Thread-topic: "Terry" filter and safety gap questions for pole transformer
I realized a minute after I posted this that I was an order of magnitude off on the resistors. It should be 1000 ohms, not 100 ohms. So it looks like I will need 250 watt resistors if I want to handle a worst-case of 0.5 amps at 14.4 KV.
----- Original Message -----
From: "Steve White" <steve.white1@xxxxxxxxx>
To: "Tesla Coil List" <tesla@xxxxxxxxxx>
Sent: Friday, February 9, 2018 5:37:20 PM
Subject: [TCML] "Terry" filter and safety gap questions for pole transformer
My spark gap coil has been running for about 6 months with a 10 KVA pole transformer for power. I pull about 4.8 KW from the wall. The only transformer protection that I am currently using is a horn gap in parallel with the spark gap. I have had no trouble with it but lately I have become concerned with damaging the pole transformer. Because of this concern, I am in the process of building a low pass RC ("Terry") filter for additional protection. I have 2 questions regarding the resistors. I see that people are using standard wire-wound resistors. I am surprised that the 14.4 HV RMS does not flash across the windings in the resistor. Is this type of resistor indeed adequate for such high voltage? The second question concerns the power rating of the resistor. Since my worst-case RMS current from the pole transformer is no more than 0.5 amperes, the power dissipation should be no more than about 25 watts.
Power = (I**2) * R = 0.5 * 0.5 * 100 = 25 watts
Therefore I assume that a pair of 100 watt resistors, one on each HV lead, should be more than adequate even for a pole transformer. Is this correct?
I also have a safety gap question. My safety gap is just a simple 2-terminal horn gap connected in parallel with my RSG. I see that the safety gaps used for NSTs consist of 3 terminals: 2 for the high voltage leads and a central ground terminal. For pole transformers, is there any advantage favoring the 3-terminal gap vs the 2-terminal gap?
Steve
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