Assumptions Limitations Adaptive Ground Fault Circuit Interrupter End Product Description Abstract A ground fault circuit interrupter, or GFCI, is a device used to protect against electric shock if someone should come into contact with an energized electric wire while also in contact with the earth/ground. A leakage current between the energized wire to ground may also exist, and vary with time. One of the functions of the existing GFCI module manufactured by the Square D Company is to trip, or open, a circuit in the event that the leakage current should exceed 4-6mA. However, since the leakage increases gradually with time, this results in the circuit tripping unnecessarily. The solution proposed by this project is to provide a control to adjust the set threshold for gradual increases in the leakage current. The expected result of this project will be an AGFCI that will monitor and adjust the threshold current that will trip, or open, a circuit breaker in a power system with the use of a micro controller. The AGFCI will be designed to fit a typical residential or commercial circuit breaker rated at 120 volts, in accordance with the specifications as provided by the Square D Company. Existing GFCI Design Requirements Introduction Design Objectives The objective of this project is to design a modification to Square D’s standard GFCI. This addition will include the use of a micro-controller to adjust the threshold point of a GFCI, depending on the leakage current detected by the circuit. Design Constraints The first of constraint is that the completed circuit will ultimately need to fit inside a typical breaker. For the time being, there is no specific size limit on the size of the chipboard in the final product. The second is the size of the program that will need to be stored in the microprocessor, as well as the speed of the microprocessor itself. These last couple of constraints will not be extremely important considerations as another micro-controller with the proper specifications can be chosen. The micro-controller will also require a power supply. Since the current GFCI has a power supply already, consideration will be taken to add a second, or use the existing supply. Measurable Milestones Functional Requirements General Background This project will produce an AGFCI that will control the operation of an electrical breaker/switch. The resulting device will fit into a typical electrical breaker designed for use in residential and/or commercial buildings. Technical Problem The solution devised to the existing problem will consist of a micro-controller to control the adjustment of the threshold value in the GFCI. The device will take information about the leakage current and act on that information based on a custom design program. This program will be written in C language, converted to assembly, then downloaded to the micro-controller. Operating Environment The product will be expected to operate normally within –35o to 80o C. It will be also be able to withstand damp conditions. Also, the entire module will be enclosed inside a breaker box, and must be able to operate inside an enclosed environment. Intended Users and Uses The AGFCI is intended for use in breaker for residential and commercial installation. It will be used specifically to protect people from electric shock, and appliances from damage due to short circuits. The Square D Company will be the sole manufacturer of this product, since they will own the result. Assumptions Limitations Range of Operations 2.0 – 20.0 milliamps High Noise Immunity Operates at 120 Volts Response Time 30 msec when leakage is less than 10 mA 15 msec when leakage is greater than 10 mA Threshold Increase Rate of 0.5 mA in 60 sec Threshold Decrease Rate of 0.5 mA in 10 sec Problem Definition Study Current GFCI Choose Solution Method Define Program Parameters Completion of Program Completion of Prototype Protoype Functional Leakage current increases according to a definite function Leakage current will have a value large enough to detect Financial budget Time Available micro-controller technology Technical Approach The first consideration was how the leakage current would be detected, but a current sensor from the original design will be used. The sensor’s output will then be examined by a micro controller. The micro controller will then determine if the circuit will trip. The next consideration was what the most appropriate coding language would be. The decision here was to use the assembly language provided with the micro controller. The team is fairly familiar with this type of language and any higher-level language would need to be converted. The choice was made to use any controller that would have the memory capability to carry all of the program code on board. The next step is to determine the method that will trip the breaker. Budgets Personnel Financial Total Estimated Time 400 Hours Total Estimated Budget $350 Testing Approach Team Members All testing will be done to meet the functional requirements as provided by the Square D Company. The code’s modules will need to be tested separately and as a whole program. Also, in addition to functionality tests, the speed of the program will be a testing consideration, since the response to a potentially life-threatening situation is a concern. This speed testing will mostly involve testing for the most efficient ways to achieve the desired output. The prototype will be tested by passing a varying differential current and observing the results. Members Paulus – Team Lead Mike Lin Pat Roehl Emeka Anyanwu Advisors V. V. Sastry James Triska Glenn Hillesland Acknowledgements Breaker Load Center The Square D Company Henry Zylstra