Barzam A.B. Automation in Electrical Power Systems (Системная автоматика)

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$5.

Field

Discharge

by

Deion

Grid

Automatic Devices and by

Changing

the

Chapter

8.

lbree'Phase

Automatic

Reclcure

251

?51

CO}CTENTS

Fieid Coii

Su

to

Inverter Oueration

ons

$7.

Beview

Questions

44.

4-5.

Asynchronous

OPeration

4-6. Separation

of SmaII Thermai

Power Stations from

Large Hydroelectric Sta-

tions rrhen

Speed

of

Hydroelectric

Generators

Increases

#?.

Preventing

Misoperation

of Protective Relaf ing

4-8. Conciusions

4-9. Review

Questiorx

Chapter

5. Aubomatie

Frequencl'

Control

;

Fl. Purpose

a.nd Specific

Features

of Automatic

F'requency Control

(AFC)

5-2. Modern

Principles

of

AFC

5-3. Short-Time

Drops

of Freguencl'

5-{. Cboice

oi Parameters

of

FARC

Devices

and Work

of Operators

5-5. AFC

anC FAP.C

Citcuits

,]5-6.]n.drrci.ionFrequenc1'fieia;,"s,TypeItBtI-c,r.1(HBI]-3).

5-?. Frequency

Rela-vs,

Type

P9-I. Empioyiag Semiconductor

Elements

,

5-8.

Conilusions

5-9.

Revien'

Queslions

Chapter

6. Automatic

Control

of Frequene5',

Real

Po*'er

and

Power Flows in

Power

Svstems

6-1. General

O-g. Ft*qu"nc-v

and'Power' iegulators

'

6-3. Devices

to

Control

Power Output

64. Porver Groun

Control

at

Therdal

Stations

6-5.

Pov'er

Group

Control

at

Hydroeiectric

Statious

S-6. Frequency

iad

Porve,r Coitrol in

Integrated Pou-er

Systems

.

6-7. Magnetic

Power Transducers

G-8.

Conclu-sions

6-9.

Review

Quest,ions

Chapter

7.

Rapid Paralleling

of Synchronous

Generators

and

Parts of Power

7-1.

General

7-2.

Precise Synchronization

by Means

of an ACT-4 Autosynchronizer

7'3.

Self-$ynehronization

of Generators

.

7-4.

Automatic Connection

of Generators b1' Self-Syrachronization

7-5.

Speed Contro] Methods

7-6.

A-sSrnchronous

Connection

of

Generators

and Parts of Power System

7-7.

Connection

of Strnchronous Motors, Preventing Their Drop-Out

oi

Step

ald

Resnachronization

7-8.

Conclusions

?-9.

Review

Questions

8-1.

General

&3.

Singie

Tie

Lines

BetweeE

Power

Stations

and

Substations

q'ith

Synchronous

a.l,^n+ar I A *f^'-ofia l-anfralc f^r Mqinf einina Qfshilifu in Dqrollol flrurolian

vsa'ser

='

;T;t;*"i'itii'

?

;ilil;;ffi; tiF"'itil"

'.

:" .

'.-

.-':". .":'.

":"

.

4-1. General

&2. Principal

Relations

Determiaing

Operation

of

Automatic Controls

4-3. Autouatic

Controls

for

Improvement

of Steady-State

Stabilitl'

Automatic

Controls for

Improvement

of

Transient Stabiiitl'

Autonatic

Devices

for Sectionalizing

Power

Systems

to

Prevent

or

Eliminate

9.

One-Phase

Automatic

Reclcure

of

Power

Trausmission

Lines

Earth

Fault

and

Tripping

of One

Phase

i6;

of

-Discriminating-

Elements

of

PARC

Devices

PARC

Circuit

fui.

of iFanC

Device

oi

Double-Shot

?ype

and^Pole'After-Pole

Isolators

in

Place

of a PARC

Device

on Lines

Supplied

at Lhe

'Elnd

Loads

8-4.

Tie

Lines

and

ParaIIeI

Links

o E mn A Io F T\^-'iaac an A ir Cirr-rrit

d-O. .tI']|'l.ff\J

UcYtr4-

8-6.

Conclusions

8-7.

Revie*'

Questions

. .

268

287

289

?ot

295

315

316

377

r02

102

103

109

721

129

143

144

r58

159

t6r

16t

165

169

175

t7b

t80

IU

187

188

i89

Chapter

q-1

q-,

9-3.

9-4.

297

29i

306

3L2

9-5.

Conclusions

9-6.

Revier*'

Questions

chapter

10.

Three-Phase

Automatic

Reelosure

of Translormers

and

10-1.

General

iO-2.

eutomatic

Testing

of

Busbars

Jor

Iusulatiou

io_g.

Fo*"r

suppil

io"consumers

After

Tripping

of Busbars

Reestablishin-e

of Substation

Connections

10-4.

Automatic

Rdestablishing

of Power

Station

Connections

10-5.

Three-Pbase

ARC

of Transformers

'

-10-6,

Ccnciusion:

t0-?.

Revie*'

Questions

Busbars

319

. 319

111

.

lal

and Automatic

' 322

' 324

09<

c QtU

i27

.:

'

327

with

Frotective

.

3tr8

358

359

360

J04

367

aAo

.f/J

374

376

377

378

Ititt

382

189

193

195

199

200

205

t+9

213

215

System 2L7

217

218

227

237

236

238

241

L+t

chapter

12.

Operation

of

ARC

aud

ATS

Devices

in coujunetion

-

Relaling

l2-1.

Acceleration

of Protection

Action

Before

ARC

1l-2.

l"""Ieration

of Protection

Action

After

ARC,

ATS, and

Remote

Connection

12-3.

High-Speed

Selective

Disconnection

lii.

SuErtations

iVithout

Circuit

Breakers

on

the High-qePion

Side

iZ-5.

Si*plifying

Protective

Relaying

of

Complex

System

Lines

it-6:

5il;iiii""g

Frimary

Conueciioi

Circuits-

and

Protective

Relavirg

ir-i

. SLrtiO

<i"ff

fransf

oimers

at Remote-Con

trolled Substations

iZ-8.

et

to*atic Discriminating

Fedundancy

12-9.

Conciusions

L2-70.

Review

Questions

Chapter

13.

Automatic

Control

Eliminating

Overvoltages

Acrcs

Equipment

13-1.

General

li-t:

O";tvoltage

Automatic

Protection

Controls

248

coNlENtS

lQ-Q.

Inuqasing

tbe

Reset-to-Pickup Ratio of

Voltage

Relay

{3-4.

Coac}usions

386

389

Chapter

14.

Automatic

Recording

of Dleetrical Variables

in

Disturbances

141. General

I L-2. A rrtnrn *tic. St rrtir,o iro.rl;,"oi +.,t' n".itt ^*".r,.

i ;-s : D;;G; l;' ii;;;;l"i";

E

i;"i'i

"-r

v;;G';itu

eu

io'

"ii.

e

"".r."

"t

i

oo'

oi

Recording Speeds During .Disturbances

{4-4.

Automatic Oscillographs

14-1. !.o"fting

the

Fauit

on Power

Transmission

Line from Fixing

Instruments

14-6. Fixirlg Instruments

74-7.

Conclusions

14-8.

Review

Questions

.

Referenees

Index

392

qot

6nE

JVU

400

403

406

4tt

478

419

420

428

P

REFACE

This is

the third

Russian

edition

of

"Automation

in Eiectrical

Power

Systems"

which covers

design and operation

of

automatic

control

deviees

intended

to

prevent

and

clear

faults

in

eiectrical

power

systems

and restore pos,er

to the

Ioads

in

the

event

of breakdown

thus

assuring

continuity

of the

suppiy.

The

reliable

and

unfaiiing

operation

of such

devices

has

been

ensured through

the

research

and

development

effort

put

into

automatic

power

control

systems.

The hook discusses

automatic

control in

conjunction

I'ith

protective

relaying,

since

the,required,.reliabilit-ti:and

econoay.of

power

s:.'srcff

operaticn

can ]ie

achieved

through

the

combined

action

of both

groups

of

equipment,

each

cate-

ring for specific

aspects in functioning

of }oads and

generating

sources.

The u'ide use

of automatic

control

systems

adds

to

the

reliability.,

stability

and economy of

power

suppi--r'

systems

and takes

some

burden

from

attending

personnel.

The book

is designed

a-q a studv

guide

for

students

of

power

engineering

secondary schools. it

ma-v

also

interest

engineers

coneenred

with the

operation,

installation

and

design

of

protective

relaying

and

automatic

device-q used

in

electric

power

stations

and

networks.

fntroduct'ion

I-1.

Purpose of Autonatic

Power Control

Systems

For

the

purpose

of

this

book.

the

term "auto.matic

control

systems"

wiil

appiy

to an assemblage

of

devices

which

are

not

protective

relays, although

interac-

ting

r+.ith

them and

performing operations

in

order

to:

prevent,

locate

and

eliminate

faults

affecting

the

whole or

part

of

a

power

system;

distribute electric

power to

the

individual

parts

of

a

power

s-vstem;

restore normal

connections

in

the

system and

the

continuit-v

of

power

supplt'

to

loads after

faults.

Early

devices

of

this

type

appeared in

Soviet

power

s1'stems

even

in

the

thi.rties

!nciuding

autornatic

transfer

equipment. aut,ornati.s

circuit

:reolosers

anci

automatic

forcing devices

for

excitation of

generators.

About

the

sarne

tinre,

work closel-v

the

above mentioned automatic

control

systems

was started

to

find

wa-vs

and means of

preventing

false

operation of

relays

under overloads

and

instabilities,

and

to use

the

self-starting

ability of induc-

tion motors.

When used on a

large scale

in

the

UraI

power

s1'stems,

these

practices

fullS'

proved

their

worth

rrnder

the

strain

of

the

Great

Patriotic

war

in 1942-1945.

As

a

result,

there \\'ere

practicallS

none

of

the

severe instabilities,

sustained

loss

of synchronism or

heavy load

shedding

which occurred

in

tire

past.

It

is

of interest

to

note

t):at at

tliat

and

later

time

the devices used

in

the

Urals

to

sect,ionalize

the

porper svstem at

will

upon a loss of

s,vnchronism

\*'ere

classed

with

protective relaying and called accordingl-l

"sectionalizing

protec-

tions".

Today

similar

devices are looked

upon

as

vital

automatic

control s1'stem

components and are

usualiy

termed

"sectionalizing

controls".

Tiie

successful

experience

gained from

the

use

of

automatic

porver

controls

employed in

the

UraI

power

system

u'as

utilized

and developed

in

the

Central

power

systems, Leningrad

potver

system

and

iater

on

in

other

regional

power

systems

of

the

USSR.

At

that time,

important

additions

were

made

to the

automatic

control

equipment

in

the form

of

automatic

frequency

control.

Techniques

have

been

developed which assure reversal

of synchronous

motors and

guick

connection

^+

o-t*^l'-^-^'.o

-an^n^tnrc {},-^rr-}, f}"o

colf-c-t-^l.rnniqqf,inn

mafhrrrl rr-io-

vI

DJSVUTVUVUO

EE!ErquvrD

uUruuS4 !!r9

ovr.

p.lsvsrvsr&survu

emergency

conditions.

With

the generating

units

at

hydro-electric

power

sta-

7Z

$IPRODUCTION

INTRODUCTIO}i

ne} at

the

central station. Such

supervisorv

control

is far

from

being

automatic.

13

devices

have come

into

use

*'hich

tions

put

under

ar:tomatic

eontrol,

automatic

aet

dre

tne reserr

ftfrrP'ol

redtci

Automatic

reclosure

equipment

was

extended

to

include

phase-by-phase

and

some

other

varieties

of

reclosure

not

onIS' on

power

transmission lines, but

also

on br:sbars

and

transformers.

Improvements have

been

made

in both

the

circuitry

and components

of

po*'er

control

systems

and new

automatic

devices

have

appeared.

AIl

this materialll'contributed

to the

creation

of

the

Unified

Power

-Grid

of

the European

USSR

and

its

trouble-free operation.

According

to

the

Regulatious

for Instaliation

of Electrical

Equipment,

the

devices

comprising

automatic

power

controL

systems

must be

considered at

the

design

stage

and

put into

service

at

newl-v*

built

Dower systems. The

iatest

ed.itlon

of

ibese

regulations

(1966) inciudes

a section

"Automatic Control

Systems"

s'hich

covers

automatic

reclosure;

autornatic.

transfer; generator control;

auto-

matic

regulation

of excitation,

voltage

and reactive

power;

automatic

fre-

quency

contro]

of

power systen;

automatic

regulation of

frequency

and active

power;

sectionalizing

_protection'-

Automatic

control

d-evices

mav

be

referred

to

any

particuiar

categor-r'

only

aibitrarily,

because

one

and

the

same

device can

produce man-Y effects.

For

example,

instantaneous

clearing

of

short-circuits

adds

to the

stabiiit'-v

of

parallel

operaiion

of

s-vnchronous

machines,

facilitates

self-start,ilg- of as--vnchronous

Ioads,

reduces-resulting

damage

and improves

the

probability

of

successful

ar,.t,ornatic

reclosure,

i;e,.

contributes,to

the glick

rest,orsiicn

of

the

norrna].

power

s1'stem

operation.

Another example

is'the effeci,ive

use of automatic

iransfer

-

devices in

the house circuits.

Those

devices, u'hen

combined

with

apprapriate

sectionalizing

technjque_,

do not ailou' single

shutdon'ns

or fauits

t.o

grou'into

a major

station

outage

which

ma1'_wel}

explnd_

into a

s-vstenr

otttage.

-There

is

a

close

functionai

tie-in

between

devices

q'hich

automaticallS'

regu-

iate

frequencS'and

activ,'e

poruer; c.ontrol

and

limit

power

florx's in transmission

lines.

unioad

the lines.

and

the

automatic

.sectionalizing

devices.

Where

svstems

are

only

loosel-v

interconnected,

parallel operation ean be

ensured

and'the

power-cariying

capacity

of

the

intertonnections

can be

better

utitized

onl-v

through

the

combined

use

of

the

above devices.

Devices

used for

automatic

excitation

regulation of synchronous

machines

improve

the

stability

ol

parallel

.operat.ion,

add

to the- performance

accuracy

of

protective relaying,

facilitate

the

self-starting

of }oads

after_ clearing

short-

cirCuit

faults and

allow

the

voitage

regulation

process to

be

performed automa-

ticall,v.

i

Ir

some cases?

autorna'r,ic

'uransfer

and reclasure equipment

can

give

a

suf*

ficient

degree

of operational

stability

to

simpiified substations

using inexpen-

sive

switchgear.

Superrisory

control

of

a

power

system finds

its

use along

with-_power

s1'stem

automation.

The

remote

control,

telemetering

and

remote

signalling

(supervi-

sory oontrol)

devices

allow

the

monitoring

and control of

remote

stations

or

uniis

to

be ceni,raiize<i

by

iransmi't'r,ing'r,he

requi-red informa^uion

over a dist,alce,

which

in

turn

makes

it

possible for

the

power

system

or its

part, to

have centra-

lized

control.

Control

operations

in

this

event are

performed

direetll'

by

person-

digital and

analog

electronic

computers.

It should be

noted

that

if

an operation

can

be

performed

automatically

or

rnanuali.V bV superviscry

coltrol

u'ith much the

same technical

and

economil

I-2.

Elements

of Automatic

Control

Systems

Any

automatic control

device including

those

used

in

power

s1'stems

has

in

one

form or another

the

follou'ing

essentials:

an

element

to

sense.

the

effect

of

an external

factor, an

element

to

convert

it into

an output

sig:rai

in

a

prede-

termined manner.

and

-an

element

rryhich

canies into

efiect

th;

action

-ot

ttre

,output.signal

qo

thAtr,She

variahle..m,ay:

be:,u.adt'r

c.ontro.l.,

fhe.se

elements

mav

use combinations. of devices

performing

aurpii{ication,

signa}

de}a-v,

logical

and mathematical operations

.(summation,

inversion,

diffeientiation.

int6gra-

tion,

multiplication. division),

and

also

transducers,

relays

and

regulaiors

or controllers.

Trar*ducers

or

measuri.n,g

elements

respond

t,o

aD

external

action.

When

converting

this

action

into an

output

signal. a

transducer

may

operate

inter-

mittentiy

or continuousil',

as appropriJte to

the

control

"ciioo

adopted.

A

relay

is

a

device designed to

interpret

an

input

value

characLeristic

of

certain externai

ph-enomena

in order

to

automatically

change

in

a stepwise

rnanner

another

value

determining

another

external phenomenon.

An autom a+"ic controller

(regulator)

is

a device

v'hich

maintains

a

desired

guantitv at a

predeterrnined

ralue

or

varies

it according

to

a

predetermined

plaq

or according

to

a self-executed

plan

satisfying the

specified,

iay,

optimum,

conditions

of

operation.

Alttough

they

ma1'

sometimes act

independentlr,

of

one

another,

automatic

control

det'ices

and

their

elements'are usuaiil.

coupled

electricalll',

magnetical-

I-v, mechanically,

hydraulicalll'

or

pneumaticaliy

to

each other

or

to

jlements

essential

to the

operat,ion

of

the

entire

automatic

systenx.

Eiectrical interconnections

of

the

individual

eiements of

a.utomatic

devices

and

various

automatic

systerns

are depicted

in

the

form

of diagrams.

Cirouit diagrams

are drawn

and

circuit symbols

are used

in

icsordance

with

pertinent State Standardstl-11.

High standards of reliability

are an

important

reguirement generally

placed

upon automatic control

devices.

Lately,

it

has

become.possible-to

regaidrelia-

INTRODUCTION

TltmEnh?rADr^r:

gr

rrrvsvullvjt

bilityas

a measurable

performance

parameter

aDd oD t}lis basis

to

better

predict

eletrrents

cesisgiYeDbythetotalnumberz|:|!'q2q'..-qn(I-4)

14

t5

of

element

failures

during

a

given

service

life.

Service

conditions

are

supposed

to

be

invariable

during

the

entire service

period.

Failure occurrence

is dependent

on

the compound

action

of

a nu-mber

oi statisticai

rantiom

processes

acting

during

time t.

The

failures

as

defined

above with continuously acting automatic

control

systems

including

regulators

(controllers)

shou'

themselves

inmediatel5'

as

Iiults

in

the

proper

operation

of

the

s-vstem

being controiled.

With discrete-

aotion

automatic

devices,

automatic circuit

reclosing,

automatic freguency

control,

and aut,omatic

sectionaiizing

devices,

for

instance; a

faiiure

rnay

mani-

fest

itself

either

as

an inabilitl'

to

operate

or as

an

unnecessary funct,ioning

operation.

Under

adverse

conditions both

types

of

faiiure may

1sst1t in a

power

slstem

breakdorna

or

may

lead

to it-s

6st.ltpment'

-

lt

is

possible

to

specifl,

the probabilit-v of no-failure operation,

P1, that

the

control

s)'stem

and

its elements shouid

have.

It, thus,

appears

necessary, b5'

the

reliability

theory,

to

resort

to

the

s,vstem

and

element

redundancy.

It is important

to

make

the

svstem

convenient

to

operate and

maintain

so

that no check

or

test can

interfere with

the

functioning of

the

basic equipment.

\^7ith a

discrete-action

automatic

controi

device the

probabiiiti'

of no-failure

operaticn

Curing

a

waiting

period

(gueuin'g

ttme) Pp should

be

at

least 0"9

t;

0.95,

these figures

being

based

ou

the

perfor-mance

anal5'sis of

sirnilar devices

in

use.

During

liolding

(srutce

time), i.e., when a need

arises

for

device

function-

irrg,

the

P,

value should be

0.95

to

0.99.

With

continuous-action

automatic

cont,rol

devices

(regulators)

the

probability

of

no-failure

operation must evident.Iy

be

not

less

than 0.gtr-21.

-

The

greater the

non-failure

probabilitl'.

the

more

dependabie

tiie

device

and,

hence,

the more

rarel-t'

it mav

be

subjected

to

scheduied

maintenance.

Probability

of no-failure

operation

P1,

as

a function

of

mean

time

I t,o fai-

iure, and

failure

rate

i

is

defined

bl'

the

exponential

reliabiiity equation:

D.

-

o-?t

'

t-v

(I-1

)

The above

expression

i-s

valid

for most

devices

in mass use

for

which

the

iailure

rate

l,

remains

constant

over

the

time

I

under

consideration.

With

devices

whose

compound

action

is

determined

by

-series connection

of

its

elements

or b5'

their sequential

functioning,

the

total

failure rate

The compound probability

of

-no-failure

operation

becomes

Pzt:

l

-

Q",

AS

Prr*

Qzt:

I

(i-5)

(I-6)

For

conservative

calculations

of

a reliabilitl.'

margin, a-s compared

to

the

actual

vaiue

of faiiure

rate, ?';

ma-v

be

approxim"t"jty'

estimated

ri*if..iy

to

the total

resistanee

of

parallel-connected

electrical

networks

I.e.

a:

lrlrl

I

fis ft'12'fg

'

'fr,

rl

tLn

(I-i

)

(r-8)

t

_7

r

I

|

1

I

T;:T;-;*TE-I

Witti

devices

the

compound

action

of

which is

determined by

parallel

eonnection

of its elements

or

their

parallel

operation

(an

example

is

parallel

redusdancy

components)

the

exponential

reliabilit-r,' equation

cannot be

used.

If

thi-s is

soi

the

iailure

probability

Q

of

a system

incltrding

n

parallel-connected

P

,:

(P

os

-

1.76P

"r)

-

P,on-out

(r-e)

'*'here

Paut

:

economic

characteristies per

operation

5lear

of

manJ,

units

in

an

automated system

P,,:

totai

annual

expenditure

required

for placing the

autonratic

s1'st.em

into service

and for

its

operation

and

maint,enance.

The

depreciat,ion period

of the

eguipment

ma_v be

assumed

to

be

15

ye-ars.

Theiefore,

the

cost

of

equipment

per

vear

of

of*r"1ioj

may

be

_evaluated

as

|lt5th

of its total

cost

including

instalia-

tion

and shipnnent,

costs

1.16:

nat'ional

economy

coefficient u'hen

P""

sum of

mone5,

is

inve,sted

in

the

indust.n'

P,,on*ut

:

ecoDomic

charact.eristies per

operation year

of a

non-automated

s1'stem

However,

to

caieulate

tlie

economic

benefits,

say,

from

eguipping

a

po.1,er

aan:lra *'i+L

6lI

+L^ -^*,.:*^l ^.-+^*-+:- ^^-+--l- :-

- - -r

r

f,-

verrurv

nrvrr

qrl

ulrE

rEltrllltu

{tulr'(rllllt|ulu

trutltrl'UlS lSj

AL pfgSgUL

faf

IfOm

gasy.

Statistical data

na1,

!s

used

t,o

determine

t,he

faiiuie probabilitl'

of

separate

elements of eguipment

and transmission

}ines.

Since the

use of a whole

assemb-

and

ir:}ur

*i"z*is*

--.+In

P;r:

PflzPs.

.-Pn

(r-2)

(I-3)

INTNODUCTION

JI

tlA

INTRODUETION

lage of automatic

power

control systemhhs

nou'

become

an integral part

of

Feedback

systgms

may

be

direct

or

elastic.

Direct

systems

have

feedback

signals.

Eiasti-c.

syste?s

have

their

feedback

signals

fed

only

Under

static

control

u'here

II

the

element

characteristic

is other

continuous

at

diserete

(r-10)

(I-

I r)

(I-12)

biiity

of a

severe

chain

fault

affecting

the

entire

power

system

is minute

and

can

be hardly determ.inedtl-l1.

I-3. Automatie Control

anil

Controllers

Automatic

control is an integral

part

of most automation processes.

The

appropriate

general-

theo-rf

is

an indivitiuai

subject. Discussed

below

are

on15'

some

of

the principles

of

the theor-r

and

the

definitions needed for

considering

actual

automatic controllers of

the

automatic

pou'er

controi

svstem.

A

manual

control

process

is

considered first.

For

example,

the terminal voltage

of a

generator

starter has

deviated

from

the

rated

value.

Observing

this

on an instrumeni,

tlie

operator

begins to

decrease

or

increase

the resistance of

tire

exciter

field

rheostat.

depending

on

q.hether

the

lohage

has increa-sed or decreased

until

the

generator

stator

terminal

voltase

returns

to

its rated

value.

Nou',

Iet us answer

the following question:

at u'irat

voltage

deviation

must

tire

operator

operate

the

exciter

fielti rheostat and

at

wirat

rate?

If controi

adjustments are begun at

ver-v

small

departures

with

perceptibie

changes

in

the field

rheosta(; resistanee

oversliooting r-ra-,, oce.ur.

x'irich

mar

also

happen

if

the'opbiator

Starts'the control operaiion

during short-time

t,ran-

sient

volt,age

variations.

A

skilied

operator

begins

to

change

the

positiorr

of

tiie

field

(shunt) rheostat

control

onll'

after

LU

exceeds a

certain permissible

talue

during a

period

long enough

to

shou' that the process

is

not

transient.

The

greai,er

the

voltage

departure.

the

more

quickl1,

he u'il} operate

the

control.

However.

to

perform

such ac.tions

quicklv

with

proper

coordination

is

not

easr

and

the

variabie

under

control cannot,

be

manuaIIl'

maintained

accurate

anb

continuous.

'

Automatic

control

(Fig.

I-1)

should

not

onIS'

remove

the

burden

of

strained

attention

and

corresponding acfions from

the

operator,

it should

also materiallv

improre

the control

process

and eliminate

the

human factor

among

other

effects.

Manual control

is accomplished

through

an

open-loop s1'st.em.

u'hereas

the

automatic

control is

performed

b_r'a close-Ioop s1'stem u'ithout

human

inter-

vention.

With

the

open-loop systems of

control

the

input.

dependhlg

on

t,he

output

value,

is

acted

upon

b5

the

operator.

In

the

case o{

ciosed-loop

systems

tfuis

action

is carried

out

b]'

the

feedback device.

Individual

elements

of

a

control

s-vstem

ma5'

also be

operated on

a

feedback

basis.

\Ve distinguish beLween

two

basic

types

of

feedback: degenerative

or nega-

t.ive

feedback in

closed-loop control

sy-stems rr"hen

the feedback

energy

is

out

of

phase

with

the

applied

signal and

thus

opposes it, and regenerative

or positive

f^^'ll'^^l' o'1.

^-

*lr^ ^rr*nrr'l ia i- *l'oo^ *'i+1" +1"^ innrr* i ^ i+ r^^-+- ..*^- rL^

rEquuqvn

wllvlr

ulrE

vu

!Pq!

ID

fB

}'rlqDe

F ruu

uuE

^uPq ut l.v.

t

lu

IEAIJUJ

|IP{Jff

UIft}

input

in

sric,h

a manner

as

to

reinforce

the

initial

power.

This

latter phenomenon

is

appiied

in

various

types

of amplifiers.

er con

ur

a tran-

sient

process

of regulation going

at

a

certain

rate

is

an

example,

Fig.

I-1.

Diagram shorving

the voltage

control

across

the

generator

stator

terminals

J

-

disturbing

ellect

...

--a:

.

:r^

I

.L

Bj'the resultant

effed,t' on'the

change

of

the

variable

under

control the

control

s-vstems

are subdivided

into

astatic

and

static

(Fig.

I-2).

\\rithin

an

adequate

control

range,

the

astatic

control

keeps

the r.aluJ

of the

variabie y

constant

rviratever the variations

of the

input

parameter

(r)

U:

Uorig:

CotrSt

Y:Uorig-kt

lb

:

tan cl

and

called

"static

coefficient".

analyzed

by means

of

the

linear-segment

-^-r:^- -l rL - -l

pur

uruu

ur

L.!e

cllaracLensl.lc

IS replaced

segments

at

different

angles.

2-2076

than

linear,

its

properties

are

often

replacement,

method,

i.e.,

the

curved

at certatn

intervals

with

straight

line

Fis.

t-3. ConFol

sYst'em

-

,l

elgurell

L

I

-

diaturbing

effect

(b)

Characteristics

of control

systen

(a)

astatic;

(b)

static

,

U

Fie. I-4.

Power

system

frequency

cbanges

after

throw-

-

i-- ^it l^orl

o

tirl ttsa nf mcpt wa

ru6,

vr^

-z

-

wlth

overshootingl

2

-

witbout oversbootrng

r-2.

INTRODUCTION

The

final

stead-v-state

output

talue

of

the-element

,"hgr-e

fr,

is the

gain

factor

of

the

element.

rf

an

automatic.coDtrol

sy-qtem

has

1,2,3,

.

.1

n series-connected

eledrents

-.;+L -^:- f^^!--- i t r .

wrurr

Haru

rasLurs

Egl;

Hgzt

Egs,

...,

kgn

respectively,

the

total

gain

factor

(a)

characterietic

or

,"o",

Tl?i"i;:

"ff;tJ"l

jTT;t:T"t*

ratic

lag

elementt

(d)

o'cillati"*

"rtffi*t

lag eleoentsi

(c)

guad-

The

dynamic

eharacteristics

is

the

time

variation

dependence

of

the

element

output

qararneter

v

:

/

(f)

a-fter-

instantaneousb'

applying

"i

*"i.toal

distur-

bance

r*'hich

change.s

abruptty

the

input

variaile

"

dv

i

"*.t"i"

final

ntinor

value

(Fig.

I-5a).

The

control

eiements-

may

be distinguished

by

their

dynamic

cbaracteristics.

Some

of

the

basic

distinctiors

are

as-'follows."

,

Si,mple

Iag

element (Fig-

r-5b).

The

characteristic

of

the

element

is

described

bv

the

exnression

t

U:Utinot(-e-71

(r-15)

2j

INTRODUCTION

INTNODUCTION

which

is

the solution

of

differential

equation

which

corresponds to

(I-17).

where

The constant

f found

in'

ment.

The

final

steadY-state

Quad,ratic

lag

elemenf

(Fig.

a

defiection

point

P

and

is

r

#

*v:kx'

(I-16)

of

the

ele-

{I-15)

and

(I-16)

describes

the time lag

value

sets

in

after

time trinar x 3T.

I-5c).

The characteristic

curve

of

this element has

described

bv

a second

order differential

equation

qtz&ytqrdyl

Tirl7

*

t't

*+Y:

kx

(I-{i)

(I-18)

(I-1e)

(r-20)

ude fa

eren

ti

4l\

tt).

osciil

rt

and

;aha:

iit

iff

I

t

J-,

ne

IEI

-4

e

)n

IS

npr:

di:

l

d

II

th

em(

rnt

aml

€Ir

kr

rnd

.er

ele:

nen

an(

ter

el

me

)n

rrd

,l-

tc

lat

1e

ler

l

I

lo

o,

l,

tr

t

-L

gI

t

lat

nd

+

reo

as

T

z

ff

tkz'

Tht

ya

-+

ig'I-

press

trl

J7

Tz:Tt

k

(I-25)

tially.

(I-26)

(r-28)

(r-2e)

Oscillati.ng

elemerut

(F

The characteristic

is ex

u'hen

oscil

sed

b secon

I-5d).

.n,

&Y

'2

)12

les

Ir

tj(

th

d

a

o

exp

gua

ns.

)co

nic

egu

ons

lec

onit

in

n

1l}er

nstar

oscill

)ne

Liol

Th

osti

osc

por

ati

dtz

dy

E

when

rr^-^ T - + ltt

\ t.o

Fie.

I-5c

and

reference

I-4J'

.rlere

llt:

/

\Zi

I

-

A

guad.ratic

lag

element,

ca_n

bg

obtained

b]'

cascade

connection

of

trvo simple

he

etetents.

Let

1,,:

1, @r\

be

the

static

characteristic

of

tlre

first

element

and

Uz:

f,

("r)

of

the

second

eiement.

tiren

?'+*Yt:kfit

is

tne d5,naraic

characteristic

of

the first element

and

?'+

*Yz:

kzh

is

the d-vnamic

characterist,ic

of

the

second

element.

itre

iesuitant

ciraracteristic

is

found

by

substituting

y,

for

c..

The

resultant

static

characierisiic

is

deiermined

Lr1'

'uire

expression

T7)2Ts

Uz:f

(rer):

l"Ittb)l:ft(r)

(i-21)

'r!L

- --*==r+--+

.1",*^mia ahrrog{,g1istic

is

obtained

as

foilou's.

From

(i-20)

lng

resurLauL

uyllcllrtlt/

uuarqr

'we

nave

,,:##+t:r,

substituting

the

value of

vr

from

(I-22)

into

(l-19)

gives

f

r€,

4vz

aTr

avz

I J-l

L-dv',-r-,f

'

L

kz

dtz

,

lrz

dt

Jt

Lkz

dt

'

k;J:litzt

Hence

**+

Qtfrz\

d'U.?

++

:

ktst

!t,

atz

I

kz

dt

'

kt

T

t

<272

Here Tt:

h

(fr)

ancl

7,,:

T

b*"

Fig.

l-Sa

The

greater

T

"

as

compared to

?r. the

grea

efore,

the

constant

7, cletermine-"

the

damping

of-the

nt

Tr,

its

amplitude. \then

no

damping

occurs the

el

llation

source.

Pure

gain

element,

in

other

words

an

ideal

element,

allou,s the

output

para-

meter to

increase

s'ith

such

a small time

constant

Z,

tbat the

term

f

H

^

(J-10)

may

be

negiertqd.

In.

thjs

qsqithe

d-rramics

rquaticn cf

the

elemeni,

has

the

form

A:

kr

(I-27y

u'hich

coincides

rn'ith

the

static

D itl

erentlating

and. inte

groting

elements uihose

action depends

on

(difiereni,iating

eiements)

and

on

rating

elements).

The

eguation

of

tlf

e

diffefent

jat

jnc'

o,'lonronf ic e. f.'!'l-.',o.

5

Ere4Es

!

lJ CD tLJI.l.LJ

lYD,

, idx

A:

trt

T

and

that

of

the

integlating

eiement

,l'dr

a:kz

J

Z,

The introduction

of derivatives

into

the

control

eguation facilitates

the

cont'rol

process.

An

integral

in

the

contro)

eguation

allori,s

the

influence

on

the

variation

in

the value

of

the

controlled

variable

to

be

continued

even

*hen

the

mismatching

quantit-r'

6ttt*"ses

to

a ver]'

smaii value,

hence,

the

value

"i

t[,

static

error is reduced,

i.€.,

the

control

becomes

astatic.

The

effect

of

the

dii-

ferc,Ttiating-elements

on the

controi process

can

be obtained

b;,'

the

use

of

elasiic

feedback.

If the

control

eguation

can be dese.rihod hr.'" s difiorpnriqt o-,,oii^-

of_the first,

second

or

thiid

order,

then

trre-.*r.or'(r;di;;;"")".-"JJ#';;;

called ccntroJ

s-vstems

of the

first,

second

and third

order-

respectiveiy.-

characteristic

eguation.

elements.

Automatic

control svstems

also

use

the

derivative

of

the

variable

heing

controlled

the

integrai

vaiue

of the

variibJe

(integ-

,atio

I the

rmol

(I-22)

(r-23)

(r-24)

T

tT2:

#+(r,

*

rn

#+!2:

tc1k2r,

Barzam A.B. Automation in Electrical Power Systems (Системная автоматика)

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