Electric Power Distribution, Automation, Protection, and Control

James A. Momoh

• Editorial: CRC Press
• Año: 2017
• ISBN:
  9781351837880
• Edición: 1
• Categoría: Technik & Maschinenbau
• Categoría: Elektrotechnik & Telekommunikation

New methods for automation and intelligent systems applications, new trends in telecommunications, and a recent focus on renewable energy are reshaping the educational landscape of today's power engineer. Providing a modern and practical vehicle to help students navigate this dynamic terrain, Electric Power Distribution, Automation, Protection, and Control infuses new directions in computation, automation, and control into classical topics in electric power distribution.Ideal for a one-semester course for senior undergraduates or first-year graduate students, this text works systematically through basic distribution principles, renewable energy sources, computational tools and techniques, reliability, maintenance, distribution automation, and telecommunications. Numerous examples, problems, and case studies offer practical insight into the concepts and help build a working knowledge of protection schemes, fault analysis and synthesis, reliability analysis, intelligent automation systems, distribution management systems, and distribution system communications. The author details different renewable energy sources and teaches students how to evaluate them in terms of size, cost, and performance.Guided firmly by the author's wealth of industrial and academic experience, your students will learn the tools and techniques used to design, build, and operate future generations of distribution systems with unparalleled efficiency, robustness, and sustainability.

1
Introduction to Distribution Automation Systems

1.1 Historical Background

Power system utilities consist of generation, transmission, and distribution functions. Several advances have been made to improve the performance, efficiency, reliability, and security of power systems. The initial design of the electricity industry by Edison in 1881, with AC generation, has changed with several modifications. This design, with its modifications, has led to the development of today’s power system utilities. The design of large-scale electric production has produced AC power at high voltage and current levels. The growth of the industry has led to many innovations, including economy of scale from large hydro, fossil fuel and, recently, small independent power producers (IPP), in what is called distributed generation. The designs of distributed generation have been based on criteria to improve its reliability, load management, and system performance in response to various disturbances. Over the last decade, protection schemes to detect abnormalities, control schemes to stabilize the system, and economic principles to ensure optimal allocation and bidding have all been implemented to ensure a network’s competitiveness in the electric market.

The generated power is transmitted over long distances from city to city or across country boundaries. The transmission lines can be rated to operate as either DC or AC systems at low, medium, or extra-high voltage levels of 230 kV, 750 kV, or 1130 kV, respectively. Efficiency and reliability at an affordable cost is the ultimate aim of the transmission planners and operators. The line must withstand and tolerate dynamic changes in load and contingency without unreasonable impact on the continuity of service. To ensure that the system meets the expected performance, reliability, and quality of supply, some standards are preferred following the occurrence of a contingency. Simulation tools and advanced technology such as load flow, optimal power flow, state estimation, stability estimation, reliability estimation, market stimulation tools, and flexible AC transmission devices (FACTs) have been developed to ensure the reliability and security of the transmission/distribution system. The transferred power is ultimately delivered to residential, commercial, and industrial customers at local but lower voltage levels. The voltage level for industrial customers ranges from 4.0 kV to 34.4 kV. Residential customers are supplied with voltage levels at 120/240 V, while the typical voltage level for commercial customers is 440 V. The distribution reliability and the quality of utility services are easily measured by all stakeholders at the customer end. With this in mind, the progressive utility must provide adequate planning and operation, as well as reliability-centered maintenance to the system, to minimize downtime of service from the distribution level up.

1.2 Distribution System Topology and Structure

Distribution system topology can take a variety of forms. The topology is typically radial or ring, mesh, or radial mesh, depending on the configuration, quality of service, and cost. The cost of operation and maintenance (or lack of it) is usually huge, so appropriate techniques used in communication technology and automation are desirable in achieving a distribution system of high quality. For example, distribution automation functions have recently been designed to support trouble call analysis, which will reduce repair crew time and ensure timely payment of bills. Distribution automation also enhances integration to system reconfiguration and restoration, thereby minimizing losses and voltage deviation, especially during an emergency. Several optimization and intelligent-system techniques are used in the design of distribution automation schemes.

Prototype work is being carried out using optimization and intelligentsystem techniques to address some of the common day-to-day problems that can affect the quality of service. Furthermore, the penetration of electronic devices such as power converters and flexible AC transmission (FACT) devices can be utilized to improve the system power quality. The future distribution network will also incorporate distributed generation, such as photovoltaic (PV), wind power, biomass, and microturbines. This has improved the capability of distributed systems to meet the ever-changing load demands at a reduced cost for capital equipment.

The transmission and distribution of electrical power is commonly based on single- and three-phase transmission using aluminum conductors from point to point or to many other points. The challenge of routing power within its capacity limits at minimum cost and minimum losses is part of the overall design problem.

Power systems (in an unbalanced state) in the new competitive environment also have to meet some regulatory requirements to ensure safety and security. The important functions and regulatory requirements that must be met are as follows:

1. Generation, transmission, and distribution must be able to meet anticipated demand with sufficient reserve margins, which could be met by demand-side management schemes or storage schemes for the distribution business units.
2. The power system, including distribution subsystems, must be cost effective with the overall goal of meeting technical, economic, environmental, and public-perception constraints.
3. The reliability and quality of power transmission and distribution must be able to meet minimum standards.
4. Appropriate cost-benefit analysis should be done to ensure priority of project execution, which will improve the performance and quality of service.

With this in mind, modern tools must be developed to support the distribution options that have traditionally been tracked as nonrigorous, simple, and error-analysis strategies.

The distribution system’s main features are shown in Figure 1.1. The sample diagram in Figure 1.1 consists of fuses, reclosers, relays, a circuit breaker, transformers, regulators (voltage), and dispersed generator/storage. We describe each of them here briefly:

Relay: a device designed to protect against overvoltage, -frequency, or -current. It relays abnormal voltage or current to the circuit breaker to open (close) a circuit from further deterioration due to fault signals.

Reclosers: devices serving as special purpose, light-duty circuit breakers for interrupting overloads but not faults. It allows temporary faults to clear and then restores service quickly, but disconnects a permanent fault.

Circuit breaker: a high-current device that automatically disconnects faulted equipment. It facilitates protection of equipment from further damage or people from injury, and it is typically rated in terms of voltage and fault current. Circuit breakers come in different forms due to the arcing phenomena caused during contact (opening/closing) at high voltage. Typical models are air-blast circuit breakers, vacuum circuit breakers, oil circuit breakers, and sulfur hexafluoride circuit breakers, which use SFL gas media for extra-high voltage, which are applications above 345 kV.

Fuses: These are devices that melt when overload current passes through it. They come in different forms of low- or high-voltage fuses made from zinc, copper, silver, cadmium, or tin materials. They are rated in terms of BIL, voltage, continuous current, and interrupt-capacity fuse coordination (time it takes for the fuse to blow).

FIGURE 1.1
Distribution system.

Sectionalizer: a device that is used to automatically isolate a fault on a line segment from a disturbance. It senses any current above its activating current followed by a line and then de-energizes using a recloser.

Renewable energy/storage: referred to as IPP, an independent power producer at the customer side. It is called distributed power resulting from a renewable energy source such as photovoltaic, biomass, microturbine, or wind power.

A complete distribution subsystem includes other pieces of equipment, such as batteries, sensors, and computer application software. Overall, the additional equipment or apparati provide functionality to ensure real-time monitoring and control of the power system distribution. It is a creative art of ingenious engineering and has served the industry for years. However, as communication and intelligent-system technology advances, distribution systems can be enhanced. The potential of this automation is a fundamental concern of the text.

1.3 Distribution Automation (DA) and Control

The term “distribution automation” is used to define the application of communication, optimization, and intelligent systems to improve the performance and functions of distribution systems during normal and abnormal operation. DA facilitates system efficiency, quality of service, and the security of the power system. These abilities are classified as DA function options as follows:

Efficiency: DA function option that controls (minimizes) losses through network reconfiguration and restoration by appropriate relocation of fuses, circuit breakers, and loads for optimum performance during an overload.

Reliability and quality: To guarantee that the system is reliable at an acceptable value of risk (given the history of recorded failures and duration), an index to quality-acceptable customer-interruption service preference is proposed. Actions to manage unreliability through maintenance or demand-side management (DSM) are planned using distribution automation. New data-gathering tools such as power management unit (PMU) and frequency recorders are used for reliability assessment.

Security: The security of distribution is enhanced using integration of dispersed energy storage, distributed generators (DGs), or FACT devices. The aim here is to reduce voltage sag and eliminate harmonics that could cause low power quality and to dampen instability caused by penetration of DGs.

The integration of these DAs will provide a platform for building a future, highly competitive, and efficient autonomous distribution system that will be able to respond to different situations and be self-aware, self-organizing, and self-reconfigurable.

We present here an overview of DAs for distribution systems. The overall structure indicated in Figure 1.2 utilizes a combination of optimization and intelligent systems to develop effective DA functions. For example, the intelligent system (IS) will be based on fuzzy logic for demand-side management ...