TRANSMISSION AND DISTRIBUTION BOOK
Electric Power Transmission and Distribution is a comprehensive text, designed for undergraduate courses in power systems and transmission and distribution. A part of the electrical engineering curriculum, this book is designed to meet the requirements of students taking. Transmission And Distribution. Front Cover. ppti.info, ppti.info Technical Publications, - pages. 10 Reviews. Electric Power Transmission and Distribution is a comprehensive text, designed for undergraduate courses in power systems and transmission and distribution.
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Electric power transmission and distribution is a huge sector, and engineers require the real world guidance of this book in order. Purchase Transmission and Distribution Electrical Engineering - 4th Edition. Print Book & E-Book. ISBN , Indeed, encouragement for the preparation of this book has come from the Institution of Electrical Engineers (IEE) Transmission and Distribution Professional.
Current Transformers 5. Voltage Transformers 5. Future Trends Chapter 6. Insulators 6. Introduction 6. Insulator Materials 6. Insulator Types 6. Pollution Control 6. Insulator Specification 6. Tests Chapter 7. Substation Building Services 7. Introduction 7.
Lighting 7. Heating, Ventilation and Air-Conditioning 7.
Fire Detection and Suppression 7. Security Chapter 8. Earthing and Bonding 8. Introduction 8. Design Criteria 8. Substation Earthing Calculations 8.
Computer Simulation 8. Protective Multiple Earthing Chapter 9. Insulation Co-ordination 9. Introduction 9. System Voltages 9.
Transmission and distribution: electrical engineering
Clearances 9. Procedures for Co-Ordination 9. Surge Protection Chapter Relay Protection Introduction System Configurations Power System Protection Principles Current Relays Differential Protection Schemes Distance Relays Auxiliary Relays Computer Assisted Grading Exercise Practical Distribution Network Case Study Fuses and Miniature Circuit Breakers Fuses Fuse Operation Miniature Circuit Breakers Chapter Cables Codes and Standards Types of Cables and Materials Cable Sizing Calculation of Losses in Cables Fire Properties of Cables Control and Communication Cables Cable Management Systems Chapter Switchgear Terminology and Standards Switching Arc Quenching Media Operating Mechanisms Equipment Specifications Chapter Power Transformers Standards and Principles Voltage, Impedance and Power Rating Thermal Design Constructional Aspects Accessories Chapter Substation and Overhead Line Foundations Soil Investigations Foundation Types Foundation Design Site Works Chapter Overhead Line Routing Routing Objectives Preliminary Routing Detailed Line Survey and Profile Chapter Structures, Towers and Poles Environmental Conditions Structure Design Pole and Tower Types Chapter Overhead Line Conductor and Technical Specifications Conductor Selection Calculated Electrical Ratings Design Spans, Clearances and Loadings Overhead Line Fittings Overhead Line Impedance Testing and Commissioning Quality Assurance Works Inspections and Testing Site Inspection and Testing Testing and Commissioning Methods Appendix A.
Drawings, Diagrams, and Manuals Chapter Electromagnetic Compatibility Standards Compliance Testing Screening Typical Useful Formulae Case Studies Chapter Supervisory Control and Data Acquisition Programmable Logic Controllers Power Line Carrier Communication Links Software Management Chapter Project Management Project Evaluation Financing Project Phases Terms and Conditions of Contract Hydro or low speed diesel 1.
If the fault persists the generator will be subjected to a second fault impact upon reclosing System Studies 27 the circuit breaker and a stable situation may be rendered unstable. Great care is therefore necessary when considering auto-reclosing. As an aid to stability auto-reclose single pole circuit breaker switching is often employed. A typical transmission system strategy is to employ single shot auto-reclose facilities only for single phase to earth faults.
If the fault persists then three phase switching takes over to disconnect the circuit. Typical delay times between circuit breaker auto-reclose shots are of the order of 0. The single pole auto-reclose technique is well established for transmission line voltages below kV and stability is aided because during the fault clearance process power can be transferred across the healthy phases.
It should be noted, however, that fault arc deionization takes longer with single pole switching because the fault is fed capacitively from the healthy phases. In addition the system cannot be run for more than a few seconds with one open circuit phase or serious overheating of the rotating plant may take place.
Distribution systems employ three phase autoreclose breakers and sectionalisers to isolate the fault if it persists. In order to avoid large angle swings, the possibility of mechanical damage to the shaft and couplings and loss of synchronism, the natural frequency should not coincide with the frequency of pulsating loads or prime mover torque.
Hunting of this type may be detected from pulsating electrical measurements seen on machine meters and excessive throbbing machine noise. In both these cases damping arises from induced currents in the damper windings caused by rotor oscillation. The damping torques decrease with increasing resistance in the paths of the induced currents.
Machines operating at the ends of long, high resistance supply lines or having high resistance damper windings can be particularly susceptible to hunting. The possibility of hunting can be seen from the equations in Section 1.
In the transient period of perhaps a second or two following a disturbance, many of the slower reacting power system components can be assumed constant. In the seconds and minutes following a disturbance such slow reacting components may become dominant. In addition, during the dynamic period, motor loads shed at the start of the disturbance may be automatically restarted.
Dynamic stability studies are more normally carried out for large interconnected systems to assist with the development of strategies for system control following various types of disturbance. With smaller industrial reticulation the preservation of stability in the transient period is generally regarded as the most important case for investigation. The adaptation of the network in the dynamic interval is left largely up to the natural properties of the system and by automatic or operator control.
Induction motors always run asynchronously and stability studies involve a consideration of the load characteristics before and after a system disturbance. For a fault close to the induction motor the motor terminal voltage is considerably reduced. For a given terminal voltage the current drawn is a function only of speed.
As the speed drops the current increases rapidly to several times normal full load value and the power factor drops from, say, 0. The torque of the motor is approximately proportional to the square of the terminal voltage.
System Studies 29 Because of these characteristics substation induction motor loads are often characterized as: 1.
Square law loads such as centrifugal pumps will recover with greater ease than constant torque loads such as reciprocating compressors.
These loads may be reconnected automatically after a delay. The system designer must, however, consider the possibility of voltage collapse upon reconnection as the starting of motors places a severe burden on generation reactive power supply capability.
The starting torque is only about 1. The motor VAr demand is, however, very large because of the poor starting power factor. The system voltage can be severely depressed before, for example, on-site generator AVR action comes into play. Checks should be made to ensure that direct-on-line DOL starting of a large motor or group of motors does not exceed the VAr capability of local generation in industrial distribution systems.
Such data collection can be time consuming and for older machines such data are not always available. For example, a primary substation infeed from a large grid network with high fault level to an industrial plant can usually be represented as a simple generator with large inertia constant and a transient reactance equal to the short circuit reactance.
Simple load representation to voltage variations falls into one of the following categories: 1. Constant impedance static loads 2. Constant kVA induction motors 3. System Studies 31 Induction motors remote from disturbance and represented as a static load : Fully loaded motors can be represented as constant kVA load.
Partially loaded motors can be represented as constant current loads. Unloaded motors can be represented as constant impedance loads. System faults will depress voltages and restrict power transfers.
Usually, generators will speed up during the fault and the load angle will increase. Some generators may experience an increased load during the fault and will slow down.
For the same proportionate loss in load during the fault, generators with lower inertia constants will speed up more quickly. On-site generators may remain in step with each other but diverge from the apparently high inertia grid infeed. Induction motor slips will increase during the fault. After the fault, stability will be indicated by a tendency for the load angle swings to be arrested, for voltages and frequency to return to prefault values and for induction motor slips to return to normal load values.
If on-site generators remain in synchronism with each other but cannot match the on-site load requirements, a decline in frequency will occur. Load shedding will then be necessary to arrest the decline. Practical examples of these principles are given in the case studies in Section 1. Type of fault three phase, single phase to earth, etc. A three phase fault is normally more severe than a single phase fault since the former blocks 32 System Studies Figure 1. The single phase fault allows some power transfer over healthy phases.
Duration of fault. If the fault persists beyond a certain length of time the generators will inevitably swing out of synchronism. The maximum permissible fault duration therefore varies principally with the inertia constant of the generators, the type and location of the fault. System Studies 33 Determination of maximum fault clearing time is often the main topic of a transient stability study.
The limiting case will usually be a three phase fault close up to the generator busbars. Low inertia generators H : 1. Location of a fault. Extent of system lost by the fault. If a main transmission interconnector is lost, the generators may not be able to transmit total power and power imbalance can continue to accelerate rotors towards loss of synchronism.
The loss of a faulted section may also lead to overloading of system parts remaining intact. A second loss of transmission due, say, to overload could have serious consequences to an already weakened system.
In order to improve transient stability, fault durations should be kept as short as possible by using high speed circuit breakers and protection systems, particularly to clear faults close to the generators.
The incidence of three phase faults can be reduced by the use of metal clad switchgear, isolated phase bus ducting, single core cables, etc.
Impedance earthing further reduces the severity of single phase to earth faults. Appropriate system design can therefore reduce the extent of system outages by provision of more automatic sectionalizing points, segregation of generation blocks onto separate busbars, etc. System transient reactances should be kept as low as possible in order to improve transient stability.
Machines and associated generator transformers with low reactance values may be more expensive but may provide a practical solution in a critical case. These devices can supply leading or lagging VArs to a system and thereby maintain nearly constant voltages at the point of connection in the system. The characteristics of such devices are shown in Fig. Normally the busbar coupler is open and grid infeed is via the non-priority busbar No. On-site generation and a major hp induction motor are connected to busbar No.
Other smaller motor loads are connected to busbars 3, 4, and 5. System Studies 35 Figure 1. The large induction motors connected to busbars 1 and 5 are represented in detail in order that slip and current variations during a disturbance may be studied. The two groups of smaller V motors connected to busbars 3 and 4 are not to be studied in detail and are represented as constant kVA loads.
On-site generator No. The results of the computer analysis associated with this system for case studies 1 to 4 have been replotted in Figs 1. Generator No.
Electric Power Transmission and Distribution
A three phase fault is imagined to occur on the 6. The protection and circuit breaker are such that a total fault duration of 0. Clearance of the fault disconnects busbar 3 and its associated stepdown transformer from busbar 1 and all other loads are assumed to remain connected. In Fig. Shortly after fault clearance, a return towards the original operating load angle position is seen.
The generator terminal voltage is also seen to recover towards prefault value. The on-site generator No. System Studies 37 Figure 1. During the fault the slip increases. However, shortly after fault clearance the terminal voltage recovers and the slip reduces towards the prefault value. Similar behaviour for motors 2 and 3 is shown in Fig. The main motor loads therefore seem to be able to operate under the fault condition; the smaller motor loads have not been studied.
This machine has a relatively low inertia constant compared to the existing on-site generator No. No changes are proposed to the existing protection or circuit breaker arrangements.
Both site generators are supplying full load. The duration of the fault has caused generator 2 to lose synchronism with generator 1 and the System Studies 39 grid infeed. The ensuing power surging is not shown in Fig. Acting as a consultant engineer to the industrial plant owner what action do you recommend after having carried out this analysis? Do you have anything to say about protection operating times for busbar 5 feeder or generator 2 breaker?
The client, not wishing to spend more money than absolutely necessary, queries the accuracy of your analysis. Would you consider a further study under these conditions with more accurate generator modelling? This study demonstrates the need to review plant transient stability whenever major extensions or changes are contemplated.
In this example a solution could be found by decreasing protection and circuit breaker operating times. Alternatively, if generator 2 has not already been purchased a unit with a similar inertia constant to generator 1 if practicable could be chosen.
Generator 1 is supplying full load at unity power factor and the grid infeed the balance of site demand. It is now imagined that the grid infeed is lost due to protection operation. The site electrical load now considerably exceeds the on-site generation capacity and a decline in frequency is expected. The mechanical driving power to generator 1 is assumed to remain constant.
As the grid supply engineer in charge of this connection you have been called by the plant manager to explain what precautions could be taken to prevent plant shut down under similar outage conditions in the future. You propose an underfrequency relay associated with the bus-coupler circuit breaker separating busbars 1 and 2.
From the transient stability studies shown in Fig. The plant manager considers that too much load will be shed by utilizing the bus coupler in this way although he is thinking more about plant downtimes than system stability. Again as grid engineer you acknowledge the point and indeed you are worried that such a large load shed could leave generator 1 underloaded. Unless some adjustment is made to the generator 1 driving 40 System Studies Figure 1.
With more thought what similar action to plant protection could be taken? In this example the crude bus coupler protection motor 1 recovers successfully. Motors 2 and 3 connected to busbar 5 will decelerate to a standstill due to loss of supply as will all motors connected to busbar 4.
System Studies 41 Figure 1.
Electric Power Generation Transmission And Distribution Book
Case study 4 The system of Fig.A typical transmission system strategy is to employ single shot auto-reclose facilities only for single phase to earth faults.
Personal information is secured with SSL technology. The ensuing power surging is not shown in Fig. About Elsevier. Updating Results. The book also shows how the more general theory reduces to the theory commonly used by practicing engineers.
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