Practical Power Plant Engineering. Zark Bedalov
and prove that the selected equipment ratings conform to the requirements set out in the design criteria. For these calculations, we will use the software from various system houses, such as Easy Power, ETAP, Cyme, and others. The plant data will be laid out on a computer and let the computer do the math. Not only that, the computer teaches you the power system functioning. One can introduce changes and alternatives and then observe the impact of the changes on the power system performance. It allows you to select the optimal solutions.
Interfaces: At this time, schematic and wiring diagrams for all the motors and valves, cable lists, and plant layouts will be prepared.
One of my bosses once told me: “Project usually fails at the interfaces.” He was right. The projects require a huge effort by many personnel working on the project, ranging from secretaries to the managers. Possibilities of errors are ever‐present. The interface changes may be due to a late design modification initiated by other engineering departments. If not well communicated and reconfirmed, the changes may not get on the drawings. This applies also for the communications between the engineering departments, the suppliers, and fabricators. If the equipment arrives to site with incorrect connections, it will lead to a lot of confusion on site, “throwing blame around of who said what, and so on.” This is where the experience comes in from working on large projects and by recognizing how the equipment is supposed to work and how it relates to the other equipment. Experienced engineers would notice problems if incorrect drawings cross their desks.
Every discipline can use approximations, add (+) or delete (−) a few inches or feet here and there on the drawings. The electrical engineers have no such a benefit. We have to produce drawings that match the equipment perfectly. Electrical drawings show several hundreds of thousands of wires, power, and controls interfacing between the various electrical and mechanical equipment. The only grace we get is that we can bend the plant cables around in the cable trays.
You may have done your job to perfection, but unfortunately, when you come to the construction site, you may face some disappointments. You will notice the supplier's actual equipment does not match the drawings you received to prepare your diagrams from. The suppliers have just got confused and sent you drawings they had engineered for a previous customer, or they had made changes but failed to inform you.
Do not panic now. This is something to get used to. It happens. Once the wires are connected, you may notice different problems stemming from errors, suppliers' incorrect designs, and of course, the wiring errors. This is where precommissioning and commissioning comes into play to make sure everything is properly tested and made to work as intended.
Everyone can make mistakes. Let us be honest about it. Even mechanical engineers can make a mistake here and there. But there is nothing like what the electrical engineers face. Thousands and thousands of wires are laid out in the field, and each one must find its proper place or it may turn out to be a major mistake and error, which will have to be troubleshooted later during the plant commissioning. Fortunately, with the advances in technology, a half of wiring in the modern plant is now replaced by communication cables, coax, a pair of wires, etc., carrying thousands of signals which can be shaped and configured as part of the plant control system. But that is another story. That certainly is a wiring relief, but our problems will now likely resurface in the software during commissioning (see Chapter 17).
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.
1.2.3.1 Cost of Change
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).
1.2.4 Engineering Documents
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.
1.2.5 Equipment Specifications and Data Sheets
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 24 for 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.