reading / British practice / Vol D - 1990 (ocr) ELECTRICAL SYSTEM & EQUIPMENT
.pdfPreface
Tne review of the original Modern Power Station Practice series carried out a few years ago revealed large gaps in its treatment of electro technology within power stations. Not unnaturally much of the content was also badly out of date. It was clear that a straightforward revision of the previous book would not suffice and that a totally new work was required. It was therefore with much enthusiasm that the team of authors of Volume D set out to write it since we all felt it was very timely to do so.
The re-organisation of power station design and construction within the CEGB in 1971 created the Generation Development and Construction Division (GDCD). The Division set up an Electrical Branch which pulled together previously dispersed skills and experience in all aspects of power station electrical engineering covering power systems and plant as well as control, communications, data and instrumentation systems and equipment. Two of the volumes of MPSP, Volumes D and F, are largely based on the work done over many years by GDCD Electrical Branch. Volume D deals with the work of some 50 electrical design specialists in the power engineering field while Volume F covers a similar level of activity in the C and I field.
One of the major tasks of the Electrical Branch has been to rationalise electrical system and plant design and development, and produce designs which meet operational needs in the most economic way and with the required level of reliability and performance. As the Head of the branch for many years I have felt privileged to edit Volume 1D. The twelve chapters describe in appropriate detail the design philosophies and techniques which have underlain the work of the Branch. They describe the solutions to the large number of design problems which have been identified and the plant which has been chosen and developed to equip electrical systems both within the different types of new power station which have been built as well as for replacement and modification tasks at existing stations.
Since the formation of GDCD, CEGB projects have included most types of generating plant including AGR and PWR nuclear stations, fossil-fired stations (both oil and coal), gas turbine and diesel driven generators and a major hydro plant at Dinorwig. While most of the electrical equipment for these different sorts of power station is similar, the electrical system needs vary widely. The designs described in Volume D therefore deal with the requirements for all types of power station electrical plant and systems.
Furthermore, while the rate of change of electrical power plant technology is not as fast as that in the light current area, there has nevertheless been considerable equipment development and an even greater change in design techniques and methodology. This is especially true in the analysis of electrical system design and performance and in some areas of plant development such as cable system design.
Since the Electrical Branch has also been responsible for control, instrumentation, communication and data systems it has been possible to ensure co-ordinated complementary development of both heavy and light current systems. The many interfaces, e.g., cabling, power supplies, instrumentation, protection and metering have been engineered with a coherent systems approach. The light current technology in the control, instrumentation and data systems area is described in Volume F. The Advisory Editor for that volume, Mr M.W. Jervis, and I, as colleagues in Electrical Branch, have always striven to maintain a close co-operation on all aspects of electrical systems design. We hope that this integration of design effort will be apparent to the readers of Volumes D and F.
I would like to record my most sincere thanks to my many colleagues who have produced Volume D and also Volume F. They have undertaken the work in parallel with their day to day responsibilities and have seen the task as an opportunity to put in writing a review of the results of their work for CEGB. I also wish to express my gratitude to Professor
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Preface
John Davies and Mr. Peter Reynolds for the great help and support which they have given me in the preparation of the volume.
I believe that Volume D stands as a record of many years of high quality electrical design activity and that it will remain relevant as an exposition of the science for a long time.
F. BEACH
Advisory Editor — Volume D
Contents of All Volumes
Volume A — Station Planning and Design
Power station siting and site layout
Station design and layout
Civil engineering and building works
Volume B Boilers and Ancillary Plant
Furnace design, gas side characteristics and combustion equipment Boiler,unit — thermal and pressure parts design
Ancillary plant and fittings
Dust extraction, draught systems and flue gas desulphurisation
Volume C — Turbines, Generators and Associated Plant
The steam turbine
Turbine plant systems
Feedwater heating systems
Condensers, pumps and cooling water systems
Hydraulic turbines
The generator
Volume D — Electrical Systems and Equipment
Electrical system design
Electrical system analysis
Transformers
Generator main connections
Switchgear and controlgear
Cabling
Motors
Telecommunications
Emergency supply equipment
Mechanical plant electrical services
Protection
Synchronising
Volume E — Chemistry and Metallurgy
Chemistry
Fuel and oil
Corrosion: feed and boiler water
Water treatment plant and cooling water systems
Plant cleaning and inspection
Metallurgy
Introduction to metallurgy
Materials behaviour
Non-ferrous metals and alloys
Non-metallic materials
Materials selection
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Contents of All Volumes
Welding processes
Non-destructive testing
Defect analysis and life assessment
Environmental effects
Volume F — Control and Instrumentation
Introduction Automatic control
Automation, protection and interlocks and manual controls Boiler and turbine instrumentation and actuators
Electrical instruments and metering Central control rooms
On-line computer systems
Control and instrumentation system considerations
Volume G — Station Operation and Maintenance
Introduction
Power plant operation
Performance and operation of generators
The planning and management of work
Power plant maintenance
Safety
Plant performance and performance monitoring
Volume H — Station Commissioning
Introduction
Principles of commissioning
Common equipment and station plant commissioning Boiler pre-steam to set commissioning
Turbine-generator/feedheating systems pre-steam to set commissioning Unit commissioning and post-commissioning activities
Volume J — Nuclear Power Generation
Nuclear physics and basic technology
Nuclear power station design
Nuclear power station operation
Nuclear safety
Volume K — EHV Transmission
Transmission planning and development
Transmission network design
Overhead line design
Cable design
Switching station design and equipment
Transformer and reactor design
Reactive compensation plant
I-1 VDC transmission plant design
Insulation co-ordination and surge protection
Interference
Power system protection and automatic switching
Telecommunications for power system management
Transmission operation and maintenance
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Contents of All Volumes
Volume L — System Operation
System operation in England and Wales
Operational planning — demand and generation
Operational planning — power system
Operational procedures — philosophy, principles and outline contents
Control in real time
System control structure, facilities, supporting services and staffing
Volume M — Index
Complete contents of all volumes
Cumulative index
Evan John Davies
Emeritus Professor of Electrical and Electronic Engineering at Aston University in Birmingham, died on 14 April 1991.
John was an engineer, an intellectual and a respected author in his own right. It was this rare combination of talents that he brought to Modern Power Station Practice as Consulting Editor of seven volumes and, in so doing, bequeathed a legacy from which practising and future engineers will continue to benefit for many years.
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CHAPTER 1
Electrical system design
1 Introduction |
5.5.3 Other safety interlocking |
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5.5.4 Nuclear safety |
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2 System needs |
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5.6 Quality assurance |
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2.1 |
Station operating criteria |
5.6,1 Design quality |
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2.2 Grid system operation criteria |
5.6.2 Product quality |
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2.3 Plant and personnel safety needs |
6 Uninterruptable power supply MPS) systems |
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2.4 Nuclear hazard needs |
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6.1 Introduction |
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3 System descriptions |
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6.2 Earlier UPS and GlS schemes |
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3.1 Main generator and station systems |
6.2.1 Motor-generator (MG) set schemes |
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3.1.1 Main generators |
6.2.2 Static inverter schemes |
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3.1.2 Generator transformers |
6.3 Development of UPS systems |
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3.2 Electrical auxiliaries systems |
6.3.1 Littlebrook D power station schemes |
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3.2.1 Auxiliaries system transformers |
6.3.2 Drax power station schemes |
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3.2.2 Interconnection |
6.3,3 Heysham 1 power station |
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3.2.3 Essential systems |
6.4 System configuration and method of operation |
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3,2.4 Emergency generation |
6.5 System considerations and components |
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3.3 Types of stations |
6.5.1 Voltage regulation |
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3.3.1 Fossil-fired power stations |
6.5,2 UPS system loads |
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3.3.2 Magnox nuclear power stations |
6.5.3 Step-down transformers |
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3.3.3 AGR nuclear power stations |
6.5.4 Standby and spares philosophy |
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3,3,4 P M nuclear power stations |
6.6 UPS equipment specification |
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3.3.5 Hydro and miscellaneous |
6.7 UPS equipment performance requirements |
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4 System performance |
7 DC systems |
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4.1 Station and unit start-up |
7.1 Introduction |
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4.1.1 |
Plant required |
7.2 DC system duties |
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4.1.2 Synchronising to the grid |
7,3 DC system design |
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4.1.3 Synchronising unit to station |
7.3.1 250 V DC systems |
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4.2 Shutdown and power trip |
7.3.2 220 V DC systems |
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4.2,1 Controlled shutdown |
7.3.3 110 V DC systems |
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4.2.2 Power trip |
7.3.4 48 V DC systems |
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4.3 The effects of loss of grid supplies |
7.3.5 250 V. 220 V and 110 V DC circuit earthing |
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4.4 Station plant outages and faults |
7.4 DC system analysis |
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5 System choice |
7.5 Battery chargers and batteries |
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5.1 Operational requirements |
8 Electrical system monitoring and interlocking schemes |
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5.2 Reliability of main and standby plant |
8.1 Introduction |
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5.3 Economics |
8.2 Operational interlocking, monitoring and indications |
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5.4 Plant limitations |
8.3 Relay systems |
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5.4.1 Switchgear current rating |
8.3.1 Switchgear auxiliary contacts |
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5.4.2 Switchgear short-circuit rating |
8,3.2 Application of interlock schemes |
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5.4.3 Large electric motors |
8.4 Computer-based systems |
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5.4.4 System performance calculations |
8.5 Maintenance interlocking equipment |
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5.5 Maintenance and safety |
8.5.1 Key exchange boxes |
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5.5.1 |
Operational |
8.5.2 Scheme application |
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5.5.2 Maintenance |
8.6 Other safety interlocking |
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Introduction
The various electrical systems within a power station include those associated with the connection of the generating plant to the grid system and the very much larger number which are provided to distribute power supplies around the auxiliary plant within the station
boundaries. The total electrical systems therefore interface with the whole of the power station installation.
The systems can be summarised as follows:
•Generator primary system and grid, typically 23.5 kV (660 MW) or 26 kV (900 MW) for units with grid voltages of 275 kV and 400 kV.
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Electrical system design |
Chapter 1 |
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•Station board system from grid, typically II kV derived from 132 kV, 275 kV or 400 kV.
•Station and unit auxiliaries systems, typically at 11 kV, 3.3 kV and 415 V.
•Einereency pow er supplies systems, typically gasturbine, diesel-driven generators connected at 11 kV, 3.3 kV, 415 V.
•DC systems, typicall at 250 V, 220 V, 110 V, 48 V.
•Uninterruptable power supply systems (UPS), typically at 415 V single and 3 phase, 110 V single-phase.
The security required of the electrical supplies is determined by the importance of the power station plant ot equipment. For example, auxiliaries associated with the main unit which if lost would immediately cause loss of unit output, clearly require more secure supplies than services such as sump pumps used occasionally. The nature of the supplies also requires careful consideration by way of voltage and frequency limits, susceptibility to transients caused by faults or switching operations and the consequences of short breaks in supplies. As a matter of course, most items of plant and equipment are specified and tested for compliance with known standards. This will include their electrical performance. If the need for new types of equipment is identified then performance limits should be defined at the outset of any development work, where standards cannot be quoted. The degree of security must also be taken into account since parts of nuclear power stations will warrant a much higher level than, say, a small hydro station.
It is necessary then, to recognise from the outset the importance of each item of plant when determining the nature and degree of security of electrical supplies it requires. The sources for auxiliaries supplies range from the grid-derived AC supplies, through to batterybacked AC and DC supplies and the 'short break' supplies.
The bulk of the electrical auxiliaries load is normally arranged to be taken from the grid-derived AC supplies. This will mean that the outline design of the electrical auxiliaries system can benefit from previous know ledge and experience when considering alternative supply arrangements to a certain level at an early planning stage of a project. The alternatives will include, for example, unit and station transformer schemes, generator soltage switchgear schemes and FIV switch isolator schemes. Detailed descriptions of t hese and other schemes are given later in this chapter.
The timely and accurate design of electrical systems is always easiest if at the outset, and at appropriate stages of the project, full details of electrical loading, rating and duty information can be established from the plant specialists, particularly for the major items, e.g., reactor, boiler, turbine-generator and operational ancillary plant. One way of achieving this is by in-
eluding standard electrical loading, rating and duty schedules in all the plant enquiry specifications, thereby committing tenderers to identify their design loads. It also assists in forming a comparison between competitive tenders and should be followed up with more accurate and detailed information at defined stages of the contract by the chosen contractors. By this means, the electrical system loadings can progressively be assembled and refined, enabling design ratings of transformers, switchgear, cables, etc., to be established for comparison of the various possible alternative electrical systems.
The system designer would always present a recommended scheme by comparing the alternatives on a basis of first and lifetime costs and suitability for duty. Until this stage is reached, the electrical plant specialists cannot seriously begin to specify their requirements. It is possible, however, that the system designer has already taken account of the commercially available equipment, which will make the specifying of electrical components more straightforward.
This chapter explains the approach and criteria used in determining the most suitable electrical systems for the various duties required at nuclear, fossil-fired and hydro power stations. There is a brief reference to other forms of generation, generally referred to as alternative sources of energy.
2 System needs
2.1 Station operating criteria
In common with all other areas of design in power stations, the electrical system designers must have a clear definition of what operating criteria need to be achieved. In the case of the CEGB, station development particulars are formulated at the early planning stages which incorporate the Station Technical Particulars (STPs). The STPs contain the requirements for the main plant availability, operating flexibility and the control of units. In addition, they will include the technical requirements for the generator transformers, the plant auxiliaries supplies and the station protection arrangements. Various appendices will detail the specifications to be met and the finite limits to be achieved. From these, it will be apparent what minimum features need to be built into the electrical systems to achieve the station output while at the same time ensuring the safety of personnel and plant, a more onerous requirement on nuclear power stations. Further documentation is prepared for nuclear power stations to cover the safety aspects in the form of a Preliminary Safety Report.
The interpretation of the STPs into electrical requirements becomes the designer's check list and generally will incorporate the following as typical:
(a)Station rated output is required over a supply frequency range of 49.5-50.5 Hz, with pro-rata
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