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Vol D - 1990 (ocr) ELECTRICAL SYSTEM & EQUIPMENT

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-411411pPP"

					Fuel oil plant
o	10,37 shows the fuel oil system at a 2000 MW,				supplies and allows for the routine maintenance of
Figure					pumps.
-	station designed to handle fuel oils delivered
owe r		vary ing in viscosity from 24 x	10-6	to	Pump drives are 415 V three-phase 50 Hz squirrel-
ship an d
	10 -3	rn 2 ,'s (24-1500 centistokes) at minimum			cage induction motors, totally-enclosed, fan cooled
	temperature. Electrical trace heating is provided				and arranged for direct-on-line starting, using contac-
c h-e supPIY pipework and operates continuously when					tors. A minimum degree of protection of IP54 is pro-
111 hut the lightest (distillate) oils are being pumped.					vided, except for outdoor use when IP55 weatherproof
afl1	is used in the fuel-oil heaters to raise the oil				is normal.

.cmperature to that required for combustion, 140 ° C
, r heavy oil and 43 ° C for distillate oil. Unburnt hot					10.3 Oil heating
il from the burners is recirculated back to the storage

The choice of electrical or steam heating depends n the availability of steam and the economics of in- o/ ailing and operating the heating system. Electrical

:race heating is ideal for oil pipelines since the heat

needed to maintain the oil in a fluid condition is ely small. Because of the large quantity of oil in

,:orve tanks, steam or electric heating is viable and :he acailabtY of steam at the storage tank location is major consideration. Fuel oil heaters require a large

at input and steam heating, when it is readily avail- ahle at that location, is preferred.

10.2 Pumps

the design of the system and the number and rating 01 the pumps ensures maximum availability of oil

10.3.1 Tank heating — electrical

I mmersion heaters are supplied at 240 V from a 415 V three-phase and neutral supply, their position in the storage tanks being below the burner feed pump takeoff level to ensure that they remain immersed in oil at all times. The heaters are controlled by two thermostats connected in series with each other: one thermostat functions normally to control the heater supply contactor, the other is a safety device to trip the contactor when the oil temperature rises above the normal limit.

To ensure that operation of the safety device is recognised, it has to be manually reset.

10.3.2 Tank heating — steam

Steam flow to heating coils is regulated by thermostatically controlled steam valves, the arrangement of

KEY

:p.sPoRv E v POW OIL

MAIN FUEL OIL

AUXILIARY JETTY

RECIRCULATING

EXPORT FLOWMETEFI STATION

••••

FUEL OIL HEATER BANK 3

BOILER 3

YPOAT

METER

5_A , ON

FUEL OIL HEATER BANK 2

L_B_CILER 2

—

HOSE

CONNECTIONS

MIXING

VISCOMETER

CHAMBER

DOKh

MAIN

04.3

FUEL OIL PUMPS

— 1,41Doe,

FIRE

VALVE

-444

VALVE

RECIRCULATING

STRAINERS

PUMPS

BOILER TRiP

BOILER TRIP

VALVE

EXPORT

,77 .2

PUMPS

SPILL

CONTROL VALVES

-0-

R1.04—L

CONTROL

VALVE

FIG, 10.37 Fuel oil system

857

11,

Mechanical plant electrical services	Chapter 10

the thermostats being as described in the previous Section 10.3.1.

10.3.3 Pipe heating — electrical

Pipe heating is achieved by trace heating applied directly to the surface of the pipe or embedded in the thermal insulation. Directly applied systems can be supplied at 240 V 50 Hz, since they are protected against accidental damage by the thermal insulation. For safety, embedded cables are supplied at 110 V 50 Hz by a transformer which has its 110 V winding centre-tapped to earth. Temperature control is by thermostats equipped with contacts which operate to raise an alarm when the control temperature band is exceeded.

10.4 Storage tank instrumentation

Storage tanks are equipped with two high-level and two low-level proximity switches. The first high-level switch trips the filling pump, closes the inlet valve and initiates a remote alarm; the second initiates an extrahigh level alarm if the oil level rises substantially above the first switch. The first low-level switch initiates a remote alarm; the second initiates an extra-low level alarm and trips the oil heating supplies if the oil level falls substantially below that detected by the first switch. This maintains the oil level above the top of the outlet pipe.

Local and remote oil level and temperature indications are provided.

10.5 Valve actuators

AC motorised valves equipped with integral contactor gear are used in oil pipelines. Actuator motors are either totally-enclosed (TE) or totally-enclosed fan cooled (TEFC), squirrel-cage induction motors of weatherproof construction (IPW to BS4999) [2], suitable for operation on a nominal 415 V three-phase 50 Hz supply. Thermal protection is built into the motor winding in accordance with BS4999, part 72 [2]. The motors have high torque and low inertia, and are designed for continuous operation without injurious heating for one complete travel of the actuator or 5 minutes, whichever is the shorter, when the supply voltage is reduced to 75 07o nominal at 50Hz. This ensures high reliability in service throughout their design life of 30 years.

The actuators have a degree of protection to [ P65 of BS5490 [3] and are capable of operation in steam and dust laden atmospheres within the ambient conditions defined in BS5967 Part 1 [27] — operating conditions for industrial process measurement and control equipment — Class D1 (5 to 100% relative humidity, — 25 ° + 70° C).

Housed in each actuator enclosure are a 415 V threephase 50 Hz reversing-type contactor, toss of supplysingle phasing protection, a 415 V/110 V transformer providing 110 V AC control supplies, valve open/close/

stop controls, a remote/local control selection switch and open/close/stop relays for remote control. Po wer and control connections are carried in flexible cables from the actuator to a local termination box. Plu g and socket connections into the termination box facilitate the maintenance or replacement of the actuator without disturbing the fixed, armoured cable conne c . tions into the termination box.

Each actuator is equipped with a valve position indicator, a potentiometer for remote position indica_ tion and valve open/close limit switches for remot e control and indication purposes.

10.6 Lightning protection

A lightning protection scheme is provided for the oil storage tanks by conductors connecting the tank to earth electrodes.

11 Air compressors

11.1 General description of plant

Compressed air at various pressures and flow rates is produced by compressors, normally electrically-driven, to satisfy the requirements of control and instrumentation, dust plant jet-blowers and dust pumps, boiler sootblowing, automatic boiler control, boiler blowdown, turbine forced cooling, breathing apparatus and reactor purging as appropriate to the type of power station.

The main building complex of a power station is served by two primary compressed air systems — 'general services air' and 'control and instrument air'. Figures 10.38 and 10.39 show typical control and instrumentation and general service compressed air systems for a power station. The 'general services' system is designed for a flow rate of 0.4-1.0 m 3 /s at pressure of 7.2 bar, the 'control and instrument air' system for 0.2 m 3 /s at 8.5 bar. Certain plants remote from the main complex, such as those producing hydrogen and sodium hypochlorite, are provided with independent air compressor plant.

Control and instrumentation air system requirements are most stringent in respect of the quality of the compressed air produced and its integrity. A typical system consists of two or three 100% duty electricallydriven air compressors, each complete with air coolers and oil/water separators, feeding two independent air receivers and air dryer systems via a manifold.

A typical general services air system consists of two

50% duty electrically-driven air compressors, each complete with air coolers and oil/water separators, supply-

ing a common air receiver.

11.2 Air compressor drive motors

The drives are usually squirrel-cage induction motors. suitable for direct-on-line starting on 11 kV, 33 kV

858

Air compressors

[

DO-

5CLECTDR

PRESS,PE

, LOV.

AFT — PCCOLER

■•1•10

• 4-04-Q

APE

•■■•=4.

• ■• 1;;.4■. ■•

, N rERCO O LE R

Lf_L

PRE

TER

om■wm

NA , 7P

FIG. 10.38 Control and instrumentation compressed air system

. , r 415 V three-phase 50 Hz supplies, of totally-enclosed :n ,:ooled construction, as described in Section 2.2 this chapter. They drive the compressors through V-belts,or flexible couplings and gearboxes. The -belts and flexible couplings protect the motor from

Ju.),k loading and vibration.

11 .3 Heaters

I katers in compressed air driers and compressor oil '-alPs are either connected in balanced three-phase nks and supplied through electrically-held contactors 415 V three-phase 50 Hz or, for ratings up to ap-

proximately 3.5 kW, at 240 V single-phase 50 Hz. Heaters are equipped with dual thermostats, one for normal temperature control and the other acting as a safety device in the event of failure of the control system. The latter is manually reset and initiates remote and local alarms to warn of failure.

11.4 Automatic and safety controls

The compressed air systems are designed to operate automatically, all operating conditions, such as air pressures and temperatures, being continuously monitored. Plant start-up, shutdown and duty selection are per-

859

Mechanical plant electrical services

		r
	APS 2 I
APS 3		APS	TO DISTRIBUTION
APS 3		APS	SYSTEM
			SYSTEM


	DUTY SELECTOR
	PRESSURE SWITCHES

GENERAL SERVICE

WATER

FLOW	1— 1)**-----
I NDICATOR
AFTERC O 0LER	)

AIR

I NLET

	FILTER

0 FLOW		I- -0
I NDICATOR	SILENCER
	SILENCER

UNLOAD IEDR

COMPRESSOR

SUCTION

VALVES

FIG. 10.39 General service compressed air system

Chapter 10

SIGNAL LINE PROM OfHER --

RECEIVERS

TO 'DIRER

COMPREBsoRs

AND RECEIVERS

CCOLVG

FOR OTHER

COMPRESSORS

orm■ MAIN AIR

— CONTROL AIR

--- COOLING WATER

860

				Heating and ventilating plant

	d in the central control room and plant failure		When steam is available, it may be used as the heat
	vrne	e displayed there. Control panels situated	source for the system, otherwise electrical heating is
I
tiarnis ar			employed. The principal electrical requirements are
	to the compressors house all the alarms, indica-
,ioro and controls necessary for the maintenance and			outlined in the following sections.
	,:ontrol of the plant.
			12.2 Control gear
12 Heating and ventilating plant			The heating and ventilation system is supplied from a

			415 V three-phase 50 Hz motor control centre.		The
12.1 General description of plant			switchboard and control panels are located adjacent
			to the heating and ventilation equipment, and accom-
H	ing	and ventilation in a power station is provided	modate the controls and instrumentation necessary for
:or die following reasons:			the automatic operation and maintenance of the		sys-
•	To protect equipment rooms, such as telephone ex-		tem.	Essential controls and alarms are provided in the

	changes, during operation by creating a positive		central control room.
	pressure in the room to prevent the ingress of
	airborne dirt.		12.3 Classification of electrical equipment
	to ventilate equipment rooms, such as switchrooms,
•			Electrical equipment is specified to either Categories I
	and to maintain the air and equipment temperatures
			or 2 of CEGB specification US/12/50 [28] to suit the
	%vithin acceptable limits.
			application.
• To ventilate equipment rooms where emissions dur-
			Category 1 is defined as equipment, malfunction
	ing normal plant operation would create a hazard		or failure of which could be the primary cause of
	If allowed to collect, e.g., battery rooms.
			unwanted tripping or closing or the immediate loss of

• To maintain a stable environment for sensitive equip-			availability of primary equipment. Category 2 equip-
	ment such as computers.		ment is that which could have a direct or immediate
•	To ensure an acceptable working environment for		effect on the operational availability of primary plant,
			if another abnormality exists or arises before the defect
	pers onnel in offices, control rooms, etc.
			is remedied, or could cause operational inconvenience.
• To protect personnel from the effects of the acci-
			The more stringent requirement of Category I is
	dental release of hazardous substances into the air		specified in areas where loss of heating and ventila-
	during plant operation.		tion is not acceptable; namely computer rooms or, in
• To provide a hot water supply.			nuclear stations, locations where either, (a), heating
			and ventilating equipment fulfils a function essential
• To remove smoke in the event of a fire.
			to the safety of personnel or to the reactor in the

[eating and ventilation systems are designed to suit the			event of an incident, or (b), the failure of a fan or
			its standby could result in the loss of differential
, pecific		requirements of each power station. All use a
			pressure which exists for the purpose of containing

	iiibination of air-conditioning units, filters, cooling	airborne contamination or the maintenance of clean
	a:r and extraction fans, water-chiller units, air dampers,	airborne contamination or the maintenance of clean
	a:r and extraction fans, water-chiller units, air dampers,	conditions.
	:oiorised valves and water heaters.	conditions.
	:oiorised valves and water heaters.	Elsewhere Category 2 equipment is specified.
	The design requirements for heating and ventilation	Elsewhere Category 2 equipment is specified.
	The design requirements for heating and ventilation
	a typical power station are as follows:
		12.4 Drive motors

		Temperature, ° C			Relative	Air changes
			max	min	humidity, 0	per hour

t	o:tirol room		22	1 8	45-55	3
■	, inpuier rooms		22	18	45 - 55	27
		,Imment rooms	22	18	45-55	12
			22		45-55	12
( .,i‘le marshalling rooms			—	10	_	2
	•rtlerence rooms		22	1 8	40-60	17
i ..N)ratories			22	1 8	40 - 60	7
I !_ht workshops			22	1 8	40 - 60	7
I !_ht workshops			_	18	_	2
		workshops	—	15.5	_	2
\14:ri stores			—	13	_
			—	13	_

In general, drives for fans, pumps, compressors and damper/valve actuators are 415 V three-phase 50 Hz squirrel-cage induction motors, suitable for direct-on- line starting. All motors are totally-enclosed and have a minimum degree of protection of 11 3 54. Those situated outdoors and exposed to the weather or situated in areas protected by waterspray fire protection, have a degree of protection of IP55 weatherproof.

Motors driving contaminated air ventilation fans could, during routine filter replacement, be contaminated themselves. To minimise contamination in these circumstances, they have a degree of protection of IP55 and are capable of being totally overhauled onsite under strictly controlled conditions.

861

pro-

85 ° C.

Mechanical plant electrical services	Chapter lc)

12.5 Air conditioning units

Air conditioning units generally consist of a chiller unit, humidifier, airheater and fan,

12.5.1Chiller unit

The chiller unit and air cooled condensers form a sealed refrigeration unit. Included in the refrigeration system is a compressor, dri‘en either through a flexible coupling or via a multiple vee-belt by a 415 V three-phase 50 Hz totally-enclosed fan cooled squirrel-cage induction motor. Hermetically-sealed motors are not used since they preclude maintenance. When oil sump heaters are used, they are supplied at 240 V single-phase 50 Hz.

12.5.2 Humidifier

Steam generated by an electrode or electrically heated boiler unit, forming an integral part of the air conditioning unit, is injected into the air stream to increase humidity. Operation of the boiler is fully automatic upon demand from a humidistat located in the air intake.

12.5.3 Airheater

A battery of electrical heater coils, heats the air progressively as it is drawn into the air conditioning unit and is automatically controlled by an inlet- air thermostat in conjunction with a temperature controller.

12.5.4 Fan

A fan driven by a 415 V three-phase 50 Hz squirrel- cage induction motor draws air through the air conditioning unit.

rated at 240 V single-phase 50 Hz and connected i n balanced three-phase banks with the star point brought out for operation on a 415 V three-phase 50 Hz four. wire supply. Each heater is provided with a spare three. phase bank of elements for use during maintenance o n the duty elements.

12.7 Cabling and terminations

Each bank of heating elements is connected by flexible high temperature single-core cable to an adjacent ju nc- tion box which forms the interface with the fixed cable system. The flexible cables have silicone rubber insulation and heavy duty oil-resisting and flame-retarda n t rubber sheaths to BS6007 Table 5 [29] allowing a maximum continuous conductor temperature of

The cables are run in flexible conduit for protection.

12.8 Water circulating pumps

Duty and standby pumps are provided to circulate water through each group of water heaters. The motor control scheme is arranged for manual selection of either pump for duty running and automatic selection of the standby unit in the event of failure of the duty pump.

. A pressure switch in the inlet pipe to each water heater is connected to raise an alarm in the event of pump failure and to act as an additional plant interlock to ensure that water heater elements cannot be energised under no-flow conditions.

13 Fire fighting equipment

12.6 Water heating plant

Water heating equipment uses electric immersion heaters complying with the relevant British Standards and the following requirements.

Steel heater bodies are coated internally with an anticorrosive epoxy-resin coating to ensure a life compatible with that of the power station. Make- up water is provided from a header tank.

Each heater is provided with a pressure relief valve, an automatic air release valve, a water temperature indicator, inlet and outlet water isolating valves, a water drain valve, thermometer pockets in the inlet and outlet pipework, and water temperature thermostats to facilitate its commissioning and safe operation.

Twin water thermostats are fitted — a self-resetting control thermostat and a manually-reset safety thermostat which is set to operate at a higher temperature to safeguard against control circuit failure.

12.6.1 Heating elements

I mmersion heaters are of the tubular-sheathed type,

13.1 General description of system

Fire protection in a power station consists of the following systems:

•Waterspray and sprinkler systems.

•External fire hydrant system.

•Fixed foam pipework system.

•Fixed Halon 1301/system.

14alon 1301 bromotrifluoromethane (BTM) gas protection is installed in cable marshalling rooms, computer equipment rooms, instrumentation rooms and false floor voids below safety equipment. Each distribution system is designed to supply BTM gas to the scene of the fire from storage cylinders, the system being initiated either automatically by heat or smoke detectors, or manually.

Fixed foam pipework systems are provided to tect diesel and auxiliary boiler fuel oil tanks, diesel generators and transformers that are too remote to be served by the waterspray and mulsifyre systems.

Foam generators are provided at each location. A

862

an alarm

of one or

facilities. Plant status

							Fire fighting equipment

	raywater system, supplemented by hydrants, provides						initiates a local audible alarm upon detection of water
,p	within the main equipment areas and a						flow or loss of air pressure in the detector pipework.
,roteetion							The alarm at the central fire panel identifies the loca-
	f fire hydrants covers those areas not provided						The alarm at the central fire panel identifies the loca-
" ;	tern o						tion of the fire, allowing appropriate action to be taken
" ;	,h spraywater protection.						tion of the fire, allowing appropriate action to be taken
`"biesei_driven fire pumps supply water to a							to safeguard personnel and plant.
		trunk main. A separate fire hydrant ring					Plant status and alarms associated with the elec-
sr	r j "' a e ppliedr			by a combination of electrically-driven			trically-driven detector air compressors, including low
sr	i r; i s. :u
	diesel-driven pumps , to provide security of supply.						air pressure alarms, are displayed on the central fire
A"spraywater systems are divided into					wet	and dry	panel. Low air pressure and loss of air pressure in the
,,,ierns, In a			dry system, pressurised water is contained				detector system are sensed and raised as separate alarms
,,,ierns, In a							in order to differentiate between system faults (causing
0.,	control valves, held closed by a compressed air						in order to differentiate between system faults (causing
,	ern incorporating heat or smoke detectors. Upon						'l ow pressure') and fires (causing 'loss of pressure').
ic,e,:tion of a fire, air is released causing the control
, a k es to open and release water under pressure to the							13.3 Diesel-driven fire pumps
,prinkler heads. A wet system is permanently filled with							13.3 Diesel-driven fire pumps
,oter , which is released by detectors incorporated in							Several diesel-driven fire pumps are provided, each
he sprinkler heads, upon the occurrence of fire. Dry							of which is equipped with electrical starting gear and
,„ re ms are commonly employed outdoors, where freez-							a 24 V battery. Normally operation is automatic, the
no temperatures are likely.							pumps being started singly in sequence, initiated by
;	Four categories of spraywater system are provided						pressure switches connected in the water ring main and
	Four categories of spraywater system are provided						pressure switches connected in the water ring main and
o	meet differing requirements; namely,				waterspray,		set to operate sequentially as water pressure falls. When
o	rtsifyre, protectorspray and sprinkler. Waterspray is						a fire occurs and water is discharged from the ring
d l a rge volume, high intensity, fine spray system capable							main, the pumps are started in sequence until the
of emulsifying the surface of burning oil and is used							discharge flow is balanced by input and the ring main
	auxiliary boiler houses, on turbine oil tanks and						pressure is restored.
in other areas where oil fires may occur. Mulsifyre is							Trickleand boost-charging facilities are provided for
,i milar to waterspray but provides a less dense cover-							each 24 V starting battery. In addition to the battery
a(je and is used on oil-filled transformers and oil							charger controls, the local control panel contains bat-
	Protectorspray is a low velocity water spray						tery condition and charging indications, pump status
,,,tem to protect plant from external					fires, typical		indications and alarms, and manual starting controls.
c samples being hydrogen storage vessels.						Sprinkler	Manual starting controls and alarms are repeated on
systems are provided for the treatment of localised fires							the central fire panel.
in equipment rooms, switchrooms and cable flats.							Figure 10.40 shows the starting scheme for a typical
Coal plant conveyors are protected by a separate							diesel-driven fire hydrant pump. The design emphasis
dry- type sprinkler system. Control valves are main-							is to minimise the chances of the diesel not starting
!ained in the closed position by a compressed air system							when called upon to do so. To this end, the design
as described above and opened by the release of air							includes the following features:
caused by a detector operating in the event of fire.							• Duplicate 24 V batteries and chargers.
Extraction systems are installed to remove smoke							• Duplicate 24 V batteries and chargers.
Extraction systems are installed to remove smoke
generated during a fire to facilitate access and minimise							• Duplicate starting contactors.
any damage which may be caused by its presence. This							• Automatic starting with engine-cranking timer and
is particularly important in the event of cable fires							• Automatic starting with engine-cranking timer and
is particularly important in the event of cable fires							repeat-start feature.
..,hich can generate large volumes of highly toxic and							repeat-start feature.
..,hich can generate large volumes of highly toxic and							• Automatic disconnection of cranking circuits when
corrosive smoke.							• Automatic disconnection of cranking circuits when
							engine is running.

13.2 Controls and alarms

The spraywater system, fire pumps and detector air compressors are designed for automatic operation.

Local control panels for the diesel-driven fire pumps accommodate all the equipment necessary for automatic operation, duty selection and manual control

indications and alarms are dis- played on the local panels and are wired from repeater

contacts to a fire control panel located in the central control room.

The operation of a section control valve, as a result more detectors operating due to a fire, raises on the central fire panel and automatically

• Remote and local manual start facilities.

13.4 Air compressors

Automatically controlled electrically-driven air compressors are installed to charge the detector systems of dry installations. Compressors are started and stopped automatically to compensate for variations in detector pipework air pressure.

Compressors are installed in pairs and are designated main and standby. Each compressor is controlled by a pressure switch connected in the air supply line from the compressor to the protection system. The main compressor is started first and the standby unit is

863

Mechanic& plant electrical services	Chapter 10

240V 1 Ph . 50H z

	'Th/The—Y-1	, - The-rY1 240/50-50V
	ECT IF IF R-	RECTIFIER-
	CHARGER	CHARGER
	UNIT I	UNIT 2
*VE	-VE	-VE

-r•

MAIN

AUXILIARY

BATTERY

I BATTERY

CRANKING

MOTOR

AUTO START

LJl

MAIN STARTING

REPEAT

0- 0

CONTACTOR

START

UNIT

AUXILIARY

MANUAL START

STARTING

....rykigNTACTOR

0 0

@ ®

L. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

- - - - - - - - - _ - - - - -

FAILED TO START

TEST START PUSHBUTTON

I MANUAL START!

■I■■

RELAY

0 0

ENERGY START PUSHBUTTON

0 0

AUTO

START

TIMER

PUMP ON DEMAND

ENGINE RUNNING

RELAY

0--.-

r77:C

FAILED TO

START_

o 01—

CRANKING

TIMER

FAILED TO START

RELAY

■imm1

`4.r•y^r^.

TIMER

ENG INE RUNNING

SWITCH

ENGINE RUNNING

RELAY

0 0

REMOTE/AUTO START SWITCHES	PUMP ON
(OPEN TO START)	DEMAND
	DEMAND
FIWT111.	RELAY
FIWT111.

Flo. 10.40 Fire hydrant pump schematic diagram

864

					Fire fighting equipment

broileht into service if the air pressure continues to					Heat-detecting cables are of two types, integrating
		Dr i ve		motors are totally-enclosed fan cooled	and non-integrating, and are supplied at low voltage
	1	j ..	cage induction types supplied at 415 V three-		from a control unit. The insulation resistance of an
		;0 Hz from contactor switchgear.			integrating cable decreases progressively as tempera-
		-			ture increases whilst that of a non-integrating cable
					drops suddenly at a specified temperature. Reduction
13.5		Trace heating			of the cable insulation resistance to that appropriate
	,. ons o f			p ipework and valve manifolds which may	to the alarm temperature is sensed by a control unit
	.„: ,pose d			to low temperatures during the winter are	which raises an alarm and initiates the spraywater
	r i,:a		lly trace-heated and insulated. Trace heating is		system by transmitting an electrical signal to actuate
-					the thermoelectric quartzoid bulbs.
TTlied at 240 V single-phase 50 Hz and is thermo-
			c ontrolled as described in Section 5.2.7 of		Heat-detecting cable continuity and supply integrity
					are monitored continuously and an alarm is raised on
	c hapter.
					the central fire panel if either fails.
13,6 Detectors and distributors					13.6.3 Smoke detection

13. 6.1			Quartzoid bulbs		Smoke detectors are of the point type, using scattered
					or transmitted light, or alternatively an ionisation cham-
I he bulb of a detector contains a liquid which has a					ber. These devices are used on their own or in com-
			point below any natural climatic figure and a		bination with heat detectors in areas such as amenity
•0 rate of expansion with increase of temperature.					buildings, administration offices, workshops and stores
\ small amount of vapour is trapped when the bulb is					where large scale, rapidly-propagating fires are un-
.;:nrietically sealed. As the liquid in a bulb expands					likely. In these situations, the detection system is used
..2,1er the influence of heat from a fire, the pressure in					to raise alarms and to locate the fire, enabling manual
, e bulb rises until the vapour is absorbed by the liquid					fire fighting equipment to be deployed and the buildings
tni bursting pressure is reached. When the bulb					cleared of personnel.
.I:atters,			one of three actions occurs:

•Fhe compressed air is released in a detector line to initiate operation of a water control valve, or;

•5. valve installed in the water pipework leading to the distributors is directly operated, or;

•Water is released from a sprinkler.

I iier moelectric quartzoid bulb sprinklers are similar those described above, but include a 'one-shot'

. eator mechanism. An electrical signal from the

,ritrol cubicle of a heat-detecting cable system (see

,„tion 13.6.2 of this chapter) causes the actuator

. ,:,hanism to operate, shattering the quartzoid bulb

.rsi releasing spray water. If the 'one-shot' actuator fails

• operate, the bulb will burst under the influence of from a fire, as previously described.

13.6.2Heat-detecting cable systems

fear -detecting cable systems are installed extensively -.Power stations in cable tunnels and cable flats, where

ne nature of the materials installed requires that fire s detected' and treated with a minimum of delay to :nit the damage to plant and the danger to personnel. tnese systems respond far more quickly than is possible

— mg conventional quartzoid bulb heat-detectors and

'nuke detectors.

In cable installations, the heat-detecting cable is 'iNPended above the cables and under the cables im-

-nodiately above the floor to provide rapid response to "olh cable and external fires.

Ionisation chamber detectors consist of a chamber in which a radioactive source ionises the air and causes a small detectable current to flow between charged electrodes. The magnitude of this current is proportional to the level of ionisation within the chamber which is reduced by the presence of the particulate matter in smoke.

Optical smoke detectors contain photoelectric devices which are sensitive to changes in the level of monochromatic light received either by direct transmission from the source or indirectly by scatter. Particulate matter in smoke varies the level of light falling on the photocell and hence the level of electrical signal flowing through the device.

A common control unit supplies the smoke detectors at low voltage and monitors the level of signal continuously to detect any variation indicative of the presence of smoke at a detector head. To prevent spurious operation, a time delay of between 2 and 10 seconds is built into the alarm-initiating circuit. If the alarm condition exists at the end of the timed period, the control unit initiates audible and visible alarms locally and on the central fire panel and indicates the location of the detector head which has operated.

Automatic supervision of detector electrical circuits and supplies is incorporated in the control unit.

A typical smoke detector system is shown in Fig 10.41.

865

Mechanical plant electrical services	Chapter 10

	KEY	RELAY	RELAY
	BREAK GLASS	RELAY	RELAY

I
I	CALL P DINT
0 DETECTOR			7 r	OUTPUTS T0
			7 r


				FIRE PROTECTION
				FIRE PROTECTION
				SYSTEM FOR EACH ZONE
		RELAY		SYSTEM FOR EACH ZONE

OUTPUTS TO CCR FOR

ALARM AND FAULT INDICATION

POWER SUPPLY UNIT

24 V D C

POWER UNIT

1 0 V A C

RELAY

UNINTERUPTA8LE

CONTROL UNIT

POWER SUPPLY

BELL

RELAY — MONITORING — RELAY

240 V

No I

UNIT

No 2

240 V D C

21 V D C

ZONE 2



		LJ
		LJ
		ZONE I				ZONE 4 ETC.
=ID		ALARM
		BELL
					ZONE 3
	ALARM BELLS		DETECTORS AND CALLPOINTS
			DETECTORS AND CALLPOINTS
				(UP TO 32 ZONES)

FIG. 10.41 Smoke detection system

13.7 Fire dampers and smoke extraction

To prevent the spread of fire and smoke by ventilation and air conditioning systems, dampers are incorporated to shut off the ducts in the event of fire. These dampers are closed either electrically by the heat or smoke detection system, or mechanically by the operation of heat- fusible links. They remain closed until manually opened when the fire has been extinguished. The dampers form

part of a smoke extraction system and are operated in conjunction with extraction and ventilation fans.

13.8 Control cabling

Connections between control units, fire detector heads, control valves, manual alarm-initiating devices and other equipment essential for the operation of the fire

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