Practical Power Plant Engineering. Zark Bedalov
Voltage Regulation 2.7.13 Overhead Distribution Lines
2.8 Transformer System Grounding 2.8.1 Transmission Level 2.8.2 MV Systems 2.8.3 LV Systems 2.8.4 Generator Neutrals
2.9 Transformer Winding Configurations and Phasing
2.11 Insulation Coordination 2.11.1 Substation Shielding
2.1 One‐Line Diagrams
Designing a Key one‐line diagram is the most important task in the development of an electrical system for a power or an industrial plant. This diagram is a result of the key decisions made by the engineers working on the project. This book devotes significant time in explaining the electrical components, which are fundamental in building the functional electrical one‐line diagram.
The one‐line diagram represents the electrical power distribution formed to suit the technological process for the proposed project (see Chapter 1). The electrical engineers must focus on acquiring information on the type of process, load magnitude, load centers, quality and availability of power, power loss tolerance, and required plant reliability.
The key one‐line diagram prepared at the initial stage of design will be conceptual in nature. It will encompass the other one‐line diagrams for the specific parts of the plant. It will serve for discussions, cost estimates, and to offer the other design team engineers a basis for their equipment selections. Figure 2.1 is not a “key” diagram, but a part of a plant one line diagram.
The design procedure in this chapter is described in light detail to arouse interest of the electrical engineers in the design and operation of electrical systems for industrial manufacturing and power plants. More clarifying details related to the specific equipment specifications, applications, and reasons for their selection can be found in the chapters that follow.
2.1.1 What Is the One‐Line Diagram, or Single‐Line Diagram?
Mechanical engineers have their “flow diagrams.” Electrical engineers have their single‐line diagrams showing the electrical power flows and plant overall integration. As the name implies, it is the principal electrical diagram or our big picture of the plant or specific part of the plant, whereby the three phases are represented in a simplified single‐line form. The diagrams show all the major transformers, loads, circuit breakers, and cables or line connections, including the ratings: kW (HP), MVA, V, A, AWG (mm2), leading to the major plant equipment. The key diagram includes references to the partial more detailed one‐line diagrams for the specific process areas. One medium size industrial plant may have 20 individual one‐line diagrams starting from the key one‐line diagram down to the individual MCC 480 V (400 V) diagrams.
Figure 2.1 Part of a plant one line diagram.
Decisions must be made on the main switchyard, the number of incoming transformers, and the selection of the plant busbar voltages for distribution of power to the major load centers for large and small loads and primary and secondary power lines to remote plant facilities.
Note: The voltages and frequency applied in this book will be those of the North American standards. The principles of calculations and application used here are equally applicable to the IEC system voltages used in the other parts of the world.
2.2 The Electrical Project
The activities presented in this book, some of it in this chapter as part of the electrical design, include the following:
Determine the site conditions and discuss the interconnection with local Utility.
Review of mechanical load flow diagrams, P&D diagrams and establish load (kW) estimates and voltage levels.
Prepare one‐line diagrams and plant design criteria.
Conduct system studies and determine electrical equipment ratings.
As the starting point, the mechanical engineers will develop 10–20 flow diagrams of the plant process. A small part of the ore handling flow diagram is shown in Figure 2.2. The process (instrumentation) engineers will develop 30–40 process piping and instrumentation diagrams (P&ID) to instrument and automate the plant, as shown on a small P&ID segment in Figure 2.3 for a feed pump. The P&ID gives us the indications on how the plant will be controlled, monitored, and operated.
Figure 2.2 Part of plant flow diagram.
Figure 2.3 A part of a P&ID diagram.
As a young design electrical engineer you have been assigned to be a part of a multidiscipline engineering team responsible to develop a project estimated to consume about 30 MW of power, or 37.5 MVA at 0.8 power factor (pf). The design team of electrical engineers and draftsmen led by an experienced senior lead electrical engineer is responsible to design the electrical power distribution system and procure the electrical equipment to power up and control the plant equipment. The plant distribution system will follow the national standards and voltages for 60 Hz (50 Hz) frequency as applicable to the location of the project.
The principal operating item in this facility and the biggest electrical load is a large 10 MVA semi autogenous grinding (SAG) mill operated as a variable speed drive cyclo‐converter. It receives the ore from the crushers,