Database Design for Electrical Panels

Transcription

1 Christian Brothers University 650 East Parkway South Memphis, TN Database Design for Electrical Panels By Shalini Gupta, Monte DePouw John Ventura MEMPHIS AREA ENGINEERING AND SCIENCES CONFERENCE MAY 10, 2002

2 1 Database Design for Electrical Panels By Shalini Gupta, Monte DePouw, and John Ventura Abstract Electrical engineers specify the design for electrical panels. The panels could be a lighting panel, receptacle panel, or a main panel. Currently most engineering firms perform all calculations associated with the design of electrical panels without the benefit of computer software. This is an inefficient and time-consuming method. Although, there is software available; most companies have not adopted them due to the fact that they are not compatible with their existing software and they are not user friendly. The purpose of this project is to design a computer program, which calculates the components for the electrical panel. Based on the goals and available resources, the following needs metric matrix has been generated: Needs Research User Interface Ease of Use Compatibility Compliance with NEC Testing Table 1: Need-Metric Matrix Description Extensive Research is required in order to perform a good design The User Interface needs to be visually pleasing The database should be easy to follow and use As the database is being designed in Ms Access, it needs to be compatible with different versions of Ms Access available All calculations performed need to be compliant with the equations and rules stated in the NEC handbook. The design will have to be tested on a regular basis to ensure the accuracy of its commands and functions

3 2 In view of the needs matrix, the database chosen for the design of the electrical panel is Microsoft Access due to the following reasons: User friendly Graphical Interface Single Screen display Easy to update the database Less prone to error Saves time Compatible with different platforms. This paper explains the fundamentals of panel design and the software design implementation.

4 3 Table of Contents: Introduction 1 Database Fundamentals... 3 Inputs and Outputs of the Automated Panel 8 Calculation of circuit Breaker size 12 Recommendations. 14 Conclusion.. 15 Appendix 16 Bibliography.. 18

5 4 Introduction: The purpose of this project is to design a computer program in Microsoft Access to calculate breaker sizes and the load totals on each phase for electrical panels in a friendly graphical user interface for the sponsor DePouw Engineering, LLC. Many of the repetitive tasks in the computing panel schedules have been automated. DePouw Engineering is an electrical consulting firm located in Memphis, Tennessee. DePouw Engineering specializes in commercial and industrial power distribution and lighting system design. A typical project design includes point-by-point calculation; short circuit analysis, protective device coordination, and wire size correction for ambient temperature, conduit fill, and voltage drop analysis. The firm currently employees three registered electrical engineers, two designers, and a support staff. A licensed master electrician is employed to inspect all projects at critical stages of construction, as well as to verify compliance with plans and specifications from start to finish. DePouw Engineering has a wide range of customers-architects, engineers, schools and sports center. The Production Manager s concern at the firm is that the phase loads, diversification of phase loads, calculation of breaker sizes and cascading of panels to a main panel are done by hand (Note: All these calculations are performed on paper and the final product is called a panel schedule). This is time consuming, inefficient and prone to error. As supported by IEEE Industrial Applications, (Volume 37- Issues 3, 1), calculations for panel design performed by a computer tend to make the complex and time consuming task of looking up tables and calculating circuit breaker ratings easier and less prone to error. Some companies have designed databases to perform

6 5 calculations for panel design, however, most electrical design companies have not adopted these programs as they are not visually appealing, or because they do not approve of the parameters used for the calculations, as the equations are based on a different version of the National Electrical Code (NEC) handbook. Hence, the production manager at DePouw engineering would like a database custom-designed for their needs and in accordance with the code specified in the NEC version adopted by the state of Tennessee. The program will display an interface, which an electrical engineer can use to enter data and receive the final automated panel schedule. The computer generated panel schedules will then be plotted by the engineer and submitted to the contractor. Microsoft Access was chosen to design the database. This is due to the fact that the company already has a copy of the software and the employers are more comfortable implementing the panel design in MS Access.

7 6 Database Fundamentals: It can be overwhelming when large amount of data needs to be tracked in project organization. Several companies still use a paper filing system, text documents or spreadsheets to keep track of information. This kind of record keeping can be tedious, inefficient, and requires a lot of physical space. A more convenient data management systems namely a database has been developed. One of the best examples of this new software is Microsoft Access. Below is the explanation of the main fundamental components of Access that were employed in the design of the program. Tables A table is a collection of data about a specific topic, such as products or suppliers (Using Visual Basic 6, 453). The tables in Access are analogous to that of Excel. Below is an example of the table where data was entered for the load type. Figure1: Load Type table used in the program

8 7 These tables were used to extract data for the pull down menu in the main form. Separate tables were used for each drop-down menu. Using a separate table for each topic means that the data is stored only once, which makes the database more efficient, and reduces data entry error. Forms In Access, users friendly forms can be created that allow the user to enter information in the graphical interface. These forms can be custom designed for the user. The information entered in the graphical form has information that is transparently passed onto the user (Microsoft Access 200 Bible, 785). The figure below represents the forms that were created. Figure2: Form View of the three-phase form

9 8 The tabular like region (containing the circuit number, the load type, description, Phase A, Phase B, etc.) is called a sub form. A sub form is a form within a main form. Below is the display of the single-phase form. Figure3: Form View of the single-phase form Note that the difference between a three phase and a single-phase form is the number of columns. In the three-phase form there is an extra column-phase C. In addition, separate calculations have been programmed in the two forms for the calculation of the breaker sizes. The user can interchange between the two forms by changing the option Phase (on the top part of the screen) between single phase and three phases.

10 9 Visual Basic Codes Once the user has completed entering the necessary input, Access performs the calculations. The code for these calculations was programmed using Visual Basic, which is an inbuilt feature in Access. Below is a sample code. This code changes the display of the sub- form from a single-phase form to a three-phase form depending on the selection made. Figure 4: Visual basic code for changing a sub-form The change of the sub form is able to take place because of the event procedure triggered by the combo box (Using Visual Basic 6, 855). (Note: In access the drop down menu is called the combo box. Here the combo box being referred to is the drop down menu titled Phase in the top half of Figure1 and Figure 2). The Phase combo box is shown below.

11 10 Figure 5: Phase Combo Box It can be observed in Figure 5 that the Visual Basic subroutine will be triggered after the user enters a value in the Phase combo box, or if the user makes a selection from the drop down menu.

12 11 Inputs and Outputs to the Automated Panel Form: The panel design program outputs the breaker sizes and the totals of the load on each phase. The inputs and outputs are presented in Table 2: Input Output Voltage Breaker Size Phase Breaker Size Wire Size Main Circuit Breaker/Lugs Panel Type New/Existing AIC Bus Mounting Entry Feeder Load Type Pole Breaker Size Load on the Phase Breaker Size Table2: Program inputs and outputs The main inputs, which affect the computation of breaker size, are the values for the voltage, phase, the number of poles, and the load on the phase. The other standard inputs such as the wire size, main circuit breaker/lugs, panel types, new/existing, AIC, bus, mounting, entry feeder, load type do not affect the calculations. Once all the data has been entered the program automatically calculates the breaker size and the total of the load on each phase.

13 12 Explanation of Inputs: The first input is voltage. Voltage plays a very important role in the calculation of the circuit breaker. The voltages can be chosen from a pull down menu in the database form or the user can enter the voltage. The voltages that have been programmed into the database that can be selected from a drop down menu are shown in Table 3. The reason that these values were programmed into the database is because these are the most commonly used at DePouw Engineering. Voltage / / / Table 3: Voltage programmed into the drop-down menu in the database The next input is Phase. The user can select from the pull down menus either a single phase or a three-phase voltage supply. This input affects the circuit breaker calculations. The number of wires constitutes the next input. The number of wires can be either two, three or four. The number of wire indicates the number of hot wires (in addition to indicating a neutral and a ground wire). The Main CB/lugs input implies whether lugs will be used or the size of the circuit breakers that will be used. The sizes of the main circuit breaker that have been programmed into the database are as follows: 20A, 25A, 30A, 40A, 45A, 50A, 60A, 70A, 80A, 90A, 100A, 110A, 125A, 150A, 175A,

14 13 200A, 225A, 250A, 300A, 400A, 600A, 800A and 1000A. These values were obtained from the NEC The next input is Panel Type. The Panel type gives an overall description of the panel. The following description of the panel types can be selected from the pull down menu in the database: critical, emergency equipment, isolated ground bus, life safety, normal, and UL listed for Non-linear. Next, the user can specify whether the pane is new or existing. In addition, the user can enter the panel name in the dialog box in the access database form. Further, the user can input the values for the Amperage of Interrupted Circuit (AIC). The AIC values that have been programmed in are 22000,30,000,42000,65000, and series rated. The user can select from a pull down menu the ampacity of the bus. The values programmed for the amperage of the bus are: 60A, 100A, 125A.175A, 225A, 400A, 600A and 800 A. These values are the standard values specified by NEC In addition, the user can enter the mounting of the panel board. The drops down menu options for mounting are: flush, surface and switchboard. Subsequently, the user can enter the entry of the panel: that is top, bottom, left and right. For each circuit (in the sub form), the user can select whether it is a one-pole, two pole or a three-pole breaker. The user can also enter the panel description and select the load type for each circuit. Within the load types pull down, there are many different choices. These choices have been abbreviated in the program; the full form and the description of these choices can be found in the Table 4.

15 14 Abbreviation BL BSP C Description BL stands for Blank, It is used to place blank values in the selected circuit group This acronym stands for Bussed Space C stands for Continuous load D GFI H H/M K R SR T WH X This implies that the load type for the circuit group is Dwelling (such as residential units) H stands for hospital load This abbreviation indicates a hotel of motel load. K stands for Kitchen load R sets the load type for the circuit group to Receptacle SR implies that the current circuit is a Spare. T sets the load type for the circuit group to Transformer. The acronym WH stands for the load type Warehouse X stands for X-ray load XH XH indicates that the load type for the current circuit group is X- Ray Equipment at Health Care Facilities. Table 4: Description of the abbreviation of the load-type options in the Access form.

16 15 Calculation of Circuit Breaker size: Depending on whether the user selects a 1- pole, 2- pole or a 3-pole circuit breaker the calculation for the circuit breaker varies. If a 1-pole circuit is chosen then, the calculation for the 1-pole circuit breaker is as follows: 1-pole CB size = SVA 80%*( P N) V (Equation 1) and, if a 2-pole circuit is chosen then the calculation for the 2-pole circuit is as follows: 2- pole - CB size = SVA 80% *( P P) V (Equation 2) Finally, is a 3 pole circuit is chosen then the calculation for the 3-pole circuit is as follows: 3-pole-CB size = SVA 3 *80%*( P P) V (Equation 3) Where SVA (P-N) V (P-P) V CB = Specified Volt-Ampere (that is the load entered by the user) = Line to Neutral voltage = Line to Line voltage = Circuit Breaker It can be observed that each of the three equations above have been divided by 80%. This is because according to NEC-1999, Article : A branch circuit that supplies continuous load or any combination of continuous load and non-continuous load, the rating of the over current device shall not be less than non-continuous load plus 125 percent of the continuous load. The 125 percent is equivalent to 1. 80%

17 16 Article of the NEC-1999 specifies that the standard ampere ratings for fuses and inverse time circuit breakers shall be considered as follows: 15, 20, 25, 30, 35, 40,45,50,60,70,80,90,100,110,125,150,175,200,225,250,300,350,400,450,500,600,700,80 0,1000,1200,1600,2000,2500,3000,4000,5000, and 6000 amperes. Based on this, the breaker sizes calculated from the above three equations are rounded of to the nearest standard ampere rating.

18 17 Recommendations The automated Panel Schedule in Microsoft Access is definitely more user friendly than the paper based design method. The database is efficient as it saves the user time and is an error free method. This program calculates the breaker size for each circuit and the total of load on each phase. The calculations in this program are the basis of the design of a panel schedule. Once the basic calculations are performed then the design engineer usually performs the diversification of phase loads and cascading of panels to a main panel. This is also being currently being done manually at DePouw Engineering. Hence, the next step would be to use this program and program additional features that will perform the diversification of the phase loads and cascading of panels to a main panel. Thus, this program would serve as the backbone for the new program. Since the company already has Microsoft Access, it would be advisable to continue the program in Access as it does not incur any additional cost and the users are already familiar with the software.

19 18 Conclusions: The Access program presents an excellent solution (to the tedious task of designing a panel schedule. The automated schedule is user friendly, has a visually pleasing graphical interface, error-free, saves time, and is compatible with different platforms. The program written has been tested, and all calculations agree with those performed manually. Moreover, the calculations are now performed faster and more accurately. In addition, all the information can be edited and stored for future reference. Overall, this program is useful, so design engineers will use it. The final automated panel schedules created using this program will be plotted and submitted to the contractor.

20 19 References National Electrical Code Massachusetts: National Fire Protection Incorporated, Sutherland R.G. A standard system for power format studies. Pruchniaki, Wayne. Peasley, Richard. &Reselman,Bob. Using Visual Basic 6. New Delhi: Prentice Hall of India, Prague, Cary. Irwin, Michael. & Reardon, Jennifer. Microsoft Access 200 Bible.California: IDG books, 1999.