AC Overload Tester for Magnet Wire

Transcription

1 Current (A) Introduction AC Overload Tester for Magnet Wire Presented By Matt Lane IPFW Senior Design AC Overload Test is a standard test method to verify thermal stability of the insulation system of magnet wire. ASTM D1676 and NEMA Standard The test subjects a twisted pair sample of magnet wire to an excessive amount of current flow until the insulation system burns out. (1) Footnote should be Arial Narrow 10 Italics gray; location should not be altered 2 Test Method Test Method Test Method (ASTM D , Section & NEMA Standard No. MW 790) The test equipment shall sink a rated amount of electrical current through the sample. The rated current shall increase, step-wise, every 180 seconds. When the insulation system of the wire breaks down ( burns out ) sufficiently as to allow 50mA of leakage current the test equipment stops supplying current to the sample. The step-wise integration of the increase in current shall be calculated to obtain the Overload Figure of Merit (OFM). Step-Wise Current Increment Over Time Time (s) 3 4 Problem Solution Superior Essex currently has an outdated tester. 40 year old technology and beginning to fail No automatic data capabilities; manual reading and calculation of results Limited to 50 Amps testing and 15 AWG wire size New tester using same theory of operation with upgraded technology Arduino Microcontroller 4D Systems resistive touchscreen display Increased capabilities Larger components for higher power output Will test up to 12 AWG, which is the largest practical size 5 6 1

2 Requirements Block Diagram Test capability of up to 100 Amps AC to the test sample Automatic data calculations Current Values for the test Overload Figure of Merit Data acquisition capabilities Must perform in accordance with the established Test Method 7 8 Arduino Arduino MEGA V operation, 256kb memory, 54 I/O pins, 15 PWM pins, 16 analog inputs, 16MHz crystal oscillator Arduino Uno 5V operation, 32kb memory, 14 I/O pins, 6 PWM pins, 6 analog pins, 16MHz quartz crystal clock 4D Systems ulcd-70dt Resistive Touchscreen Display 7, Diablo16 processor, 32kb RAM 9 10 Motorized Variable Autotransformer 240V/0-208V Single Phase 120V AC Motor Controlled Voltage increases from 0 to 208V depending on what current is required at the test sample at that time. Current Transformers 208V/26V 8:1 Ratio As voltage rises on the primary side, it lowers on the secondary side, resulting in stepped up AC Current

3 Shunt Resistors 150 Amp AC, 50mV, µω Will be able to hold apparent power at the test sample fixture of 2.6kVA without melting Essentially just a copper bar with a very low resistance Current Sensors Non-invasive, split core current transformers Can measure up to 150A AC. Max peak current = * 150A = 212.1A Current at output of sensor = 212.1A / 2125 turns = A Current Sensor Shield Arduino can only handle voltage (between 0V and 5V) so the output current needed converted into an acceptable voltage. To do this, a burden resistor was added to a shield for the current sensor. As the current is alternative around 0 and to maximize measurement resolution, the max voltage at the burden resistance needed to be max accepted voltage, 5V / 2 = 2.5V. Burden Resistance = max voltage / sensor current = 2.5V / = 25Ω Just used a 33Ω resistor Arduino can not measure negative voltage, so added 2.5V to the circuit to make the voltage measurable. 2 resistors added, 10kΩ to avoid too much energy consumption. Also, a low reactance capacitor, 10uF a few hundred ohms was added and provides an alternative path for the alternating current to bypass the resistor Current Sensor Shield Circuit and Board Solid State Relays 3 to 32VDC input, 120V 4A output Used by the microcontroller to switch the AC motor on to raise and lower the wiper The Arduino IDE was used to design the software. It uses a C++ type language that should be familiar to anyone with knowledge of C. 4D Systems Visi-Genie was used to design the test screens, which operated with the host Arduinos. Visi-Genie is a very visual, drag and drop environment, providing a What-You-See-Is-What-You-Get (WYSIWYG) screen. The core of the environment uses non-returnable structures to both setup the microprocessor and loop the program. External functions are written and called upon in the scope of the loop

4 4D Systems developed a library that integrates an Arduino host called geniearduino (geniearduino.h). Using this library and Arduino coding, user inputs were accepted and processed via an on-screen keyboard. Test Screen Test Screen 2 Test Screen Test Screen 4 Test Screen

5 Keyboard Inputs Keyboard Inputs Keyboard Inputs Calculations to determine current values for the test So for example, if the wire to be tested is 18 AWG: Functions to determine current values for the test Functions to determine current values for the test

6 Current Sensing Open Energy Monitor is an organization that developed an Arduino library for sensing current. Master Reader / Slave Sender The current sensing code and library required a lot of simultaneous resources Too time consuming to study the library and try to make adjustments to clean it up. Solution was to utilize a second Arduino as a slave sender to handle the current sensing and send the data to another Arduino acting as a Master Reader Arduino code for testing relays Arduino code for testing relays Lessons Learned Accomplishments Sometimes, you are at the mercy of your stakeholders Do not solder anything until you re absolutely sure of your design Do not start chopping up your code if you are having a problem before checking all physical connections and setups. Make frequent backups of your code as it is starting to come together Project approved and parts purchased Test screen developed and accepting user inputs Arduino code processing user inputs and determining current ratings for the test Current sensing code is working and Arduino is reading current SSR code is working and the relay circuit from the Arduino to the AC motor is functioning as expected

7 Going Forward Demonstrations Next steps Integrate test start commands from the test screen to initiate the test, sense the current, and control the relays as needed Complete test screen design to show outputs to the user (test results) Draw and receive the test equipment enclosure (to be manufactured by Buckeye Shapeform) Get certified calibration for the tester Deploy the tester to the Test Lab User Inputs Arduino processing user inputs and determining current values Slave Arduino current sensing Master Arduino relay control Twisted Pair test sample being overloaded and burnt out Questions/Comments Thank you for time 39 7