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

-7-.*

tE2

CIIAPTER FrvE

AUTOMATIC

FREQUE}iCY

CO}qIROL

163

w'here

and

The

symbol

.K

is

called the

load frequenc-v regulating effect.

It. characte-

rizes

the

changes in

the

poy'er

drawn b-v

the

consumers

including the }osses in

tire

supply

circuits caused b5' frequencl'

variatjon-s

in lhe

power svstem.

Tire

value

of the

coefficient

ff

is dependent on the

load

parameters

ancl

the

voltage

drop

in the

power

S]'Stem

units

is

the freguencl'

Iog'ers.

The

ff

value

also

varies

with

tire tinre

of

dav,

it is different on

working

da1's and

holidays

and depends

upon

the

yearll'seasons.

Tests

shou- that

the value

of the

coefficient K

ranges

from

1 to

3.5. Jts

mean

vaiue

is 2

to

2.5.

belov'4g.p.Hz,

some

types

of

steam

tur-

ertain

turbine

rotor

stages

with

resuttant

a

srave

breakdo$'n

in rhe .^o,oi

";:?;;';;;,"

;;#i:"il;#?X"i,i|f,""X":rllij;

r into

separatelv

op-eriting

sections

u,ith

manY

consumers.

in

ta

f

tn

r*-hich

is

caused

by

a

loss

in

operating

a.t.the_

lo

sefiing"

(Fig.

-b_?j

st,

the

init.ial

valui

of

the

power

loss

(5-s)

(5-6)

From the relationship

(5-4)

it

is

possible to

determine the

value the

qrrellc]'will

attain n'ith a

power

deficit

of

AP96.

when

f ,n

:50

FIz and

K

AD

O

Lf

onHz:

0.5

+

:

0.25

(AP

90)

l\

Tire freguencv

changes from

the

f;r,

value to

the

fr;,,

value

graduallv.

rather

tlian

inst.antaneou-si1'.

at

a

certain

tirne constant dietated

b1'the

inertia of

the

rotating

mass of

the porn'er stslem

(part.i

of'the

t.urbines.

generators,

motors

and

mechanisms) and b1' the

lt,gulating

effect

K

of

t.he

load.

Tlie frequenc-r raries

iu

time

approximatel-r,

exponentiall-t,.

\\rhen the fre-

quency

decreases

from

l,

to

f,

i:: !t-

Llor,

(1-

e-1lrti

(5-s)

an

d

u-hen

the irequenc5'

(untii

the

frequency

an

d power

regulat,ors start operating)

increases

from

f,

to

lz

fre-

Thus

lz:f

t*

Llott1rl-e-tlrt1

Llr:

+

LJott (1

-

e-urt1

Po'wer svstem

operation at a

lou'er

frequenc-v

State

Standard

i5-rl

affects

the

quality

of

povrer

because

of the following:

Tlre

time

constant

T1 can. be roughly determined by tire

expression

T

Tt=-tsi=

(5-11)

where

f"-u..ir,",

is the

inertia const,ant

oi

tire

power

svst.em.

Since the

fror.i4er o{urls 10 to

16 s,

Z1

is

about 5

to

E

s.

Smal}er

?".v".;as,-

corregpond

to

parts

of

the

power

system where

power

uniLs

finar

varue

",

,.-n:1,';

ii;.ilnds

to

ap,

f

t

trn:

I

in-

Ll,

o,

(5-e)

(5-10)

values of

rated at

specified

by the

is not allou'ed

The

new

where

(5-12)

than that

supply

and

AF,

,,r,:

0.5

O-#

r,

(the

initial

frequenc!

f tn

is

supposed

to

be.

50

Hz).

CEAPTEG FryE

AJter

poiut

c

(Fig.

5-1) the

frequencv foliows

curve 2

rather

than

curve

-2.

The

equation

of curve 2

may

be approximateiy written

as

f

ab:1"-(lr-

f t

rin)(l-e-tlrt1

AUTOMNTIC

FREQUENCY

CONTFOL

165

(5-14)

If

at_the frequency

lu

another

group

of

the

AFC

devices

operat.es,

the

porper

Ioss

wili

decrease

again.

The

process

of

further

freguencl'

changing

proceeds

similarly, If

after

operation

pf

the

AFC devices

the

generated

power

exceeds

Fig. 5-1.

Frequenc5'

cbanges

"OtaB"OX:lieficit

and after it is eliminated

by

the

power

drawn

by the

load

remaining in

operation

the

power

system fre-

queucy wiii

i:egin to

increase.

if

such

a

pfocess

occurs at the instant

correspond-

ing

to

point

b

after the

operation

of

an

AFC

group,

the

final

frequency

value

of

Izttn

will

exceedthefrequency

16

and the

power

system

frequency wiII start

to

restore

itself

(curve

3).

The

approximate

equation

of

curve I

is

!0":la*(lztin-

lu)

(-r-'/rr)

(5-15)

The

frequencS'

time

variation

during the

operation

of

the

AFC

devices can

be found b-v using

the

approximate

value

of

expression (5-10).

Since in the reeion

of

small vaiues

of

I

Frequency

cbanges

in

tbe

case

of

power

deficit

(approximate

plotting)

e-tlrt

x

(I

_tlT

i

expression

(5-10)

may

be

presented

in

the

form

af,

=

*

(Ll*,+)

(the

minus

sign

stands

for

a decrease in

the

frequency

and

increase).

AFC

deYittt

*T:.j1vgn

lriority

io

order

to

avoid

-qerious

faults.

The

AFC

devices

had

to

be

used

economic*iry,

"na.;;11

iuautities

were

used

to

seiectiv-

ely_control

large

power.

loads-

--

\4;ith

such

frequencl'

control.

excessive

power

to

the

consumers

has

often

been

switched

off

ir

iniuffi.i,',,i'disconnection

t,oo.k

place

*'hen

the

frequency

was

held

at

a value

of

47.0

Lo

\7.5

Hz.

Later-ti,J'l"sie

groups

of

AFC

de'ices

l:.:

:"uppiemented

q'ith

others

to

prevent

the

frequency

holding.

This

some_

what

improved

the

service,

but the

faults

*"r.

"oi

"o*pletel-v

eliminated.

5-2.

Modern

Prineiples

of

dFC

(5-16)

(5-17)

the plus

sign. for

an

time which

are

I{odern

integrated

high-power

syst,ems

with

long

extension

1ines

are par-

ticuiarlv

noted

ti.,:

*:::*ii:t;-"i'p;--rrbr.'.#"gl"sies.

A deficit

in generated

atl

the

power

s'srems,

erc.

rt

*."

iiir#i;;h:

filrjir";fJffi

i;:":?""

and

in

dvnamics.f

p;;;;;;

ili.

necessary

ro

consider

rhe

demands

to

season,

days (woiking

days,

days

off

ioa

n"rib*vrl,-

tnr-ti**-oi

,

tnvolve

of spread

according

day

and

Henee,

when plotting

the

relation

I

:

q

(t),

straight

lines

may

be substitu-

ted

for

the

curve sections

(Fig.

5-2). The

greater

the number

of AFC

groups

and

the

more rapidly their

function, the less the error.

frequency

changiug

process

in

The

points

marked

a', b' aad c'

are

plotted

more

obtained b_v rough

plotting.

accurately with the use

of re-

166

CE'APTEA,

FNTE

AUTOI\IA?IC

FREQUENCY

CONTROL

167

rypair

work'

Thus,

in

the

case of an

integrated

powered

system

the

task

of

determifi+g

the

maximum

rated

power

deflciency'becomes,

io

u

g.rut

extent,,

a

probabilit-v

problem.

The

following

formulates

the principles

of the

modern

AFC:

L.

The

AFC

system

must

eliminate

all-of

the

manl'

possible

faults

regardless

'

the

s5'51sm

and

its

growth

rate.

i

must

alu'a1's

be

close to the power

loss,

elf

to

this value.

e

referencesl5_2,

5_3].

ency

control:

>ed

controi

iraving

different

frequenc_v

the

frequency

decrease.

se*inss.

rt is

used

to raise

rhe

rrequ#.j::11J.":l#t"'#

;ilr$di:':l:'jil;

to

pretent_frequency

holding

and slou'

freqt:encj,

Ioss. u.,hen

the generated

pou'er-

is

g]os']r;

reduce.J

in

an emergenci,.

3rd. categor)'1

an

auxiliarl'

one

rvhich

provides,

u,hen

possibie.

selective

operatioD.

it is

deSigned

to

facilitate

the

}oad

t.ripping

and iircrease

it-q

volume

:r

.

generat

eci

-

poiner

caused

b

-r,

se

para

t itr g

I

groups

ranges

from

48.5 to

46.i

Hz

Liformlv

distributed

u'itirin

this

range,

i

FIz-ias

dictated

bv tire

accirracl:

of

ihe

instruments

a'd fresuen',

?ltlittXllhe.

ireguencS'

relavi

such

as

measuring

The

time

settings-of

tlie

AFGI devices

must be

as srnall

as practicable.

Theiri'alue

is

determined

b_,1 the

reguiremeuts

to prevent

malfunction

during

transieni.-procasrej

in

the voltage

circuit-s

in

case

of

ieenepgizing.

Tire

operatin[

time

of

tlre

AFC-I devices

witli

relal's

I{Bg-011

and

llBt{-3 is

d.ZS t.o

0.5 s rnfi

with

transistorizeci

relavs

Pq-1.

0.1 to

0.{5

s.

All

the groups

of the

AFC-iI

devices

have

the

same

operating frequencl.

of +S.S

Hz. but their

time

settings

var-}

'rvith

various

units

from

5

to

40..

and-mal

run

up t,o

g0

s in power

svstems

including

hvdroeiectric

stations rvhich

may

be

mobilized

in the

case

of a

break-

doyn

affecting

the

frequenc--v.

Adjacent groups

of the

AFC-II devices

operate

at

3

to

5 s time

intervals.

\lriren

the number

of

AFGI

and

AFGII

operating groups

is

large (10

to

20

grouP-"

in_ga-ch

frequenc-1'

con-trol

categorl')

ivith

sfraiJ f,,oqu,''rcy

operatilg

s.teps (the

AFGI

units)

and small

operating

lime

intervals (rlie

AFb-Ii

units;l

the

operation

of

adjacent

groups

ma5,'not

5e

-selective

because

of rela1,

setting

scatter.

.ou'ing

to

the

stochastic

character

of

the

;he

spinning

reserve

of

ther*"t

,tuiioo.

afety

contained

in the

calc,ulatio"i.

----

.e

loads

the

rotal

power

of ;,fri;h

is

not

of

the

AFC

system

is to

match

t,he

opera_

same torrtq. ;l_t_-:;j i::.":::,1,".s"'.':-s

(AiGi

an<i

AFGII)

for

*ip;;;

the

:s-,

they

are

installed

directlv

at

the

I

the

automatic

control

devic.e_.

br, the

operatin-g

margin

it

is

advisabie

io

.ne

teed

lines

running

from

tire

porver

ations.

lhe

f5equerrcr

of the

receiving

_qvsl,em

hronism.

disconnect,ion

of pait

of the

I

resynchronizat.ion

of

t,he

grid

svstero

nique

of

AFC

for

resl,ncluonization

is

T$f

,$i:T:,1':tj:*,:

ily::::.,1:f i.l1

in

po

v,er

f ro

m

_t !i

e

gri

d

po

u.e

r

:if.*Ig

r::l:1,,-""":_

^Jj;iii;;ii*r,.'"?J.lt,j,lTi',iit*'t.oflll1"l1l,1;

";".:':,7

a

sYn-

The

power

capacity

of

a

power

svsten

of the

APrnu*

of the

power

loss

ci'onism

seizure

on

flre

*i;;.y;#*

;i""ii#

f."il'

il';.,1{:

ff:;l

r;.*l':ir*,*"":

"1:1.

.::

d

j

n

r

h e

po

wer

sl,s

t

em

n e

t*

o rks

1,,"

ll:.,:"

h*;;1

* i * ; l*:;'

e

f

t

;

i.

-,;

i.G

i','

",

["

I

yfJ,

:

T.

"

il

#.,n.I

"

lf

;

1i.f",""';i,t#'.?:fJ."s':?,1^q*iij:.

Tt!::-':

iyil:.'":iT:

1""1*:",,i?,#:

ji?#

JJ

ffi

i: :H

I,

il; li:

"

H

j*:*.

L,t :

"

J"

",i,

i;,,*,

ffi .:

. ll

;*";

#

i,,1

f,:

"'

fffJ?:li:1,,::""::'"i::ill

i{:qr;;;i'

'-;':""1T";,.*[T.'j'i",:ili"i:l

cont.rol

devices:

IH

t:ly*ns

are

'."o'o*ona.t"".

";i*#r#,1,."i'r"'j;o:r,1l,ll'ir1""t&lency

Ioads

connected

to

the

AFGI devices

in

each

area

pou'er

pool

must

be equal to

the

maximum

value

being

determined

by

considering possible

emergenc)/

Porc-i:

k"APr^,

r.,q#o.i;ffi.{:::;,lyir!i=g!:.:"fiT"

ll

*X.f,l"H:;'*if;l':;'0,::tilS':?.,fi

power

flow

and-direction

"naei

the

prefault

tor,Jitioos

(or

without

the

indic.a-

-T---

CHAPTER FNTE

AUTOIT{-A."IC

rREeUENgy

CorqfR

OL ,t

Ao

tion)

and

changes

in

the

value

of

current

or the

value

and directjon

of

pos'er

flow

in

tbe

line

or transformer.

(b)

Freguencv

changing

rate.

(c)

.Drop_

in

the forward-sequence

voltage,

if the

loss

of

real

power

involves

a

considerable

reactive

power

loss.

The

freq,uenc-v

contro]

must be as

quick

as

practicable,

the voltage.control

operation

of

the

AFC

s5'stem

must be isoiated

against the

duration

iit

short

circ_uits

being

cleared

by the

protective

relaying

sl,stem.

The

use

of

automatic

sectionalizing

frequencl-rJsponsive

controls employed

as

stand-by

equipment

for

an

auxiliarl' frequenc.v

control

device

or subsiituied

for

it

is important.

These

controls separate

som! generators

of

the power

sta-

tion

to

supply

its

auxiliaries

and

jsolate

generatbrs

and

individual stations

carrving

a

roughil'

balanced isajln-iJ.

The

automatic

sectionalizing

controls

maintaining suppll'

to tire

auxiharies

of

thermal

stations

utilize

two

starting

elements:

one futtliion.

at 45

FIz

u'ithin

0-5

s

and the

other at

47 Hz

within

30

to 40 s.

The

automatic sectionalizing

controls

holding

powcr

supplv

to the

most import.ant

consumers

mal,

hav6

a

frequelcl'

setting

ranging

from

46.5

Lo

47.5 Hz-

and an

operating time

of

1 s

or iess.

If this

is

the

case, their

operation

ma1- not

be seleitive

rejative to tiie

AFC

devices

of

the

power

svstem_

\X7L^- rL- aT:

'

li'nen

ine

Ai"C

devices

are used

it

must be

remembered

that the

frequencl'

ylaVl

ma]' respond

not,

onll' to

drops

in

the

frequencl'

due t,o

a lack

of

poo'ci.

.but

also

to

a number

o{

other

causes

outiined

belon'.

An eiiective v;er,

of

nnitisa-

ting

the

effects

produced

b1'

misoperation

of the

AFC devices

is

given

bv

tire

use

of

an

automatic

ioad

reclosure

device u'hich

operates after

iestoring

the

frequenc-r.

Therefore

the

AFC

deviges

must

be combined s'ith

the

freoriencrl

automatic

ioad

reciosure

devices

ts-!,

5-31

trn

addition

to

the

above-described

AFC

principles,

frequency

control ma1,

be

accompiished

by

otiier metl-rods.

Let

us

cbnsider

sonre

of

th.-..

techniques.

AFC

deuices respornlue

to

frequ.eruy change rate.

Taking into

account,

(5-4),

expression

(5-17)

can be transformed

into

It

is

good

practice

to utilize

the

rate

factor

of

freguencv

decrease

to

addi-

tionally

reduce

the

load

in

the

areas

where

the

irequencl,

drop

rate

is

far

higher

that

at

the

power

loss

of

the

whole

poirr;;;;-

(see

above).

The

rate

faitor

3"i.1t#::ncv'decrease

mav

ur

"r"i-*iir

ir"iririiiec

io

i*^ri'ioiioidu"l

power

-

1;: ii+* l,^11-::i.eB.",t. i":,

operale

-as

tlle

Af,'Gli

category.

A,P

o/o:

(ry)

*r,

(5-18)

It

is seen

from (5-18)

and

Fig.

5-2

that

the

rate at which

the frequency

changes-at

the

begin-ning

of

disturbance

is the

criterion

determining

the

relativ-e

value

of

the power

loss.

The higher the rate,

the greater

the

relaiive

value

of

po\per

loss

and the

larger

the load

to

be tripped.

At

the same

time,

u'ith the

same

relative power

ioss

(i.e.,

with

the

same

frequency

changing

rate), loads

that

differ in

abiolute value

are to

be

connected

from

the

AFC device when

faults

occur

in areas,

power

systems

or

pov/er pools

having

different power

ratings.

In this

connectiori, the

"eitiog.

of such an-AFC

+*g-._

T+e_+++syste.m

:ma;r*e luffi

startirrgrespondfng

LotA

to

the

absoiute

vaiue

anti to

the

rate

of frequency

drop.

5-3.

Short-Time

Drops

of Frequeney

t?0

CIIAPTER

FIYE

AUTOMATIC

FREQUENCY

CONTNOL

177

the

system

becomes

different.

The

areas

iackins

acti'e

freguency';

areas

^yiJh,excess

po*rr-

h;;-;;;ii!n"r,

mentioned,

the

AFC

devices

-operating

lith

a power-deficit

facilitate

reiynchrol

nization.

At the

same

time

resvnchloniza_

tion

may

occur

in

certain

caies

without

_,'^l:,

t\.

po\\,er

svslem

llr

(Frg.

J_+a),

rtnose

emf

Etr:Ero,o"*

sin2nf

,t

(5_1g)

be

out

-of

s_vnchronism

reiative

to

the

stat.ion

y'f

I'hose

emf

po'wer

have

the

tro*est

frequency.

As

alreadv

EH,H

devices

restore the

porver

suppll'to

the

consumer.

An

iriterruption

in

the supp-

ly

ma1' halt

a

production

process.

For

this reason

it is

advisabie

to use

the

means which

can

prevent,

unu'arranted

operation

of

the

AFC devices.

Tiiis

chapter

considers some

of these

means.

Changes

uL tiLe'irequency

oi

uoitage

h,eld

by asyrrcItronous

and synchronotts

Ioads

after

the

subslati.on

is deencrgized.

When

a power

supplr'

Iine

or

power

transformer

is

disconnected.

ther

bus-

bar

voltage

of the

receiving

substa-

tion

disappears,

but not at

once.

\4'!r9re

asvnchronous

morors are

used,

the

voltage

drops

to

a value

of 0.1

0

20

40

60

rc7y

Fig.,..

l-3,

Cpelqtrnq

trequ.o-.i,

of

relal,

I'lErI:011'

versus

i'clfige (eiperimental

dataj

to

0.15

ot_Un

in 1.0 to

1.5 s.

Tire

pro-

cess-

is

-prolonged

(self-excitation

takes

place)

if there

are paraliel-connected

banks of

capacitors

in

service.

Svnchronous

motors

and

capicitors

ma-v hoid

a voltage

with

a

decreasing

freguency

for

a longer

iiil.,

aiirirg ieveral

seconds.

Induction

underfrequenc-v

relays

HBrJ-011

and.

I4BrI-03 are ineffective

when

the

volt_age

drops

below

20-25

per

cent

of the

rating

(Fig.

5-3) and semi-

sonduetor

underfrequency

relays

Pq:I, belou-

5

to

10 pei

cen"t

of

the

nominai

vaiue.

Under the

conditions

being

considered

several

methods

mav

be

used to

prevent

unruanted

operation

of

the

AFC devices:

t. The

substation

loads

ma1'

be

connected

to

the

AF.GII devices

having

a

considerable

operating

time which

exceeds

the voltage

decal' time withoui

using

AFGI

devices.

2.

Tire

feed lines

may

be

furnished

with

a device which

blocks

the

AFC

units

with

the aid

of

active

p!we1

or

current relays

that

break the

operational

circuit

of the

AFC unit

after

the

line

is disconnecied

and

no ioad

curient flows

in it.

The

use of

a

current

relay

is

permitted

if the

minimum load

curuent

in

the Iine

exceeds

tbe

short-circuit

cunent generated

by

the ioad when

a short

(E*-4")#T::

I

rMP

I--

trrrMP

u

Ir

'-T-

i

E.n

:

E^."*

sirr2nf

,t

(5_20)

Fig.

5-4.

Frequency

variatjon

irr

asvn_

citrorlous

operatiort

i1)^

ergmeltart'.

circuit: (D)

elecrric

centre

vott-

3q9_

rn

as;-nchronou

s

operatj

on

;

-l'_

Luine.

voltage;

s

-

envetope

oi

voillsb

ir"t"ii'""o

ous

peaks

u.here

1",

is

the

egualizing

current

Thus

Lt

p:

The

relationship

between

The

voltage

at

arbitrary

the

system

and

stat,ion

Iz{ft

point

P

U

p:

Enr--

jI"ezj\tp

frequencie-q

is

as

follou,s

(5-21)

(5-22)

clrcurt

occurs

on

the

line

ne

Changes in the

frerycncy

is

pulled

out of

synchronism

duri.ng

Loss

ol

syruhronism.

When

a

power

the

freguency

of the voltages

at various

systen

parts

of

Generally,

determining

U"

:

f

(t)

is

compiicatedtb-81.

To

obtain

a

gualita_

tive

analysis,

he|

|

Ev

r

:

I

En

I:

1.

Taking

into

account

(s-{g)

and (5-20),

CEAPTER

FI\TE

-

\

'

"-^.

J

nLu

.1Ll7L

-r-;;;

sln

Znlzt

(5-24)

With

xMP

:0'5zvn'

point

P

coincides

with

the

electric

centre.

The

electric

centre voltage

0x:f

sin

Znlp*f

sin

2nlrt

U

*:-"in

Zr,

'+

tws2x

*

lt:!z

7

(5-25)

(5-26)

lJz

fset

t

s

fsd

*4

tta*3

fsrit

*2

fsel

r

fs7

fsct

-

.tet

'

,

Iset-2

t ,- a

'5ff

a)

I

sct-4

{t4

t

l--

t2

ff

,

called

the

carrier

frequency

(Fig.

5-4b)

tb-81.

1l

t"^t]:l:

fron

(5-26)

rhat

the

frequency

rela1,

n,ilr

respond

ro

the

frequenc.i,

E-i-r.-^ < < -L r .

^--^E:::,TY-Yur.-.Ine-operatrng

area-q

of

an

AFC

device

utilizins A frprrr.,o...,

\'.

tVIJe

yllll q-ll1

1 f tn l-{U-'.I\ ^-J ^ +:-^ --r

--vYelsvtr

*^.1 ^__ a_-_, rrh, __:I--_--_v--,b

q.vsLi

vr

qtr

r\.r

U

Utr\,fgg

UtrlllZlng e ,fpfilronr\

:bli

:'#Ji::i'i l,*l"jl, r* li1:,T.r"

q,ith

setings,;;=

0;,,;:

:

?i"' ifj, il: ?,

t"

: T*f { ^*;i.iriti.."

i;

;i',,"i;;'i'

Ei

offi

.:.,iiiin

iit

;

a

0.25

0.5

0.75

1.0

t.25

t.5

(q)

t.7s

2.0

2.2s

lr=lsett4

f2=fss1

-2

fz=frrt-4[AFc

toes

fr

1lr,,,

'*

7

lzlfot

*,1

+

-t

-r

.2

lrset-.t

I1:*.;'*,.alrlr,:1,_*lg.{:,,":,i"'in.

.#"Ji.';r":i1JJ,T"i,liiJf

ilj"

'i;

determined

b5,

the

.elationship

i1

fi

r.

v,here

Ut:,..,

(t__!tlt_)

f

b_27)

uz:

n"

#

(5_2E)

The generators

M and

y'f

are

inciuded

in

r*,

and c"rn.

respectiveiy

as

tran_

haracteristic.

that

an

increase

in

the

time

dela5,

and

;v,settin-g

of

the

AFC

de'ices

reduce

the

"r.u.

of

AFC

Ioss

of

synchronism.

ny

i,n

case.

o!

power

i.nru,sh

during

short

circuittb_sl.

rort

circuit

occurs

due

to

an

inciease

in

the

active

cuit

current

fiows.

The

active

power

loss

AP"c

_

3.r3cn8c

The

three-phase

sbort-circuit

cur"ent

llz

fsct

*4

I +a

fsa*2

{ . *1

f

set

f .-1

.sct

,

I

set

-2

f

stt

-3

!

set-4

fset

-5

0-25

0.5

a.75

t0 t

25

{.5

(6)

2.0

2.2s

Hence

(5-2e)

(5-30)

(tss1)

!ot'4

'f

set

'3

tsct

*2

tvt

*/

*a

fttt'/

fnt'2

!set'5

fset- 4

fsrt-5

t.o

t.zs

t.5

/.75

2.0

2.?5

Fig.

5-5.

Generalized,pick_up

areas

of

AFC

devices

in

o

-

al

*

ur

-

too

v;

bi

tra-

o,

trl

f1p:

o.b

5,;

asynchronous

operation

(c)

lr?

Dore

than

I

s

-'-

AFC

H--

does

not

oprrht"

f,

=,fo1

-4

t2=

t

,4*f

'

fr=fn1

+J

.2

'Stt

t,

=

frry+5

$'loi.'4

=

f

*/

*5

-fr=frr1*5

;;

:

dffi;ri*411"rt.r"1#H

rnr

p"i;t

oI

short

circuir

ft""

:

resistance

to

the

point

of

short

circuit

FTqE

-.!,UTOMATIC

FREQUENCY

CONTROL

The

maximum value

of AP*.

Thus

and

is determined

from the condition

aaPsc

n

-;lfr-:u

ottsc

P

r(6C

-

*JC

apscmar:ry+

IJ one

takes into

account that

the

short-circuit,

reactive

pos'er

calculated

r*'hen

the

equipment

3U:

^,

Qsr:-;

then

the

maxirnum

inrush in real

po$'er

(4P",

*.r),

k\i-:

(0.5Q""),

k\i.A

5-4,

Choice

of

parameters

of FARC

Devices

and

$'or!

of

Operators

r

systern

frequency

by

mo_

aprd

connection

of

tripped

t,he

power

s-/stem (through

3rrrontsm

catchment).

it

is

ice-s

s'ith

the

FARC'units.

to

the

tast

groups

of

rhe

A

,,

,o':t:l;"l'J:iffilr.Jt1,.p"J:$

lrt

th9.

firstl

groups

of

the

AFC

devices

whicir

lre

most.

liable

to

function

ar

short-time

small

frequtrc-r'drops..Besides,liJr

"*rrul

as well

to

use

the

FAHC

units

on

loads

supplie.'i.om'self-cooiail;;"ilstat,ions,

i.€.,

those

without

personnel

and

remote-controi

dcwino.

Like

the

case rvith rho atrn ;:::i^:^ aL^ nr hA

sroups'

their

i'..g:,to.I'..iti's''"

r""Lt""r'ri;;

iffi"t."tl,tL?:trit-t1"it,jf

;iffj

setting

is

10

ro

20

s.

ihe

fina"I

time"seiti"g;;;

be

different

depending

upon

iocal

pourer

st'stem

conditions.

ir;i,rt*"";ffi-'s5,stem

or

a,

individuar

net-

me

interval

at

u,hicli

the

adjacent

FARb

g=orp,

operare

load

connected

ro

rhe

FARc"d;"i**.

l=

Liri"r,

uniformly

:oups.

uence

h-r'

t,,e

FARC

device-q

is

tbe

rel.er-ce

of tliat

I

bv

the

AFC

devices.

To

*rt".

tl.-oplrnting

condi_

operational

current

easier.

s_hen

;

FARd

;;;;;

the

iatter

are

made

to

function

in turn

at,

l_s

to

prevent

the

freguency

drop

and

its

The possibilitl'

of

reconnecting

load.s

tripped

b],

the

AFC devices

to

another

power

source

bv

the

automatic

transfer

unils

shouid

be

ruled

out.

At

the

same

time,

when

reclvering

tn.

]r-il;;"y

and

eiiminatins

t.he erncr.'pnari cirrro*i^-

(5-32)

(L33)

(5-34)

choosing

(s35)

(b-36)

With shorl

circuits dictating

disconnection

of

the

consumers or

entailing

heavv voltage

drops

across

the

unfaulted parts

of

the power

system,

the result-

ing

power inrush

will

be obviousiy less

and dependent

on

the

amount of

tripped

power.

I\,Iore

than that.

in

certain cases the pou'er tripped

ma],

exceed

the

value

of

inrush. Pow*er inrushes

caused b5 short

circuits

should

be

taken

into

ac-

couni. s-jth

self-contained

small-rated

power

svstems

(up

to

500 I,{W)

wl:ea

damaged

equipment

cannot be rapidl-v

.fripped

and

in

the

presence

of

lines

possessing

high resistance

(35

kV

and

iess). ReaI

pos,er

inrushes up to

50 to

70

i\f\4l

have

been

encountered

in

pos?er

svstems

rn'ith

short

circuits. If a short

circuit

is

quicklJ'

cleared the

freguenc-v

has no

time

to drop to

the

value

at whic.h

the

first

group

of

AFC der.ices functions.

Therefore,

in low rated power svstems

rapid

ciearing

of

fauits

is regarded

as the basic

measure

to prevent the

AFC

device-s

operat.ing.

The

short,-circuit

clearing time

in

cable circuit,s equipped

with

react,ors

is

of

2 to 3 s. Such periods

are sufficient

to

decrease frequencv

to

47.5-48 Hz in

pov,'er

svstems

rated

for

400 ltfti

or

less.

As mentioned above, the

restoration

of

suppiy

to

the

consumers after clear-

ing

a short

circuit and raising

the

frequency

in

a

power

system is

accomplisbed

by

the

frequency

aut,omatic

reclosure svstem

(FARC).

Changes in the

t'requcnty

due

to sluggish

operati.on

ol the speed

gouernors

of

hgdraulic

turbtncs. When

the ratio

between tbe power

demand and

generat.ion

abruptly

changes, the turbine

speed governors

have no time to

make

the requir-

ed

alterations to the water

volume

for tbe turbine.

The result

may

be

a decrea-*e

in

the frequency

of the power

system in

spite

of

the

lact

that the underloaded

generators

'may

have

some

reserve

power.

This

was

the

cause of a frequency

decrease

to 46.5

Hz in

{0 s and

operation of

the

first

groups

of AFGI devices.

It is again the

FARC

svstem that

corrects the

malfunction of

the

AFGI

vlces

m a

their

operation

when

the frequency

decreases because

of

the

turhine

speed

governors.

responsibte

fo,.a'*ii?ri""i

il-ffi;""y

and

elimi""tilg-

the

emergenc)i

situation

M;--.--* ,:,

fl?glgoty

of

"

gi-ty

of

"

gilot-o

"!""

-

be

reestablished

as

quickly

as

'practicable.

^ '

r-Y

ro

rne

trlppe(

!

the

slow operation

of

AUTOIdATIC

FB,EQUENCY

CONTROL

777

Tbe

circuit

of

an

shown

in

Fig.

5-6.

An

auxiliary

relay

and

a

AFC

device

without

subseguent

automatic

reclosure

is

underfrequency

relay

trips

the

breakers

via

an output

ii*"

r"f"V.

Simultan*ouri--o

a

prohibitive

signal

is fed

when

the

tinre

l9r*y

z-R

is

"l::rgIoI

"-rong

period,

its

rhermar

srab'itv

is

obtained

bv

breat-inltir'.'"oi...t

,I:i

yfi"h-inrroducer,

"*l"ut_rimirins

resistance'

Th;

time

reiay

resets-whel_thr_+:ffi;**is:ecovered

and

the

frer

guetrcv

rerav

conract

opr"r.-ine

reravs

rAR=i"i

"sii;;r"??

deenergized.

5-5. AFC

and

FARC

Circuits

\

s

.o

.\

k

f-^- vT flo

ttuttt

a,

-*

ol

{s!

busbar

sustem

b

a

fnm

I/T

of Znd

husiar

b

sYtt'm

Au{omatic

emerqencu

t-rtpptng

czrcui#

ot'

rreguency

drop

Automcf

ic

reclosinq

clLe,-

freouencu

res

I

ora/.ton

Fig. 5-6.

APC

circuit

with

prohibiting'

oprr"tioo

of

ARC

device

installed

on

connection

to

the ARC

devices

which

respond

to

the

discrepanc,r'

a-nd

are

instalied

on con-

nections.

These

ar"irri

do

trot

cali

for reclosure'afte;

the operation

of tlie AFC

reset

trcguency

.i

th';

;;iri.

The

coita

cL

3A.R-2

makes

the circuit

of

relav

A7'R

whose

reset

i.

a.iayea

*iL"

ti.

"t*"ture

drops

out.

The

circuit

of

rela-v

zAR

is opened

by

the

contact

3AR'3-

and

vice

versa.

The

circuit

diagrams

of the

AFC

devices

with

a

subsequgn-t

:{RC

after

fre-

quencT recoY€r];

lfiy-fe-nq

are

illustrated

in

Fig-1-!-I.lq{ftg'^]ht

circuits

are made

ro

confoi*:to

tn"lrequrrr.;'rela5ri

type t'tnU-0l1

(l'IBq-3)

(Fig'

-S-1Ol'

Let

us

consider'the

diagri*

of

ttre AFC-device

in-SS'.5-7'

The

underfre-

qo"n"v

"*trv

ff"p-t"t.;

F6.-ioses

tht

time

relay

!R -'*'!gse

contact

TR-2

swirches

on

the

"uiiti*l'rela-vs

IAR

and

LAR.

The

ielay

lAF

trips

the

break-

"rr.

bo

closing

the

coniact

3AR-1r_the_relay

7AR

cbanges

the

resistance

con-

neeted

in seriels

*ith

oo,

of

the

":"*

?i"ltf":'::;:.1?;i-J"rttl?

f

ili-flrll

if,;

Fig.

5-7.

ARC

circuit^,T-1!_subseguent

ARC

afrer

recovery

of

frequency.

FARC

#'=f*s'rT:*:L#,i"i"a#,}"#ffitfj#t#i,t,"tt#}"n:r"r,""1."i#1:

The

conracts

3AR-1-and

3AR-2

gpgn, while

the.conta

ct

3AR_3

c'0ses.

relav

ZAR

cl0ses

and

;-;;ir;'t,^i,o-f1ffi.;";i,'irs

circuit

is

olened

bv

conract

ArR-r-

The

reray

iia

fii.m

u_p

and

,*uJ"rr..the-breakeri.

The

sii

ff-i"ol::ldl"Jfi::T,:i,l;*j

it$+.i^"i.""i,o

ro

rhe

circuft

is n".,*,

?he

the

rle-

oevrce

is

indicateg

ry

th-e

signat-;rhy;

;Ff

;#l#."-t'

operatio-n

of

the

It

is

advisabre

to

use

the-d'evic;;il;ff'F,g

.+/;h.-"

there

is

a

provision

,r1r::.

automaric

,;i;;;

ii

tl,

gi'rnro

"loo?rtioo

oorv

_;fr;

rhe

rripping

"-r

I

AIITOI{ATIC

SREQUENCY

CONTROL

t79

effected

by

the

AFC device

aud on condition

that

the

normal freguency

is

established.

In

the

variant

shown in Fig. 5€

the

contact of

the

underfoequency

relay

Fr?

closes and

makes

the

time

relay

?.R. On

expiration of

tbe

set

period,

the

con-

Lact

TR-Z

makes

and closes the

relays

lAR to

?AR,

and

the

signai

relay

^9J?

picks

up. The

relal' /,4R

makes the tripping

circuits of

the

breakers.

Tbe circuit

given

eguipment

is eonneeted

or

not

connected

to

this

or

that

group

of

the

AFC

devices.

IAR-I

Bloe*ing

in

stqrttnc

ctrcuil

"o/

ARC

devtc?

trom

y

I

h)

From VT

(c)

/:\

,Iu

,,

a

tc

z0

J0

+0

s0

60

70

Ec

sc ro0 tlljia

ufi

Fig.

5-9.

Connection

of

frequencS,

relay

,;

noirrg;'

tiansiormer-.

(a)

through

vo]lase

stabi

lizer

ys;

-

(b)

through

inleryening

lransformer

or

autotrans-

lormer-

I..."n0

v-oltage

rel

a1';

tcl-itriiielr rnlerrenrne,

trenFfnpfrer nr er!r^r.ohor^'*--

f ormer

T and

yo

Io,fner

I ano

Yoltage

--re-l

a]_'--.!.-)_

through

-intirrening

E"trltdr-"t

or

autotlansro.-?t

and

stabiiizer:

l?

-

6erjes

iesisior;

(di

Eraorrrzer

output

Toltagc

U^,,i versus

U._

at

vgriotrs frenrrmala. t R^ E-. ^ ^

-.^

--sut

- -ln

various

freguerrcies:

.1

-

50

tlz., 2

_

46

H.z; J

_

L6

Hz

.

Fig.

5-E. AFC circuit

u'ith PARC device

ernploying relal PIIB-5S

F.F

-

contact of frequenc5 relal;

T.R

-

time relal';

.AI.R

-

reiay Fitlr delaTed arma-

ture dropout in reset;

IAR-?AR

-

auxiliart

relays;

SJ?

-

signal

relay

of

the

rela5, /,4.fi is

controlied by

the

iontact ATR-I

which

is closedu'hen cur-

rent

flows

in

the

coii of

relal ATR. The

contact

2AR-I

breaks

the

circuit of

the

relay ATR.

The contaet

ATR-L in

its

turn

breaks

the

circuit, of reiay

lAR

(0.8 to

1.0 second

iater)

and

removes

the tripping

pulse

from

the

breaker.

Thi-s circuit

of

the

device

permits

the

opened breakers

to

be

ciosed

manually

q'hen

the

contacts of

the

underfrequency relay remain closed

for a long

time

(in

the

case

of baked contacts

or

wben

an

emergency dictates

that the

consumer

be

connected manually

because of

a frequency

fall

in

the

power

system). This

is

the

advantage

of

tbe'variant.

Closing

the

relay

2AR

cadcels

the

operative current

flow

in

the

time

relay

of

the

ARC unit,

thus the

frequency recovery is delayed. Reclosure

\r'iil-take

lace only after

the

contaets of

the

und uency

relay open

and

the

relay

Good

results

are

obtained from

the

circuit

sbosn in

Fig. 5-8,

when

the ARC

devices

are

installed

on

the

connected

equipment,

regardless

of

whether

tbe

L

inten'ening

transform

er

(aut

o transform-

rs in the

voltage

of

tbe

secondary

wind_

n

be

chaneed.

charact,eiistic

of

tbe

stabiiizer

that

a

rt terminais

of the

stabilizer

u,ill

be

at

on

of

the

fregu.ggcy

relav

at the

preas_

ge

of the

stabilizer

deciea-.es

but

not

:ration

of

theJreguelc],

rela5-

may

be

in Fig.

b-9i.

The-voltage

rela.,,

..iiio*

.acts

and

raises

tire

inpu-t

voitage

of

ib;

evices

utilizing

the

circuits

shorra

in

3.5

s

to

provid6

reliable

di-"sliniration

#;,hid';i,;";;#JH:i,1,""'rlj'?#'::-,'"?"1+;T";;'#"^*iTffi

"lfil

of

in

rcy'

relal'

through

a

voltage

circuits

and

voltage

stabilizer

does

in

this

respect

it

has

an

not

reguire

such

switchinp

advantage

over

the

circuitE

Fig.

5-96

and

c.

CEAPTE.R

FTT'E

AUTOM.4.TIC

EREQUENCY

COhICROL

t8t

5-6.

Induction

Freque.ncy

Relays,

Tlpe

trBq-Ol1

(trBrr-3)

For

the

internal

connections

of

the

relay

and

the

construction

-of

its

sensing

element

see

Fig.

L10.

Magnetic

structure

-/-

carries four

series-connected

coils

Z

w\ic\.

together

with

capacitor

C form

an inductive-capacitive

circuit

(cir-

cuit .I).

A

current

flow

in this

circuit

builds

up the

fiux'O,

in

poles

J anil 4.

Fig.

5-10. Frcquency

relay,

type

I,IBTI-011

(a)

relay

internal

connectioru:

(b)

relay

conatruction

Poles 5 and

6

carry

\wo

Z

coils which together

with

resistors.R,

and ,R,

form

an

inductanee-resistance

circuit

(circuit

1/):

The

current

flow in t[is

circuit

builds

up

tbe

flux

O11.

'

Voltage is

supplied

to

both of those

circuits from the

secondary windings

The

required

torque

is

determined

by

the

following

expression

where

/c

-

proportionality

factor

t

:

angle

between the

flux vectors

ti'1

and dls

Capacitance

C

and

resistance

.R

are so selected

that

the angle

between

the

Pt

":.d.(D11

vectots

is zero,

i.e., the

torque

is egual

to

zero

(more

exactiy,

it

is

insufficient

to

overcome

the torque

of tprin

g

i7).

The

relay

contaets

in

this

ea-ce

are ope_n.

\4';hgn^

the-

freguency

variesi

thJangir

,f

+

O and

the

rela1,

iot*,

aluminum

sleeve

9

fixed

on

J0,

tends

to

turn-.

In'the

case

of

an increase

in

frequency,

the

flux

(b1

lags the

flux

(bi1

and

the

torque

assists

in opening

the

contacts.

\4liren

the

frequency

decreases,

the

flux

b1

iead.s the fiux

Os

and

the

rela;'

eloses its

contacts.

The

operdting

setting

of

the

reia-v

is

controlied

by

means

of a

doubie

rheostat

-Rt integrai

wiih

the

reiay

case.

The reiay

scale may

be

cbanged

bv

"a"vion

the

resistance

.Rr.

.

The

relaS'-has

a

permanent

magaet

l8

acting

upon

steel

rod

-Zg

s,hose

func-

tion

is to

add a

count.er

torque

to the

torque

of

spling

-77. Such

a

construction

improves the

performance

of the

rela-v

as

the

freguenc,v

slightly

departs

from

tbe

operating

frequency

when

the

spilug torque

js

iniuffiJieni.

t"

"aaiiir",

it impro_ves

the

reset

factor

of

the

reli-v.

Aluminum

sleeve

g

is

positioned

in the

air

gap,-iretu'een

the

reLa-v

poles

and steel

ci-Iindrica]

core,g.

10

is

fixed

hv

polished

si,eei

journais.ZJ

p'hich

are carried

b-r upper

bearing 12

and

lor*'er

b*"t-

ing 13.

Relay

contacts

/5

and

76

are

shorted

clock*ise

by

silier

rocking

bridle

ia

of

sieeve

9

(top

vies').

Given

in'Fig.

5-lf

is

the

reiay

circuit v'ith

a

minor

alteration in

the

internal

eonnections

in order

to

ss'itch

over

the

reset

setting

of the

relay

after

funetion

of the

AFC

device.

The sr*'itching_

is

accompiisheJ

by ciosing"

tbe

relay

con-

Laet

1AR-l.

The

reset

setting

of

the

relal'

cir

be

cha-nged

afGr

it

has

ii.6a

up,_v'hich

is

clear

from

its

vector

diagram

(Fig.

b-12).-

.Let

voltage

(i,

at fuequency

I:

rolzn

Hz"be

"pili"a

to

rela-v

circuits

.I

and

.I.t.

. Ih.

shift

angle

_q1

between

the

current vector

i1

and

the

voltage

vector

U,

is determined

by

the

relationship

between resistaice

-Rr and indlctip;;:

tance

s1

of

.circuit

I

la)

(5-38)

.

Il.

sh.ift

angle

p11

between

the

current vector

.I11

and

the voltage

vector

U,

is

determiqed

by

th_e_relationship

between

resistance

l?rr and

indlctive

t"r"1

tance

r:s

of.

circuit

II

\

.J

^J

M

-

ki}n@1siu

rp

(5-37)

(5-3e)

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

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