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Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
I have a 24 KJ Aerovox capacitor which I am using to construct an impulse generator. The capacitor is one of those 2-terminal units. I plan on connecting one terminal to a dedicated earth ground. Should I also connect the case to earth ground or just leave it floating?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
The case will always have _some_ potential with respect to the "HV bushing" terminals. What will determine that potential, if you make no intentional DC connection (wire or resistor)? Any guesses as to upper and lower bounds on the voltage to which it will float?
Suppose the DC voltage rating on nameplate applies to the voltage between terminals HV1 and HV2. Then what's the tolerable DC voltage between case and HV1, or case and HV2? Not a rhetorical quesiton; I really don't know the answer. If I needed to know, would start at the websites of companies that make similar-looking capacitors today.
Are you equipped to measure the capacitance between each of the three pairs of terminals? That could tell you right away if the unit contains two HV caps in series, with their common terminal connected to case. If there's just a single multi-microfarad HV cap, generally isolated from the case, you might be able to determine if it has an "outer foil" associated with one of the HV terminals.
Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
I looked at as many pulse discharge capacitor company web sites as I could find. I couldn't find any guidance on how to connect the case on a 2-terminal unit. I have a capacitance meter that I can use to check the various capacitances. Unless I can find information to the contrary, I will just leave the case floating and keep it insulated away from potential conductors.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
I "ALWAYS" assume that there is a dangerous path between case and HV's and isolate instead of ground case...just too dangerous to guess what somebody puts inside these things!
Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
I decided to do a high impedance bonding instead of a direct ground. I used two high voltage 2 megohm resistors in series as a high voltage 4 megohm resistor. I connected this resistor between the case and ground (earth). This seems like a good compromise to prevent the case from floating at some undetermined voltage level. I should be testing this in the next few weeks.
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Pulse discharge capacitor grounding
