role of flexible ac transmission in power system contingency

ROLE OF FLEXIBLE AC TRANSMISSION IN POWER SYSTEM CONTINGENCY

bySayandev Ghosh

Jyotiprem Bag

Sayantan Datta

Suman Khan

Anirban Biswas

Under the Guidance of

Sri Chandan Jana

(Assistant Professor)

CONTENTS

Introduction What is Contingency? Methods for contingency analysis Contingencies Remedy Results Future Scope References

Introduction

The concerned factors for a power system are : Stability Reliability Security Continuity in supply

For this security analysis is performed to develop various control strategies to guarantee the avoidance and survival of emergency conditions and to operate the system at lowest cost.

WHAT IS CONTINGENCY?

Any line overload, line outage, bus faults, bus overvoltage can be considered as a contingency.

With increasing trends of interconnection of power system these contingencies affects other power system. Hence consideration of these contingencies has been vital.

METHODS FOR CONTINGENCY ANALYSIS

The best possible method for contingency analysis is Newton Raphson Method. But because it is time consuming and tedious, a fast algorithm is adopted. The method is known as Linear Sensitivity Methods or DC load flow Method.

STEPS OF CONTINGENCY ANALYSIS

Y-bus formulationBase case load flowCalculation of sensitivity factorsContingency Selection

Calculation of Performance Indices (PI) Ranking of Contingency

Y-BUS FORMULATION

11 12 13 1

21 22 23 2

31 32 33 3

1 2 3

.............

.............

.............

.............................

.............................

.......

N

N

N

N N N NN

Y Y Y Y

Y Y Y Y

Y Y Y YY

Y Y Y Y

ij jiY y, 1

n

ii ij igi j

Y y y

The algorithms for load flow study are :•Gauss-Siedel Method•Newton-Raphson Method•Decoupled Method•Fast Decoupled Method

The best method being N-R method. Here N-R method is adopted for deducing the base case power flow for IEEE-14 bus system.

Load Flow Study

IEEE 14 BUS SYSTEM

Contingency Analysis using Sensitivity Factors

One of the easiest ways to provide a quick calculation of possible overloads is to use sensitivity factors.

The factors are derived from the DC load flow come down to two types:• Generation shift distribution factors• Line outage distribution factors

Generation Shift Factors

lli

i

fa

P

l = line index

i = bus index

lf = change in megawatt power flow on line l when a change in generation

iP = change in generation at bus i

The generation shift factors are designated as :-G

G

i

LOAD

Line Outage Distribution Factor

The line outage distribution factors are used for the testing of overloads when transmission circuits are lost. By definition, the line outage distribution factor has the following meaning:

, 0l

l kk

fd

f

,l kd = line outage distribution factor when monitoring line l after an outage on line k

lf = change in MW flow on line l

0kf = original flow on line k before it was opened

G

l

LOAD

k

G

CONTINGENCY SELECTION

PERFORMANCE INDICES

The contingencies are selected by calculating a kind of severity indices known as Performance Indices (PI).There are two kind of performance index which are of great use, these are :•Active power performance index (PIP) •Reactive power performance index (PIV).

Here only PIP is considered.

ACTIVE POWER PERFORMANCE INDICES

The line real power flow performance indices (PI), as given below

The PI’s ability to distinguish or detect bad cases is limited when n = 1, which is known as Masking Effect.

But trying to develop an algorithm that can quickly calculate PI when n = 2 or larger has proven extremely difficult.

2

max1 2

lnN

m lm

m lm

w PPI

n P

CONTINGENCY RANKING

The contingency cases should be ranked in the descending order of PI values.

The case with highest PI should be considered the most fatal.

CONTINGENCY REMEDY

In order to avoid the fatal effects of contingencies FACTS device has been introduced in the power system network.

FACTS Device• Because of deregulation and restructuring of the

electricity markets use of Flexible AC Transmission Systems (FACTS) devices are inevitable.

• The maximum capability of power systems can be exploited by means of FACTS devices.

FACTS are classified as :•Shunt compensation (e.g. SVC)•Series compensation (e.g. TCSC)•Phase angle compensation (e.g. TCPAR)

PREFERRED DEVICE

Here we are interested in controlling the line power flow by controlling the line reactance. Hence series compensator is preferred. Here TCSC has been preferred as series compensator.

TCSC

is ic c

iL

v

1scR

scR 2

• Thyristor controlled series compensator in short TCSC is basically a thyristor-controlled reactor connected in parallel with a fixed capacitor.

• From steady state point of view, it allows rapid and continuous change of line reactance thereby apparent impedence.

TCSC FUNDAMENTAL IMPEDENCE

21 22 sin 2 C cos tanTCSC cX X C

Where,

2

1 2

, =

4 , C

c L cLC

c L l

c LC LC

L

X X XX

X X X

X X XC

X

is ic c

iL

v

1scR

scR 2

OPERATING REGION OF TCSC

Inductance Region

Capacitance Region

Resonating Region

STATIC MODELING OF FACTS DEVICES During the steady state, the

TCSC can be considered as a static reactance –jxc .

The change in the line flow due to series capacitance can be represented as a line without series capacitance with additional power (complex) injections at the receiving (S,)and sending (Sir)ends as shown in fig.

OPTIMAL LOCATION FOR THE PLACEMENT OF TCSC

The real power flow PI sensitivity factors with respect to the parameters of TCSC and placed in line-k are defined as

The sensitivity of PI with respect to FACTS device parameter xk, (xckfor TCSC) connected between bus-i and bus-j for the case n =2, can be written as

4

3max

1

1lNlm

m lmmk lm k

PPIw P

X P X

at x 0ck ck

ck

PIa

x

CALCULATION OF SENSITIVITY FACTOR

2 2

20 0 2 22 2 2 2

2cos sin

ck ck

j jc ijX X i i j ij i j

k ck

P P rx r xV VV VV

X X r x r x

CRITERIA FOR OPTIMAL LOCATION

The FACTS device should be placed on the most sensitive lines. With the sensitive indices computed TCSC should be placed in a line (k) having largest negative value of the sensitivity factor.

RESULTS

BASE CASE POWER FLOW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

-100

-50

0

50

100

150

200

Rated power flow in MW

Base case power flow in MW

No of Transmission Lines

Pow

er F

low

in M

W

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

PI sensitivity factors with respect to the parameters of TCSC

PI sensitivity factors with respect to the pa-rameters of TCSC

No. of transmission lines

PI

valu

es

LINE OVERVOLTAGE DUE TO FAULTTransmission line no No. of Lines overload due to fault

1 4

2 4

3 3

4 4

5 1

6 2

7 6

8 7

9 5

10 1

11 3

12 5

13 3

14 4

15 3

16 6

17 3

18 1

19 1

20 3

PI WITH RESPECT TO SEVERITY

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

50

100

150

200

250

Transmission Line No

Perf

orm

ance I

ndic

es

DIFFERENT CASES FOR OPTIMAL PLACEMENT OF TCSC IN DIFFERENT LINES

0 5 10 15 20 25

-0.5

0

0.5

1

1.5

2

Series1Series3Series5Series7Series9Series11Series13Series15Series17Series19Series21Series23Series25Series27Series29Series31Series33Series35Series37Series39

No. of transmission lines

Diffe

rent

case

s for

pla

cem

ent o

f TCS

C

Optimal Location for the Placement of TCSC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

PI sensitivity factors with respect to the param-eters of TCSC

PI sensitivity factors with respect to the parameters of TCSC

No. of transmission lines

PI

Val

ue

BASE CASE POWER FLOW AFTER PLACEMENT OF TCSC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

-100

-50

0

50

100

150

200

Rated power flow in MWBase case power flow in MWBase case power flow changes after TCSC placement in branch 9 (in MW)

No. of Transmission Lines

Pow

er F

low

in M

W

TCSC PLACEMENT IN 14 BUS NETWORK

is ic c

iL

v

1scR

scR 2

TCSC

The characteristics of the TCSC

placed in the line 8:

The capacitor fundamental frequency

reactance (50Hz) is Xc = -58Ω.

The value of the ratio rx = Xc/XL = 10,

which yields a resonant point at r =

151.5 O.

The adopted firing angle limits are

αmin = 155O and αmax = 180 o.

The firing angle αo = 175o and XTCSC = -58.17 Ω

The characteristics of the TCSC placed in the line 11:

The capacitor fundamental frequency reactance (50Hz) is Xc = -75Ω.

The value of the ratio rx = Xc/XL = 10, which yields a resonant point at r = 151.5 O.

The adopted firing angle limits are αmin

= 155O and αmax = 180 o.

The firing angle αo = 156.5o and XTCSC = -141.2 Ω

Conclusion• The contingency analysis has been performed for all

the bus faults and line outages with respect to the real power flow.

• Ranking of the contingencies has been done with the help of PI index.

• PI index shows that the line no. 8 is the most severe.• Apart from that we can also see that in the base case line

no. 9 is overloaded.• Optimal location for the placement of TCSC has been

performed by sensitivity factors with respect to TCSC parameters which shows that TCSC should be placed in line no. 8 and line no. 11 for avoiding the overloaded condition of line no. 9.

Future Scope

• Voltage levels should be considered.• Cost of TCSC should be taken into

account.• Scope of further optimized methods for

TCSC placement • Probabilistic approach for

contingency analysis to yield better results.

References

•Abouzar Samimi and Peyman Naderi “A New Method for Optimal Placement of TCSC Based on Sensitivity Analysis for Congestion Management”,Smart Grid and Renewable Energy, 2012, 3, 10-16,•Singh S.N. and Dravid A.K.,”PLACEMENT OF FACTS DEVICES IN OPEN POWER MARKET” Proceedings of the 5thInternational Conference on Advances in Power System Control, Operation and Management, APSCOM 2000, Hong Kong, October 2000.•Wood and Wollenberg, Power Generation,Operation and Control ,2nd edition,1996•T.V.Trujillo,C R. F Esqivel and J L. G Zavala,”A phase Domain Modelling of Thyristor Controller Series compensator for active Power Flow Control in Unbalanced Electric Transmission Networks”,ISSN1405-5546,2002

ACKNOWLEDGEMENT

To make our project successful we are sincerely thankful to our guide Sri Chandan Jana, Dept. HOD Prof. D.M.Kar. Also we are thankful to our project group members for their cooperation, parents for their support & using the various facility of internet.