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Vol D - 1990 (ocr) ELECTRICAL SYSTEM & EQUIPMENT

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3.3 kV and 11 kV switchgear — circuit-breaker equipment

4.2.13 Control/selector switches

he interest of uniformity, control switches are

Ill t -it of, or below, selector switches, and located to the rid

ti,nalls have pistol olp pattern handles. Padlocking lacilities are provided for locking control switches in 'neutral position and selector switches in each on. Control switches are spring-loaded to return

:o 11(: neutral position when released.

4.2.14 Switchboard/circuit identification

Fo avoid, as far as possible, the risk of injury to per- ri ncl and operational error through mistaken identi-

lication of circuits, labelling is provided as follows:

•On each switchboard or separately-mounted relay panel.

•On each circuit at front and rear, on the outside of the enclosure.

Also, unless otherwise obvious, labels are provided to lientify the function of:

•Fach control, selector, pushbutton and other switch, relw„ instrument, current and interposing transformer, transducer, indicator lamp, etc. Where relays are mounted away from circuit-breaker panels, each relay is labelled to show its circuit designation and the relay duty.

•	Each position of every switch.
I	■ ternal circuit identification labels which, for pro-

minence and clarity, are fitted on removable covers or parts are repeated on a non-removable part in or on the enclosure.

AN an additional aid to identification, coloured symhols are provided at the front and rear of each circuit ui a switchboard. These symbols are illustrated in

5.36.

4.2.15 Indicating instruments

Indicating instruments and relays are of the flushmounted pattern. Ammeters are scaled to indicate full- Had current at approximately 75% full scale deflection.

\ddirionally, those in motor circuits are usually of the ppressed scale type, i.e., suppressed at the upper end.

4.2.16 Test devices

I or the purpose of primary injection testing, portable
L.1 0 ices are provided for the connection of test leads
'0 th e busbar and circuit disconnecting (isolating) con-
!ski, in	the switchgear enclosure from which the circuit-
hreaker	is disconnected when withdrawn. The devices

must, when in position in the switchgear, be capable

ot withstanding for 15 minutes a DC test voltage 01

System rated	DC test voltage, kV
voltage, kV	Phase/phase	Phase/earth
3.3	10	7.5
11	36	25

The rating of the devices is dictated to some extent by the method of fitment to the switchgear. Generally, those for circuits rated up to and including 800 A are required to have a thermal capability of 400 A, and those for duty in equipment rated above 800 A, a thermal capability of 1000 A.

4.2.17 Circuit-breakers

Circuit-breakers of the same type, current rating and circuit duty are required to be interchangeable; likewise, those of the same type and current rating, but of different circuit duty, subject to any modification necessary to control, indication and interlocking circuitry. Operating mechanisms are of the dependent power solenoid or stored energy type, provided with a shunt opening release and a mechanical opening release. The latter device must be available for use at all times, except when deliberately padlocked inoperable. In this context, 'available for use at all times' requires that, where the. release is located behind a door, the door must not be lockable.

Indication of the closed/open state of the circuitbreaker is provided mechanically, and driven positively in each direction. The indication is inscribed: 'ON' in black letters on a white background, 'OFF' in white letters on a green background, and is operative whatever the duty mode, i.e., the 'service', 'disconnected', or an 'earthing' mode.

Shunt opening release circuitry is taken through auxiliary switches driven by the circuit-breaker operating mechanism. It is necessary to switch the protection circuitry in such manner to ensure de-energising of such circuitry when the circuit-breaker is open. However, to ensure reinstatement of continuity when the circuit-breaker is closed, the switches are arranged to close before the main circuit is established.

Locking facilities are provided, whereby the circuitbreaker can be prevented from being closed and also of being opened by operation of the manual opening device when closed in an earthing duty. Each of these locking requirements is met by the application of a single padlock, or a single key lock, and must not entail the fitting of loose components in addition to the padlock or key lock. Locking of the manual opening device is provided to prevent inadvertent opening of a circuit-breaker when used for an earthing duty. It must not, therefore, be possible to gain access to any part of the closing mechanism which would allow defeat of the locking of the manual opening device when the circuit-breaker is closed in an earthing duty.

Whilst, when a circuit-breaker is employed in an earthing duty it is necessary to render inoperative its

373

IP'

Switchgear and controlgear	Chapter 5

Al: CIRCUITS

SWITCHING

		PE VIC
	AIR	PE VIC
	AIR
CIRCUIT BREAKERS

	ALTERNATIVE
	SWITCHGEAR
	AS SPECIFIED

DIFFERENTIAL

PROTECTION

RELAY

AND

TEST

FACILITY

WHERE SPECIFIED

ILL

CNEP

0 CURRENT '6

AND

EARTH FAULT

PROTECTION o RELAY

AND

TEST

FACILITY

OUTPUT FOR REMOTE

INSTPLJMENT

'TRANSDUCER WHERE SPECIFIED)

POWER FLOW

FIG. 5.34 l I kV or 3.3 kV switchgear — typical transformer feeder circuit

374

3.3 kV and 11 kV switchgear — circuit-breaker equipment

DC CIRCUITS

IEN DC

220V DOOR 250V DC

CLOSING COIL OR

SPRING CHARGE MECHANISM

CONTROL SELECTION SWI T

REMOTE

CLOSING MECHANISM

.EMCFE

• O( AL CONTROL Syr ITCH

NEUTRAL

LOCAL TEST

,C1CAL :

OPEN CLOSE

CB LOCATION SwiTcH

17,1,

10 01

AND ANTI-POMP CiFiCoiT

CLOS:NG CONTACTOR OR

SPRING RELEASE COIL

iNTERPOSE

I Li

CB TRIP

RELAY.CLOSE

CB POSITION SWITCH INHIBIT CONTACT

—1—

TRIP

0—o

COIL

INTERPOSE

RELAY-OPEN

TRIP CIRCUIT

SUPERVISION

--C

PRE-CLOSE RELAY

..• uTA RECEIVE -

- A , RELAY

TRIP RELAY

C•RCul T

AJSE

:AERATED

ZuRRENT

SHUNT REINFORCING

L27

L28

INTERTFIIP

AG RELAYS

PAuLT

PE REQUIRED)

0-0=D

0-4

P SENO

—11

oT , Enr.aiaL

TRIP CIRCUIT

SUPERVISION

AFTER-CLOSE RELAY

TRIP CIRCUIT

SUPERVISION RELAY

7141'

PRE•CLOSE

RELAY

I CB LOCATION SWITCHES

I 0

8-0

4._

RENICIr.E

LOCAL I TEST

0-0 O I 01 .0

I .

I I

I LU ,

EL, ! 0-0

I NTERPOSE RELAY - 'OPEN

CB -POSITION SWITCHES

1- o—o

0.--...--....---rnIn--0

C ■■•■0 0--44m)r

0..

Cm0 I 0.■

—7

INTERPOSE RELAY • 'CLOSE

.•.r

0-.—,-.—rrY-1-0

O—( ■-0 4I—....).

0.-----■0 I 0-0

'BUSBAR•PREPARED FOR EARTHING

0—C ■-0 I 0....--.

c■.......■0 i 0-0

LOCATION SWITCH

-1–

o—(--o 0........

..40

0—(.-0 I 0—o.—4.)--. .o

—I—

TERMINALS FOR EXTERNAL

'CIRCUIT PREPARED FOR

0—(A.--0 1 o--■ )-0 CABLING

EARTHING' LOCATION SWITCH

0—C8A-4:1 . CI• m)...

04—C.■-0 0—■')--0

c—i. 01

18.-0 0—■ )-0

'SPRING CHARGED SWITCH

—

1—

					Or
SPRING FREE SWITCH		IrI.	i'''' I 0•1— •

O—C..-10 0-1—..)--•0	°—			io	, o	r

04—R■ 3-0

I-SEATER

FIG. 5.34 teorit'd) 1 kV or 3.3 kV switchgear — typical transformer feeder circuit

375

Switchgear and controlgear	Chapter 5

AC CIRCUITS

BREAkE ,, CB

o =`,11,'-' 7,Ej';' ,TER.°AsTri2rMas

REST.IC - E0 EARTH FAULT

PROTECTION

0- - - -IV, r-

- - 0

OUTPUTS FOR

0 -LI

31-

RE VOTE INSTRUMENTS

-,■e , _j1- -Er= 3- —

4 4

Flg.

, __ -I-

-, ,

-- --- -.'-jI

' W

.--. "'"

I',..;ZR

- --- -- tPART;

-. .---

WART

■

-71- -i

: / ■ _1-: I= r. : =

I L-, -I-I- -I '

I ' I I

Ci=l=1)

METERING

OVER 4111

FREOUENCY

80--

%LAN,

PROTECTION

El)

11331 AC

r231:j

BUS

0212

17LE16

F13[

1 3

l tu

ES	1
	2OLTAGE SELECT ON RE L
	C	fo 01

o—K. 91

FR:, 5.35 11 kV or 3.3 kV switchgear — typical unit transformer circuit

376

3.3 kV and 11 kV switchgear — circuit-breaker equipment

CIC CIRCUITS

227, DC OP 2OTV DC

io 0

P '

'• "EP LOG r, b

TO REMOTE PRE-CLOSE TRIP CIRCUIT

SUPERVISION RELAY a

cEEP FPED0E ,,C , PI, O- ECT ■ ON

RECE yE -0 0-

, w

L7 D-

he ipAuf

_OCATION SwiTTCPES

4.71,0„7-1._ I

29.8i3

—

0--+0 0

INTERPOSE RELA• OPEN

CO POSITION SWITCHES

0---0 • 0

0—....Cm.,.....0

c■■■

0 I 0-0

Cm. 0 I 0.-.-.m

0 ; 0--....■.",

INTERPOSE RELAY CLOSE

p--Mr1---0

c.--C ■--0 I c.--■.),-0

o—o c--.::

DUSBAR-PPEPARED POP EARTHING

0----Cm---0 I 0—■)—/D

0-...-0

LOCATION SWITC},

-1-

0—(m.--.0 0.---■)--0-

0---1,: ■—o I 0—...)--0

0 4 0.

-••••- ‹

TERMINALS FOR EXTERNAL

CIRCUIT PREPARED FOR

.0•;.-

-(14•--0 I 0--aw).--0 CARING

EARTHING LOCATION SWITCH

}...... {■■••■3 0.--■ )--C1

;0;

;C•E■0 1 0---.00-0

c_.....)_,

0.--C ■-0 } 0.---.■ )---0

0---40

07 C

1.13 01

•

SPRING CHARGED SWITCH

I, I 01

SPRING FREE SWITCH

°-11.<

1-+13

.EATEP

13■ITC

1•fFD

}TO

VOLTAGE CURRENT AND POWER TRANSDUCERS

SHOWN IN BROKEN LINE WHERE SPECIFIED

PTSE POST TRIP SEQUENCE EQUIPMENT

FIG. 5.35 (cont'd)

11 kV or 3.3 kV switchgear

— typical unit

transformer circuit

377

Switchgear and controlgear	Chapter 5

A
A		A

	BS 381C			SIZE IN MILLIMETRES
COLOUR	BS 381C	REMARKS	DIM
COLOUR	COLOUR	REMARKS	DIM
	NUMBER			1	2
				1	2

FRENCH BLUE	166		A	75	50
MIDDLE BROWN	411		B	25	16
BRILLIANT GREEN	221			25	18
CANARY YELLOW	309			65	55
SIGNAL RED	537
WHITE	W
BLACK	B

NOTES

1 PANEL No I SHALL I N ALL CASES REFER TO THE PANEL ON THE EXTREME LEFT WHEN LOOKING AT THE FRONT OF THE BOARD LEFT HAND FUTURE EXTENSIONS SHOULD USE THE SERIES IN REVERSE. COMMENCING 42 41 ETC

gEmmmi n 5

E ZYU000

COLOUR	L	60£	LCS
NUMBER

	n
A40.00			A4000EA400C3
I				1.	'1
.991	LU'	J- 60C LLZ	99L	LIPL	I 60C	LCS

25	26	27	25	29	30	31	32	33	34	35	36	37	38	39	40	41		42	43	44	45	46	47

	LAVO00							A4000						AU000					-	A		00
																								,
tC5 760Cr						FLee						T		601F					1			I
tC5 760Cr			.		5	FLee	60C	LES			991	1.t1-1		601F	SLC		B		99,•	.7	iZZ	60E	LCS
			.	6	5						L		LZZ							.7
				6

																					REPEAT
FIG. 5.36 Coloured symbols for additional circuit identification of switchgear

378

1111111mm

3.3 kV and 11 kV switchgear — circuit-breaker equipment

o pening• electrically, the means adopted must not lock ihe opening mechanism mechanically.

To ntinimise the risk of physical injury to perwacred in the maintenance of a circuit-breaker,

injury from inad‘ertent tripping of the operating H.e,:hanism, provision is made for slow closing and Whilst the means of slow closing/opening is use. movement of the circuit-breaker contacts must

ifl under the control of the operator; opera-

:cumin v.holly

. ion of the n anual opening release must not negate function. However, to safeguard against attempted

,[0,are of a circuit-breaker other than by energy pro- Jed by its service operating mechanism, it must not

he possible to use the slow closing facility when the ,ir,:uit-breaker is in the service position, or employed

in an earthing duty.

Except where for economic reasons it is desired t o avoid the provision of heavy current DC battery

,u rlies, no distinction is made as to technical merit N.qween closing mechanisms of the dependent power

.olenoid or stored energy types.

The interrupting systems of air circuit-breakers com-

ri,c fixed and moving elements of the 'butt' or 'clip Jilt] blade' type, opening in 'arc chutes'. Both fixed

inoN„ ing elements incorporate main and arcing conthe former for current carrying and the latter ior drawing the arc and relieving the former of the

Lon,equential burning. The arc chutes comprise, essentially, enclosures of insulation material containing

•large number of 'splitter' plates, which envelope each phase of the contact system.

13aically, the process of interruption is as follows:

•The main contacts part, followed by parting of the arcing contacts.

•An arc is drawn between the fixed and moving arcing contacts.

•'File arc is transferred during the motion of the

m1)\ ing arcing contacts across 'arc runners' in the are chute.

• the arc is forced by thermal and, in some designs, deliberate magnetic effect into a lengthening loop

in the arc chute, where it is split into many small series arcs, cooled and extinguished.

a fact that the higher the energy of the arc,

!he !:!reater its propensity from thermal/magnetic influence t.o penetrate upwards into the arch chute.

on ■ ersely, the lower the arc energy, the lower the ir klucernent so to do. Thus air circuit-breakers have

cendency towards producing arcing times at low

. =rerils significantly longer than those of currents 11 C,il- T the 'rated' breaking capacity. The current at

arcing time is a maximum (termed the 'critical , urrent') which may have a duration of many cycles,

=s u•tially of the order of less than 5u7o of the rated

ipitci

To improve the performance at low currents, particularly at the higher voltages, an air 'puff', derived from the device(s) used to damp the arrest of the motion of the contact system at the open position, is directed at the underside of the arc to assist its movement upwards into the arc chute. The air puff is, of course, produced at each opening of the circuit-breaker, but is of useful effect only at low currents.

By virtue of the relatively high arc resistance generated in air circuit-breakers, the transient recovery voltage (TRV) appearing across the breaker at interruption is well damped, i.e., air circuit-breakers are inherently 'soft' (see Section 10.5 of this chapter).

4.2.18 Circuit-breaker operating mechanisms

Dependent power solenoid mechanisms are of the 'trip-free' type. Dependent power operation is defined as an operation by means of energy other than manual, where the completion of the operation is dependent upon the continuity of the power supply (to solenoids, electric or pneumatic motors, etc.). A 'trip-free' circuitbreaker is one in which the moving contacts return to (and remain in) the open position when the opening operation is initiated after the initiation of the closing operation — even if the closing command is maintained. However, it is recognised that, to ensure proper breaking of the current which may have been established, it may be necessary that the contacts momentarily reach the fully closed position.

Means are provided for de-energising the solenoid coil immediately after the circuit-breaker has closed. The insulation materials of the solenoid coil are chosen to minimise the generation of flammable gases in the event of overheating of the coil through failure of interruption of the supply upon completion of the closing stroke. Additionally, the coil is, as far as is practicable, so positioned in the switchgear to minimise the risk of ignition of such gases from arcing of the main and/or auxiliary contacts during operation.

Stored-energy mechanisms are of the motor-charged spring type. The definition of 'stored-energy operation', being 'an operation by means of energy stored in the mechanism itself prior to the completion of the operation and sufficient to complete it under predetermined conditions'. Such mechanisms are provided with electrical and also local (i.e., at the switchgear) manual mechanical release of the closing energy. The local release is usually, and preferably, by pushbutton, shrouded or recessed to prevent inadvertent operation and padlockable inoperative.

With the circuit-breaker in the service position, recharging of the spring(s) is required to commence i mmediately and automatically upon completion of a closing operation. The recharging time must not exceed 30 s. It is further required that a charged spring(s) must not be released by the shock of operation of the circuit-breaker. Similarly, release of a charged spring(s) whilst the circuit-breaker is in the closed position must

379

1000

Switchgear and controlgear	Chapter 5

neither cause opening of, nor damage to, the circuitbreaker.

Means are provided for charging the spring(s) manually. This permits a service closure, i.e., a full energy closure, if the spring charging motor or its electrical supply fails. Mechanical indication is provided to show the state of the spring(s). It is inscribed 'SPRING CHARGED' when the mechanism is in a condition to close the circuit-breaker and `SPRING FREE' when in any other condition. Where necessary, provision is made for indication of the state of the spring(s) at a remote point. Figures 5.37 to 5.44 show detailed views of the 1 I kV and 3.3 kV circuit-breakers and their cubicles, which form part of the switchboards illustrated in Figs 5.25 to 5.31.

5 3.3 kV switchgear — fused equipment

The technical specification for fused equipment is discussed in Section 5.2 of this chapter.

5.1 Required performance

Definitions and, where necessary, explanations of the rated characteristics are given in Section 4.1 of this chapter.

5.1.1 Rated voltage

Established designs, i.e., those evolved during the currency of British Standards BS162 and BS3659, are rated 3.3 kV. However, to align with IEC Standard values, the presently assigned rating is 3.6 kV.

5.1.2 Frequency and number of phases

This switchgear is always three-phase, 50 Hz.

5.1.3 Rated insulation level

The 'classification' of the insulation of established designs — again those evolved during the currency of BS162 and BS3659 — is based upon the achievement of clearances between phases and clearances phase- to-earth to the dimensions specified in those Standards for 'Class B'. However, here again, to align with present thinking within the IEC, the 'rated insulation level' is assigned in the case of the established designs, and specified to be proved by type test for the newer developments, in accordance with Table I, List 2, of BS6581: 1985 (IEC 694; 1980).

5.1.4 Rated short-time current

The present requirement is

(a)Busbars and the conductors connected directly thereto, up to and including the busbar side terminals of the main circuit fuselinks, have a rated

short-time current capability of 26.3 kA for 3 s or 43.8 kA for 3 s, corresponding to system shortcircuit levels of 150 MVA and 250 MVA respectively, both levels occurring in CEGB installations,

(b)All current carrying parts on the circuit side of the main circuit fuselinks are rated to carry the prospective rated short-circuit current of the busbar system, i.e, 26.3 kA or 43.8 kA, as limited in magnitude and duration by the highest rating fuselinks permissible in the switchgear.

(c)All components forming a circuit path to earth have a rated short-time current of not less than that of the busbar system, except that the duration of the short-circuit current may be reduced to, but not less than, 0.2 s.

The rated peak withstand current capability of the components in (a) and (c), and the prospective peak value of the first major loop in (b), is 2.5 times the AC component of the rated short-time current.

5.1.5 Rated normal current

Predominantly this class of switchgear is assembled into switchboards in association with circuit-breaker equipment. Accordingly, the rated normal current of busbars is chosen as described in Section 4.1 of this chapter for circuit-breaker equipment. The rated normal current of circuits is as declared by the manufacturer.

To allow for the longest likely starting time (run-up to operating speed) of direct-on-line motor drives, each circuit must be capable of carrying for 2 minutes, without damage, a current equivalent to six times its rated normal current. This is in addition to the temperature rise limits specified in the relevant British Standards, and also the constraint of 50 ° C under 'rated normal current' with respect to main circuit terminals.

5.1.6 Rated breaking current of switching devices

Each switching device has a rated short-circuit breaking current capability, in accordance with BS5311, having an AC (RMS) component of not less than the 'takeover' current of the highest rating of fuselink permissible in combination with the switching device. The 'take-over' current of the fuselinks is defined as the RMS value of the symmetrical component at which the pre-arcing time of the fuselinks is equal to the minimum opening time of the switching device. The opening time of the switching device is defined as the ti me elapsing between the instant of energisation of the trip coil and the instant of separation of the contacts, no allowance being made for the operating time of other protective equipment.

5.1.7 First-pole-to-clear factor: 1.5

380

i. 5.37 II kV air circuit-breaker shown withdrawn from the type of swiichboard illustrated in Fig 5.25

luawd!nba pasnj leabilowsns A1 EE

Switchgear and controlgear						Chapter 5

			CUBICLE TRIP BUTTON LINKAGE

		MIMIC DISPLAY		ARC CHUTE
		MIMIC DISPLAY

				SECONDARY
					CONTACTS
		In____\

					OPERATIONS
	AUXILIARY				COUNTER
	SWITCHES

AUXILIARY

SWITCHES

ANTI PUMPING

RELAY

OPERATING

HANDLE APERTURE

PIVOT WHEEL LOCK

ASSEMBLY

MANUAL

TRIP BUTTON

ARC CHUTE

SPLASH PLATE

CLOSING

CONTACTORS

\ tatofee

iticgactirg lai?

ilic

algititIttlii y

M■

CUBICLE RELEASE

MECHANISM

11MV BUSHING

RACKING IN CAM

OPERATING

SHAFT

AIR CYLINDER

ISOLATING MECHANISM

ASSEMBLY

TRIP COIL

MAINTENANCE

HANDLE SHUTTER

TRIP MECHANISM

FIG. 5.38 Front view of 11 kV air circuit-breaker shown in Fig 5.37 with covers removed

382

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