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

_]

I

AUTOMATIC

FREQUENCY

CONTROL

I1t:

0)L77

(542\

_

At

a frequenc],

equai

to

the preassigned

setting value

of operating

frequency

the reactance

is

'

r1r:

rcet: osetlll

6-43)

Using tbe variable

resistor.R2,,

set the resistance

of circuit

II so

that,

9ri: 9r

(5-44)

183

The inductive

reactance

of

circuit

I

is

qJaLr-+

(b4o)

^

(')LI

At

a

frequency

equal

to

the

preassigned

setting

value

(or

:

oleer)

the

iuduo-

tive

reactance fi1

has a

definite

value

rr:

Eset: 6)"etLr-

^ + F-4I)

'

@cell-

I

-Since.R1

is

constant,

the

angie

between

tha

current

11

and the

,to\Lage

[J-,

will

change with

a

change

in the

frequency.

Wheu the

frequency

decreases

as

eompared

n'ith

the

operating setting

frequency,

tbe

reactance 11

and

tbe

angle

91

decrease

and

vice

versa.

The

inductive reactance

of circuit Ii

is

fron

Yf

ol

busbar

a

system I

6

-

from

llT

'

ol

husbar

5

systenE

sAn-I

-

relsy contact

to

control

reset

setting;

,S

-

knife

blades sypplyrng

a.c. voltage

are

closel

first

ani

tben

its

is

ctoset:'tn6

orier

is

reveise

when

the

switch

is

openel);

presence

ol voltage

Fig. 5-L1.

Connestion

of underfrequencv

relav

14B9-0U'

when reset

seti'iag

rs conirolled

-

Iu

tiris

case'the

impedaaCe

ZlyviJ|have

a

defiuiie

vaiue

with

ro

:

o)aetZrr:

:

EZt,

where

E

is

the

proportionality

factor.

The directions

of the

currents

-f1

and

.f11

and

fiuxes

tb1

and 611

are

the

same

and the

angie

p

between

the

fluxes

is zero.

The

torque

of

the

relay

is aiso zero

and,

if

there

is no

spring

torque,

the reia-v

is

in

a

position

of indifference.

It the

-s1'stem

frequencl'

exceeds the

operating

frecuenc;' the

reactance c1

increases

to

an

amount greaier

than the

reactance c11.

The flux 01

begins

to

Iag-the

fiux o11

and the

reiay

torque

acts

to

open

tbe

contacts.

If

tlie

system

frequency

decreases

in

comparison n'ith

the

operating settirl.g

freguency, the

reactance

t7

dccreoses niore

than

the

reactance c1i;

the

flux

(D1

starts

to

lead

the

flux dr11

and

the

rela1, closes the

contacts

(function

of

the

underfrequency

rela_v

is

meant)

After the

relay

contacts

have closed they

will

again

opon,

if

the direotion

of

the vector

CD1

coincides

with that

of

the

veotor

Orr.

To overcome the

friction

torque,

the vector

6,

must

somewhat

lag

the

vector

iilr,

io order

to

pro-

mote

a negative torque

so that the

relay

is reset

at a

frequency

a

bit

higher

than

the

operating frequency.

This

determines the

reset

factor

of

the

relay.

This desisn

aliows

the

reset fr

frequency,

it is

sufficient, when

the

contacts

are closed,

to

increase the

angle

switcb

(when

turned

on,

lts

blade

supplf

ing d.c.

Power

L

-

pilot

lamp

indicating

$

\\

tl

6

< uset

Qrea

(") (b)

Operating

diagram

of

relay I'IBrI-011

(I'IBrI-3)

Fig.

5-12.

of

ts anl

voltages of

lelay

circuit I;

(b)

same

of relay

circuit fI

g11

between the

current 111

and the

voltage

U,,

i.e.,

to d.isplace

the

flux

O11

184

CIIAPTER FTVE

direction

towards

the

horizontal axis.

Such an increase

in

the angie

grr

is

obtained

b_v reducing

the

resistance

.Ri1.

As

said above,

a

similar

method

is used

to

controi

tbe

reset

frequeDc5,

se1-

ting

of

the

frequency

relay

employed

b-v

the FARC

devices.

It

is ciear from

the

diagram

in

Fig.5-12 that the

relay,

t1'pe

tr4Bg-0{t

(I4BII-3)

may

perform

the

function

of an overfrequenc]

relaS'.

To this end, it is sufficient

to ehange

the

eonnection

polarity

of

the first

circuit

or

cbange

the

position

of

the

contacts

by arranging

them

so

that they

close when

the

flux O, ]tgt

the flux

(b11.

5-7.

Frequeney

Relays,

Typ"

Pq-I,

Employing

Semieonductor

Elements

Since

197{

the

underfrequency

rela-vs,

t-vpe PTI-I

(Fig.

5-13),

based

on

semi-

conductor

and

logic elements

are manufactured

in the

USSR.

The

relays are

free

of

the

imperfections

inherent in

the

t-vpe

I{B-{ reiays, i.e.,

the

seti,ing

of the PrI-I

relay

is

practicaliS'

io6*nendent

of

the

voltage

magnitude

and

does

not'misfunction

Thgn

the

voltage

suddenl-v

changes.

For a

complete

internal

wiring

diagram

of

the

relay

see

reference

t5-r01.

Through

a decoupling transformer

f

aud a

band filter ^F

n'hich

eJiminates

uJ seqlo

ur

!.rft'

Lrrrlrirtil'rr/lcl

rJ.l.rlB

rirBrlrt,uLJJ.D.

IIIe

I'elaLIrgg poslLIOn

oI

pursgs

upgl

AU?OMATIC

FREQUENCT

CONTROL

Il,

Uprz

^.

' r-_

lP -J.Ps-L---

PR-I

PR.z

Fig.

5-13.- Semiconductor

(d)

simplified schenatlc

dia

urderfrequency

relay PtI-i

gfam (shown

ln

broken

line are

cireuits used to

controj reset

sctting oI

lrequency

relay)

(a)

bloch

dlagram;

(b)

tirnepulse diagrams;

(c)

phase-shift

networks;

186

circuit

voltage

disappears.

The

contril sign;.f

from

PW

is fed

through

ampiifier

.4

to the output

ele-

ment

OE.

'Ihe

phase-shifting

network

converts

the circuit

frequency

changes

into

chasges

in the angle

g

betv,een

tbe IJ1and. i,

vectors.

When voltaEe

Ineasure-

ments

are made between

points a and

b

(Fig.

5-t3c)

the angie between

the

U1

and

U,

vectors

is

determined

from

the expression

I

r,ilL

-'a

(l)L

tan o:

-;-:---

'

ttli

f,rc

AUTOM,A.TIC

FREQUENCY

CONTROL

frequency

only

by 0.2

Hz max.

and from

-40

to

+40"c

by

0.3

Hz max.

The

operating time

settings

are 0.{5, 0.3

and

0.5 s.

-

The

power

consumption

is 10

VA max.

for the

a.c.

circuits,

10

W

max.

Ior

d.c.

circuits at

110

volts

and

20

W

max.

for the

d.c.

sircuits at 220

volts.

The a.c.

and

d.c, circuits

allow

prolonged

operatiou

of

the

relay

at 110

per

cent of

Uroted.

The base

and

dimensions

of

the

relay

are

the

same

as

those

of

the

I,IBri-3

unit.

The

d.c. output

is from

terminals

-Z

and 3.

The

power

is

applied to termin-

als 7 and

8.

Thetelay

reset

setting for

operation

of

1ne

f'AnC

unit

is changed

by reconnecting

contacts 5

and 6.

The output

circuits

are

cotrDected

to termin-

als

2

and 4.

t-t;

tfrtiT:":^-.,

^^^^-+i^, ^,^*^-+^..^^r :- ^..4^*^+: --a--,

3.

In large

power

systems

numerous

emergenoies

resulting

in

critical

falis

of

the

frequencl.'

are

possibie,

therefore

the

AFC

systein rnust

be

capable

of

"self-adjus'cmeit",

i.e:, whatever

'rhe'fault,

i,he

amount, of

tripped

load

must

correspond

to the

power

deficit. This

requirement

is

not

met

by

the

AFC

devices

with a

smali

number

of frequency

control

groups

when these devices

are

serving

Iarge

power

consumers.

4.

The

AFC

system with two

frequency-control

categories,

AFGI

and

AFC-II,

and

v'ith

a large number

of

group-"

in

each

categor5,'-considerably

satis-

fies

the

"self-adjustment"

requirement.

Coordinated

operation of

the

AFGI

aad AFGIi

categories

is

a

further development

of

this

system.

5. The

further

improvement

of

the

AFC system n'i1l

be

apparently

combined

v'ith the

operation

of an automated

load-controi system to

which

rn'ill

be

added

the

function

of control of the AFC

devices

(parameter

adjustments,

determina-

tion

of

required

unloadipg, etc.).

6.

Combined

operation

of the AFC and FARC

devices facilitates recovery

of the

normal

power

supply after

clearing

the

cause that made

the

AFC devices

function

and

corrects

malfunctioning

of

the AFC

devices

when

short-duration

falls

in

the

power

system frequency

occur.

CITAPTER

FIVE

187

(5-45)

An 0.4'change

in

the

angle

g

corresponds

to

a change

of 0.1

Hz

in

fre-

AFC

devices.

The

operating frequency

may be

adjlsted

either

in

l-Hz strPs

by

a

switch

or

continuously

witnii

I

Hz by

means

of

resistors

/fi

and

Zft.

The

time setting

of

the relay

is

controlled

by

ibanging

the

circuit

capacitance

with

the

aid

of

capacitors

6C

through

8C.

-

Relay

specifLcatio-ns. The

rated

voltages are

100

volts

for an

a.c. circuit

under

ointiol and

110

and 220

volts

for

the

operating

direct

current

circuit-

The

operating settiug

range

is

from

45

to

50 Hz

and

the reset

values

range

from

46

io

51,

Ii.z.

The-minihum

difference

between

the

operating

and

reset

ngquenclgs

Is lgss

f,nan u.'I

n-L,

Lil€

uPurauruB

II|,quEuuJ

rD

urus

u'

the'voltage aeross

the circuit under

control

varies

from

0-2

to

Variationi

of

the ambient

temperature

from

-20

to

+40'C

change

7. To

prev'ent

the

IAFC

devices,

at substations

having

synchrouous

and

asynchronous

motors,

from

misoperation

when

the feeder

is

tripped

blocking

should

be

applied.

For this,

active

power

or current

relays

which opeD

the

opera-

tive

circuit

of

the

AFC

device when

the

feeder

is

tripped

can be

used.

8. When

a

power

station

with

a heavy

power

deficit

is

isolated

from

the

rest

of

the

power

system

under an emergency, the

separated

area must

be

pro-

vided

rn'ith

lcca1 frequency

control

in

addition to the

AFC

system.

The

local

frequency

control

units

must

automatically

come

into

operation

when

the

1.3

of Uroted.

the

operating

188

CHAPTEfr

FIVE

Chapter

Eir

AUTOMATIC

CONTROL

OF

FREQUENCY.

REAL POWER

Af\rD

POWER

FTOWS

nV

POWER

SYSTEIIfS

5-9.

Review

Questions

1. What

is

the purpose

of automatic

freguency control?

\4Ih]'

are AFC

devices consider-

:9

":_ipfortalt

elements

in

power

automatic

control

s]'stems'to prevenr-i"riii

;if;;tfig

the

entrre

systeml

2. What

are the

advantages

and

disadvantages

of

the

AFC

system

*'ith

a

great

number

of

fregu_en-cv control

gror:ps?

-

3.

lVhat

afe the

nurno-.e and valrres of the f.imo sptfinoc rrcai hrr rho AFtl-T ond iFt.-TT

devices?

.

4.

Draw

a

diagram

of

an AFC

device n-ith

blocking

from an active-power

relar- respond-

ing

t_o tb_e.real

Pos'er

floq'in

tbe

Jeeder. 11'hat

shoutd

5e

the

operating

iettine

oi ihis ieiav?

5. What

are

the

purpose

and settings

of tbe

FARC

devices?

6. Desmibe

the

operat.ing principle.of

the.HBtl-3

(IIBTI-011)

induction

frequencv

relal'.

7.

Describe

the

operating pririciples

anci cbaracieristics

of tbe

pt-f

semico'nductir

IrequencS

relay.

8. How

are

the

operating

and reset

frequenc5'

settings

of the

tr{Brl-4 and

prl-I

rela1,s

adiusted?

--'-'i

-'

-

--'-''

9.

lVhat

is tbe

purpose

of tLre additional

{in

a

local area)

freguenct'

control

and tbe

automatic

sectionalizing

controls

responding

to

frequency?

10. What are

tbe. causes

of

.possi'ble

opiration

oi tbe'frequency

relays

of

AFC

devices

in

the

case

of

loss

of s1'nchroniim

in a p6u.,er

system?

11. Name the

causes

of

sbort-time-decreasis

in the

power

slstem

frequenc-r-

where

a

spinning

power

reserve

is

avaiiable.

6-1.

General

^^.Y*,.:.1"-"1,9:f:!r,h-1g,

the,current

frequency

in power

systems

musr

be

vvss^4qvu'>rvY

Du'sLaruEu

at

a value

oI

5U

-+-

[J.t

H'z.

Short-time

operation

at

^ c-^---

I

"r

'iro""at

ln this

case,

the

d"i"ff?rili.J#l

rous

electric

clock

time

should

not

be

r

specified

value,

tbe

dispatcher

of

the

lerating

power

system

must

bring

the

f the

load

frequency

continues

to'

tal]

rsted,

the

Cispatcher

aust

ensure

rees_

ions

b--v

}imiting

or

tripping

some

loads

regulating

instructioni

[er-,

6-2J.

rirements

for

the power

suppll'

quality

]auses

a

labour

productivit5,

reduction

wered

freguency

(belou,

4g.E

Hz

during

IU

Tin)

is

econonlica!.ly

so

unattractive

t

I6-3i.

rows

that

the

use

of automatic

ioad_

bhe

amplitude

of the

frequency

varia-

Lions,

however,

do

not

exeeed

the

iimits

in the

absence

of coutroi.

ns

having

generated

po\iler

reserves

the

frequency

kept

at

the specified

value)

e4v

gvou

evv,r,,Lrrruar

roau

arrocaf,ron

;;il";il

ilii.

inlilri{J'iir"i"Jiirti:

In the

conditions

of

integrated

nowcr

qwqf

oyno rlro ^^-*t^+^ -*J ^-^-^-:-^r

Tt-1Y*::1.:r_Jh,9

generated

power

at the

siations'ro*.ti*5r

it*ii"asible

due

to

insufficient

transmission

capaeity

betweeu

and

in

the

links

ffif"i;

Tt;

systems'

Under

such

conditioni

th;

;;in

p"tiorc

of

the

automatic conrrol

t

190

CIIAPTER

SIX

devices

is

to

ensure

the maximum

Iinks

as

c&n

be

permitted

bv

the

practicable

steady-state

power

transmission

over

those

stability

requirenents.

AU?OMATIC

CONTROL

OF FREQUENCY,

REAL POqIER,

POWER

IILO\F

191

k)

Fig. 6-1.

Freguenc-v varjations

in power

system

{o),separate,

operation. of

parts

of..integrsted

poller

s}-rtem;

no

freguenc}

regrulators

are

utedatre€rulatingstations;

(b)parallel

.operationof

integrated'gystemi

no ireqiencl.

regu-

lators

are

used

at regulating.stalions;

.(c)._frequencl'

regulbtors

are turn6d on.:pirallei ope*ra-

tion

of

powet

system

parts

is

shown

in

tlie

ieft-hand

bart

of acce)erated

recorti cf recoidine

frequencl

meter.

Separate operation of

IPS

parts

ii

shos'n

in the

rigbt-band

portion

-

If

the

amount of

the

power

exchange

between the power

systens is

specified

in

an agreement, a factor

often

practised

in

many

couniries,

or

when

this

amount

is specified

according to

a

load-control

schedule,

then

mainteuance

of

the

Thus,

nowadays

automatic

control

devices

are responsible for

sustaining

the

loael

frequency

of the

int.egrated

system,

economicai

load allocation

among

'

The

closer these

minimum

and

maximum

values

to

one

another,

the

easier

the

operating

condition,

for

the

speed

gov-ernor,

but the

gen;;tt"g

unit

is

less

able

to

participate

in

t.

e common

coniroi process.

,

,.^^Ilrtt_l:l^o:-!Tt that

the

maximum

vaiue

does

not

interlere

wirh

the

fuIl

l::.t-t

HtrucraLruu

aus

can

even permlt

a

certain

overload,

when

the

svstem

Hz

19.5

50

Hz

49.5

54.5

:{,

s

\

a,

s

e,

\

b

L

s

A.

2t.55

P.n

rrom

a

common

system.

regulator

providing

for

the

speeified

*oar

oil;g"];:

tion

and the

share

of

each

p-ower

staiion

in tf,e

common

pQwe-r

regulatiop

process

or should

operate

in

compliance

with

tne

specifi"a

io"a

i"n"aui"i

ii'i,

io,portant

AI.]TOIIATIC

CONTROL

OF FREQUENCY,

REAI, POT{rER,

PO]FEN

FLOTfl

193

CEAPTER

SD(

that the

schedule

be corrected

as

to the

frequenc-v

and real

power

flow over the

tie

lines.

In

the

so-cailed decentralized

control

systems

the

group

control

devices of

individual stations

used

an astronomical

time

clock

as

the

central

regulator.

Such

a referenee

clook had

to

be

instalied at each

power

station

to

provide

exact

time

indication

within

a 24-hour

period

to

*0.05

s.

System

control dnuices act upon

the station

generators through the

group

control

systems and control

the

ioad foeguency, real

power

and

power

flows

in the

power system

and

its

parts.

With

a

centralized

AFP

&

FC

system,

the

control

pulses

acting

upon

the

station

controllers are

produced

by

the

central

regulator.

The required input

information

and

mode

of regulation are

preset,

the controllers

of

the group

control

devices of

the

individuai

power

stations being

acted upon by remote

control.

In

practice,

this

type

of centralized

regulation

'was

used

in small

power

poo!.s

worki.g

in

isolation from

the

integrated

power system

or was

used

as

a

means

of

centralized

control of a

group

of

power

plants

from

the load dispat-

chiug

departm.ent of

the

power

s1'stem.

Witil

the

decentraiized AFP&FC

s-vstem,

the

controi

signals acting

upon

the

generating

units vrere

to

be

executed by

devices

installed

onl-r' 31

the

re-

gulating

power

stations

without using

remote

controi.

However,

the

necessit-v

to

correct

the

output of

certain

power

stations

v'ith

the

aid of

the

power

fiows

on

the transnission lines made it

impossihle

to

givu

up

remote

eontrol

and'in

fact

caused an increase in

the

nunaber of

the

remote

control

channeis.

Due

to

integration of

the

power

systems

the

decentraiized

regulation

method

turned

out

to

be unfeasible as

it

was

n.ecessary

to

limit'the

action

of

the

group

control

devices

with regard

to power

flows

in

the

tie

lines

and

to

take

into

account

the

losses in

the

transmission lines,

aII of

which

needs

a fairl-v

Iarge

amount

of remote

control

equipment.

Tire

group

control

devices

installed

in

some

of

the

power

stations

for decentralized

regulation

have

proved

useful

in

accomplishing

power

flow limitations

on

tie ]ias5

t6-al.

\ryith the mixed

AFP

&

FC system

used

in

the

integrated

power

systems

of

the USSR

economical load

allocation among

the

generating

units

is

obtained

b1'using

a

preplanned

schedule

prepared

in each

power

system

b-v

group

control

station

controllers.

Practice

shows

that

unplanned

departures

from

the

pro-

periy

designed load schedules

do not

exceed 2-3

per

cent.

The

variations cause

changes

in

the volume

of

planned pos'er

flows

over

the tie

Iines

and

in_the

power

s-vstem

frequency. Correction

of

the

above-mentioned

parameters is

placed

witb

tLe

central-regulator

acting

upotr a certain

number

of

the

power

stations

u'hich

deai

with unplanned ioads.

In-a

number of cases

the task of handling

unpianned

Ioads

is

assigned

to

one bydroelectric

power station

possessing the needed

geueration reserve.

Simultaneously

this station

perform the

load-frequency

regulation

function.

The central regulator

must consider

the

power

exchange

@

the tieiirrks trctwuen-aower

where

P

:

power

output

of

the regtlating

(pilot)

po\

;er

station

Po,:

planned

power

of

a

power

station

(optimum

when

there

is no

de-

parture

from

the

planned

value)

Lf

:

frequeney

departure' from

the

preassig:red

(rated) value

LPtt: pou,er

flow

departure

from

the

planned

value

X

and

'C

:

iegulation

fact'ors determining

the

share

of

the

regulating

statiou

in

ihe

control of unplanned

}oad changes.

The

factors

are

selected

so

tliat

optimum regulation

is achieved

When

several

power

stations handie

the

unplanned

load

variations

their

group

control

s-vstbms are activated

from a central

regulat'or

installed

at

the

load control

centre. The

participation

of

each

power

station

is

determined

by

patcher

cannot directll'

control

the

settings

of

the

corresponding

apparatus,

functions

simiiar

to the above must

be

performed

by

the station

operators

according

to the

directions

of

the

power

system

dispatcher

or

independently

making

the

necessary conections

against

instrument

readings.

power

system control a

iimited

number

of

pon'er stations.

-

When accomplishing

such

a

system

of mixed regulation

tire

central

regulator

of

the integrated

power

system may

act

upon

the regulating

power statioos

through

the

regulators

of

individual

parts

of

the

power

system

rather

than

directly.

6-2. Freguency

and Power Regulators

Thc

primary

regulator of

thc load-frequcruy

and real

power or,

in other

words,

4L^ ^--^ J -^--^-- ----4--^ --:+L^--+ -.L:^L +L^ +-.-]-i*^ -n-^rnf ar

i,ge speeo governor

is

a

proeess

apparaius

wif,ilout

'w$.Ic.ir

LIle

i,ururDe-geneiai,{rr

unit

cannot

work

undei

conditions of

varying

load.

If the

generating

unit

r3-2076

792

gapls5sisn

[6-5)

tl

P:P-,--l-K, I uat+K,Lf+C, I

aP*dt

,t.

..1

.J

00

+

ctLP

il

(6-1)

overloads.

The

principle

according

to

which a regulating

Ioad

frequency

and

po\per fiow

control

functions

power

station

performs

the

is

given

by

the following

-=.G.-*

,t

o(

t94

CEAPTER

SE

operates

at

a

preassigned

speed

(at

a

preassigned

frequency)

and

under a certain

electrical

load,

tbe

amount

of

steam

(or

water)

supplied

to

the

turbine

cor-

responds

to

this ]oad.

With

a change in

the

electrical

ioad

and no

change

in

the

anount

of

steam

(water)

fed

to the

turbine per

unit

tirng

i15 speed wiII

alter and

the

generating

unit

v'iii

decelerate

if the

electrical

]oad

increases

or

accelerate

if

the

electrical load

deereases.

To

automaticaliy

reestabiish

the

initial

speed, the

steam

(water)

florv

to

the

turbine

and

the

electrical ioad

must be

brought into

agreement. This is

AUTOMATIC

CONTROL

OF FREQUENCY,

REA],

PO

TER,

POIFER

FLOW

The

steady-state

coefficient

s

is

equal

to

the ratio

of

the speed

change

to

the

incremental

output

Power

An

s:

tan

o:TF

loading

them

to

a

value

determined

by

the

limiter

settings.

Tli

secondary

regulators

ol

load"-frtqirn

y

and

real

pow_er

make

it

possibie

to

restore

the

fiequencl,

to the rnitiai

(nominai)

vaiue arler

operai,ion

oi

tiie

the

power

station

(6-2)

-l

P,+AP

Fig. 6-2.

Characteristics of speed regtla-

Fig. 6-3. Load sharing among

generation

tion

by the

prinary governor

unjts

with

different steady-state characteri-

sticsn:q(P)

provided

by

the

primary

speed

governors.

Usualiy

these

are mechanica] centri-

fugal

regulators

which,

as others,

can regulate

according to

the

transient

(1)

or.

steady-state

(2)

characteristics

(Fig.

6-2).

In

some constructions

the

mechanical

speed change

detector

is

replaced

by

or

supplemented

with

an

electrical

sensing unit

(a load-frequency

control

attachment).

In

the

transient

mode

of regulation

the

process

takes

place without

appre-

ciable

overcorrection and residual

decrease

in

the speed

as

the

generator load

increases.

The characteristic

n

:

g

(P)

at each

time

instant. is determined by

a straight

line

paraliel

to

the axis P.

In the steady-state

mode

of regulation

the

steam

(water)

flovr

to the turbine changes

only

after

a

certain

speed

change.

Devices to Control

Power Output

There

are

se\zeral

ways

of ensuring

that

the por*'er s.vstem load variations

are

taken

care of

by

separate

generating units at

one

power

station

or

a

group

of

pou'er

stations.

(a)

The

characteristic z

:

p (P)

of

the

generator

responsible

for

handling

the loads has

the

smallest

stead3r-state

coefficient.

(in

the

limit-transient

cha-

to

When

the

l,

(point

load

frequency

(speed)

\F

sunnl

b),

the primary speed

v and the load will ris

of

the generating

unit

falls from

lr

(point

a)

governor will increase

the turbine steam

The

section,

bc determines

the

residual

the

reguiation'process, i.e.,

the steady-

Ner*'

steady-state

noncompensation

of

state

error.

operation results.

.L- ^--^l -l---:--

Lu€ sPecu

uufrug

central

regulator

The

toiai

output

generation

of

is

allocated among

the generating

the

power

station

set

by ihe power

controller

units

in compliance

with

a

preselected

mode.

13*

-.-I-_

19i

r96

GAPrER

SS

ALTTOMATIC

CONTNOL OF FREQUENCT,

RF-AI

POWffi.,

POFSR FLO]ii

case of

faults

in

the

remote-control

channels

or when

a

posrer

station

with

its

area is separated.

In

the

apparatus put

into service, provision

is

made

for

devices

s'hich

allov'the load

settings

to be

changed

manuali-v. Use

i*"

also

made

of

instruments

indicating

the

load

assignment sent to the

stations.

(c)

Distribution

of

the loads

among

the generating

units

of

a

power

station

and among the power stations

taking part

in the

freguency

and power

regula-

v'on

is

according

to the

increme-ntal

characteristics

u'ithout

communication bet-

tieen

the power

station

group

controller

and the

central

regulator

effected

With.generating

units of

the

same

t-vpe,

for

example, tbe

load

is

uniformly

sbared

hl'tU

the

nachines.

When the-machines

are

of

distinct tvDes. theloai

is

so

divided that

in

terms

of reference

fuel

the

relative

incremenial

iuel

con-

of the

integrated power

system

as a

!"

t'"tt*J

singie whole

in

rel.ition to

its partici-

;i\

-

pation

in the

common

regulation

sy-

r{47

l.-

:. -

!ir,eul .

To

stalion2

Tbe

schematic

diagram

of

the

_]X-

scheme

for centralized

frequencl'

and

e=/r(0/

\

po\,l'er

regulation

is

shoq'n

in

fig.

6-4.

The

central

frequencl'

and.

power

regulator

instaLled

at

the load-dispat-

ching

department

contains:

(1)

h{easuring

element

-I

respond-

To

stqtion,

itg,!9

gnanggs

il the

frequenc-r.

<.-

(2)

Functional

converters

2 which

show

hou' the load

of each station

in-

volved

in the

regulation

depends

on

Fig.

6-4.

Diagram

of centralized

frequenc-v

the

variable

common

to the

entire sv-

and

power

regulation

stem,

in

the

function

of

u,hich

the load

0-2

0.4

0.6 0.

E t.0

a

ft)

ta

20

J0

+0

50

ntw

/t,.\

is

allocated

among individual

power

generation

or

the

relative

incremental

rctional

converters

are

shaped

templates

;unent

of

the

remote

control transducer.

ting

a

reversible

motor

q'hich

actuates

ncy

departs

from the

rated value

until

rormal

value,

thus

transient

frequency

reguiation

is

attained.

(o)

,ue,

""*,-o,ll,1

,T

ii$13-'Ji:'l::;1,1'1"1";"1-'r'i""f;:',1",,o*,

(b)

!,.ater

consumption

through

the

remote-control

devices.

Frequenc5-

regulation

is

effected

against

the pulses

generated

b5'

a

s1'nchtorrous

time clock.

If individual

pou'er

stations

are

furnished

u"ith

such

clocks, there

is

no

need

(at,

the

first

sight) to

use

remote-

control

means.

As mentioned

previously,

once

the

so-calied

decentralized

AFPC

system v'as

suggested

which,

hou'ever,

proved

unfeasible as

it

q'as

found

neces-

sarl'

1o take into

accouut the losses

in

the

networks

r+'hich

meant greater

use

of remote-contro]

devices than

in

the

case of

the

centralized AFP & FC

s1'stems.

Hou'ever,

when

use

is

made of

group power

regulation

within

a

power

station,

the

distribution

of

the load

among

the

generating

units

relative

to

their

incre-

mental

fuel

consumption

is rational

especially when the regulatio.n involves

generating

units

of

-different

t5rpes and

capacities,

a

feature characteristic of

some

thermal

stations.

,rfnw

(4)

Remote-control

equip.ment

feeding the

control signals

to

the

power

sta-

tions

in

c-ompliance

with

the

output

pulses

of

tbe

fu"nctional

converters

of

the.central

reguiator,

i.e.,

in

accoidanie

with

the

required load

of

the

p**t

station.

. .A-t

the

power

stations,

the

received

signal

acts

on the iocal

distributor

which

consists

of

a

group

regulation

controlier

and

a

frequency

corrector.

The

frequency

coffector

operates

either

contiuuouslv,

creatin-E

steadv-sta

f,rons

aDd

rreguency

ltmitation

or

it

only

interrupts

the

action

of the

central

regulator

wlen

the

freguenc5'departs

frcm the preaisigned

limits.

The frequeucy

and

s'ater

consumption

g

at hydroelectric stations

are shos'n

in

incremental

fuel

consumption

b

is

meant

an increase

in

the

reference

fuel

(in

tons)

per

1

MW

increase

in

the

generation.

By

Typical incremental

fuel consumption

curves

b of

thermal

eneratins units

ig.

6-5. Bl

t

consumption

of

the incremental

corrector

also

reduces

the

etteci

of false

signals

froi the

centrd

r;fiilt*

ii

j

,;:-"

-:

''

?6-

.--r*-_

198

CEAPIER

SD(

AUTOMATTC

CONTROL

OF

FREQLTENCy,

REAL

POWER, POWER FLO\V

199

wate.r

cotrsumption

g

is

understood

an increase

in the

water

supply

(in

cu.m)

per

1- s'

when

the

generation

is

raised

by

{

I\{W.

\Vith

the

hydroJl'eciric

genera-

tors

b

is

assumed

to

equai

i.g,

where

?,-is

a

conversion

factor

to

be

used in

re-

computation

of

the

characteristics.

It

is

seen

from the

characteristics

shown in

Fig.

6-5 that

an increase

in the

-steqm

.su.pply

to

the turbine,

or

u'ater

to

the hyd'roturbioe

carrses

an increase

in.

fuel (water)

consumption.

Tire incremental

consumption

transducer

takes

this

regularity

into

accouni,.

The

foilowing principle

"iartti*iilr

t."o.ducer

operation.

A synchronous

motor

connected.

to_ thl

power

system

voltage

(Fig.

6-6)

actuates

the

hand

of

the

electrical

clock.

If

ihe

power

svstem

operates

at

the

v

I

(,)

(6)

Fig.

6-6.

Operation

oI

frequency regulator

based

on comparing

astronomical

(a)

expranaro,r

ai"L"jo:tiil":fJ"J#ti,,

u,.-.,,,

diasram

rated

frequencl',

the

hand

of

the

electrical

clock

and

the

hand

of an

exact

as-

tronomical

clock

wiil

coineide.

\Vhen the

frequency

departs

from the

rated

--value

the

clock

hands become

separated

by

an- angle

"0.

fir.

Ionger

aoa

great"r

the

frequency

departlue,

the

greater

the

-angie

d'eviation

betw-een

the-hands

t

6,:

I

Mdt

6

The

value

of angle

61

is

determined

by the

difference

between

the

ical

time

?asr:

I

l,t

dt

It is

c,learfrom

the

last

expiession that

a decrease

in

the freguene5,

increases

the

difference

between

the

astronomical

and

synchronous

time.

Thrr.,

this

difference qualitativel-v

is

similar

to the

changes

in

tbe

relative incremental

fuel.(water)

consumption

per

unit time

and

maiserve

to

a

degree

as a criterion

of

the

regulation

lystem.

The principles

undeilying

the

device

comparing

the

electrical

time with

the

astronomicaliime

and

the

d-esisn of

the

devic! intu-srat-

ing

element

are iliustrated

in Fis,.

6-6ii

-

- o

6-4.

Poq'er

Group

Control

at

Thermal

Stations

In process

at the

power

siations

with

ts

(at

present,

most

of

the

power

is

or.ration

of

operation

of

each rinit

in

'Ioad,

and economical allocation

of

the

;:,fiT".:E"l*"'ifi'l*:*

H;:?

ro

the

turbine,

depending

on

the

resistive

load

of

the genirator,

utilizes

the

mechanical

or eiectromechanical

governor

of

'the

turbine,

i'hi"n

is

coupled

to the

controller

oj

t{te

group

control

system,

and

the

regulators,

ofien

e}ectronic.

which

operate

the

boiler

mechanisms

so

that

the

steam

parameters

(pressure

and

temperature)

a*,

the

turbine

input

are

held

at

their

optimai

values

iortesponding to ihe

gene-

rator load.

To

optirnize the

operating

conditions

of

the

generating

units,

some

electrical

polpr

stations

use electronic

computers.

Regulation

on

the

basis

of maintaining

the

relative

fuel

consumption

cons-

tant

or,

v'itii

individual

units

of

the

same

type,

on

the

basis of

ensuring

the

maximum

station

efficiency-as-a whole,

allows

the

loads

to

be

economiially

allocated

lm_o+g

the

individual

units without

much

difficulty.

Figure

6-7

iilustrates

the

schematic

(biocki

diagram

of

a

regulating circuit.

The

relative

increment

oJ

the

power

station

is

set

ilanually

or"this is

?ccompl-

ishd

by

an overall

regulating-device

u'hich

takes

network

losses

into

account-

Regulation

of

operatjon

of a

gnit

with

a monotube

boiler

is

effected through

where

lret

:

referense

freguenc-v

value

l ry,

:

system

voltage

freguency

q

:

proportionality

factor

From

(6-3)

to

(6-5)

it

foliows

that

L,T

:

Tort

--

/

r!t,,

:tr

I

At d.t

:

q61

,.|

t0

(0

6)

r

J

0

(6-3)

astronom-

(64)

aottr

and the

synchronous

time

T,cn:n!

f,r^at

the

air

regula-tor

which

controls

the

firing

and

steaming

rate

of

the

boilJr.

rrr1.^

^__r_^l _

.l-

, rl

.

r

/6 5)

amplifies

the

signals

from

the

turbine

inilt

rt""*

pressure

Power -ngeter

of the generator,

the

frequency

variation

meter

load

allocation

device.

gauge,

the

real

and

the

resistive

CEAPTER

SB.

The

pressure

transducer_

generates

its

outpu!

signal

until the

steam

input

paraEeters

are

worked

out

by the pressure

regulatoi.

These

parameters

shouid

ge-rrespo_nd

to the

required

pressure

which

must

be eusured

-by

the

regulator.

When

the pressure

drops to

a value

dangerous

to

the turbine

operation,

the

safety

means

come

into

action

and

disconnect

the

unit.

AUTOM.A.TIC

CONTROL OT

FNEQUENCY,

REAI

POWER,

POWER FLOW

2Al

Fig'

6-7..

Schematic.diagrap

of

_freguencl'

and

pou'er

automatic

re6jriation

at

tlrermai

station

*-ith

individual

boiler-turbine-generator

unlts

The

output

signal

from the

resistive load

allocation

device

is

being

fed

to

each unit,

with

due

consideration

to the

relative

incremental

fuel .oor"u-p-

tion

characteristic,

until the

relative incremental

consumption

b*'

of

the

sta-

tion

and

the

output

signais

from

tire

devices

producing

the

data on the

lalue

of

reiative

increase

in

the

fuel

consumption

in

terms

6f reference

fuel br;

;i

the

pou'er

system

s'ith

the losses

in

the

netw'orks taken

into

account

are

balanc-

ed.

The

position

of

the load

allocation

device

ancl the poriler

setter

may

be

controlled

manuallv (from

!\q

groqp

control

station

srvitchboard)

or Uy tfre

device

making

.the

station

folldw

the

specified

operational load

sched;i.,;y

a

computer

or by the

central

regulator

of

the power

system.

6-5.

Power Group

Control

at

Hydroelectric

Stations

The best fle.xibility

in

regtlating

the

frequency

and

power

is

provided

by

the hydroelectric generators.

At bydroelectric

stations with

one-tfre

machinei

it

is

fairiY

Qasy

to

eflect a

group

control

system

and ensure

the

auiomatiocon-

nection of shutdos'n

units

to

it.

The

service

regulations

state

that in

case

of a

freguency faii

in

the

power

system

provisions

be

made

for

automatic connection

of

the shutdown

hydrbelec-

tric

generators

(frequency

starting)

and

change-over

of

the

hydroelettric

ge-

nerators

used

as

s5mchronous^

capaci_tors

to

power

generation

duty,

the

settiigs

of

the

automatic

controls

being

48.8 to 49.7

Hz.

Figure

6-8 illustrates

a circuit

for automatic

connection

of

hydroelectric

generators

in

case

of a

frequencv

fall

in

the power

systeri'.

The starting

of individual

units

(or

groupi

of

generators)

is

provided.

frorii

a

programmiqg

time

rela5'.

By

means

of

operation

keys

each

generator

is con-

nonf o.l fa 1|'n l"'ol'^-. ^f +l^^ -^--.i-^l ^^---^-^-

tTrL

- -- - -, - - L:,, ! r

svvwu sv

uus

!Bo!€1rr

\rr

ul.rv

rEuLuteu

DUquuuue.

rllg sgqugll{/g Lrmg

In.Ler\.ars

are

selected

ei'r,her

'r,o

preven'r,

simuitaneoui

connect,ion

of

the

generator-s (severai

99c9nd,s)

or to

prevent

connection

of

the generators

(1-2

min),

if

the

frequency

is

recovered

after

the

foregoing

machines

have been connect.ed.

. ltr

starting

automatic controls

are

turnei

oo b5' the

underfreguencv

re-

Ia}'Fft.

The

time_to

send

a

pulse to

connect

the

first

seouence sroup'of

genera-

tois

is

determined

b-v

the

setting

of relal'

7?n

h;;t;;;;b.5=:."-f"i".:;[i;

prevents

the

device

from

functioning

at random

sholi.--tirne

closurei

,if tl:e

underfrequenc])

ieial'coni,acts,

like

in

the

case

of voltage

surges

anri

at,

s-vncirro-

DOUS SWrngS.

The time

relay

1?R is

thermal

resistant.

In

opeiation.

its instantaneous

contacts

lTR-I

open

and

a

series

resistor

is

conneited

in series rvith

its

coil.

The

contacl

ITR-? cioses

an

auxiiiarS'rela5,

IAR. The

latter

in turn

makes

the

circuits

of

a

sequence-action

i,ime

relay-2TR

and

q'ith

its contact

lAR-3

feed-. the

operating current to

the

first-seguence

aufomatic starting

bus.

The

sequence-action

relay ZTR

determines

the

intervals

at

which

the

next of

the

machines

in the

seguence

wili

be

turned

on.

The

intervals

At

bet*'een

the

con-

trol

pulse.s^ge

Pj_egdiusted

b-v setting

the programming

re1a5's'ithin

tbe

range

of

10 to

120

s. Thb

machines

are

connected

sEquentialiy

at d.ifferent int,ervais

by

means

of operation

keys

OK

and auxiliary

reir-vs

UFR.

The contacts

of

tirese

relays

close

the

automatic starting

circuiis

of

the

corresponding

maclr.ines.

_

The

sequence

in

u'hich

the

various

devices

are

used

in connectin!

the

h-,*dro-

electric

generator

for parailei

operation is shou,n

in

Fig. 6-9.

In

case of

an

emergency

fall in the

frequenc-v,

the

starting device

of

the

hydroelectric

generator

ma1' function

in conjunction

p-ith

an a[tomatic

opera-

tor,

if

it

is

available

at

the

hydroelectric

station.

F

\

*o

\

o

.s

\

s

:\

s*

ES

.$t

?t:

\i

At

thermal

stations

the

shutdo*'n

generating

units

cannot be

immediately

invalved

i;t

regu)ation

of

frequency

aid

real

po*er,

since

it talies

much time

to

bring

the

boiler

and turbine

into

operation

fron

cold.

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

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