High Voltage Testing Team 5: Justin Bauer, Matt Clary, Zongheng Pu, DeAndre Dawson, Adam McHale
Presentation Content Introduction Basics Defining High Voltage Risk Factors Safety Issues with High Voltage Short-Circuiting Dielectric Breakdown Arcing Project Relevance How to Mitigate Issues Tesla Coil Van de Graaff Further Precautions
Introduction High Voltage is typically just electrical energy at voltages high enough to inflict pain or even death to living organisms. High Voltage Testing is the utilization of breakdown, conductivity, polarization, and dielectric losses in electrical insulations in the presence of electric fields.
High Voltage Testing Basics Safety Safety Glasses Gloves HV Suit Technique High voltage power lines Grounding System Tie grounding straps from jacket & pants together
Defining High Voltage How to determine high voltage Possibility of causing a spark in the air Danger of electric shock by contact or proximity According to Internal Electrotechnical Commission, high voltage is defined as: > 1000 V rms for AC > 1500 V for DC Definition may differ based on context Some organizations consider > 600 V high voltage General public considers 100-250 V high voltage
Risk Factors Voltages over ~50 V can cause a dangerous amount of current to flow through human body Can cause heart fibrillations Wet skin decreases resistance, increasing current Burns can occur Strong electric fields can produce sparks Can potentially arc to anyone standing in the vicinity Arc flashes, electrical explosions due to a low impedance connection to ground Max temperature can exceed 10,000 kelvin Can cause severe injury to workers
Safety in High Voltage Operations Safety precautions in high voltage operations are similar to that of lower-level voltages. Shorting a large difference in electrical potential induces current < 100mA : pain, muscle contractions, and upset breathing 100 200 ma through the human heart causes heart fibrillations Power is dissipated in the form of heat Often leads to burn injuries
Short-Circuiting Electrical connection is made between two positions of drastically different electrical potential Large influx of current through shorted path Floating remaining electrically connected to position of high voltage but disconnected from ground Birds on power lines
Dielectric Breakdown Voltage builds up across a gaseous medium Surpasses dielectric strength and the medium begins to become ionized Conductivity of medium rises Insulators may become conductors Current passes through medium, further sustaining ionization Principle of lightning strikes
Arcing Dielectric breakdown on smaller level than lightning strikes Pulses of current through relatively small gap of air Common household static electricity May ignite flammable gases or liquids May damage or interfere with electrical equipment Principle of operation of Van de Graaff Generator
Project Relevance Lightning can generate up to 100 million volts Not reachable given normal lab equipment Small scale machines with similar characteristics are used (Tesla Coil and Van de Graaff Generator) High voltage test procedures still apply
Project Test Equipment Tesla Coil kv to MV range large currents (above 20A) Cannot be within 10 ft. radius Van de Graaff Generator 2-3kV generated averages 50 microamps cannot cause human harm, but may damage electronics
How to Mitigate the problems For Tesla coil testing Make sure metal cases associated with tesla coils are grounded Keep a safe distance away from the corona discharge Use adequate fusing to limit the maximum current on our device Always discharge capacitors before adjusting a primary circuit.
How to Mitigate the problems For Van de Graaff testing: Make sure metal cases associated with Van de Graaff are grounded properly keep any other electronic devices( cell phone, laptop, etc) away from the generator Discharge metal sphere before touching it
How to Mitigate the problems Proper placement of lightning rod (highly conductive metal, enough height, right path to ground) Faraday cage to protect our detecting device Proper ground for detecting device as well Safe distance
Further Precautions High Voltage Suit Made from Nomex aramid flame resistant fiber & micro stainless steel fibers Techniques Arm behind back rule Lockout/tagout
Questions?
References http://www.aharfield.co.uk/lightningprotection-services/about-lightning Plasmasonic DRSSTC Instruction Manual http://en.wikipedia. org/wiki/dielectric_strength