I'm new designing a high/medium voltage (V <=10kV) with low voltage and low current (10mA). There will be only a few HV relays. Their coils will be triggered by LV.
I have read some literature about this subject. I have known that noise could be coupled to the parasitic capacitance at the insulation: "If noise couples through parasitic capacitance on the board or in the insulation, it can easily propagate to very sensitive areas of the board".
So, it could be bad news if this capacitor discharges its own charge and starts having continuity between 2 isolated points where should be isolation.
How could I avoid these capacitor effects? How can I stop the noise running through Capacitance between 2 isolated (or potential different) points?
Best Answer
Parasitic capacitance is created whenever there are two conductors. The capacitance can be estimated with capacitance calculators. Parasitic capacitance values on PCB's typically exist in the pF range for traces and planes. Large plane to plane capacitance can be in the 100pF range (a 1000mm^2 has roughly 150pF of capacitance between planes).
Usually plane to plane capacitance can be used to your advantage in low voltage sections of a PCB. A ground plane can act like a bypass capacitor (with values of a few pF) which will cut out very high frequencies.
If you don't want these capacitave effects, then don't place traces or planes adjacent to each other. You wont' be able to eliminate capacitance entirely, but it is easy to make the values negligible.
You probably already know this already but I'll include it for anyone else with the same question:
With high voltage you need to consider creepage and clearance between traces, and at 10kV also the breakdown dielectric voltage of PCB. High voltage can arc between traces, so proper distance needs to be placed between them. Here is a calculator for distance.
Source: http://www.smpspowersupply.com/ipc2221pcbclearance.html
It might be wise to build the board out of something other than FR4 with such high voltages on the board. Follow the guidelines here