When to use computer-based power analysis tools
With the vast amount of power analysis design tools available today, electrical engineers can be overwhelmed when choosing the right tool to use. Learning these tools and knowing when to use them can help an engineer be more efficient with his or her time and results.
- Understand how electrical calculations were performed during the pre-desktop computer era and the challenges it posed.
- Differentiate between the two basic types of power analysis tools available for electrical engineers.
- Learn the challenges an electrical engineer may encounter when choosing a specific type of tool.
One of the biggest challenges for electrical engineers is to find their own path to efficiently design a project’s electrical system. By mixing the best approaches used by other engineers, one can find ways to surpass previous efficiencies. A key to achieving this goal is to understand what tools are available when given a new project.
Knowing how calculations have evolved can really help us appreciate the tools we have today. Electrical engineering was formally considered an occupation in the late half of the 19th century when electrical power distribution was fully commercialized. Electrical engineers of this era performed manual calculations with slide rules, but as the power systems became more sophisticated, the calculations became more complicated. As alternating current (ac) systems dethroned direct current (dc) systems, and transformers and 3-phase systems were introduced to the system, non-manual calculation tools were necessary to eliminate the negatives of manual approaches: human error and demanding work.
They used to do what?
Seasoned engineers often tell stories about how “back in the day, you didn’t have this or that” before the age of digital computers and computer-aided design (CAD) software, and most of the stories are true. Prior to the 1950s with its analog computers and analyzers, and the 1960s with digital computers, engineers did most their calculations by hand with the aid of slide rules. With the introduction of the per-unit system to address the change of voltages on transformers, and the introduction of symmetrical components to address the complication of three-phase systems, manual calculations became more labor intensive.
For larger projects, things can get complicated when engineers calculate all the basic parameters needed for a complete electrical system design using hand calculations. Let’s not forget the challenge of saving copies of the calculations. However, by being up-close and personal with the results, engineers from those times were able to build a natural knowledge of how the systems worked.
The handwritten form is the primal way of performing calculations, and it’s not going away. For the engineer, the key is to know which tasks are better performed using handwritten calculations. One of the good things about this format is that it is free. You only need a pen (or pencil), a piece of paper, and a calculator. This is as simple as it gets. This type of tool is perfect during a project meeting.
For example, conversations during the meeting may involve asking the lead electrical engineer to give an estimate of a circuit breaker size on a 480 V to 208 Y/120 V, 45 kVA, transformer primary side. Knowing the simple formulas to convert Volt-ampere into full-load amps) at a specific voltage (see Figure 1) and any code factors to be applied in the situation (i.e., NFPA 70: National Electrical Code table 450.3(B)), the engineer can calculate that the breaker size will probably be 70 A.
Remember, there are additional considerations to be taken into account, such as the type of overcurrent protection device or transformer type, but overall this is a good example of how to quickly and efficiently use handwritten calculations without running into major complications. Today, manual calculations can also be assisted with the use of published tables by manufacturers and vendors. These tables can be great resources when a specific product is being used in a project. For example, Cooper Bussmann’s Selecting Protective Devices Handbook is a must when doing coordination studies using fuses and other types of overcurrent protection devices. Eaton’s Consulting Application Guide Technical Discussion is another good example of a manufacturer’s published guide that has essential information that can help an engineer throughout his or her design.
Computers and software
The desktop computer began to make its appearance in the 1960s and became commonplace in the 1980s. Software products for these computers were created to help users with their daily needs. With this same mentality, programmers have created different tools to analyze electrical systems. With the arrival of computers, storage capability also came into consideration. A key aspect of using software tools is not only the capability of software products to calculate values, but the option to store, print, and share results in a clear and organized way.
Most software products started with a spreadsheet format, which eventually took over as the primary tool for electrical calculations. Most of their evolution was purely driven by user needs. At first, these types of software calculated nonlinear load flow, short-circuit currents, and voltage drop in a quick and simple way. The interface between the software and the users consisted of collecting all the information needed to calculate a value. The software required the user to input these values in a spreadsheet form. Much of the existing software still uses this type of spreadsheet format but has an updated, more user-friendly interface that looks less like a typical spreadsheet.
When Microsoft released the powerful Excel program in early to mid-1990s, companies took it upon themselves to create a large number of templates for calculation purposes. This helped them take control of and analyze the information the way they preferred. Another advantage of using Excel is the option to export spreadsheets into AutoCAD. Using DotSoft’s XL2CAD, a third-party software, an engineer can easily import Microsoft Excel spreadsheets into AutoCAD drawings (see Figure 2), and therefore saving the time it takes to type it into an AutoCAD text table.
In today’s world, spreadsheets are still very useful for tasks such as: panelboard schedules (to calculate connected and demand load; see Figure 3), reviewing metered information (to calculate sum, average, low and maximum values), and for service/feeder calculations.
The majority of companies own Microsoft Office licenses, which includes Excel. As a result, using this software can be seen as a no-cost option. There are still companies that are hesitant to spend money on new software that promises to facilitate all their needs by a single click of a button. These companies have already spent years of effort creating all these spreadsheet templates and have mastered their use. Alas, most companies eventually encounter the frustrating task of updating calculation values when there is a design change.
For example, most of these spreadsheets are separate, so if the mechanical engineer changes the horsepower size on some of the project’s motors, the electrical engineer has to make these changes in multiple locations. In addition to updating all spreadsheets affected by these changes (panelboard schedules, equipment schedules, riser diagrams, service calculations), the engineer must update all files created and imported into the AutoCAD drawings. This is where sophisticated software can be a game changer.
The key to knowing when to invest in these programs is to really understand what the company’s typical project portfolio is. If a company is traditionally hired to do electrical design on large projects that consist of multiple bus points and equipment, then a power analysis software package can be a useful tool. With the creation of the Microsoft Windows operating system, electrical system analysis programs have evolved drastically. Programmers, as stated before, have been working to meet the needs of their users with every update. SKM Systems Analysis, ETAP, EasyPower, and CYME Power Engineering Software are good examples of how programmers took advantage of the Windows operating system.
SKM is the one of the most widely used software packages in the industry. SKM has been around since the 1970s when its calculation modules used a basic spreadsheet format. It wasn’t until Windows 95 was introduced that SKM released Power Tools for Windows (PTW), and the rest is history. With PTW, SKM managed to combine all of its modules into the same platform, making it extremely convenient to have everything in one package. PTW carries a long list of calculation modules, but DAPPER is its primary product. DAPPER, or Distribution Analysis for Power Planning Evaluation and Reporting, performs all basic calculations needed for a project and more. This module performs demand load analysis, load flow voltage drop, motor starting simulation, traditional fault analysis, and load schedule documentation. It also performs feeder, raceway, and transformer sizing, but engineers should always maintain control of this task. It helps them catalog the decisions they made so they have a record when clients or reviewers make inquiries regarding sizing equipment.
ETAP is another widely used software package that can simulate power systems. Its history can be traced back to early 1990s when, in collaboration with Texaco, it became one of the powerhouses in power management with its real-time monitoring, helping customers in controlling operation, maintenance, and planning of their electrical power system. Throughout the years, ETAP has consistently added modules to its now vast list of software solutions. Just like SKM, ETAP has the Network Analysis solution that includes arc flash analysis, load flow analysis, short-circuit analysis, and so on.
Today’s version of software packages gives engineers the option of drawing the whole electrical system as a one-line diagram. The software requires engineers to input information for each component to allow the program to perform its calculation. When the input information is completely placed in the one-line, the program conducts all calculations selected from the list mentioned before at once. It will even give the user warnings and errors when information is missing or abnormalities appear in the results. Compared with the old way of using Excel spreadsheets, software packages are convenient and save engineers time when a change in design occurs. Engineers simply need to open one file, make the changes in that file, and all of the calculations will be updated simultaneously.
Documentation is also as convenient as performing calculations when using these software packages. Results can be shown in the one-line, but the software can create reports where it shows all parameters and results in a single document. This is great for quality control, including the documentation of all of calculations. Also, files can be imported into AutoCAD. As a result, creating panelboard schedules using software packages is one of the more valuable tools that an electrical engineer can use.
Using software packages might be overkill for some projects. That is why it is important to understand the project’s electrical scope before deciding what tool to use. Sometimes the project is small enough that using Excel templates alone will accomplish the calculations needed. If an engineer or company already has access to software packages like SKM or ETAP, the following rules of thumb can be applied to help you decide whether to use them:
Determine if the project includes any of the following tasks:
- Performing voltage drop calculations for more than three feeders
- Performing short circuit calculations for a multi-voltage level system
- Creating five or more panelboard calculations.
If these items apply to the project, then a sophisticated software package like SKM is a good candidate for performing calculations. Setting up the project accordingly from the beginning will be beneficial for both the project and the engineer’s work.
Another general tool available to electrical engineers is the Internet. However, be cautious to avoid relying on untrustworthy Web sources. The most trusted sites for electrical information typically are the manufacturers’ websites. With their help, electrical engineers can get information values that can help select equipment. Some manufacturers might even perform calculations for the engineer, saving time and resources. Developing a strong relationship with manufacturers and their representatives is key for electrical engineers.
There are also online discussion forums available to assist engineers in decision-making. Mike Holt’s Forum is a great place where new and seasoned engineers exchange knowledge for the same purpose: to achieve the best design possible. Engineers can talk to industry peers to help guide them in the completion of their design. Magazine articles are an additional tool to keep current with today’s technology.
Even though engineers started using AutoCAD as a tool for creating technical drawings, computer-aided drafting software products are moving toward performing calculations that can be used in combination with the drawings. These types of software products are marketed as CAD because of their additional capability of mathematical modeling. As explained before, by having calculations, drawings, and reports under one roof, electrical engineers can minimize labor hours and human error, specifically when making changes to the design. Software products like Autodesk MEP and Revit are incorporating plans with families, elements, schedules, and diagrams, making the electrical power system analysis and design more integrated than ever before.
With time, electrical engineers will develop their own best practices and will bring new skills to the table, leaving their own footprint on the project design. It is important to keep in mind that just because machines can provide quicker and clearer results, they may not always be the best option. Understanding the true benefits of any tool is essential for engineers to efficiently design and review results, specifically to aid in supporting and documenting their design decisions in the event other engineers, clients, or reviewers inquire about the electrical system.
Manuel E. Hernandez is an electrical engineer with Primera Engineers. He has experience in building systems engineering for a variety of projects in the commercial, educational, and health care markets; his experience includes the use of SKM Power Tools software, Arc Flash Analysis, and AutoCAD drafting.