Educación y Cultura - Uruguay
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Plan
• Introduction• Power system stability and distance protection• Power swing detection methods
• Simulations • Tests • Results and conclusions
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Introduction
Events that cause significant transient response:
• loss or application of large blocks of load,• line switching, • generator disconnection, • faults,• etc.
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Power system stability vs distance protection
• Power oscillations: balanced events• Power swings affect the transmission lines relays• Distance relays elements may operate during a power
swing, if the impedance locus enters the distance operating characteristic
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Power system stability vs distance protection
Impedance seen by a distance relay located at the bus C: (in case | EA | = | EB |)
( )
−++=
2cot1
2δjZZZZ LBA
C
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Traditional power swing detection
• Characteristics:- positive-sequence impedance - measuring the time that the trajectory remains
between the inner and outer characteristic
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Traditional power swing detection
• Time over setting time delay- power swing⇒ tripping of the relay is blocked during a certain time
• Time shorter - short circuit⇒ tripping of the relay is allowed
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Modern methods for power swing detection
• Characteristics:- because of numerical relays implementation- “permanent” measurements
• Evaluation of trajectory:- speed- monotony- zones of steady state instability
• Electrical system centre estimation• etc.
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Uruguayan electrical power systemUruguay.• Max. distance 600 km• Population: 3.4 millions
Electrical power.• Installed generation: 2.3 GW• Peak load: 1.4 GW
Transmission lines. • 500 kV: 770 km• 150 kV: 3 550 km 2006 data
• Hydro (1.4 GW) and Thermal (0.9 GW) generation
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New Uruguayan near scenario
Incorporation of new consumer with generation capacity • Thermal units for 140MW (10% of max. load)• injecting the surplus to the Uruguayan power system
⇒ It can lead to out-of-step conditions and misoperation of distance relays
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Simulations and tests performed
Study of the behavior of line protection relays of the transmission lines near the new consumer during power swings:
• numerical investigations • experimental investigations
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Simulations and tests performed Time-domain simulations (DSAT, ATP)
– DSAT - Disturbance simulations in 150 kV lines near Fray Bentos
- Three phase short circuits (worst cases)- Calculation of critical clearing times (CCT)- Sudden line openings- Unexpected loss of generation and load shedding
- Selection of the set of pairs “contingency – protection line relays of interest” to be simulated further in ATP
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Simulations and tests performed
ATP (ATP-EMTP Alternative Transients Program) - Contingencies
a) three phase short-circuit over critical time, without automatic reclosing, in FBE-SJA 150 kV line, near FBE,
b) three phase short-circuit over critical time, without automatic reclosing, in MER-YOU 150 kV line, near MER,
c) sudden total load shedding in BOT,d) sudden loss of one of two generators in BOT.
X
XX
X IΔΔ
I
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Simulations and tests performed
Laboratory equipment- SIEMENS 7SA611 (21) and 7SD522 (87L/21) line
relays- OMICRON CMC256-6 test set (secondary injection of
three phase voltages and currents)
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Simulations and tests performed
Experimental investigations
• Vs and Is signals in selected lines were generated and stored with ATP in pl4 format
• Voltages and currents generated with the test set were injected to real distance protections
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Simulations and tests performedExperimental investigationsResults of simulation
Example: case b)
• three phase short-circuit in MER-YOU 150 kV line (near MER)• over critical time• without automatic reclosing
Voltages and currents (FBE→ SJA )simulated and injected (5 sec)
Δ
I
X
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Simulations and tests performed(relay’s oscilographic registers)
FBE→SJA relay Picks-up: • the reverse time-delayed zone
and • the non-directional time-
delayed zone• only at the end of short-circuit
SJA→FBE relay Picks-up:• the forward time-delayed zone
and • the non-directional time-
delayed zone • Relay’s “Power Swing” signal is
set on during most of the fault
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Simulations and tests performed(relay’s oscilographic registers)
Relays flags:• “Power Swing”• “Pickup”
Currents
iL1 iL2 iL3 iE
t/s-0.10 0.00 0.10 0.20 0.30 0.40 0.50
I/A
-20
-10
0
10
Voltages
uL1 uL2 uL3
t/s-0.10 0.00 0.10 0.20 0.30 0.40 0.50
U/V
-50
0
50
t/s-0.10 0.00 0.10 0.20 0.30 0.40 0.50
Relay TRIPDis. PICKUPPower Swing
FBE→SJA relay Picks-up: • the reverse time-delayed zone
and • the non-directional time-delayed
zone• only at the end of short-circuit
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Conclusions
Simulations and tests under different system conditions have shown:
• line distance protections located near the new consumer operate properly under power swing conditions, blocking the relays avoiding them to operate and lead to major outages.
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Thanks for your attention