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.

9

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