Dr.kulkarni

Phase Shifting Transformers

Prof. S. V. Kulkarni

Department of Electrical Engineering

Indian Institute of Technology Bombay, INDIA

[email protected]

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Outline

Introduction

Applications of PSTs

Basic Concepts

Design Considerations

Other Technologies

Concluding Remarks

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Need for Phase Shifting Transformers



Power systems are becoming complex



Devices useful in controlling power flow in a complex interconnected

network are desirable



Power system deregulation and market mechanism



Power flow from generation centers to load centers in an efficient way



Major disturbances and system blackouts



_{Stability of a large interconnected system can be improved}



Overloading and under-utilization of transmission lines



_{Lines can be optimally loaded}



PSTs would be more relevant when penetration of intermittently

available renewable energy sources increases in the system

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Functions of Phase Shifting Transformers



Power flow control between the sending and receiving ends

of a transmission line



Control of power flow between two parts of a large power

system network



Improvement of system stability and reliability



Re-routing of powers through transmission lines leading to

their optimum utilization/deferment of investment costs for

new lines: Congestion management



Avoid/minimize loop currents and corresponding power

flow

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Representative and Notable Applications of PSTs

i.

Control and increase the power flow between two large systems:

PST option was found better than HVDC and series capacitors

(Ref: Patel, B. K., Smith, H. S., Hewes, T. S., and Marsh, W. J. Application of phase shifting transformers for Daniel-Mcknight 500 KV interconnection, IEEE

Transactions on Power Delivery, Vol. PWRD-1, No. 3, July 1986, pp. 167–173)

ii.

Kothagudem thermal power station:

- 500 MW evacuation – 220 kV lines would be overloaded

- One option: 400/220 kV ICT – which would also increase the loading of

the underutilized double-circuit 400 kV line

- System studies indicated reverse flow – from 400 kV to 220 kV

- Hence the option chosen : ICT with a phase shifter

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Representative and Notable Applications of PSTs

iii. Reduction in loop flows

400 MW 300 MW _{400 MW} 100 MW 100 MW “Loop flow” 100 MW 400 MW 300 MW 400 MW Area-1 Area-2

Ref: Kulkarni, A. M. Power System Operation and Control – NPTEL Web Course, Module 4 : Voltage and Power Flow Control, Lecture 19

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Power Flow Through a Transmission Line

The real power transferred to the receiving end is proportional to

the angle difference whereas the reactive power is proportional to

the magnitude of the voltage drop across the line.

G

P

jQ

S









V

_V

_

₀

Load

P

jQ

S





sin

V V

P

X





cos

V V

V

Q

X



X





V

(

V

V

)

V

V

X

X









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

Current (and power) flows through low impedance paths,

governed by Kirchoff’s circuit laws, irrespective of line loading

and thermal limits



In order to control the flow of active power and reactive power,

regulating transformers can be used



Magnitude-regulating transformer:



The reactive power flowing through a line can be controlled by

adjusting its tap setting



The transformer can also be used to modify the magnitudes of

reactive powers flowing through two parallel transmission lines



Phase-shifting transformer



Control of active power flow between two interconnected parts

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Source: S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design, Technology, and

Diagnostics, Second Edition, CRC Press, Taylor & Francis Group, New York, September 2012.

1 1 1 2 2 2 1 1 1 2 2 2 o 1 1 1 2 2 2

0.425

0.3

1.00

0.425

0.3

0.4354

0.1525

1.05

0.4146

0.4475

0.1817

0.3148

1.0 4

0.6683

0.2852

S

P

jQ

j

a

S

P

jQ

j

S

P

jQ

j

a

S

P

jQ

j

S

P

jQ

j

a

S

P

jQ

j

 















 















 





  









Bus Load_Bus

1 I 2 Load 0.15 L I j 0.15 V I1 I2 j =1.0 0 I L V S | | 2 1:1 1:a 1

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Improvement in Stability



Equal area criterion for assessment of stability



Without PST

 Accelerating area: abcda, Decelerating area: defgd, Margin: fghf



With PST

 When the power angle is α + β while swinging, a phase-shift of α is

introduced

 Accelerating area: mnopm, Decelerating area: pqrstup, Margin: tuvt (> fghf

Source: S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design, Technology, and

Diagnostics, Second Edition, CRC Press, Taylor & Francis Group, New York, September 2012.

 P _Safety margin c e Pmech a b d g h f 0 0  Safety margin m n r s u v o p q P   t Pmech Without PST With PST

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Power Flow with Regulating Transformers

Source: S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design, Technology, and Diagnostics, Second Edition, CRC Press, Taylor & Francis Group, New York, September 2012.

Ideal Transformer In m Im S Sm n Z 1 Y= 1:a V V_m a _n n V_m

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

Off-nominal tap ratio, a may be real (e.g., 1.04) or imaginary

(e

or 3

shift).



Lossless transformer:





or

Now,

Multiplying both sides by

m n m m m n m n m n n n m m n

S

S

V I

aV I

I

aI

I

a I

I

V

aV Y

aY V

Y V

a



 

 



 

 





 





,

S



V I

S



V I

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If a is a real number, and we can draw an equivalent π

circuit for this case

:

a



a

But if a is imaginary (as in a phase shifting transformer), the Y bus

is not symmetrical, and we can’t draw a π equivalent circuit.

m a Y _n ( a a 1 Y) Vn m ( 1 a ) Y V 2 2

*

Now,

a I

I

a a Y V

a Y V

V

I

Y

Y

V

a Y

a Y

a a

a

V

I

Y

Y

V

aY

Y







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

_

_{     }

_{  }





_

_{     }





_{  }





     

  





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Design of PSTs

Phase-advance

A leading quadrature

voltage drop is added

to the source voltage

Phase-retard

A lagging quadrature

voltage drop is added

to the source voltage

Phase-advance and phase-retard modes

Source: S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design, Technology, and

IIT Bombay



PSTs are manufactured in different ways depending on the power

output, the rated voltage, and the amount of required phase shift.

 Single-core design: for smaller voltage and power ratings



Disadvantages: taps at line ends – tap changer cost increases,

vulnerability to system transients

Phase-advance mode (OLTC without reversing switch)

Source: S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design, Technology, and

Diagnostics, Second Edition, CRC Press, Taylor & Francis Group, New York, September 2012. Ve V_SR V_LR V_RR 2 R₁ R₂ S L L L S S  V_R 1R R R Y B B R Y

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Two-core design: larger ratings

Source: S. V. Kulkarni and S. A. Khaparde, Transformer Engineering: Design, Technology, and

Diagnostics, Second Edition, CRC Press, Taylor & Francis Group, New York, September 2012.

V_AA’

V_LR V_SR

Series unit

Exciting unit (Main unit) a’ a A’ A S L S L S L  R R Y Y B B B’ B V_BB’ 

Advantages:

The series and exciting units can be independently designed, reduced

tap changer cost

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 Mechanical:

Low cost

,

slow, wear and tear, step-control

 Solid-state:

Smooth variation, fast acting

,

high cost,

complex control



Hybrid:

Cost-effective



OLTC based PST:

15

to + 15

_{(coarse in step of 5}

₎

and Power Electronics based PST

5

to +5

(smooth)

 Overall –20

_{to +20}

_variation

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 Reduction in line reactance through a series compensator

(capacitor):

 Thyristor Controlled Series Compensator (TCSC)

Voltage Source Converter (VSC) based series compensator

High Voltage DC Transmission

Other Means of Power Flow Control

VSC

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Challenges



Need for co-ordinated PSTs

 Issue: “You work, I enjoy” – PST deployed in one region may

benefit an adjacent region

 Optimized location is valid for a given operating point

 As the base case changes the location of PST changes – use

truck mounted PSTs

 Expansion of network – optimum location will change

 PST design and control strategies can be site-specific – detailed

systems studies are necessary

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Conclusions



PST – a cost-effective option with conventional technology

 Advantages: optimal line loading, stability improvement,

elimination of loop flows, deferment of investment in

transmission infrastructure, damping of low frequency

oscillations

 Potential of PSTs is unexploited in India

 Relevance of PSTs is more now in the context of deregulation

and penetration of intermittent renewable energy sources

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References

 Reddy, T., Gulati, A., Khan, M. I., and Koul, R. Application of Phase Shifting Transformer in Indian Power System, International Journal of

Computer and Electrical Engineering, Vol.4, No.2, April 2012.

 Belivanis, M., and Bell, K. R. W. Coordination of Phase-Shifting Transformers to Improve Transmission Network Utilisation, Innovative Smart

Grid Technologies Conference Europe (ISGT Europe), 2010 IEEE PES.

 _{IEEE Standard C57.135-2001TM, IEEE guide for the application,} specification, and testing of phase-shifting transformers.

 Kramer, A. and Ruff, J. Transformers for phase angle regulation considering the selection of on-load tap changers, IEEE Transactions on Power Delivery, Vol. 13, No. 2, April 1998, pp. 518–525.

 Iravani, M. R. and Mathur, R. M. Damping subsynchronous oscillations in power systems using a static phase shifter, IEEE Transactions on Power

Systems, Vol. PWRS-1, No. 2, May 1986, pp. 76–83.

 Iravani, M. R., Dandeno, P. L., Nguyen, K. H., Zhu, D., and Maratukulam, D. Applications of static phase shifters in power systems, IEEE Transactions on

Power Delivery, Vol. 9, No. 3, July 1994, pp. 1600–1608.

 Del Vecchio, R. M., Poulin, B., Feghali, P. T., Shah, D. M., and Ahuja R.

Power transformer design principles: with applications to core-form power transformers, Gordon and Breach Science Publishers, Canada, 2001, pp. 499–

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 O’ Kelly, D., and Musgrave, G. Improvement of power-system transient stability by phase-shift insertion, Proceedings IEE, Vol. 120, No. 2, February 1973, pp. 247–252.

 Hertem, D. V., Verboomen, J., Cole, S., and Belmans, R. Influence of phase shifting transformers and HVDC on power system losses, IEEE Power

Engineering Society General Meeting, 2007, pp. 1-8.

 Kulkarni, A. M. Power System Operation and Control – NPTEL Course, Module 4 : Voltage and Power Flow Control, Lecture 19.

 Sweeney, B. Application of phase-shifting transformers for the enhanced interconnection between Northern Ireland and the Republic of Ireland,

Power Engineering Journal, June 2002, pp. 161-167

 _{Verboomen, J., Hertem, D. V., Schavemaker, P.H., Kling, W.L., and} Belmans, R. Phase Shifting Transformers: Principles and Applications,

International Conference on Future Power Systems, Nov. 2005 , Vol. 6.



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