Small Signal Stability of a Large Power System as Affected by New Generation Additions by Prabha Kundur

8/16/2019 Small Signal Stability of a Large Power System as Affected by New Generation Additions by Prabha Kundur

1/5

SMALL SIGNAL STABILITY

OF

A LARGE POWER

SYSTEM

AS AFFECTED

BY

NEW GENERATION ADDITIONS

S.

Arabi P. Kundur

Fellow, IEEE

Powertech Labs Inc.

Surrey, British Columbia

Canada V 3W 7R7

Abstract: Significantnew generation additions, prompted by open

access, may significantly change the small signal stability

characteristics

of

a large power system. This paper

analyzes

such

characteristicsfor the4400MW proposedgeneration additions in

the Central and Southwest System.

Non-linear time domain simulationis complementedby linear

eigenvalue

analysis

for more insight

and proper design

of remedial

measures. Power system stabilizers and a Flexible AC

Transmission System FACTS) device are

used

to improve inter-

area damping. The analysis and design procedures, based on a

new generationof

tools,

areoutlined.

Keywords:

Eigenvalue Analysis, Power System Stabilizer, FACTS.

Small Signal Stability, Inter-Area Oscillation,

I. INTRODUCTION

Open access in the North American interconnected power

systems has prompted the addition of many new generating

units. One exam ple of this is the proposed generation additions

in the southern region of Central Power and Light CPL)

company, known as Rio Gran de Valley RGV) and Corpus

Christi CC), which are under the administration of Central and

Southw est Services CSW S), as shown in Fig.

1.

Traditionally, these regions h ave im ported power from other

regions of Electricity Reliability Council Of Texas ERCOT)

via three north-south 345 kV lines, as well as the 138 kV

network. The proposed generation additions, consisting of more

than

4400

W of gas and

s team

turbine units with fast exciters,

will result in heavy export to the rest of ERCOT. The export

situation has increased the imp ortance of ser ies compensation

on the 345 kV lines interconnecting CC and RGV. Initially

RGV was under investigation for import limitations

[l].

P.

Hassink

D.

Matthews

Member, E E E

Central and Southw est Services

Tulsa, Oklahoma

U.S.A. 74121

In this paper we will show that, without any remedial

measure, the dam ping of inter-area oscillations of the system

may deteriorate significantly under the new conditions. As a

result, remedial measures are proposed which include new

Power System Stabilizers PSS), as well as utilization

of

a

Flexible AC Transmission System

FACTS)

evice.

II.

DYNAMIC STABILITY ANALYSIS

A.

Analysis

Procedure

The analysis procedure is shown in Fig. 2. Note that a full

system model has been used. A reduced model

was

not

produced since not only can today’s tools and computing

machines easily handle very large systems, but also system

characteristics could readily be de termined w ithout resorting to

model redu ction and the asso ciated extra effort. The latter was

particularly important considering the large number of

combinations

for

variou s proposed plants and othe r variations

in the system showing different characteristics.

The Rest

of

ERCOT

N.

Edinburg

Rio

GrandeVallby

Fig.

1.

Proposed Generation

Sights and

345

kV

Network.

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SystemModel

Fig.

2. Dynamic Stability Analysis

Procedure.

B. Analysis Tools

The Program for Eigenvalue Analysis of Large Systems

PEALS)

was used to perform part of the studies. Powertech

has developed a new tool for Transient Security Assessments

TSAT)

[2-31

which has been used in this study extensively.

Additionally, Powertech, together with several utilities in the

US and Canada, are developing a new tool for Small Signal

Security Assessments SSAT )

[3-51.

The focus of the new tools is on issues critical to utility

applications making them su itable for comprehen sive stability

assessments covering a w ide range of operating conditions. The

features related

to

dynamic stability analysis

are

as

follows.

Contingency screening

and

ranking:

This can be used to

quickly scan through all contingencies and rank them in

terms of their severity. Only critical contingencies are hen

submitted for detailed contingency analysis.

Detailed contingency analysis: This determines the

accurate dynamic responses of the system.

No

modelling

comprom ise is required in the analysis. Several advanced

techniques are implemented to speed up the com putations.

Damping computations:

Multi-channel

h o n y

analysis and

recent advanced algorithms in eigenvalue analysis

techniques such

as

implicitly restarted Arnoldi method,

sensitivity calculations, and mode traces are implemented.

Determination

of

po we r transfer limits:

This can

be

used

to

compute the maximum power that can betransferred over

an interface, subject to the implemented stability indices.

C. Poorly-Damped Inter-Area

Modes

Fig.

3

shows the time response of the system under summer

peak conditionssubjected to a critical line outage, both before

and after the proposed generation additions without any

remedial action, which demonstrates the deteriorating effects

of

the new generation on system damping. Small signal stability

analysis of the system identified two inter-area modes of

oscillation whose dampin g can deteriorate significantly due to

the addition of new generation , as indicated in Table 1.

These modes can be generally confirmed by Prony analysis

of

various signa ls in the system . However, the large change in

the frequency of these modes makes it difficult to recognize

them without looking at the mode shapes. The mode shape i.e.,

right eigenvector entries corresponding to speed deviation)

overviews are shown in Fig.

4

and Fig.

5 .

They do not change

significantly

as

the new generation is added not presented).

Area

8,

which contains the new generation, is the most affected.

III. REMEDIAL MEASURES

Equipping the new units with PSS proved to be an effective

means of increasing system damping to acceptab le levels. The

damping situation can be further improved by adding PSS o

some existing units, as well as providing a supplementary

controller to the f15 MVA Static Synchronous Compensator

STATCOM) to be installed in RGV in the near future. The

design procedu re is outlined in the follow ing subsections.

A. Device Location

The first step in the design p rocedure is finding the location

of the device. In the case of STATCOM, it has been decided

based

on

other considerations, but the PSS locations were based

on participation factors. The overv iews of participation factors

of modes A and B,with the proposed generation additions, are

presented in Fig. 6 and Fig.

7.

They w ere computed with every

PSS out of service. The proposed generation additions have

increased the participation of area

8

significantly.

m m

Fig. 3. Time Response to a Critical Line

Outage

before

Remedial

Measures.

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A .

I4

Fig.

4.

Overview of Mode Shape

A

without Proposed Generation.

I

4

7

a

9

Ll

L 2

L 3

1 a 1

Fig.

5.

Overview

of

Mode Shape

B

without Proposed Generation.

Fig. 6. Mode

A

Participation Overv iew with Propos ed Generation.

A r r -

I6

==i

~

Fig. 7 . Mode B Participation Overv iew with Propos ed Generation.

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Case

Without Proposed

Generation Additions

With Proposed

Generation Additions

B. Feedback

Signal

Selection

Mode Frequency Damping

(Hz) Ratio

A

0.66 0.03

1

B

0.84 0.038

A 0.46

-0.078

B 0.66

0.012

Every new PSS was selected to be of delta-omega-P dual

input) type with equivalent speed

as

he feedback signal

[ 5 ] .

n

case of the STATCO M, self bus frequency was selected after

examining several bus frequency and line pow er flows [3].

The signal selections were based on comparison of

frequency responses for the worst post-fault damping situation,

an exam ple of which is show n in Fig. 8. Finding the worst

post-

fault damping situation was one of the

tasks

performed by

TSAT using its multi-channel Prony analysis feature.

Case

With

PSS

or all

R O O S ~ ~nits

C. Required Compensation

Mode Frequency Damping

A

0.47 0.069

(Hz)

Ratio

B

0 66

n nm

The phase compensation was based on p roviding lead angle

to reduce the feedback signal lag as much

as

appropriate. The

basis for appropriate level was imp roving the damping torque

of both inter-area and local modes, while increasing the

synchronizing torque slightly.

The gain compensation was then determined to achieve

desired damping, without significant adverse effects on other

modes, as well

as

avoiding unacceptable limit saturation for

large signals. Eigenvalue analysis results

of

the effects of the

PSS nd supp lementary controller of the STA TCOM , with all

the proposed generation additions, are shown in Table 2.

With abovePSS and

the RGV STATCOM

x

0.00

M

.a

200

250

CI T f I I Rn

Fig. 8. A Frequency Response for PSS Application.

~

~

~ A 0.46 I 0.102

B 0.66 0.043

Table 2. Inter-AreaModesAfter Remedial

Measures.

D. TimeDomain Venjicatwnand Robustness Checks

The final gain of the controllers was s et using time domain

simulations, when the system was subjected to severe faults.

Fig. 9 shows an example of time response, where the proposed

generation additions are equipped w ith the described PSS.

Prony analysis of TSA T was used to scan several post-fault

signals as

he new units were placed in-service one by one and

gradually loaded to

their

maximum o utput, up to the transient

stability limit of th e system. With all proposed units equipped

with PSS, nd for

a

large number of faults, a minimum damping

ratio of about 0.03 was encountered during the scan. The

process was repeated for several loading levels and operating

conditions to make sure that the designed controllers perform

satisfactorily under all likely situations.

IV.

CONCLUSIONS

Addition of significant generation may change the small

signal stability characteristics of

a

large power system

significantly. For the CPL system, without any remedial

measure, the proposed generation additions cause the system

damping to deteriorate quite significantly. At the same time,

equipping the new units with properly tuned PSS has proved to

be sufficient for improving the system damping to preaddition

4.00 6.00 8.00

10.53

-*-

l 0.u)

Fig.

9.

Time Response

to

a Critical Line Outageafter Remedial Measures.

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levels. More PSS or supplementary controls of available

FACTS

devices can further improve the damping situation.

Analysis and design p rocedures

based on

a new generation

of tools were presented. Non-linear time doma in simulation was

complemented by linear eigenvalue analy sis, which assisted in

providing more insight, placing the damping devices, and

designing the damping controls.

V.

REFERENCES

“centr l

nd

South

West Services CSWS) Tmmiss io n

Syskm St :

Rio Grandc

Valley FACTS

Studies),

” EPRI, Palo Alto,C A 1998, R-

111048.

P. Kundur, G.K. Morison, and

L.

Wang, “Techniques

for

On-Line

Transient

Stability

Assessment and

Conml.” EEEPES Winter

Meeting,

Panel Session, 23-27 January2o00

Singapore.

S. i nd P. K d u r “A V ersatile FACTS Modelfor PoWemow

and

Stability

Siulations ” IEEE Trans. Power Systems,

vol. 11

no. 4,

November 1996, pp.

1944-1950.

S. Arabi,

G J .

Rogers, D.Y. Wong,

P.

Kundur and

M.G.

auby.

”Small

Signal Stability Rogram Analysis of SVC and HVDC n AC Power

Systems.”

IEEE

Trans. Power

Sysrems,

vol. 6 , no.3. August 1991,

pp.

1147-1 53.

P Kundur.

Power

System Stability &

Control.

McGraw-Hill Inc.

1994.

VII. BIOGRAPHIES

Saeed

Arabi was

bom

in 1951 n Tehran,

Iran

where he xweived his B.Sc.

d e w n

Electrical

Engineering from Sharif Un iversity

of

Technology in 1974.

After graduation he worked for both government and private companies before

coming

to

Canadain 1979.He eceived hi

M.Sc.

and W.D.degrees in

Electrical

0-7803-6420-1/00/ 10.00c)2 EEE

Engineering

from the U niversity

of

Manitoba in 1981 and 1985, espectively.

From

1985

to

1987

he

was

with the Department

of

Electrical Engineering,

Concordii University,

Montreal,

s aVisiting Assistant Professor. In 1987

he joined

tbe Power System Planning Division of Ontario Hydro. Since

October 1993 he has been with Powertech

Labs

Inc., where he is currently

a

Senior Eng ineer.

PrabhashaokarKundur m i v e d the M.A. Sc. and Ph.D. degrees from the

University of Toronto,

Canada

in 1965 and 1967. espectively. He taught

at

Mysore and Bangalore Universities during 1967-1969.

n

1969 he joined

Ontario

Hydro whem he was Manager of the AnalyticalMethods& Specialized SNdies

Lkpartment in thePower System

Planning

Division. He

leftOntario

Hydro in

1993 o oin Powextech Labs nc. in Surrey. B.C.,

Canada,

where he iscurrently

thePrcsident and Q?o. He also holds the p ositions of Adjunct Professor at

the Universities of Toronto, Westem

Ontario,

and British Columbia

Dr.

Kundur was

elected

aFellow of

lEEE

in 1985 nd is

a

memberof several IEEE

working groups and task forces. He

is

also a member of CIGRE study

committee38 and severalof ?

task

forces.

PaulHassink received

his

Bachelors

degree

n Electrical Engineering from the

eorgia

Institute

of Technology

n 1979 nd his

Masters

of

Science

in

EIectrical

Engineering from F4udue University in

1980.

He

is

a

Registered Professional

Engineer in

the

State of Texas, and amember of IEEE and NSPE. He has held

engineering and management positions in the Central and Southwest system in

both he

power

system

protection

and planning areas since 1981. He

has

served

as he hair of the ERCOT Transient Stability Task Force in 1996, he ERCOT

Engineering

SuboommiaCC

in 1997.and the ERCOT Ad hoc Taskon

Unplanned

Transactions in 1998. He has provided written and oral comments before the

Texas Public Utility Commission on ransmission pricing methodologies and

gemator interconnection i ssues and served on he Independ ent System Operator

Working Group,LossesTask

Porce.

David

Matthews joined the Central and S outhWest System in 1972 and is a

Consultant Engineer

in

the T ransmission Planning Section. He

works

in the

mas of transmission

planning and pricing. He received

his

Bachelor

of

Science

in

ElcCaicalEnginewing from New Mexico State University in 1969.

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Documents

Small Signal Stability of a Large Power System as Affected by New Generation Additions by Prabha Kundur