reading / British practice / Vol D - 1990 (ocr) ELECTRICAL SYSTEM & EQUIPMENT

fixed station two-channel transmitter outputs) and the received signals are connected via a combining amplifier to the two fixed station receivers (Fig 8.76).

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Flo. 8.76 Dinorwig power station, connection of fixed stations to radiating cables — block diagram

of channel 2 sited at the high altitude upper wat er reservoir.

•Radio channel 3 Transmission channel, coverin g the underground 400 kV switching station and 400 kV cable tunnel.

The fixed equipment operates from 110 V AC teed supplies (battery backed).

A block diagram of the radio system is shown o n Fig 8.77.

14.4.3 Handportable radiotelephones

Two-channel handportable radiotelephones (handpo r t. ables) are provided for use on the operations and maintenance channels and single-channel handportables for use on the transmission channel only. In accordance with CEGB regulations, the maximum output of th e handportable is 0.5 W effective radiated power (ERP),

14.4.4 Controllers

14.4.2 Radio channels

Three radio channels are used at Dinorwig power station. These are listed below, together with their function and area of cover.

•Radio channel 1 Operations channel (covers underground, external administration building, external lower reservoir area).

•Radio channel 2 Maintenance channel (cover as channel 1), but with facilities to extend to the upper water reservoir when mobile staff are working or travelling to/from the upper water reservoir. This is to minimise the broadcasting of station radio traffic over a wide external area from the antenna

The system has four controllers, with channel allocation in accordance with their function, as shown in Table 8.8.

Each controller has facilities to:

•Monitor the status and alarms of the fixed stations.

•Monitor the use of the system by other controllers.

•Select and monitor each radio channel.

•Control the use of talkthrough for each radio channel monitored (to enable handportables on the same radio channels to speak to one another).

•Interconnect radio channels.

•Broadcast on all radio channels.

•By-pass receiver voting control on each radio channel.

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•Provide loudspeaker, microphone or, alternatively, handset operation.

•Pro ,,ide indications that the fixed station is transmitting and modulating.

14,4.5 Fixed stations

l'i\cd station details are listed in Table 8.9.

Fixed station transmitters 1-6 operate in the quasisynchronous mode (synchronising of transmitter frequencies to prevent generation of audible interference by two signals of the same frequency but different phase) to minimise mutual interference in areas of transmitter overlap.

Receiver voting techniques are included in the scheme which routes the best received signal from a trans-

mining handportable to the controller monitoring the channel. The fixed station receher voting facility will switch from one fixed station receiver to another on receipt of a stronger signal when a transmitting handportable moves from one fixed station receiving area to another.

The common equipment cubicle, used by all systems, is located in the underground machine hall and is the local point of the system. All fixed stations and control units have direct circuits, albeit via 50 Hz isolation equipment if necessary, to the common equipment.

Most circuits between the common equipment cubic!e, the fixed stations and the controllers, are routed \.ia dedicated short-time fireproof multipair cables hich provide a minimum of 20 minutes security of operation at 1000 ° C in the event of a fire along the cable route. The circuits to the remote fixed station at the location of the upper reservoir, however, are routed via pairs in a CEGB pilot cable between the telecommuni-

cations room and the upper water reservoir equipment room.

14.5 Sound-powered telephone systems

I wo separate sound-powered telephone systems are provided at Dinorwig, which will operate if all electricity supplies in the underground plant areas and tunnels are lost.

One system is provided for use in the 400 kV cable tunnel and the other primarily for use between the above-ground station gatehouse and the underground areas, should other communication systems fail. The telephones, being dual purpose, are able to work with or without a power supply. Use of a power supply,

however, improves the quality of receked speech. -Ilk calling signal from a telephone is generated by a handcranked generator mounted in the telephone. The received calling signal operates a hooter mounted in the telephone.

14.5.1 System 1 — 400 kV cable tunnel system

This system is provided for operational and maintenance use. A telephone is fitted at each of the 400 kV cable joint bays, the locations at which repair work may be carried out.

All of the telephones in the cable tunnel are connected via discrete 25 kV isolation transformers to a common four-pair cable for parallel operation. The four-pair cable is extended to the sound-powered telephone equipment in the 400 kV switching station but electrically isolated from the tunnel by 25 kV isolation transformers.

The system equipment in the 400 kV switching station is powered from a 48 V battery supply for security of operation, which is converted to 110 V AC for transmission via the tunnel isolation transformers to all the telephones in the 400 kV cable tunnel, where it is then converted to 24 V AC. However, should the power fail, the system will function in the sound-powered mode.

A selector switch on each telephone enables the telephone user to ring either all tunnel telephones and the telephone in the transmission district engineer's office in the 400 kV switching station or the power station CCR. A call initiated from the power station CCR supervisor's desk will call all tunnel telephones and the transmission district engineer's office in the 400 kV switching station.

out the site for connection to the dispersed contractors offices and working areas.

The on-site requirements for telecommunications services to the contractor's premises is high and to some extent unpredictable. Provision must be made for adequate access to the site telecommunication services, as required, during the construction period. Flexibility to respond to all foreseeable requests during the construction period is important. The provision of ducts throughout the site enables additional multipair and/or fibre optic cables to be routed where required. Some contractor's working areas are re-occupied during the construction period and their needs may be completely different from the previous occupiers. Furthermore, legislation affecting telecommunication services is evolving which sometimes requires alterations to existing telephone cabling. It is not easy to reinforce, or change, telephone cable routes on a construction site which could involve unplanned excavation or (as in the past) the temporary provision of poles and overhead li nes, which are subject to damage by mobile cranes.

Underground duct routes of one, two and four 100 mm PVC ducts connecting into heavy duty carriageway boxes are provided. Carriageway boxes with robust removable covers ensure immunity from damage by contractor's loaded vehicles. The provision of strategically placed carriageway boxes and adequate spare duct space ensures flexibility of response to requests for changes to the telephone cable network.

15.3 Telecommunications systems and services

The following telecommunications systems and services are required for construction sites:

•PABX operated by the CEGB to provide on-site and off-site telephone services for all construction site personnel, i.e., CEGB, consultants and contractors.

•Emergency telephone system for reporting accidents, fires, plant emergencies, etc., to the gatehouse and/ or medical centre.

•Site emergency warning system.

•Pay telephones.

•Radio paging system.

•Site radio system.

•Handportable radiotelephone communications.

•Data, telex and facsimile services.

15.3.1 Private automatic branch exchange ( PABX)

It is present CEGB policy to provide a single PABX for all telephone services for a main construction site. The PABX provides all on-site and off-site telephone services for CEGB site staff, contractors and other site organisations. The PABX is located in the Main

Construction Site Office which, as previously stated, i s

the focal point for the site telephone cables to tractor's offices and working areas.

The PABX belongs to the CEGB and the use of the PABX and the cabling to the contractor's premises is provided by the CEGB as a free site service. 'On-sit e

only' telephone calls are also provided as a free site service. The contractors pay for the telephone equipment on their premises and also pay for all their

ing telephone calls to off-site locations, via the PSTN, The extent of use of the PABX telephone services by the contractor and the costs for which the contractor is responsible in respect of their use are detailed in his contract document.

The PABX will nowadays be a modern SPC telephone exchange, as described in Section 5 of this chap, ter, having connections to the BT PSTN and the CEGB CTN, and with facilities for connection to the remote main offices of the site major contractors. Routebarring arrangements on the PABX will restrict PABX telephone extensions from gaining access to direct lines to CEGB or contractor's remote locations, if a particular PABX telephone extension user is not permitted by current telecommunications legislation to use them. PABX telephone extensions restricted to on-site telephone calls only will be barred from access to the PSTN, CTN and other off-site telecommunication circuits.

15.3.2 Emergency telephone system

The emergency telephone system (ETS) is entirely separate from the PABX. The ETS telephone exchange is usually located in the construction site main 11 kV substation from which radiates all the 11 kV site supply cables to the dispersed on-site temporary 1 1 kV substations.

The telephone cables associated with the ETS also radiate from the 11 kV substation: they are installed and laid in the same trench when the II kV site supply cables are provided to the distributed 11 kV substations. The ETS telephone cables to each distributed 11 kV substation are terminated on a distribution box on the fence of the substation and an ETS telephone is installed on the substation fence wired into the distribution box. ETS telephones required in the working areas of the site are cabled to the nearest ETS distribution box.

The ETS common equipment in the main substation is powered from a battery supply having a minimum standby capacity of 24 hours.

It is CEGB practice to use a PAX for the ETS. ETS telephone extensions located at internal and external working areas are able to dial the security officers in the site gatehouse, or the medical centre, in the event of an emergency.

15.3.3 Site emergency warning system

A purpose built site emergency warning system (EWS) is provided, controlled from the site gatehouse and

• Fire first aid team — three signals of 0.5 s on and 0.5 s off, followed by a pause of 4 s before

repeating.

• Spare signals (use determined by Site Manager) — three signals of 2 s on, 0.5 s off, 0.5 s on, 0.5 s off, 0.5 s on, followed by a pause of 4 s before

repeating.

The transducers use pairs in the ETS telephone cabling

network.

Each transducer may be tested for correct operation from a nearby test pushbutton. The test button is act ated for use during the test at the gatehouse control panel.

15.3.4 Pay telephones

lay telephones provide direct access to the PSTN for !dephone calls to off-site locations but they require ad- ‘ance confirmation that the caller will pay for the call. l'sso types of pay telephones are provided on CEGB i.onstruction sites and associated worker hostel sites,

coin-operated and pre-paid card-operated. Insertion of the coin or card enables the call to be initiated and the cost of the call to be recovered from the appropriate number of inserted coins or by magnetic deletion oil the inserted 'phone card' of the appropriate number ol pre-paid call units. Telephone calls to the off-site BT l'SIN telephone operator service and the off-site public emergency services are available without the need to insert coins or a 'phone card', but on-site emergencies %% wild normally be reported to the on-site emergency , eo,ices using the ETS, PAX or PABX telephones.

Coin, and card operated pay telephones are usually prm ided and installed by BT, and the CEGB provides all necessary on-site facilities.

is required to provide kiosks, or appropriate accommodation, for pay telephones which are

It is necessary for the pay telephones to receive call charge pulses from the off-site BT PSTN telephone network to operate the coin payment and card payment equipment of the pay telephones. At sites having a rise of earth potential problem, the transfer of pulses through the isolation equipment fitted on all working pairs of the incoming BT telephone cable presents problems and special isolation equipment is necessary. Isolation equipment is not necessary on sites being served by incoming fibre optic cable.

15.3.5 Radio paging system

A radio paging system is provided for each construction site using techniques and equipment detailed in Section 7.3 of this chapter. The direct speech facility is not used.

The system is completely separate from the power station system. The two systems operate on different frequencies so that there is no mutual interference during the period when both systems are in use.

Paging is a particularly useful facility for the site staff, many of whom could be anywhere on the site. The facility provided by the pager alphanumeric display enables the paged person to respond to the call when convenient and allows the paging person to carry on with other work in the meantime.

The system should be capable of providing for the needs of all nominated site staff including CEGB, consultants, contractors, etc., who will benefit from its use.

Access to the system from the site PABX will enable the paging system to be used from most locations on site and the provision of good coverage of the site by one system only will justify the cost of additional slave transmitters and antennas.

In addition to access to the system from the PABX, separate direct access will be available by the site PABX operator who will also have facilities for pro-

viding limited changes to the system, e.g., to enable spare pagers to replace faulty pagers and respond to the same PARX pager code.

15.3.6 Site radio system

A radio system is prw,ided for construction site use and is completely separate from the systems provided tor the power ,;[zliion

The system is pro \ ided for use by the site security and medical teams and operates on UHF channels ;elected from the group of frequencies allocated to the Joint Radio Committee of the National Fuel Industries.

Fixed stations are provided at the construction site gatehouse or main sire office, and are operated by the security and medical staff, and the telephone operator. The fixed stations provide communication to all external areas of the construction site during the initial site preparation and, if necessary, are extended to indoor areas of the site by the use of one or more fixed stations also controlled from the gatehouse, site office or ambulance room.

The fixed stations operate to handportable radio telephones (handportables) carried by the security staff, the medical teams and other nominated staff.

Some site ambulance(s) have been equipped with hanciportable holders into which the handportables may be inserted when the medical staff are using the ambulance. This enhances the performance of the handportables and the signal received by the handportable is relayed through a loudspeaker unit in the holder. However, this arrangement has been found to be unreliable due to intermittent failure of the plug/ socket and is no longer recommended. A standard vehicle-mounted radio is nowadays preferred.

The radio system uses open channel working so that all handportables are able to monitor the transmissions from the fixed station and consequently be aware of all emergencies.

More recent systems use radio trunking techniques and handportable or mobile radios having pushbutton keypads.

The equipment and techniques used are detailed in Section 8 of this chapter.

15.3.7 Radio telephone handportables

Handportables for operation on the single-frequency si mplex channel of 169.050 MHz, as detailed in Section 8.2.4 of this chapter, are provided for local point-to- point communication on the site and for other commissioning purposes.

This VHF channel supplements the UHF handportable system for construction site security and commissioning purposes.

15.3.8 Data, telex and facsimile services

All major CEGB construction sites have art on-site computer for site management. Data circuits are pro-

vided to link the on-site computer to one or more of the major CEGB computing centres. The data circuits are either routed via the CEGB corporate data network (CDN) or via direct circuits rented from BT or MCL. Data terminals at the construction site have access to the local computer and some have direct access to the major CEGB computing centres.

Proprietary equipment is used for the data applications. The equipment is usually updated and/or replaced during the construction period to keep pace with current developments.

Access to the BT Telex Network and proprietary equipment is provided for sending and receiving telexes.

Proprietary facsimile equipment to operate via the CEGB Corporate Telephone Network and the BT PSTN is also used to transmit and receive visual information and documents at remote locations.

16 Future trends and developments

1 6.1 Connections to off-site telecommunication networks

Currently, the majority of CEGB power stations rely, for off-site telecommunications, on access to the British Telecom telecommunication network, the connections being made via BT multipair telephone cables to the power station, as described in Section 2 of this chapter. However, the requirements for telecommunication circuits to power stations are increasing dramatically and alternatives to existing practices are being considered, as listed below:

•The use of fibre-optic cables to replace or co-exist with telephone cables.

•The use of microwave links to replace or co-exist with telephone cables.

•Access to telecommunication networks other than the BT network, e.g., MCL networks.

The use of fibre-optic cables has the following advantages:

•Wide frequency bandwidth and high data transmission speeds.

•Using digital signalling techniques many circuits for data, telephony, telemetry, etc., may be carried on each fibre core.

•No conduction of the rise of earth potential during faults on the electrical system from the power station to the off-site telecommunication networks.

•Reduced space taken in cable ducts.

The use of microwave links also enables many circuits

the power station could include the Mercury Corn-

,,..),floritcd in the earth wire, or alternatively wrapped the earth %%ire, of the CEGB 400 kV and 275 kV

1,.w,iniion lines. This will eventually provide access to the network at most of the 400 kV and 275

othstations many' of which are co-sited at, or near,

\.•

Kill power stations.

16.2 On-site cabling

j ,2 ,A range of cables for telecommunications is being doeloped which is suitable for use at future nuclear 1,,mer stations. These are cables having a sheath which

• duees only a small amount of toxic fumes when it ', ur ns: they also incorporate an insulated single-core ,, r ih %%ire for remote earthing of telecommunications ,Httipment connected to the PABX system, for PABX

:.:lephones which use an earth recall facility for transfertelephone calls to other PABX extensions.

16.3 Telephone exchanges

\, detailed in Section 1 of this chapter, two telephone

... whanges, a PAX and a PABX are at present provided to ,,crve the needs of CEGB power stations. In addition, here is a separate automatic Private Control Exchange which is provided for Grid System Operations telephony purposes, details of which are included in

hapter 12 of this volume.

Consideration is being given within the CEGB to reducing the number of telephone exchanges in a power

,.][ion from the three mentioned above to either:

•No telephone exchanges, i.e., a PABX and PCX.

Ihe PAX would combine the presently-provided

PAX and PABX, with the PCX providing automatic telephone facilities for system operation telephony needs.

•One telephone exchange to serve all automatic tele-

phone needs of a power station and providing PAX, \BX and System Operation telephone requirements.

lio[h the above options may only be viable when the ( EGO becomes an 'approved maintainer' by the 'Department of Trade and Industry', so that full main- , :rt.ance of the telephone exchanges may be carried out. This would enable CEGB staff to exercise control of :h ,! maintenance and to carry out repair work should lie equinment fail, thus minimising the outage time

the equipment. Approved maintainer status would " 1 ■0 enable work to be carried out by CEGB staff if ti(Itistrial action is being taken by the existing licensed

'approved maintainers' (public network contractors and PABX manufacturers). The CEGB as an 'approved maintainer' would thereby be able to provide the service which at present is only permitted on the PAX.

16.4Radio systems

The radio systems used in power stations, which are described in Section 8 of this chapter, have been de- ‘eloped since radio speech communication for rco.ing, power station staff was first introduced in the 1960s. However, much of the equipment is now obsolescent and ready for replacement. Also, in 1986, the Department of Trade and Industry advised the Joint Radio Committee of the nationalised fuel and power industries that the 12 UHF channels, which have 25 kHz spacing between adjacent channels allocated for the exclusive use of the industries, were to be changed by 1991 to 24 UHF channels having 12.5 kHz spacing, using the same UHF frequency spectrum. The channels had previously been used almost exclusively by the CEGB but other bodies of the fuel and power industries made known their intention to make use of these additional channels.

The CEGB set up a working party to consider their requirements and to report on what action should be taken. They reviewed the existing radio systems operated by the CEGB which generally use dedicated RF channels for particular functions, i.e., operations, maintenance, security, emergency, etc., and also the use of trunked radio, the technology for which has recently become available. Of the systems considered by the working party, the trunked system offered the most effective way of providing the presently perceived needs of the power station user for medium and large stations. It was also considered that small stations would use the same basic radio equipment without the trunking operation, which is not suitable for less than five radio channels.

16.4.1 Trunked radio system

The working party agreed that a multichannel trunked system, using one dedicated channel for signalling/ control and the remaining channels for speech traffic, would be most suitable for large and medium power station use. All user groups would have access to all speech channels, thus optimising total system use.

The system would comprise three sub-systems, i.e., antenna system, fixed station/control equipment and radiotelephones, each of which is to be discrete to facilitate alternative provision of supply. Figure 8.78 shows a block diagram of the system.

To originate a call, a roving user would switch on his handportable radio telephone and seize the control channel. The control channel would allocate a free speech channel to the mobile user and transmit a code back to the roving user's radiotelephone to switch it to the free speech channel. The roving user would then receive a dial tone. The roving user is then able to

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key the required control point or direct telephone (connected to the central control unit or radio FAX unit), or key a telephone extension on the power station FAX or PABX.

A call for a roving user would be routed via the central processor unit, which will allocate a free speech channel and transmit a code on the control channel to alert the roving user and also to switch the handportable to the allocated traffic channel. The traffic channel would be held until the originating caller releases the call or, alternatively, the call may be released after a pre-programmed time-out period.

It was also agreed that the following applications would apply to all stations:

•Plant operation.

•Plant maintenance.

•Fuel and waste handling.

•Station services/safety.

•Security.

•Fire.

•First aid.

•Visiting personnel/contractors.

In addition, for nuclear stations, there would be a health physics application. The various user requirements are listed below.

Radiotelephones

•Keypad.

•Pre-programmed single-button call to user's control point.

•Abbreviated keying of users contacts simulated dedicated channel.