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

fntrance

I

tAtEtc0

Intrance

2

2A2B2C

C

Fig'

11-6.

Schematic

diagram

of ATS

deiice r'ith

the

use oI

control

statjon

AUTOIIATIC TRANSFER

TO RESERVE

SUPPLY AND

EQUIPMENT

343

reset

time has elapsed,

the

relay

lATR

makes

the closing

circuit

of

the contac-

tor

of

Entrance

2.

AJter

the

contaetor

2L

has

closed., the

auxiliary contact

2L-BC-1

makes

and closes

the

rela-v

2ATR which

opens

the

coil

circuit

for

closiug

the contactor

.2.L.

Not'

Entrante

g

performs

tbe

function of the

main suppiy

and

Entrante

7

is

used

as

the stand-by

suppl.y

source

The

time taken to close

the

stand-b5'

supply

by means

of the relay

CfR is

0.5 s in order to

prevent

the

application

of

the stand-by

supply voltage

to tb.e

coasting

excited srmchronous

and'asyn.chronous

motors.

If no

delay is reguired

in

the operation

of the ATS device, the

jumpers

(bridges)

2J

ar.d

4-I must be

removed.

A

simplified contactor

circuit for ATS

operations is

shown

in Fig. LL-7.

Contactor KI of. the main

suppi-v

entrance is normally

closed.

When

the entran-

ce is deenergized the

contactor drops

out and closes its

auxili&r5r

csrtrrct which

closes

the

circuit of the contactor

K2

rhaL

switches

on

the

stand-bv

sunnh' ent-

rance. The instant,aneon*s

ATS ac.t.ion is det,ermined

by the

tripping,ii*e

ot

contaci,or

K-Z and

the closing

time

of

contactor

K2.

The

ATS device is isolated

by closing knife switch

J.

t1-5.

Self-Starting

of

an Aqmchronous

Load

Interruptions

f.o

the

normal

power

suopi5'

uccur riu:ing

faults

in

the

porp-el

suppil'

circuit and

wben

the

ARC and

ATS devices

operate.

Short

time

(0.72

to 0.15

s)

interruptions hardiy

brake the

asynchronous

load

and most of the

motors

do

not lose

synchronism.

That

is s'hy,

q'here

high-speed

protection

units

and breakers

are used, tbe

short

circuits have

but Iitt,ie effect

upon the ioads

and

causeno self-unloading

of

the power

svstem.

With inter-

ruptions

of

seconds

and more,

n'hich

occur

*'hen

the

ARC

(except

HSARC) and

ATS

devices-operate,

the

as5'nchronous

motors

may

decelerate

and even stop,

and

the synchronous

motors

must

be

transferred to

asynchronous

starting

n-i[h

subsequent

reslachronization

otherwi-se

thel'

]s5. their slnelrronism

and must

be

disconnected.

Because of the

above reasons

the

supply

lines

generallS.

carr-T

a

current in

excess

of the

normal

value

after voitage

reestablishment.

Stand-

From

entrdnce

i *a'r;1

,

Load

11-7.

Circuit

of

ATS

device

emplol,ing

contactors

If

there

is

a

possibility

of the

aslnchronous

load

self-starting (synchronous

motors transferred

to the

aslnchronous starting

mode are

also

as,vnchronous

loads), the

proteotive

relaying

calculations

must

take

into

account

an

increase

in

the

currents.

This

phenomenon

is evaluated by

a starting

factor

K,

whose

value

depends

on

the

composition

of the load

and

whether

the

motors are fur-

nished s'ith

a

protector

that

deenergizes the

motors

when

the

voltage drops.

Voltage

protection

must be installed

on

less

important

equipment-which

is

disconnected

in

order

to

faciiitate the

starting

of the

motors

driving important

the value

of

.I(

wrlrg.

from

1.5 to

3

and

ma

be

ro

determined n the

CEAPTE.R

ELEYEN

AUTOMATIC

TRANSFER

TO*KESENVE

SUPPLY

AND

EQUIPMENT

To

evaluate

the value

of the

periodic

component

of the

J*rur**

currenr,

use

is

made of

a term

"critical

slip" s"r.

Approximately

the

critical slip

5", XL

'&m

(it

holds when

rv

N

m

and

.R"1 is

far less than

e-tl1-101).

Placing

(1,1-1)

we

obtatin

t:&

: t / ,

,

/

$cr

\z

**y

'-\

,

I

The

periodic

component

of the starting

current

(with

s

:

1)

I

,

-

--JPh--

znrl/

!-s!,

\4lith

asynchronous

motors,

sc,-

:

0.1

1o

0.?,

hence

(1,\-2)

(11-2)

into

(11_3)

(11-4)

Fig'

t1-8-

Equivaient

circuit

of

asynchronous

Fig.

11-g. Simplified

equivalentlir-

motoi

cuit

of

asynchronous

motor

]lttf^f-ryy:]:ll"*,"pqlied

to

the

moror.a

heavv

currenr

surse

occurs,

its

::::."*::s^_d'.1.^'-^l:..qLt-1h-ereJ3cF"J;irh';;#il;;;,;T;.;";;l;;:

nent

surge

of the

starting.gu.rre-nt).

Correspo"dirg

il;hil;;;;rii

i. iir."#iij-

mum

reactance

value,cu

y!i:\

then

rapidlli

ioc.ea"ses.

The

,i"rtin[

current

chan_

ry;

age.riodicaii-v-

The

inirial

surge

of

si,arting

current

d;;a.is-

ii

t-z

"y.t*.

IItg;,t1^-tOt

and does

not

effect

th-e

pro*,ectori

-having

operating

times

of 0.06

-

Uon

t"xt

(11-5)

In

value

this

cunent

is

equal to the

short-circuit

current

behind the lumped

inductive

reactance

c-.

Under normal

operating conditions

the

current

value

is determined

from

(it-3).

II s

-

s,,,

tben

r-

tn-

(1

1-6)

across

the

(11-7)

(1

1-8)

to

0.1

s.

upn

Thus,

the

starting

Iine

(at

rated voltage)

current

of an

as-\'nchronous

motor connected

has

the follorn'ing

multiplicitv

factors

Kr.

^:

*:

V

t++

r--

K,.^*l/

r

+

(+)'

Fig'

11-10.

oscjliogram

of

currents

during

starting

of asynchronous

motor

-l;r.

-

initial

value

ot

starting

current,

containing

a.c.

component

and

d.c.

coEponent;

JO-

periodic

componenlr,rJ.r

;ji5al

current (current

corresponding

to

As

the

reactance

cn

rises

verl,

quickiy

and,

in

addition,

the

resistance

of

the

stator

winding

is

ima}I

us

"om$"rea

witnJhe

inductive'reactance,

a good

analvsislnav

be

obtained

from

a

simpiifi.d

"di;*teoi.i.""il-frif.

rr-s;.'iir.

current

flow

in

this

circuit

is

or.

\47hen

s".

:

0.04,

As it

:

$.1and

s,,

:0.03,

Kr.-

is

about

3.4

and

when

{cr:0.2.

and

sn

:

Kr.- is

about

5.

follows

from

(11-3)

and

(11-5)

(11-e)

\4/hen

s

:

s.. the

current

equals

A.77Ir.

If. a

uph

decrease

in the

slip

(Fig.

11,41).

rTnltofo

'

v^eq6v

nT

atoa?ao-

346

CHAPTER ELE\EIi

ses

in

proportion

to

it.

For example, if

a

motor

is

connected across the line

at

a

voltage

equal

to 70 per

cent

ol Un,

the starting

current

will

also

be 70

per

cent

oi the

nominal value

wheu

the

motor is

started.

\\rhen the

voltage

is

reestablished after a successful

reclosure

or after the

operation

of an ATS. device,

some

of

the

motors disconnect

(the

motors of }ess

important

ioads).

Besides;

the load

of

consumers

substations

includes

not

oniy

the

asynchronous

motors.

Therefore, with

respect to the nominal

current in the

line,

the multiplicity

factor

of

the ]ine current

during an

automatic reclosure,

or ATS operation,

is less

than

the

multiplicity

factor

of

the

starting

current of

an individua-

I1;r

start,ed

motor.

h{oreover. the

J(,

va}ue

becomes less a}so

because.

aft,er

automatic reclosure

(1-2

s after

the voitage

has

disappeared), the

asynchro-

rrous

mot,ors

of

most

of the

mecbanisms

are

nnl.t hrol.o.l o li++lo --fLar *1r-- o*^-*nJ

rn},".

vur

l

qAUu

u

Il(,llE,

lqUtIsMAlr LTVUIJ}JSU.

lllUD,

if tiie

value

of

tiie

motor slin at tire momeni

the volt,age

appears across

the-supplJz entrance

is

known.

the starting

current ma5' be det,er-

mined

more accurately

from equation

(11-3).

In foreign practice.

the

application

of ARC

and

ATS

devices

was purposely

limited.

as it

was

feared

'that

there

mav be asvnchronous

T

-?'r2

4m-br

u'here

is a

certain

AUTotrIATIC

TRAliSprjR TO RESERYE

SUppL-f

AND

EQUIPIIEI\:T

f-0

\Vith

due

consideration

to

(11-3)

u'e have

Trr:;

--Q

nrl,

"i,,(l-+)

I

Taking

into

consideration

(II-2),

we

obtain

T -!

u'un

-rtL

=T

,*+r(1=+)

.ftr\s"/

1i: ,

Tnr:E

, ,

n"

- =

I

s

,

s.rJ

"-

(

,-

--;i

The torgue

developed

br- the

motor at the nominaj

is

its

maximum n'hen

s

:

scr

ri2

T

o..

n,"t:il-!-eh-

'*n1

hence

(1-t1)

(11-r2)

terminal voltage Un.pn

(r1-13)

(tr-M)

T

_T

^

m-'m.

UsualIl'

the

lorque

is

under

a

rated

load

NA

t.0

n9

U.t

n, < n

Fig..

!1.-11.

Changes.

in current

closures

of

the unbraked

asj,ps6t.rous

motors.

"""ti*d-,Lljg"l.l::d^:19:

:f,:t)'o-

Service

experience

has

shovl, however, that

at

cnronous moror

versus

sllp

tro-power

periods

of { s

or more, i.e.,

u'hen

no

ARC and

Arq

devices,

"t',*t"r:'IlTt:J;::Ifi:

il',H'ff:u"hH;i"ili

biocking units-[11-11],

even

if

asynchronous

motors

are conneit,ed

in

paralle]

s'ith

capacitor banks.

Where

the

capacitor

banks

are

present.

the emf

decaying

tige

of coasting asynchronous

molors becomes

greater

but

does

not

exieed

0.5

s.

The duration

of the

self-starting

process

depends

on

the

magnitude of

the

voltage

that

appears

across

the

mol.or terminais

after

a succesiful

ARC

and

ATS

operqtio_n,

-the

reactionarl'

torque

of

the

driyen

mechanism

and the slip

value

to

which

the

motor is braked

up

to the instant

the voltage

is reestablished.

In

order

to

explain

the

ba-sic

conditibns which

determine

a

successful self-start,

let

us

consider the

specific

features

of

asynchronous

motor

operation

under

nornal

and

emergerc-lr

conditions

(at

the normql

and

decreised voltages).

The torgue

developed

by a

motor is

determined

by the

power lost

iilthe

resistance

,Rrls

of

the

equivalent

circuit

to

the

vaiue

of

the

torgue

developed b5'

the

t*:

T.,nf

T,, (11-i5)

\\'hen

in

relat.ive

units

the torgue

of

an

as\rnchronous

motor

^t

uph

1!

t"''

'\T:;

)

lrr,.

rrrax

..

+

,a'.

scr s

Usually

/-.

n,r,

is

approximatelS,

2t^.,

In

compliance

u'itli

(11-16)

the

initial t,orque

developed

by

the

motor

when

s:1is

(1r-16)

(11-17)

I sc.

:0.2

and

Urn

:

Un.pni

is approximately

0,4 r*.

-"o'

E

0

r--

T

-tl

_\

\

t

\

l

cieney

of the

moior-mechanism

unit,.

(11-10)

the

required

speed

and attain

normal

slip, provided

the torque develope by

CI1APTER

E.LE\EN

AUTOMATIC

TRANSFER

TO

RESERVE

SUPPLY

AND

EQUIPMSNT

349

motors and

reactionary

torques

are

shown

in

Fie.

11-12.

So

that

an as,vnchronous

motor

can

gain

speed

and drive

a

mechanism

rp-ith

a

constant

reactionarv

torque"

it has a

squirrel-cage

rotor

(a

deep

bar double-u'ound

rotor)

and a

charac-

teristic

at v,'irich

fn, is

greater

than l,.

whate-

ver

the

slip

ma1'

be

(curve

4 in

Fig. 1.1,-t2).

TS ^ *^+^- L^^ ^ -L^ J --e-- -- I rL-

rr

d

l.u.LrLUl rras

a

prrasr-r,yuttuu

roLUI'

auu

Lll.t}

reactionar_v

torque

has

a

characi.eristic

depen-

dent

on

the

slip

(curve

2), then

the

mbtor

generall,l'

can gain

speed. for

in starting

the

terminal

voltage

of

the

motor

is enough

to

develop

a torque

in excess

of the

reactionar-v

torque.

As can

be seeu

frcm

(tt-16),

the torque

developed

bg the

motor is

directl_r- proporiro-

nal

t,o

the

sguare

of

the voltage

across the

stator

terminals.

In

order

to

ascertain

t,he fact

::t^t:t-e:t"^lT"k:

the

calculations

more

complicated

withour

any

positive

influ-

ence

on the

answer.

In the

case

of the

self-starting

of

all the

receiving

substation

asynchronous

motors

their

reactances

are

calculat'e.{

in csmrl-iance.*ith

(r1-5).

ii

tn-

-"i}lpU"rli

tT.#i

,} *" p""i"'Ji"

component

of the

starting

currint

is

knovn,

then

- s

Un-ph

An.ph

--iif-:-

f=-:-F-

,'

sx

rts.

m/2.

!

where

/no is

tbe total

norninal

current'of

ail

the

as5rnchro[olLc

motors.

If

only

a

feu'of

the

asynchronous

motors (e)

are

setrf-started,

the

reactance

of

these

7

xrn,

gs:- sm

s

(1

1-f8)

(11-19)

(11-20)

Tbe

totai

sLarting

cun -

nt

is

t-

-

6. SS-

Un.

oh

t-)-r,J-+.-J-+

-5

I

-'

|

*t

|

*rTt.

IXi

pQn'er

s!'steno.,

Iine,

and

transformers.

resDect_

pplication

and

tbe

stator

*,inding

terminals

of

ninals

which

provide,s

the

self-starting

can

be

re

initial

torgue

is aboui

b0

per

cent"

ol

t[;

r

normal

vo}[age.

sr,

s,

o

An.

ph

zml

pJh

:

fs.

sscm.

ss:

(t1-21)

(11-22)

(11-23)

whether

a

important

motor

is

capable

of self-starting

after

reclosing

across

the

line,

it

is

to know

the

value

of this rloltage

across

Lhe

motor terminals,

(rr*"r

+"ri+#

0.3

-

":=

+0.7

(z.f

rlf

z1)

a:0.43

,'^t

zr1'r-T{,

c1

d

%:43

','^',

s,st:Dtiet

Tests

cariied

,out

by

sopg

organizations

show that

self-starting

of asr.nchro-

:.tYi.::l"j:_.",t-!ale

nlace

at

motor

terminal

voltages

even

less thin

Z0

f"t

"*"t

rJr

Llrv

ilulIIlIIaI

value.

lrence

or

Fig.

11-13.

Calculation

diagram

(o)

circuit

diagram;

(b)

eguivalent

circuit

AJter

an interruption

in-the

supply,

the

first

to

self-start

must

be the

motors

of

the

most

importaut

mechanisms.

So

that

v/e

may-calcuiate

the

value

of the

asynchronous

load

which

may

re-

main

connected

and

determine

the

value

of the

Lsl,nchronous

ioad

r*-hich

must

be disconnected

by

the

undervoltage

protection

or"other

ng

oI the

nost important

motors,

we

assume that

the

braked

e rong

tlme

perrods

to

attain

reguired

speed

and

heav5r

volta

drops

lmes)

neve

reactatrces

in the

equivalent

circuit

(Fig.

Il-lg).

To

incjude the

(which,

in

rurn,

mayipoil

the produ;ri;;;il;;;i

and

curre"t

o".itJi'j;'#;t

CE.{PTER

ELEVEN

of1s.

For

more accurate

calculations

to

determine

the asynchronous

load

tvhicir

ATTTOM.A.IIC TR.ANSFER

TO RESENVE SUPPLY

AND

EQUIPMENT

plaee

r*'hen,

after tbe

ATS device

has closed

the section breaker

and

during

the self-starting

bperation.

the voltage across

the S.l and .9f.I

busbars

remains at'Ieast

70

per

cent

of

L'r.

'

Assume tbat

tbe aslrnchronous

motors

connected to the S.I.I

section have

stopped

com-

pletely

r*'hile

it s'as

deeiergized.

in this

case, the closirg of

the section breaker

is irquivalent

i,o a sf,ortcircuit

bebind

a riactance

egual invalue

to

tbdreactance

of the ^S.I.I

motoriv'aiting

for

self-starting as determined

from

(11-18)

Un.

ph

*m'

ssrr

-

Kr.

*]

n. rn. ssrl.

rthere

the nominal current

of

the motors to

be seII-

started is

r.

t

n. m. asll

*

pxW

'

m. ssII

(Lt-27)

V

:

U

".

inrr

cos

gII

zmtT

Er-Ph

I

t_

t

*r,

I

-T-

I

\'*

B

(o)

(rL-26)

ma))-

remain

energized

Ir'Ph

xtr

and

its

self-starting

can

take

place after

the voltage

is

reestablished,

attention

must

be

paid

to the

ccasting

and

acceleration

of

a

group of asynchronous motors,

i.e.,

to the fact,

tirat

in a

first approxination

the

inertia

constant

of

a

group

of

paralleied

mechanisms

may

be

taken as

the

v'eighted-mean

of

the

inertia

constants

of

tire individual

mechanisms.

The

aclual

^h.rontorictin nf f hc f nv'nrroe dpr:alnnpd hrt t lrp rnntnrs

wuqrqvuvt

roLrv

vr

-f +'I.^ -:--^- +---.^;-;*nnr,{nn* F^- i-c*-'.^^ {L^

ul

LIlc

Hr

Yerr LyPt,

rD rrI-IPUr

L(rlrL. I ur

rrrE-tqrrus-r

(rrE

U

tests

at high-steam

pressure

st.ations

Jrave shorvn

that

to ensure

the self-starting

of

the station-service

as-vnchronous

motors

with no-po$rer

interval-c

greater

-l

,E

zl

tr

Fig.

t1-14. Calcuiation

dia-

gram

and

P

fi:.911

cos

9f

:

?tSrl

cos

EI

Prrr: Si11

cos

9tr:

?rrSttl

cos

P11

than 0.5

s the busbar

voltage

of

the station-serlice

section

after

the operation

of the ATS

devic.e must

noi be less

than

75 to

80

per

cent

of

Ullt-t2}.

Thus.

the linal-decision

on

the

seli-startiug

of

tbe

ioad composed

of

as-vnchronous

motors

is better made

after

fuli-scale

experiments

hale been canied out.

Tbus

IUi-,.

pn

cos

P11

,1, ^o\

rrn.

sslr

&;FF

('rl-zor

According to the

condition

of

the example,

the

^S.I busbar

voltage

decreases

after the

section'breaker

is

closed and becomes

egual Lo

0.7

[in; tbe

torque

developed

b1'

the motors

connected

to

,91

decreases-in

proportion

to

the square of

the voltage,

and tbeir

slip

increases.

The slip depends on

the coasting

characte-

ristic and

their operatlr'ri

ciuration

at the

reduced

voitage, i.e., on

thc

duration

of

the self-starting

process.

-

To find

the critical conditions,

s.e assume

that

the

seU-starting of

the S,r motors

will

be difficult

and

Iong, n'hich means

that the slip

of the

motors

rrill

attain

tbe s.,

value.

lVben this is so,

the

torque

developed

by

tbe

.S.I'motors

q'ill

be

at

its

max-imum

(at

a

given

voitage

across

tile stator

terminals),

u'hile tbe

current

s'ill

be

of

about

50

per

cent

the

itarting

valie

rrhen

starting

the standstill motors

at tbe

rat,ed

voltage,

the torqrie being

aimost

full1,

reac-

tionarv.

The impedance

of the S/

motors

ai

slip s

:

scf

is determined

from

ti:e expression

le.r,

at

s:scr

l="^Er/

,u(+)':t.k*r,

Fig.

11-15. Eguivaient

circuit

(11-29)

(11-30)

(11-3r)

this

b-v

an

example.

Substation

sections

S.I and

.9.If are supplied

lrom

transformcrs

?,I and ?.1.I

and operate

separately.

The

pos€r

outputs

of

the

trarisiormers

are

.S' and Sr1r.

The

loads of

each section

are

as1'nchronous

squirrel*cage

motors'

As this

impedance

is almost

fuIly reactive,

then

to simplify the

calcuiations,

tbe egui-

valent circuit

1Fig.

tt-tSa)

corresponding

to

thd

startine

pioi"ss peiiod,

v,hen

tbe

51 moiors

are

braked

and

the ,9.I/

r:notors

Start

giining

their

spe"ed,

may be

presented

with

less

detail

(Fig.

rt-15b).

In this circuit

the eguivalent

reactance

reg

is

deterrnined

from

$1-241

(rt-2s)

v-here?1

and

?ll

arethecoefficientscharacterizing

the

power

transformer

loads

under

norma)

operatiug

conilitions.

X, i - +!.n .. *^ {^.

AS.

m

^o luE

D4lre-Jvr

IXThon

p

forrlf

^r.trrc nn tr*ncfnrrncr TII aft.er ii.

is

trin

llrE

4ru us,vlvv

vrv!-vo

Irom

translormer

?.I. Find

the

percentage

of

asynchronous

load

at

q'hich

self*starting

[.

o;

cos

tPrr

352

In

order

to

sustain

the residual

voltage

across

the

section

busbars

at

a value

not iess

l|lfjo

pet

cent

of

U,, when

the

self-star"ting process

t fri

pt""q-ii1["ria';;;pi;-;irh

(17-22j,

so

that

4m.

ss:'Tt

:

2.33

(r1i

rs*xt)

-

Z.z}zs(l

+p)

a

\4'hen

the

self-starting

process.proceeds

quickly

and

tbe

siip.

of

the

motors

supplied

from

.s/

rises,

but little

aJcompared'witu

iul

irorm;i

-=l;.,li"

lir,i,i

#inil"""ond

rerm

of

[i"t;lJr]-:tti

be less,

i'e.,

a

greater

percentage

"f

;h";sd;#";;";l;;;?"1,"6;i;;ii*

*ri-

-

\47hen

determining-the

input

power

of the

motors

left

for

self-starting,

after

the

oper-ation

of

the

ATS devices

of the

transformir

or reactor-connected

station-

service

line,

as a

first

approximation

oo,

-"5,

use

Table

t!_z.

i

Table

II_2

A.

pprox

i

rn a

te Permissibl

e_

Fercel

ta

ge

o f

As5,n

chronous

Load

Left

in

ATS

Cycle

for.-S.tt_St"itl"g

----

ATITOMATIC

TRANSFER

TO

RESERVE

SUPPLY

AND

EQUIPMENT

(referred

ro

the

power'of

s"ppti-ir"ir"..ro"i?.t

Circuit

reactance

up

lo

station-servi

ce

busbars,

2-d

k\'

(reduced

to

power

of

suppl-v

transformdrs),

o/o

Deenergized

section pickeri

up

.b}' transforsrer

-

unioade<i

I

loaded

8117b

,{50

'.

A t(\

:100

80

10lrus

t2

|

tzo

14

|

too

Tl:_:,:b]r^-:_::5lly"r*d

on

.rhe

assumprion

thar

the

multiplicit_v

r,ruL'Le.u

{rrr

Lre

assumptron

tnat

the

multiplicitv

factor

of

starting

c.itrrent

retratil-e

to

the

no,ninai,value

is

b,,the

ter.iln-ui"r'.oitrse

af

ouqrvrrJg

!'t{!rui-lL

i's!aLrYe

Lo

[-ce

noI]lnai,l'alUe

lS

b,,the

terruina-l

vOitagg

cf

asynchronous

morors

aft,er

ATS

operation

is

55

0r,o

of [.in,

and

cos

,

:

cr.sil

a-\Jr-rL/r.ru'uus

r_LruL0r's

arr,er

/\rD

operatlon

ts

JDy6

0I Ll

n,

and

cos

cp

:0.95.

\\rhen

the

deenergized

secrion

is

picked

up

by

;

I;"eJe

J;;;i;;er.

ir

is

assumed

that

the

"t-rTiri,'."ii'""'ir[J'fi?:,:i":L:JJXl1tt,tr-1t"J='?."-*"1'""1;

it.tle

as

compared

l:tr.h..rir.

norma]

r'alue

(roughl;'

twi;)

and the-iransform*r."",

;;;;#';;

CHAPTER

ELEVE}i

353

where

The transforrner

reactance

(r1-33)

(t

1-34)

(1

1-35)

n'e

obtain

(11-36)

(IL-37)

arC

3

--(

I

3U2n

on

u."/'o

"ri:_E_ffi

substituting

this expression

into

(1i-33)

and

taking

(ir-Bz)

inro account

jOL

Su

_

{*.

mP*.

sslr

,

Xs.

'TISTJ

z.aa (r

*

F)

u""

%

JUT;

-

-4

",

"*

fi,

=

t .aaq;

hence

Ks.mPm.ssrl-g

1^ro

100

I fi".--.

\

cosqrr

--"tr\u'{r--:-iTF-

r.<

rl/

Consequently,

the power

oI

the self-_ctarting

motors

should

be

Pm.

ssrr

--(

srr

[0.

ne

4:

-{P+

"r

l

"9,s

qrr

-

--L

-u""oioL*fi

I-4

,,)

K".^

If

in

the-exanple

heing

considered

?1

:

0.?;

X",-

:

4.3; cos g'

:

Cl.S;

(i.e.,

e;

:

0 and

c"/211 (

1)

and

ueco/o:i0%;.Lhen'

the

p^.,,u

:

s,1

(o.s-H€)

-

o. 4.s11

-

If the

power

output

of transformers

?1 and

TII are

esual and

this is the case

with the

loads

of ,S1

and .9.I.I,

tben

the lormal

ioad

of section

S^r/

(fbr

the

given

example)

Pm.

nIl:0'7Stt

cos q-0.56511

,,

Hence., the

asynchronous

ioad

percentage

which

may

be left

under

voltage and

can

be

self-started

after

the

ATS

operation

is

a'4

o:d* 100 =

70

per

cenr

.

Thus,

when

the

voltage

drops, the

protection

must

trip about

30

per

cent of the

section

asynchronous

load._

If transformer

I/

is

not

loaded

and ii

is intendeil

only for

backing up

trnasformer

TII, then

1,

:

0 and, as seen

lrom

(11-37)

the

power

cf the seli-starting

mdtois

ma-v

be egual to

h F

0.43.10C

cos

grl

Pp.ssrr-ru

GF)f;".%-

d

infinite-power

busbars

or

to-

the geneiation

busbars,

provided

tire

generators

concerned

are furnished

with

higli-speed

excitatioo

'fottiog-an"i".r

and

auto-

mat ic voltage

regulators.

---

---b

T"-

promote

an

effective

performance

of the

ARC

and

ATS

derices.

one

has,

in

addition

to

ensuring

the

s-elf-startilg

o{ imporiant

i""ar,

t"

p..r,*"t

the

trip-

ping

of the

asYnchronous

motors

oll4 given'loads

in

the.trorlt-iime

no-power

untered

during

the

ARC

ana

aTS

cycies.

llowing

step-s

are.

taken:

Lors

rated

at

3

kV

and

more

no

under_

rtime

setting

must

be

sufficient

to

over_

rd

witir

a

view

to

facilitate

the

self_

le

of undervoitage

protection

having

a

trips

the

breaker

at the

mentioned

iol_

(1

1-38)

For the

given

erample

'

P^'"stI

:0'8Stt

If the

normal

load

of the

section amounts

to

70

por

cent

oI the

transformer rating,

then

be

reestablish

normai

operation

upon

completion

:..^r_Tr_t:q f-"tom.a

tica

il

r,.

.

Fo r rhis,

use

i.

I

"

a.

of

eF.C'a.:ri

#

;;i;;

t^_ -^ -

rUI

I'EUU-

sures

in

one

or

several

groups.

orrnrng

sequen

tbe motor

need not

tripped.

0.8

4r\A - r r.n^r

tw

-

t=v70

23-2076

(d)

For

important asynchronous

motors

use

is

made of magnetic

starters

having

a

AUTOMATIC

TRANSFEN

TO

NESERTUE

SUPPLY

AND

EQUIPIUE}iT

is pressed,

the

capacitor

is

protected

against

j

I i -.

I

st"rt

I

Stop

!

J-

i

autotransformer

.4[r

and the

circuit

including

diodes

D2 and,

D4 holds

the

star-

ter locked

untii the

Starl buttor'.

returns

to the

initial position.

Simultan*ouriy,

the

-

capacitor

C starts

to

charge

through

diode

DJ used

to

bypass

the

auxiliaiy

Fram ARt

deyiu

::1i^l^ih'.:tTl:' Il',1 lry-fyT

button

A

I

e -

CEAPTER ELEVEN

rated

for

voltages

up to

1000

volts,

dropout deia-v

overlapping

the

no-

Fig. 11-16.

Schenratic diagram of delal'ed starLer

power

intervals

in the

ARC or ATS c3'cles

(an

example

is shou'n

in

or

immediateiv

start

tlre motor

after the

voltage is

reestablisherl

(an

in

F'ig.

71=17)

[1i-13'

l1-14].

overvoltages

b-v diode

D4.

with

respect

to the

discharging

current,

f !- [

the

main and

auxiliary

coiis

rurn

out

to

I | |

be

cumuiativeiy

connected

in

series.

In this

i i i

Fig. 11-1ti)

example

i-<

Fig.

11-17. Schematic diagra.r.n. of. start.er for immediat,e

reclosure when

voltage

rs reestabljshed v'itliin the specified

time

(a)

with

control contactor:

(b)

with button-type device;

St

-

starter; f,R

-

rela]

n'ith

delayed dropout

of

armature

(up

to

3

s):

D

*

rectifter.

Position

of contactor: J

-

to be

closed;

Cl

-

closed;

Op

-

opened.

T.ransfer.

from

position

J

to

position

Cl

is

performeo

without interruption

If

the

siaitei.

has

to

disconnect

due r,o

irn;ediate

#,ffi!'i

;"r',Tl"l"i;'"-J-"lj

operation

of

some

seryice

automatic

device.

reesi.abiisireri

then

connected

in

series

q'ith

the

Stop

butt-

on

is the

contact

of the

output relay

of the

automatic

device.

The

contact

opens s'hen

the

service parameters

reach

critical

values.

Stand-by

moior

Fig.

1t-19.

ATS

device

of motor

The

device shown

in

The hoiding

system

of

Fig. 11-16 operates as follows.

ttre

starter has

two

coils. main

and

auxiliarv.

carrieo

J.- auxilia:1'

reiay;,t

-

rc)al

.with

deiayed

reset; a

_

signalling

rclay;

J

-

tripping

deviee.

Position of

auxiliary

contact

of

circu-it

motor cofr€sDonds

to closed stste of the hregker

rela)';

4

-

pressure

breaxer

Of workins

f,ne at[ernat

. ..a. I I

eurrent rectrrreo D

r.

I nt

.

a I . .t

' .l

tf. ,l

olooe l)t

ls Ieo Lo

lne

marn

coII. Arler

f,.oe

v9

uug

I

motor

after'its.terminal

voltage

is

reestablished,

mmeora

oI

a rrrpped

provided

that

the

interruotion

40r

!1J-

starter

has been switched on,

its

auxiliary contact .K

turns

on

the step-down

JJO

CIIAPTER

ELEVEN

t3_the

qo\il_ei

supply

has

not exceeded

the dropout

time

of the

auxiliar_v relay

7R

v'ith

dela5'sd

reset.

The eircuit illustrated

in

Fig.

11-{7 is

one

of

the

most simple variants

of

various

slarter

designs

with

immediate

reelosing

when

the

vo]tage

is reestab-

Iished within

the

specified

time

tr1-131.

From the- point

of

view

of

safet5' regu-

Iations and

production

processes

an uniimited

voltage reestablishment

waiting

time for

reclosing

tiie

breakers cannot

be

permitted.

The

circuit of

a magnetic

starter providing

no immediate

reclosure

after

iire voitage

has been reestabiished

is

shown

in

Fig. 1L-18.

When

it is necessar-v

to

reclose

it

after a specifled period

or in

a'preassigned

sequence. the

circuits

shown

in brqken

line'

can be used bv

connecting ihem,

for instance,

to the

ARC

device

of

the

given

unit.

In

those

cases, when

tiie

generation

units

have

fo

perform

the dut-v

of a

stand-

b-r,

source

for each

other,

only one of

the.motors

operates under the normal

-^-J:+.:^'^^ /.-.^-l-:*- ^-^ T]:- t1 1.'\ rrTL-- :r -'- lr-- ,r ?

(;uilur

Liurr.s

\wurHrrrH

rrrre. .r tg.

t

r-rJ).

yv.uet

II ls

olsconneeteo Ior anY rgason

and,

in

particular,

when

t,he

main source

wori<ing

voitage

faiis

or faiis sharpiy,

the

stand-b5'

motor is automaticalli'connected.

It

is supplied

from

the stand-bi'

s0urce

[

1

1-15].

1 1-6. Conelusions

1. Tlie

use

of

ATS devices

at

po\tr'er stations

and substations

of

power

systems

helps to

ensure

a dependable

power suppiv and in

many cases

simplifies the

circuit,

and protective relaying. The combined operation

of

ARC and ATS

devices adds still more

to

the reliabie

operation

of

power svstems.

2.

The use of

ATS

devices assures sectionaiization

of

substation

busbars

and reduces

short-circuit currents, faciiitat,es

the equipment,

operation

and

cuts

dorvn

costs.

3.

ATS

devices

produce

the. best, resuits

when a deenergized network

includes

Iighting and

heating

loads

and also

asvnclironous

motors

u'hose

self-starting

ma*v be

attempted

after.the

power

supply

is

reestablished.

4.

\4/hen

a network incorporates

synchronous

notors, operation of

the

ATS

devices

of

the

supply

service entrances must.

be coordinated

with the

action

of the aulomatic

controls

which

transfer

the

motor

into

the as5'nchronous

starting

mode and

perform

resynchronization

aft,er tire supply is reestablished

in

a

rva-r,' similar

to

thaL

used bv

t,he

ARC

devices of substations

with

s)'nchro-

nous

}oads.

Conneet.ing

a stand-b-v source

to excited asynchronous motors

sliould be

avoided

as

far as

practicable.

In

particular

cases,

such connect,ion may be

effected

after checks

to see

whetirer it is t,oleralile as to

the

mechanical

strength

of the motor and

its resvnchronization and

if such connection

will not disturb

AI]TOMATIC

TR,A.NSFER

TO RESERVE

SUPPLY

AND

EQUIPMENT

6.

When

ATS

devices are

used, the

protective

relaying

calculations

must

be always

carried

out

with

consideration

given

to

the

increased

currents

erlcoun-

fered by

the

motor

and an exces,sive

starting

current

inrush

as

compared

to

the

current inrush u'hen

cutting in a fuliy

stopped

asynchronous

motor.

7.

Automatic switching-on

of

stand-by

supplS

sources

needs

investigations

into

the condit,ions

necessarj*

for the

self-starting

of important

nrechinisms

which ensure

continuitl'

of

production

processe-s

(examples

are station-service

auxiliaries

and industrial

productive

mechanisms).

11-7.

Review

Questions

1. \\rhaf

js

thc

difference

bet'iveen the

automatic

trans{er

to stand-b-y

po\\.er

arrd arrto-

rnatic

reclosure?

2.

On which

po\\'er

station auxiliaries

are ATS

devices

most

Dracticable?

3. How is the

operation

ol tbe

ARC and

ATS

de','iees

instalied

on tbe step-dov,n

power

transfcrmer,.

of substations coorriinated?

4. \4Ih-v

does the

.excitation

forcilg

oJ

generators

faciJitate

the

self-starting

of

asy'ncbro-

nous

motots in

the

station

house circuits

af

ter

operation

of

the

ATS

devices

on

thi

trarrsicrmers

which s31Rf)r'power

to the

station-service

secticns

from the

generating

soltage

lusl";i

.5.

Hou'does an

increase

in

tbe

output

po$'er

rating

oi

po*'er

tran-*foinrers

eiiiploS'ed

by

substations effect

the,self-starting,

conditions

of the consumers'

asynchronous

moi,oti

being

supplied from

the

substation

busbar sections?

6.

De-scribe

the

specific

features

of a system

used to

control

tlre

contactors

and

magnetic

starters of asynchronous

motors left

for the

self-starting

purposes.

,ers

ul .rbluuuJ'ultuus ruLrLOrs

relr

IoI tne

setl-slalllng

purposes.

7, \\'hat are tbe

conditions

d.etermining

successful

self-stlrting

of as_vncirronr_rus

motors

after

the

operation of ATS

devices?

8. Enumerate

the

djsadvantages

and advantages

of the.seclional-ized

suppi

6. .Unumerate

trJe

dlsadvantages

and advantages

of tbe.seclionalized

suppil

to

busbars

with the

use of ATS devices as compared

to

a circuit n'ith

parallel-connedred'sectjons.

9. Hos'is the.use

of alt AT.i

deviie l,aken

into

account. n'hin

accon:rplishirrg

the

nrotect-

wrLIl Lrle

use or.r\rD oevlces as compare0

IO

a clICUtt \l'Itn

parajlel-connected

SeCtjOnS.

.

9., Hos'islhe.use

of alr AT*i

deviie l.aken

into

account. n'h'en

accon'rp)ish!rrg

the

protect-

ive reJaf

ing of

consumers

and

supply

units'of t.he

pon'er

system?

10.

Hox is

the

presence

of synchronous

mol.ors

supr,lied

from tire busbar secrions of

10.

Hox is

the presence

of sy

ts

oI t.ne

po\\'er

s]'steml

us mol.ors

supplied

from

tbe

busbar

sections

of

circuits of ATS devices

sliould

beas

simpie as

possible.

These devices

ment

supplied

from

an alternating

operating

current

source.

Chapter

Tu;elue

OPERATIO]T

OF

ARC

AND

ATS DEVICES

I}i

CONJUNCTION WITH

PROTECTIVE

RELAYING

I

vz

tf

lz

Fig.

12-1.

Characteristics

of

protectjon

units u,hen

their

operation

is acce-

terated

.belore

automatic

reclosure

OPERATION

OF ARC

AND

ATS DE\/ICES

WITH

RELAYING

35f,

I2-1.

Lceeleration

of Protection

Aetion

Before

ARC

acceierating

the

protection

action)

the

number

of -successful

automatic

reclo-

sures

is

materiail-n*

reduced.

In

the

case

of

conneetion

to a

persistinE

short

circuit,

retripping

is

performed

seiectively,

fls

the

non-selective proteciion

is

aut,omaticalll'

disconnected.

Accelerating

the

action

of the

protection

before

ARC

operation in the

ARC

c.ircuit

on Fig.8-3

can

be realized.

if the

break

contaet

of

ti*e

relav

ZJ?

is

a pplied.

12-2.

A,eeeleration

of

Protection

Aetion

After

ARC.

ATS,

and Remote

Connection

Al,celeratirrg

the protection

action

after

the

breaker

is closed

by

an

ARC

or-ATS

device,

or

remot,ely

b1'hand

or

a remote-control

system,

allon's

a

faul-

forlolo-an*lr.}'^i*-^J;^+^l-'.i^^l^+^J:f^^L^-r.--*--.:r

uvu

vreJJerr!

f

v !E ruuEuto

Ltrr

\

lDulcl

L,utl

11

a

stlur-L-uII'{.iul

L

c(]lll]guLlon

ls

ma oe

l^^-:+^ +L^ f^^r rL^r rl. - ^l---- - -r

oespii,e

ine iact

inal

t.ire eiement

proteciion

is

de]aved

in time.

This

method

minimizes

the

effect

of

sliort.-ci.rcuit

connect,ions

on the

opeiation

of the

ioads.

The

damage

is

mitigated

and

the parallel

operation

sfibilit]'

of

the

power

svstem gerrerator-s

is also

improved

lt2-11.

It is

advisable

to

u-se the

accelerated

protectioti

in all

instances rvhen

irigh-speed

prorection

of an

eiement

is

not

used

at

a}l

or

it

covers

onlv

part

of

the

line.

-Acceleralilg

the protection

act,ion

after

ARC

operaticrr

in

the

circiut.

of an

ARC

device

silc'*'n

in

Fig.

8-3 can

be.

accornplisherl

bv using

the

coniact

oi

relay

TR. the

operating

t.ime

of

rvhich

is

0.1 tb

0.15

s.

The time

durins

u'hjch

the

a_ccelerated

protectiori

unit is

set

inlo

operation

b1,

the

instantaneousi,ontact

of

relay

TR is

det,ermired

by the

finai c.ontact

time.-Tire

closure

of

this

contact

resets

the

device.

operation

of tlre

4RC

device,

the

non-selective

high-speed

protection

ryaticall-v

rendered

inoperative

for a period

great6r

than

that

needed

the

Iine

b1'

the

selective

protection,

sali,

bi,

" "-urr.nt

protection

with

a

opera.ting

time

characrerjstic

(Fig.

[Z_t1'.

is

auto-

to

trip

stepped

Section

The

use

of accelerated

nrot.ce.t.inn hefnro +ho AEIa ^*^-a+i^- *-r-^^.:. -^^

sibie

ror

an

ARC

device-d

il

i;;lr;d

;;i-:""il;""ii#';i:.rT#".",1.',,ftT;

srure

ror

an

Aflu

devlce

to

be installed

oniy

on

the pilot

section,

ensuring

reclosttres

of all

the

sections

of the

outgoing

line

chain.

This

method

produc.es

chain.

This

method

produc.ei

)v

PtvuuL.u-

9::1l:t:llt ?l,short

lines

or.

u'hen

the"circiit

breakers

of

receiving

substation

lf^::t 3!aqlea

for

automatic

reciosing.

Thc

characteristic

of the prodecrion,

wnose

operation

is

accelerated

before

the

ARC

operation,

is shor+,n-in

broken

Iine.

of the

When

a

fault

occurs

on

any

section

of

the

transmission

line

the

breaker

either

the

second

zone

may

be

accelerated

after

the

ARC

operation

or the

first

zone_

rDay

De

prolonged

b1'means

of an accelerating relal',

i.e.,

0.3

to

0.5 s

after

faults.

as after

AF-C

oncratinn lha incrrlo+i^*

-

r

*-

-

rlroutq

urull

+J.^ *^:^-:+

Lrlv

IrraJUr J L

^r ^- ^^-

ur uiusEs

cteS,rec

*'l

AU

e

detay

-i4L ^--t

wlLllt uL

of

the

first

zone

of

t.he

remoi.e

protection

incl lengthens

the

zone

of.

action

tI

JbU

CIIAPTER

TWEL\IE

is

moment

the

actiori

zone

was

oniy

80

of the

starting

current

inrush

in the

formers

is

accelerslsfl

t1t-{J.

The

prote

currents

is acceierated

up to

0.1-0.fSs

i:

due

to the

nonsimultaneous

closule

of

to

connect

sucir

a

protection

to

the

cr

saturable

auxiliary

iurrent,

tran,qofrmer

r

in

the ze.ro-sequence

current

is eiimir

The method

i:

also

applied

in

order

t,o

reaiize

the

high-speed

plotection

of

long

5-00-\\'

Lines

through

the

u-se

of

"trial"

devices

$,hich

su'itch

on

the

nonselective

high-speed

proi,ection

for

a

certain

time,. u,itli

the

iine

ciosed

at

one

end, wiien

the

mainirigh-speed

prot.ectioo

of

t-he

given

iine

ii-inoDeratiye.

12-3.

High-Speed

Selective

Disconnection

,

T.\.

ioj.nt

operation

of

the

protective

rela_ving

and

ARC

devjces

allows

selectl"'L'

cllsconlreotions

to

be

a.ccompiished

br,

lionselaiii've

Drotec.tior:

units.

Two

methods

are

developed

in

the

'USSR

iiz:g,

ti-sl.

+

a

-2

t

OPERATION

OF A-RC AND -4,TS

DSV'ICES

UIITH

RELA-\"ING

S/hen a fault occurs

in the

action

zone

of

the instantaneous

protections

of

two

adjacent

sections

(sectian

II

and

section III

at

point,SCr.

for instance)

both sections

are

tripped

and

reclosed

by the ARC device.

\4lhen the

automatic reclosure

is

successful

the

suppiy

is

reestablished.

If

the

short

circuit

persists.

both sections

are

disconnected again.

Next,

tbe

operation

of

the

two-shot.

ARC device

in the second

cycle

.n'ill

reclose

section -f.I/

361

IIEIIT

i

sct

t

AKLZ

Wrno*

i^P.l

lt

ti

flRnt

.J

l,QC.l

i._i-i

J

+

L^-2

t

SC,

Fig.

12-3.

Characteristies of

protectiri:.1?rr1,'tn*

during sequential

automatic

and

.*ii}

not'r'bclose

seCtiorr iI,'as

t]:c latt.er ii: iuinis].ieo rcitii a

sirrgie-sLot ARC

device.

The figures

found near

the

ARC

s1-mbol

in Fig. 12-2

stand for

the

number

of

automatic

reclosures

nerformed

bv

tire

ARC

devices.

\4lithin

section

.I

(a

^power

traniformer)

protected

b]'a

curreni

cutolf

or

differential

protection,

the

ARC

device

does not

function

wlien

tirese

protec-

t,ions

operate.

Therefore

r+'iren

there is a

persisting

fault

n'ithin

t,ireir

active

zone

and sect,ion

II is

tripped,

the nonselective disconnection

is

corrected

b1'the

ARC

device instalied in

section

//

(on

breaker

2).

This

method enables

a rapid

selective

disconnection

to be obtained

u'ithout

using

costiy

and

complicated

protections,

confining oneself

to

the

use

of ordi-

nary

current

cutoffs

or

single-stage

distance

protections.

The

disadvantage

of this

method

is the

possibilitv

of simultaneous

protective

operations

on

tq'o

adjacent

sect,ions

and

ihe

deeneigizing

of

the load-s supplied on'"t

a

sound line

for

the

operating

tiroe

of

the

ARC

device and

closing

of

the breakers.

\4rhen

the

ARC

device

or

a breaker

fails

the

fault,

u'iil deveiop.

The

method is

applied

t'hen

single- and

t'q'o-shot

ARC

devices

are used.

Three-shot

automatic reclosing to

correct

the

nonselective

operation

of

tlie

prot.ection

is not

practicable,

as

the

result

is

a

prolonged

interruption

to tjre

sert'ice,

which

i-q determined

by

the

operating

time

of

the

three-shot

ARC

devices.

(b)

Sequential automatic reclosures

o.f

trartsmisston

line

sectians.

In

addition

Fig-

12-2.

correction

of

nonselective

acl.ion

of

protec.tion

by ARC

devjce

e

protectlon

*'nlcn

seec[rvery lsoonnecteo a

sectrons.

eacn sec-

q

tive

current

cut,off

or nonse

t

--

r^r

.r rrvusrL_r\'v

tive

dist.ene.e nrntpe.{inn ic rrqorll oo f},o..1 ,1 ;+i^-^l

gu

vrrv

quurulvlJal

covers the

section

under

protection

an

part

of

the next,

one

(Fig.

i2-Ji. Like

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

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