Voltage Stability Assessment in the Presence of Optimally Placed D-FACTS Devices

Abhishek Rathi, Abhishek Sadda, Lalit Nebhnani, Vaivaswat Manu MaheshwariUndergraduate, Electrical Enggineering

Malaviya National Institute of TechnologyJaipur, India

Overview Voltage Stability

Distributed Flexible AC Transmission System Controllers

Analysis of Line Impedance Sensitivities

Development of equivalent two bus system

Calculation of Global Voltage Stability Index (GVSI)

Identification of Effective D-FACTS Locations

Algorithm to assess voltage stability

Case Study

Conclusion

IntroductionVoltage Collapse

Flexible AC Transmission System (FACTS)

D-FACTS

smaller size, light weight and less expensive

provide distributed reactive support to locations in the system where support

would be the most useful

clamp onto transmission lines

can be made to communicate wirelessly

D-FACTSRecently Introduced D-FACTS Device

Distributed Static Series

Compensator (DSSC)

• Series power flow control

• Provide reactive or capacitive

compensation

• Attach directly to line

• Able to send and receive signals

wirelessly

Line Impedance Sensitivities Power Injection Sensitivities (PII)

State Variable Sensitivities (SI)

2 cos( ) sin( )G G BP ij ij iji V VVi i j i j i jx x x xij ij ij ij

2 sin( ) cos( )B G BQ ij ij iji V VVi i j i j i jx x x xij ij ij ij

1[ ] [ ]SI J PII

Identification of Effective D-FACTS Locations

[SI] = [SIƟ SIv]

SIv Sensitivities of voltage with respect to line

impedance

Lines with higher sensitivities are able to provide more

control

2 2 2 2/ ( ) ( ) / ( )eq loss g g g load g gr P P Q P P P Q

2 2 2 2/ ( ) ( ) / ( )eq loss g g g load g gx Q P Q Q Q P Q

Development of Equivalent Two Bus system

g loss loadP P P g loss loadQ Q Q

1 0osV eq eq eqz r jx

Calculation of Global Voltage Stability Index (GVSI)

GVSI =

• Increases with increasing load • Reach the value ‘1’ at critical point of voltage stability

Algorithm

A

A

• Standard IEEE 30-bus system with base load 100MVA

• Bus no. 26 is the weakest bus

• Solved for uniformly increasing load conditions (at an increment of

1% of base value keeping the load power factor constant)

• Then solved with application of DSSC at the most sensitive lines

• Impedances are allowed to change by + 30%.

CASE STUDY

Variation of GVSI for different operating conditions

Variation in weakest bus voltage

ConclusionDeveloped equivalent two bus system can be applied to any multi bus

power network

Value of GVSI is sufficient to assess overall global voltage stability

Placing D-FACTS devices on effective lines will provide the desired

control

Methods are shown to be general and may be used to identify other

appropriate D-FACTS applications

Thank You!