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

[he iests need not be carried out immediately follow- lu g each other. 80% are carried out with the engine

in its standby (kept warm) condition and 20 07o are carried out at the hot equilibrium condition.

•The reasons for any failures to start are noted and hc CEGB requires additional start tests if 50

consecutive successful starts without failure are not achieved.

5.4.3 In-service operational testing

In order to ensure that diesel generators are at all ti mes available for their emergency role and able to carry their rated load, periodic testing at intervals not greater than one month is carried out.

Each diesel generator in turn is started manually and synchronised as described in Section 5.3.3 of this

chapter, and loaded up to its full rating. Any surplus generation over and above that required by the station auxiliary system is exported to the Grid system. The unit is left running until all conditions have stabilised and to allow the operators to check that all auxiliaries are running correctly. Where appropriate, failures of duty auxiliaries are simulated to ensure that changeover to standby auxiliaries takes place correctly, after which service is either restored to the duty auxiliary or the standby unit is changed over to the duty auxiliary.

Such tests at nuclear power stations are fully recorded for inspection by the Nuclear Installations Inspectorate.

It should be noted that throughout the test, the diesel generator can take up its emergency role immediately, the test being terminated by automatic means (see Section 5.1.1 of this chapter).

6 Additional references

E/ESS/EX. 32000: Technical Specification and Schedules for Seismic Qualification or Electrical Plant

CEGB Standard 239903: Piping systems — Low pressure water services

CEGB Standard 23992: Piping systems — Oil services

CEGB Standard 20752: Fuel oil storage tanks

CEGB Standard 989907: Noise limits for new power stations [SI 44-3: Electric Motors Specification 3300 V and above

EFS 1980: CEGB General Specification for electronic equipment Smith, G.: Storage Batteries: Pitman: 1971

6.1 British Standards (BS)

/35417: Specification for galvanised mild steel cisterns and covers, tanks and cylinders; Part 2, Metric units: 1973

BS440: Specification for stationary batteries (lead-acid Plante positive type) for general electrical purposes: 1964 (withdraun and replaced by BS6290)

BS799: Specification for oil burning equipment; Part 5, Oil stora ge tanks: 1975

BS806: Specification for design and construction of ferrous pipi n2 installations for and in connection with land boilers: [986

BSI 123: Specification for safety valves, gauges and other sa cetv fittings for air receivers and compressed air installations 1976

BS2594: Specification for carbon steel welded horizontal cylindrical storage tanks: 1975

BS2757: Method for determining the thermal classification of electrical insulation: 1986

BS2869: Specification for fuel oils for oil engines and burners for non-marine use: 1983

BS3605: Specification for seamless and sselded austenitic stainless steel pipes and tubes for pressure purposes: 1973

BS4675: Mechanical vibration in rotating machinery: 1978

BS4999: Specification for general requirements for rotating electrical machines:

Part 3: Terminal markings and direction of rotation: 1981

Part 20: Classification of types of enclosure: 1972

Part 21: Classification of methods of cooling: 1972

Part 40: Characteristics of synchronous generators: 19 7 2

Part 51: Noise levels: 1973

0S5000: Specification for rotating electrical machines of particular types or for particular applications; Part 99, Machines for miscellaneous applications: 1973 (1981)

BS5169: Specification for fusion welded steel air receivers: 1985

BS5311: Specification for a.c. circuit-breakers of rated voltage above 1 kV: 1976

BS5514: Reciprocating internal combustion engines: performance

BS6290: Lead-acid stationary cells and batteries: 1983/84

introductio n

2 General requirements

2 1 Sources of supply

2 /.1 Choice of supply

2.1 2 Supply variations 2! 3 Applications

2 2 Motors

2 2.1

Motor ratings and supply voltages

22 2 Design standards

22 3 AC motors

2 2 4 DC motors

2 3 Safety considerations

2 3 I General requirements

23 2 Equipment enclosures

2 3 3 Control and trip circuits

2 3.4 Interlocking

23 5 Emergency trip controls

2 6 Switchgear and contactor gear

2 7 Radio and television interference

2 8 Noise levels

3 Cranes

3.1 General

3 2 Power supply and distribution

33 Crane motor drives

3 3 1 Motors

3 3.2 Motor protection

3 3 3 Motion control - direction

3 3 4 Motion control - speed

33.5 Braking systems

3 4 Control station systems

3 4 1 Cab control

3 4 2 Radio control

3 4 3 Pendant control

3.5 Crane controls, interlocks and limit switches

35.1 Control equipment cubicles

3 5 2 Protective panel

3 5.3 Limit switches

3 6 Anti-collision system

37 Travel motion supply systems

3 7.1 Long travel

3 7.2 Cross-traverse

37.3 Alternative supplies for long travel

38 Crane earthing

39 Crane services

310 SPecial features required for nuclear plant cranes

3 10.1 Duty categories

3 10.2 Design requirements

4 lifts

4 1 Types and general requirements

2 Supplies and distribution

4 3 Motor room equipment

4.4 Lift drive systems

4 4-1 Electrical

4 4.2 Hydraulic

4.4.3Motor protection

4.4.4Brakes

4.5Lift car and landing equipment

4.5.1Landing control facilities

4.5.2Car control facilities

4.5.3Car lighting

4.5.4Telephone

4.5.5Maintenance facilities

4.6 Safety devices and systems 4.6.1 Fireman's control system 4,6.2 Flood control system 4.6.3 Travel interlocks

4,6.4 Lift car emergency hatch

4.6.5Audible alarm

4.7Lift shaft lighting

4.8Earthing

5 Gas producing and storage plant

5.1Introduction

5.2General requirements

5.2.1Safety assurance and standards

5.2.2Lightning protection

5.2.3Motors in hazardous areas

5.2.4Switchgear and contactor controlgear

5.2.5Control and instrumentation equipment 5.2,6 Transformer/rectifier equipment

5.2.7Frost protection

5.2.8Earthing and static protection

5.3 Hydrogen producing plant - electrolytic cell process

5.3.1General description of plant

5.3.2Classification of plant areas

5.3.3Electrical, control and instrumentation equipment

5.4Hydrogen producing plant - methanol chemical reaction

5.4.1General description of plant

5.4.2Classification of plant areas

5.4.3Electrical, control and instrumentation equipment

5.5Methane production plant

5,5.1 General description of plant

5.5.2Classification of plant areas

5.5.3Electrical, control and instrumentation equipment

5.6Nitrogen storage plant

5.6.1General description of plant

5.6.2Electrical requirements

5.7Carbon dioxide storage plant

5.7.1General description of plant

5.7.2Electrical requirements

6CW electrochlorination plant (sodium hypochlorite production and storage)

6.1General description of plant

6.2Classification of plant areas

6.3Electrical, control and instrumentation equipment

6.3.1General

6.3.2Production control panel

6.3.3Sea water feed pumps and strainers control

6.3.4Transformer/rectifier controls

6.3.5Sodium hypochlorite storage

6.3.6Dosing pump controls

6.3,7 Electrical distribution

7 Water treatment plant

7.1 Description of plant

1 Introduction

This chapter describes the main electrical requirements of ancillary mechanical plant in a modern power station. Such plant, whilst not directly associated with the main generating units, is essential for the operation of the power station. It includes cranes, lifts, gas production and storage, electrochlorination, water treatment, coal ash and dust plant, precipitators, fuel oil, air compressors, heating and ventilation, and fire protection.

2 General requirements

2.1 Sources of supply

2.1.1 Choice of supply

The electrical systems of ancillary mechanical plant are fed from the power station electrical auxiliaries system to suit the specific requirements of the plant in terms of load, security of supply, limitations on

supply voltage and local distribution requirements. The supplies may be AC, taken directly from main switchboards or distribution boards (which may be located either remote from or local to the plant), or DC from the DC distribution system. The DC distribution system is supplied by battery systems incorporating charging equipment supplied from the electrical auxiliaries system.

The following supplies are available in most modern power stations:

•11 kV, three-phase, 50 Hz, resistance earthed, with a maximum symmetrical short-circuit fault level of 750 MVA (39.4 kA).

•3.3 kV, three-phase, 50 Hz, resistance earthed, with a maximum symmetrical short-circuit fault level of 250 MVA (43.8 kA).

•415 V, three-phase and 240 V, single-phase, solid- earthed, 50 Hz with a maximum symmetrical short circuit fault level of 31 MVA (43.8 kA).

,

• 110 V, single-phase, 50 Hz, one pole solidly earthed from one or two sources, for instrumentation supphes.

battery float voltage but which may fall to a value

`:,iderably

esent lower than the rated battery voltage in of charger failure, as the battery discharges.

+roltage ranges and variations are as follows:

•240 V, single-phase supplies are used for miscellaneous small power requirements, including lighting, heating and motor drives up to 0.75 kW.

•110 V, single-phase instrument supplies are used for control and instrumentation needing high availability but which can tolerate short breaks of up to 10 ms in the event of supply changeover or system disturbances.

•110 V, single-phase centre-tapped supplies are used to supply portable tools through socket outlets, where personnel safety considerations require a maximum voltage to earth of 55 V.

•DC supplies are used when supply interruptions are unacceptable, control supplies being at either 110 V or 48 V and motor supplies at 240 V DC.

2.2 Motors

2.2.1 Motor ratings and supply voltages

Motor ratings comply with the relevant British Standard. For power station requirements, motor ratings and supply voltages are categorised as follows:

Up to 0.75 kW — 415 V, three-phase, 50 Hz occasionally

240 V, single-phase, 50 Hz

110 V, single-phase, 50Hz

250 V DC and 110 V DC, battery or rectifier derived.

0.75 to 150 kW — 415 V, three-phase, 50 Hz

250 V DC and 110 V DC, battery or rectifier derived.

Above 150 kW — 11 kV, three-phase, 50 Hz

3.3 kV, three-phase, 50 Hz

DC supplies derived from rectifier equipment.

2.2.2 Design standards

The basic requirements for motors associated with ancillary mechanical plant are the same as those applied

for main plant auxiliaries and are based upon the appropriate British Standards, as qualified by CEGB standards. Typical main plant auxiliary-drive requirements and the selection of motors are discussed in detail in Chapter 7. An outline of the requirements applicable to the majority of motors is given below.

Rating up to 0.75 kW

General design is in accordance with BS5000 Part 11(1].

Motors are continuously rated in accordance with BS5000 and suitable for continuous operation in 40 ° C ambient, Winding temperature rises are in accordance with BS5000 [1], except that Class B temperature limits (130 ° C) are applicable, even though Class F insulation may be used.

Motors are capable of three consecutive starts, fifteen starts per hour and of operating under varying supply conditions, as follows.

AC motors and DC motors fed from rectifier equipment must operate continuously at rated load with supply frequencies of 48 to 51 Hz and voltage variations of +6% of nominal, and must also be capable of short term operation under emergency conditions with supply frequencies down to 47 Hz. In addition, when specified for essential duties, motors must operate continuously at 75% rated voltage and 50 Hz frequency for periods up to 5 minutes and be capable of recovery to normal operation following a supply interruption lasting up to 0.2 s.

DC battery-fed motors are required to operate continuously with supply voltage variations of +10% of nominal and for up to 30 minutes at 80% of nominal.

Motor enclosures are built to one of the following standards, as classified in BS4999 (21:

•Drip proof to IP22 — protected against solid ob-

jects greater than 12 mm and dripping water when tilted up to 15 ° .

•Totally-enclosed to IP54 — protected against dust and splashing water.

•Totally-enclosed fan-cooled to IP54 for indoor use and 1P55 — protected against dust and water jets

—weatherproof for outdoor use.

Ratings above 0.75 kW and up to 150 kW

General design is in accordance with BS5000 Part 40 [l].

Motors are suitable for continuous operation in 40 ° C ambient. Winding temperature rises are in accordance with BS5000 [lb except that Class B temperature limits (130 ° C) are applicable, even though Class F insulation may be used.

Motors are capable of two starts in succession, followed by a 30-minute cooling period before another attempt at starting is made, and of three equallyspaced starts per hour under normal running condi-

tions. Also, they must be capable of starting when the supply voltage is 80% of the nominal.

Windings and insulation are designed to have a minimum life of 18 000 starts and bearings are designed for 40 000 hours' running.

The AC and DC supply variations which the motors are required to operate under are the same as thos e described above for motors rated up to 0.75 kW.

AC squirrel-cage induction motors are started direct_ on-line at rated voltage. Pull-out torque is specified as not less than twice full-load torque for all induction and commutator motors.

Most motors have a maximum continuous rating ( MCR). When appropriate, motors may have a duty type rating (DTR) or short term rating (STR).

Motor enclosures are built to one of the followin g standards as classified in BS4999 [2]:

•Drip proof to IP22.

•Totally-enclosed to IP54.

•Totally-enclosed fan-cooled to IP54.

•Totally-enclosed air-cooled with an integral heat exchanger to IP54.

•Totally-enclosed air-cooled, with a machine-mounted heat exchanger to IP54 for indoor use and 11 3 55 weatherproof for outdoor use.

The maximum rating of 415 V, three-phase 50 Hz motors is generally 150 kW. These motors are controlled by contactors incorporating overload protection and protected against short-circuit by fuses.

Ratings of ISO kW and above

General design is in accordance with BS5000 Part 40 (lb

The operational requirements for this range of motors are generally as described above for ratings above 0.75 kW and up to 150 kW, except that machines of 1500 kW and above are totally-enclosed, closed air circuit, with water-cooled heat exchangers, either machine or separately mounted. The maximum cooling water temperature is specified as 30 ° C.

All 11 kV motors are protected by circuit-breakers. 3.3 kV motors are protected either by motor switching devices incorporating fuse protection or by circuit' breakers. Circuit-breaker-fed motors are equipped with terminal boxes capable of withstanding the full system three-phase symmetrical fault level.

2.2.3 AC motors

Cage induction motors

Three-phase cage induction motors are the most widely used for ancillary mechanical plant demanding stant - speed drives because of their low cost and high reliability. They are discussed in detail in Chapter 7.

control and instrumentation cubicle, is supplied from the 110 V AC instrument supplies system.

Equipment requiring guaranteed supplies for control purposes, such as switchgear and contactor gear, is connected to the station 110 V DC or 48 V DC distribution systems.

Equipment which can accommodate the occasional supply interruptions and variations in supply voltage and frequency detailed in Section 2.1.2 of this chapter, such as crane control equipment, is normally supplied from integral 110 V transformers.

Control circuits incorporate a 'test' selector switch to enable functional checks to be made in the control circuits without operating the plant. This is important, since it not only permits routine checks to ensure the correct operation of the equipment but also verification that protection and safety interlock circuits are functioning correctly.

Switchgear closing circuits are connected through 'plant protection interlock contacts' which ensure that the plant can only be started when in a safe condition.

Switchgear trip circuits are connected through 'plant protection trip contacts' which complete the trip circuit in the event of plant malfunction, or of a plant condition arising which could jeopardise the safety of operation. Also connected into the trip circuit are contacts on plant protection devices, which operate to complete the trip circuit in the event of a fault developing on the equipment. The 'plant protection trips' and 'plant protection devices' are fundamental to the safety of the plant and are either connected in such a manner that their failure will cause the plant to trip, or, as in switchgear circuits, the protection contacts are wired in a manner which enables the integrity of the wiring, connections and supply to them to be continuously monitored by a supervision relay.

2.3.4 Interlocking

Interlocking takes two forms; mechanical and electrical:

Electrical interlocks include limit switches, pressure switches, position switches and transducer contacts which continuously monitor the state of the plant, and are connected into the control circuit to ensure that the plant can only be operated in a correct sequence, and in safety. These circuits also include circuit-breaker, contactor and relay position contacts, which are crossconnected into other circuits in the control system to ensure that the correct electrical control sequence is followed, subject to the plant state being proved correct by the interlock contacts.

Mechanical interlocks take the form of linkages, cams or other mechanisms which prohibit the operation of a device when it is unsafe to do so; for example, by preventing a cubicle door being opened if the supply disconnector is 'on', or by preventing a non-load- breaking disconnector from being switched 'off' when the associated contactor is 'on'. When it is required

to interlock between different items of plant or devi ces to ensure that they are operated in the correct sequenc e or combination, coded-key interlocks are widely used Used either singly, or in conjunction with key-exchange boxes, they ensure safe operation and also 'authorise' plant operation and access for maintenance.

2.3.5 Emergency trip controls

Since the majority of power station plant is unattended, it is not general practice to locate emergency trip c on _ trols adjacent to drive motors or plant but rather to incorporate such devices in the control station, which may be either local or remote. Interlocks and strict Operational safety procedures ensure that safety is mai n _ tamed during both normal operation and maintenance .

An emergency trip device normally consists of a red mushroom-headed push-to-trip button, with an integral shrouded or key-operated trip release device to ensure that a deliberate action is necessary for the operato r to reset the trip circuit.

2.4 Environmental conditions

2,4.1 Ambient conditions

The design of the equipment has to include adequate protection against the ingress of water and solids, and be suitable for continuous operation over the full range of ambient temperatures or, if the equipment is subjected to radiant or conducted heat, at the maximum operating temperature likely to occur in service.

In the interests of standardisation, equipment is generally specified in three classes, as follows:

Applies to equipment located indoors in a non-corrosive atmosphere, in which the ambient temperature range is 0 ° C to + 40 ° C. Enclosures are protected against falling dust to 1P30 of BS5490 [3].

Ambient Class 2 Applies to outdoor equipment in a corrosive atmosphere, in which the ambient temperature range is — 25 ° C to + 55 ° C. Enclosures are protected against airborne dust to IP44 of BS5490.

Ambient Class 3 Applies to equipment in special situations where the atmosphere is corrosive and the ambient temperature range is — 10 ° C to +70 ° C. Enclosures are protected to IP55 of BS5490.

For most power station equipment,

is provided for indoor use and Ambient Class 2 for outdoor use, where it may be subjected to sunlight, wind, rain, snow or freezing conditions. For harsh en - vironments, such as boiler houses, equipment is specified to Ambient Class 3, in view of the greater risk of water and dust ingress and the wider operating temperature range. Exceptionally high conditions of

such as may be found underground, are

1 1 1 i d it Y 'd individually and treated as special cases.

,h,".,1 ,' i d e r e

IrLiuipment for use in hazardous areas complies r h e requirements or 13S5345 [5], which classifies

,is zone 0, Zone 1 or Zone 2,

-

An area in which an explosive gas/air mixture is continuously present or present for long

periods.

An area in which an explosive gas/air mixture is likely to occur in normal operation.

An area in which an explosive gas/air mixture is not likely to occur in normal operation and, if i t occ urs, will exist for only a short time.

\I] areas not classified as Zone 0, 1 O r 2 are deemed be non-hazardous.

2 4.3 Nuclear environments

i icior buildings at nuclear power stations present environmental conditions which have to be n into account in the design of electrical equipment

, r Incillary mechanical plant.

11.ic equipment is designed to operate in the envi- -ormental conditions which occur when the reactor is commissioned, on-load or shut down for main- ',N,ince. In addition, the possibility of reactor system or seismic disturbances is considered and the

.,;I:prncru designed accordingly, having regard for the Iserutional role of the equipment during and following

•ern.

l'n%ironmental conditions to which equipment may

.. .....:\po ,;ed during its operating life are dependent upon Joign of the reactor system and the location of

equipment. In addition to the temperature radiation lewls and humidity range occurring

7ing normal station operation; short-term large varia-

• , t1N in temperature, pressure and radiation levels may during maintenance or reactor system faults.

2.5Electronic equipment

[ eli ,,ure that electronic equipment is of consistent

•;i1J.Ird and suitable for operation in a power station

.•.%ironment, the CEGB has its own specification, EES ".)), [61 v.hich lays down basic design parameters

.t .1 irinent type tests. Electronic equipment is classi-

•J Jecording to its environment — Class B3/X for -door equipment and Class Cl/X for outdoor equipRequirements appropriate to these classifications

."e ii)ulated in the specification. Because of the

''''' 051 1Y of electronic equipment to its environment,

General requirements

these classifications cover environmental temperature, humidity and levels of electrical interference to which the equipment may be subjected during operation.

Equipment may be subjected to radio frequency and cable-borne interference. Common causes of radio frequency interference are portable radio transmitters, fluorescent lamps, DC relay operation and the switching of AC supplies. Cable-borne interference reaches equipment in both power and signal lines as a result of coupling at the source and between cables, the main cause being the rapid change of current due to switching and fuse operation. EES (1980) [6] specifies tests designed to demonstrate that equipment is unaffected by levels of interference appropriate to the environmental classification.

Environment Class B3/X covers a temperature range of — 5 ° C to + 40 ° C, a humidity range of 5 07t1 to 95 000,

and mild levels of radio frequency and cable-borne interference appropriate to control/equipment rooms and other areas associated with power generation plant.

Class Cl/X caters for a temperature range of — 25 ° C to + 55 ° C, humidity up to 100% and interference levels si milar to Class B3/X.

2.6 Switchgear and contactor gear

Switchgear and contactor gear for use with mechanical ancillary plant is provided to the same standards and specifications as that used elsewhere in the power station, and is described in Chapter 5.

2.7 Radio and television interference

All electrical equipment is designed to restrict radio interference to the limits specified in British Standard BS800 [7].

2.8 Noise levels

Maximum levels of noise are specified which (a) satisfy the recommendations laid out in the Department of Employment 'Code of Practice for Reducing the Exposure of Employed Persons to Noise', (b) are consistent with the established limits of person-to-person and telephone communication, and mental concentration, and (c) are consistent with the limits of noise transmission which can be achieved at reasonable cost, to areas beyond the power station boundary.

The specified limits in noise level are outlined below:

Local- to-plant Surface noise level local-to-plant measured at a distance of 1 m from the plant surface is 93 dBA maximum for plant generally and, for plant provided with a noise enclosure, 90 dBA maximum at the enclosure surface and 110 dBA inside the enclosure (if access is necessary when the plant is operational).

Control rooms Background noise level must not exceed 67 dBA at 62 Hz, ranging to 33 dBA at 8 kHz.

Control areas Background noise level must not exceed 83 dBA at 63 Hz, ranging to 54 dBA at 8 kHz.

Off-site The noise level at the nearest residence or community must not exceed 67 df3A at 63 Hz, ranging to 33 dBA at 8 kHz.

3 Cranes

3.1General

Power station cranes include:

•Overhead travelling cranes in areas such as the machine hall.

•Goliath cranes in outdoor areas such as the CW pumphouse.

•Grabbing cranes, in coal and ash plants.

•Travelling stacker/reclaimer machines in the coal stockyard.

•Maintenance hoists.

•Reactor pile cap cranes.

•Reactor charging machines.

•Nuclear fuel flask-handling cranes.

Cranes provided for power station construction purposes only are not dealt with in this section.

The diversity of locations and operational require: ments of these cranes necessitate specialist requirement s too numerous to describe here. The principal desi gn requirements which apply to the majority of cranes o n a power station site are described in this section. These relate specifically to overhead travelling cranes ar i d goliath cranes but many of them form the basis for the design of the more specialist cranes, such as reacto r charging machines. Specific design features for nuclea r power station cranes are discussed in Section 3.10 of this chapter.

A typical cab-controlled crane, as used in turbine halls, is illustrated in Fig 10.1.

Cranes vary in rating between 5 t and 350 t, and may be equipped with up to two auxiliary hoists. In so me instances, two cranes are required to work in tandem for large lifts, such as turbine rotors.

Operational requirements, together with the heavy and frequent usage during the power station construction period, are carefully considered when establishing basic design requirements. Since the cranes may be in service from early in the power station construction period, their design must be adequate for the environmental conditions and power supply variations which occur during that period: these conditions may be more onerous than later, when the power station is operating.

The design requirements described in this section supplement or supersede those of British Standard BS466 [8].