1. Corona Threshold Voltage
Team Tesla:
Chris Rowan
Anthony Thompson
Brandon Sciortino
Philip de la Vergne
Aaron Wascom

2. Presentation Purpose
This Presentation describes the preliminary design for the electrical breakdown experiment by Team Tesla for the LaACES Program. It fulfills part of the LaACES Project requirements for the Preliminary Design Review (PDR) to be held February 5,2013

3. Document Scope
This Pre-PDR Presentation specifies the goal, objectives, background, and requirements for the electrical breakdown experiment and provides a guideline for the development of this payload under the LaACES Project. As such, these topics provide the basic for developing the PDR document and presentation.

4. Mission Goal
To study the effects of humidity and temperature on the electrical breakdown of the atmosphere to prevent sparking and ensure safety.
We want to do this to further ensure the reliability of electronics operating at varying temperature and pressure and humidity conditions.

5. Science Objectives
To conduct an experiment of the breakdown voltage in air at varying altitudes
To observe the effects that temperature and humidity have on our expected recreation of Paschen’s curve

6. Technical Objectives
Measure temperature, pressure, humidity, current, and discharge voltage for the duration of the flight

7. Science Background: Electric Discharge
Results from the creation of a conducting path between two points of different electrical potential
Three Types:
1. Corona Discharge
2. Spark Discharge
3. Brush Discharge
Electric discharge happens when there is a conducting path between two electrodes of different electric potential. In other words, when the medium changes from an insulator to a conductor.
We want to create a corona discharge while preventing a spark discharge so that we don’t endanger any payloads. In order to do this, we must understand each of the different kinds of discharges.

8. Science Background: Corona Discharge
Occurs when the threshold voltage is breached
Only requires a high field strength
Current ranges around micro amps
If the field strength in front of a sharp point of a conductor exceeds the breakdown field strength for the medium (in this case air), a corona discharge will take place.
It may also happen if a grounded, sharp conductor (at zero voltage) is brought near a charged object, like a piece of plastic that has been rubbed.
This event demonstrates that it does not take a high voltage to cause a discharge, only a high field strength, which is ideal for our payload experiment due to our weight restrictions.
It may be maintained as long as the breakdown field strength is exceeded in some region—that is, as long as the voltage of the electrode or the charge density of the charged insulator is high enough.
The current in a corona discharge can be as low as micro amps.

9. Science Background: Spark Discharge
Occurs when the threshold voltage is breached
Complete ionization between electrodes
Maintained through a continuous high voltage source
At the other extreme of the discharge range, we have the spark. Like corona discharge, the discharge starts at the point where the breakdown field strength is exceeded.
However, unlike corona discharge, the ionization takes place all the way between the two electrodes.
If the electrodes are connected to a voltage supply, the discharge may turn into a continuous arc, but in the normal case of a spark from an insulated conductor, the discharge is a very fast process.
Typically, the process is extremely fast. However, a spark may be maintained if it is continuously powered.

10. Science Background: Brush Discharge
In between the corona and spark discharge
It may appear as irregular luminescent paths
Occurs between corona and spark discharge and may look like irregular luminescent paths.
Almost all discharges from insulators are brush discharges, like the crackle that you hear when you pick up a charged photocopy or that you feel when you pull a sweater over your head.

11. Science Background: Corona Threshold Voltage
The potential at which corona is found to originate
Ohm’s law regime
Once the threshold is breached, current increase proportionality with voltage
Past the threshold, current increases rapidly and leads to a complete breakdown and arcing or sparking at a point called the breakdown potential

12. Science Background: Avalanche Effect
Ionization of neutral atoms becomes possible when the KE of free electrons increase
Ionization of neutral atoms becomes possible when the KE of free electrons increase

13. Science Background: Paschen’s Curve
V=f(pd)
The minimum of this curve corresponds to the minimum Pxd product for which the ionization effect is maximal

14. Science Background: Humidity
Partial breakdown threshold reverses from decreasing the threshold to increasing it once the pressure drops below a certain point
20,000-25,000 ft.
Humidity can affect the magnitude of the current moving through the ionized air by up to 20% in a pulse corona
Pulseless corona and negative corona is not affected by changes in humidity
In cases where a pulse corona is created, humidity can affect the magnitude of the current moving through the ionized air by up to 20%

15. Science Background: Atmospheric Conditions
This graph lays out the conditions of the atmosphere during flight
For the duration of the flight we will be ranging from 0 to ft inside a temp window ranging from bla to bla with presures of bla to bla
Flight profile of expected payload environmental conditions

16. Science Background: Temperature
Temperature decrease  ionization energy increase  avalanche effect decrease  breakdown voltage increase
Temperature decrease  ionization energy increase  avalanche effect decrease  breakdown voltage increase

17. Technical Background: Electrodes
Electrode - an electrical conductor that is used to make contact with a nonmetallic part of a circuit
An electrode can be classified as either a cad or an depends on its charge or polarity
Cathode: negatively charged electrode that attracts cations
Anode: positively charged electrode that attracts negatively charged electrons

18. Technical Background: Positive vs. Negative Corona
More stable discharge
Linearly sensitive to changes in humidity
Produces less ozone than negative corona
More self-sustaining discharge
Humidity has little to no effect
Can only be sustained in fluids that contain electronegative molecules

19. Technical Background: Electrode Geometry
Point
Small surface area
Concentrated electric field
Different geometries provide varying high-potential surface areas to ionize the gas flowing past them
Electrode Geometry
For a stable discharge, a point-plane geometry must be used. Since electrons flow from negative to positive, the anode needs to be as pointed as possible, like a needle. This will allow for the avalanche effect to begin. The cathode must then be a plate, to reduce the likelihood of a spark discharge. As the charge moves through the E field, its constructed as it moves back into the smaller surface, therefore causing a pulse corona.

20. Technical Background: Electrode Geometry
Plane
Evenly distributed electric field
Larger surface area

21. Technical Background: Electrode Configuration
Point-Plane
Surface area ratio
Ionization energy
The extremely large ratio of surface area between the point and the plane and the concentration of ionization energy built up at the point allows for the lowest onset voltage for corona discharge.

22. Technical Background: Electrode Composition
Surface
Texture
Impurities
Surface Area
Electrode Material
Dielectric Strength
Conductivity
ough has increased numbers of weak points per unit area of electrode
Smooth creates a more uniformed electric field
In general, the rougher the surface finish, the lesser the breakdown voltage
Impurities are examples of any substances located on the electrodes that would interfere with the conductivity within the medium
Examples may be : Condensation and containments
Increasing the area of the electrode makes it more difficult to maintain a given breakdown voltage
The materials durability (dielectric strength) and conductivity have an effect on the voltage breakdown
Steel
Copper

23. Technical Background: Previous Experiments
A mathematical model of the modified Paschen’s curve for breakdown in microscale gaps
Influence of Axial Magnetic Field on the Electrical Breakdown and Secondary Electron Emission in Plane-Parallel Plasma Discharge
Stainless steel electrodes
Mean discharge current determined by voltage drop over R
Breakdown voltage is mean value recorded from Oscil.
Copper anode and SS cathode
Voltage increased by increments and allowed to settle
Current spikes from 1 nA to hundreds of mirco-amps
Voltage quickly reduced to zero

24. Technical Background: Measurements
Measurements during flight:
Temperature
Pressure
Humidity
Voltage
Current

25. Technical Background: Environmental Sensors
Temperature Sensor
Small signal p-n junction diode
Pressure Sensor
Piezoelectric sensor
Humidity Sensor
Capacitive sensing element with on-chip integration
Temp Sensor - Forward bias voltage of the diode varies linearly with temperature
Pressure Sensor - difference in output voltages relates to pressure
Humidity Sensor - Outputs a voltage varying linearly with RH

26. Technical Background: DC to HVDC Converter
An electronic circuit which converts a source of direct current from one voltage to another
Due to the payload size and weight restrictions, the required voltage for discharge is improbable with on-board batteries alone

27. Technical Background: Current Sensor
Pico ammeter
Voltage drop across resistor
Radio Frequency Interference
Band of frequencies produces upon discharge
Use a circuit diagram for a pico ammeter as a basis and adjust it to measure microamps.
Another method is to use measure radio frequency interference. When the corona starts and stops, it will produce radio wave disturbances. So we could have an AM radio wave antenna around the spark gap and identify when the disturbances happen by recording an AM radio frequency and looking at the data.

28. Science Requirements: Spark Gap
The gap distance shall be 1mm
The electrodes shall be composed of copper
The electrodes shall be rough and clear of impurities
The electrode configuration shall create a positive corona discharge
-The gap distance needs to be 1mm because 1mm is the smallest gap distance that we can accurately measure and still get reliable results.
-In order to ensure the accuracy of our results because a previous experiment we are basing our payload on also used copper for their material of choice
-The electrode configuration sh-The electrodes shall be rough and cleaned to lower the required breakdown voltage needed to produce a corona discharge
all facilitate corona discharge and inhibit sparking in order to ensure the safety of the payload
-The discharge shall be stable

29. Science Requirements: Power and Sensor
The spark gap shall be provided with a maximum of 4.5kV
The payload shall record temperature, pressure, humidity, voltage, and current across the spark gap
The payload shall be fully operational throughout the entire flight profile
-The spark gap shall be provided with enough of a voltage difference to produce a discharge at ground level with a gap distance of 1mm, which is 4.5kV
-The sensors must be operational throughout the flight and must measure temp., pressure, hum., volt., and current across spark gap so that the experiment is a success

30. Technical Requirements
The ammeter shall have a minimum accuracy to the microamp range
The HVDC shall operate in all environmental conditions
The output voltage of the DC to DC converter shall be controlled through an on-board interface
All data shall be time-stamped and real-time clock must be synced to the payload GPS -
-Like our sensors, the HVDC will remain operational throughout the flight
-The output voltage of the DC to DC converter needs to be controllable to ensure safety
-All data must be time-stamped and real-time clock must be synced to the payload GPS to ensure accurate altitude data.

31. Technical Requirements: LaACES
The payload shall not weigh more than 500 grams
The payload shall not exceed 3 oz / in2 on the smallest face
The payload equipment shall cost less than $500
The payload shall have two holes 17 cm apart running the length of the payload to comply with LaACES management requirements
-The payload shall meet all geometry, mass, and budget requirements set forth by LaACES management

32. Project Management: Team Contract
Team Meeting
Disciplinary Action
Communication
Version Control
Decision Making
Team Roles

33. Project Management: Organization
Task
Member
Project Management
Anthony Thompson
Science Requirements
Chris Rowan
Electronics
Aaron Wascom
Flight Software
Mechanical Integration
Philip de la Vergne
System Testing
Brandon Sciortino
Calibrations
Data Processing and Analysis
Documentation

34. Change Control & Update Procedures
Changes to this Pre-PDR document shall follow all regulations set by Team Tesla’s contract and only be made after approval by designated representatives from Team Tesla and the LaACES Institution Representative. Document change requests should be sent to Team members and the LaACES Institution Representative and the LaACES Project.

35. Project Management: Master Schedule

36. Reference Documents
:8080/Medical/research/CoronaDischarge.doc
- Switzerland