Zark Bedalov - Practical Power Plant Engineering

You as an electrical engineer will prepare or work on the following drawings and documents:

Equipment and installation specifications.

System studies: Load flow for voltage drops, short circuits for the equipment ratings, large motor starts, and relay coordination.

One‐line diagrams.

Design criteria.

Layouts for electrical equipment, lighting, cable trays, load Lists, cable schedules and terminations, embedded grounding, equipment grounding, lightning, and power corridors.

Prepare schematic and wiring diagrams for each motor, valve, and feeder,

Review of civil, mechanical, and instrumentation drawings.

Review of suppliers' drawings, and more.

That is a lot. A project of this magnitude may require thousands of electrical drawings and hundreds of documents.

At the project meetings, you will note that the design is still open to changes. With the design criteria and key single‐line diagram in hand, you will be discussing with your civil, process, and mechanical counterparts on what is possible and reasonable and what is not, and what will cost “an arm and a leg” and what may be a more reasonable option. The developer may suddenly decide to add another process line in the plant, which may stretch your “almost finished” power distribution system or completely change it. Remember, a plant change on paper is 10 times less costly than doing it during construction ( Figure 1.2).

During the plant design, an electrical engineer with his team of designers must prepare the following documents:

Drawings: Drawings are being prepared for the specific electrical equipment and as layouts for the equipment installations. The former are included with corresponding equipment specifications, while the latter are part of the construction (installation) specifications. The drawings are to be prepared by experienced designers with a help and under the supervision of a lead engineer. Figure 1.2 Cost of change.Initially, the drawings are prepared as preliminary and issued to various suppliers for tendering purposes. Once a winning bidder is selected, the preliminary drawings are updated and finalized based on the fabrication drawings received from the selected supplier and finally issued for construction. The drawings must be marked with appropriate revisions as they are being revised and issued.There are different methods of marking the drawing revisions. Here's one. The preliminary issues of the drawings are labeled with revisions, Rev. A, B, C, … or PA, PB, PC, …. The final drawings for construction are marked as Rev. 0, 1, 2, 3. Minor changes not affecting the contents or performance may be modified without raising the revision number.

Reports: During the project, many situations are encountered where the engineer is required to prepare official reports to evaluate various options and make recommendations of possible changes and improvements to the project. The changes may be due to the project cost reductions, technological changes, or changes to the site or operating conditions.

Coordination with other engineering disciplines: The electrical engineer must also review the mechanical, process, and civil engineering drawings to familiarize themselves with the buildings and mechanical equipment, as well as to insure the mechanical equipment includes appropriate electrical parameters specific for the project.

These documents will be prepared by the lead engineers for the electrical equipment, such as transformers, motor control centers (MCCs), VFDs, switchgear, etc. Revisions to these documents may follow the same procedures as identified for the drawings. Following a receipt of the tenders from the suppliers, the engineer prepares technical tender evaluations with appropriate conclusions, recommendations, and specific conditions for purchasing the equipment. As part of the award of contract, the specifications and data sheets are updated to match that of what was agreed on “as purchased” (see Chapter 24for some specification details and data sheets).

A typical small or big project requires a number of specifications with data sheets to be written. The specifications define the equipment performance requirements and workmanship. The data sheets cover the specific equipment rating requirements. The specification for a particular piece of equipment can be updated from project to project with some minor changes. It is the data sheet that changes in a big way as the application and ratings may be completely different from project to project.

Hopefully, the new specifications will be similar to those of your previous projects. Often, one can change the project name and the spec number and then revise the data sheet to suit the equipment you need for your new project. Try not to repeat yourself in the documents. Sooner than you think, someone will call and ask you: “What do you want: 1000 A breaker written in the specification or 1200 A breaker listed in the Data Sheet.” If you want to talk about the breaker in the specification, just note: “For the ratings, refer to the Data Sheet.”

From project to project, try to maintain the same ID number for the same design product, if the project permits it. For instance:

Specification and data sheet, respectively, for MCCs on project ABC: ABC – xxx – TS31 – DS31

Specification and data sheet, respectively, for MCCs on project XYZ: XYZ – xxx – TS31 – DS31

Try to group the documents for the type of equipment and services. Leave some gaps as there are differences in scope from project to project. When you are dealing with equipment like MCCs located in various different parts of a plant, write a common spec with several data sheets added to it for different areas.

Here is a list of specifications from a recent project in Minnesota on a 55 MW power plant using turkey litter as fuel:

1 Electrical contribution to mechanical engineers' specifications.

1 Main power distribution

1 Plant equipment

1 Services and plant installation