Switching in Electrical Transmission and Distribution Systems

René Smeets, Lou van der Sluis, Mirsad Kapetanovic, David F. Peelo, Anton Janssen

• Publisher: Wiley
• Year: 2015
• ISBN:
  9781118703625
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Power Resources
• Index: Technology & Engineering

Switching in Electrical Transmission and Distribution Systems presents the issues and technological solutions associated with switching in power systems, from medium to ultra-high voltage.

The book systematically discusses the electrical aspects of switching, details the way load and fault currents are interrupted, the impact of fault currents, and compares switching equipment in particular circuit-breakers. The authors also explain all examples of practical switching phenomena by examining real measurements from switching tests.

Other highlights include: up to date commentary on new developments in transmission and distribution technology such as ultra-high voltage systems, vacuum switchgear for high-voltage, generator circuit-breakers, distributed generation, DC-interruption, aspects of cable systems, disconnector switching, very fast transients, and circuit-breaker reliability studies.

Key features:

• Summarises the issues and technological solutions associated with the switching of currents in transmission and distribution systems.
• Introduces and explains recent developments such as vacuum switchgear for transmission systems, SF6 environmental consequences and alternatives, and circuit-breaker testing.
• Provides practical guidance on how to deal with unacceptable switching transients.
• Details the worldwide IEC (International Electrotechnical Commission) standards on switching equipment, illustrating current circuit-breaker applications.
• Features many figures and tables originating from full-power tests and established training courses, or from measurements in real networks.
• Focuses on practical and application issues relevant to practicing engineers.
• Essential reading for electrical engineers, utility engineers, power system application engineers, consultants and power systems asset managers, postgraduates and final year power system undergraduates.

1
Switching in Power Systems

1.1 Introduction

As electricity comes out of AC outlets every day, and has done so for more than 100 years, it is nowadays considered a commodity. It is a versatile and clean source of energy; it is rather cheap and ‘always available’.

The purpose of a power system is to transport and distribute the electric energy generated in the power plants to the consumers in a safe and reliable way. Generators take care of the conversion of mechanical energy into electric energy, aluminium and copper conductors are used to carry the current, and transformers bring the electric energy to the appropriate voltage level. Society's dependence on this commodity has become extremely large and the social impact of a failing power system is unacceptable. The electrical power system is the backbone of modern society.

Switching operations in power systems are very common and must not jeopardize the system's reliability and safety. Switching in power systems is necessary for the following reasons and duties:

• Taking into or out of service some sections of the system, certain loads, or consumers. A typical example is the switching of shunt capacitor banks or shunt reactors, de-energization of overhead lines, transformers, and so on. In industrial systems, this type of switching is by far the most common of all the switching operations.
• Transferring the flow of energy from one circuit to another. Such operations occur when load current needs to be transferred without interruption from one busbar to another, for example, in a substation.
• Isolating certain network components because of maintenance or replacement.
• Isolating faulted sections of the network in order to avoid damage and/or system instability. The most well-known example of this is the interruption of a short-circuit current. Faults cannot be avoided, but adequate switching devices in combination with a protection system need to limit the consequences of faults.

Figure 1.1 provides an overview in orders of magnitude of the power switched in electrical-engineering applications.

Figure 1.1 Overview of the power being switched in electrical-engineering applications.

Switching in electrical power systems re-configures the topology of an electrical network; it involves the making and breaking of circuits and causes a disturbance of steady energy flow. Therefore, transients have to be expected and are observed in the system during the change from the situation before to the situation after switching. Transients are abnormal patterns of current and voltage that have a limited duration. Attention should be paid to these phenomena because they very often exceed the values met during steady-state operation. Fundamentally in nature, any change of steady-state conditions generates transients.

The essential parameters in electrical systems are current and voltage. During switching operations, transients can be observed in both. Regarding operations related to switching-on (making or energization), the components of the system are mainly stressed by current-related transients. On the other hand, at switching-off operations (breaking or de-energization), voltage-related transients will especially stress the switching device performing the operation.

In a generalized concept, switching devices (dis)connect a source circuit to a load circuit (see Figure 1.2). Both circuits are a complicated combination of system components: lines, cables, busbars, transformers, generators, and so on. Through reduction of the complexity to relevant simple electrical elements, either lumped or distributed where necessary (refer to Section 1.3), the switching transients can be more easily understood.

Figure 1.2 General concept of a switching device located between a source- and a load-circuit.

1.2 Organization of this Book

The aim of this book is to describe and explain to technically interested and practically oriented readers the variety of switching processes and devices in electrical power systems, avoiding (as far as possible) deep physical details and formal mathematics – although both of these are in fact pillars in the resolution of problems encountered in the high-power switching technology. Numerous examples of measurements and observed effects have been selected from realistic tests of a wide variety of switchgear at the KEMA High-Power Laboratory of DNV GL – Energy, where real service conditions are simulated in powerful test-laboratories (see Section 14.2).

The book is divided roughly into two parts. The first part (Chapters 1 to 5) focuses on the switching phenomena and their description.

The second part (Chapters 6 to 14) describes the technology of the devices that must perform switching in all experienced varieties and their impact on the power system.

In Chapter 1, the necessary background on the practical aspects of switching is given. The origin and role of the two key phenomena governing the switching processes are described: the switching arc and the transient recovery voltage (TRV). Due to the nature of the transients that accompany switching, the general description must, in principle, be in terms of electromagnetic fields and travelling waves. However, at sufficiently low frequency, a simplification of the relevant circuits in terms of lumped elements can greatly facilitate mathematical formulation and calculation of the TRV characteristics in the majority of the practical cases.

Chapter 2 deals exclusively with faults in power systems. Essential transients of fault-current events are identified, together with their impact on network components....

Table of contents

• Cover
• Titlepage
• Copyright
• Dedication
• Preface
• 1 Switching in Power Systems
• 2 Faults in Power Systems
• 3 Fault-Current Breaking and Making
• 4 Load Switching
• 5 Calculation of Switching Transients
• 6 Current Interruption in Gaseous Media
• 7 Gas Circuit-Breakers
• 8 Current Interruption in Vacuum
• 9 Vacuum Circuit-Breakers
• 10 Special Switching Situations
• 11 Switching Overvoltages and Their Mitigation
• 12 Reliability Studies of Switchgear
• 13 Standards, Specification, and Commissioning
• 14 Testing
• List of Abbreviations
• Index
• End User License Agreement