Problems with tesla coil, looking for suggestions

[ttwitchh]

I'm not sure if this is the right place to post this, but at this point I'm a little bit desperate, so hopefully I can get some suggestions here...

I'm working on a project in which I'm building a Tesla coil. We're using a 15kV transformer, about 15nF capacitance (six 10 nF (16 kV rated) capacitors, three sets of two in parallel) , 10 winds on the primary coil, ~2000 winds on the secondary.

When we first turned on the tesla coil, we got some nice looking 8 in. sparks from the dome, spark gap was firing like a gatling gun - the whole thing was really nice and impressive. We let it run for a little bit, may have turned it off and on, and we watched some impressive sparking happening at the base. The middle of our capacitor bank sparked to ground (~6 inches away - apparently the wooden base is grounded, who knew...) and blew one of our capacitors.

We decided to isolate the capacitors, so we build a box for them out of nonconductive plastic, placed that in the circuit, turned it on, and blew another capacitor. So we built an airtight tube, filled it with insulating oil, placed the capacitors in and sealed it. Turned it on, and watched a big, thick spark arc through the oil as it broke down (again, breaking down across ~6 in., and blew two more capacitors .

At this point, we're all out of ideas. Our personal deadline for the project was the end of next week, and we have no idea where to proceed. The breakdowns that we're seeing suggest that we're getting voltages well over 30 kV, approaching hundreds of kV, just at the base of the tower. We have no idea where this voltage is coming from, so we have no idea what to try next. We're extremely hesitant to try again, as all we have is a single capacitor left.

Please, any thoughts or suggestions would be wonderful. Thanks so much.

 

[Dmytry]

You have pairs of capacitors in series, connected in parallel?
There's the thing. Consider that:
a--||-b-||--c
the voltage on point b is floating, and charge there may accumulate over time.
The leakage of those two capacitors will not necessarily be equal. You need to connect 3 capacitors in parallel, also in parallel with a resistor (e.g. 100M resistor made of 10x 10M in series), then connect *that* in series. So it is like

+--||-+-||--+
+--||-+-||--+
+--||-+-||--+
+--r1-+-r2--+

where r1=r2=100M
Then *hopefully* it won't blow any more.

Also, what is your TC circuit? Draw it. There are different circuits. You must ground the primary, through separate ground ideally (maybe your grounding sucks).

 

[0xDEADBEEF]

Did you use leak resistors that force the voltage to spread evenly over the capacitors?