Timeline for Transient current value
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Sep 10, 2020 at 11:30 | comment | added | Verbal Kint | @Andy aka, TVS are costly and mostly used in clamping networks for switching circuits. I have rarely seen them in a back-to-back configuration for ac protection - maybe for data lines - but never for a direct connection on the grid. | |
| Sep 10, 2020 at 11:08 | comment | added | Andy aka | @VerbalKint they definitely need to be fitted after a fuse because they tend to fail short circuit. Varistors can be flaky and sometimes they are used with GDTs but, TVS diodes aren't really man-enough for 400 volts AC yet so what to do! | |
| Sep 10, 2020 at 11:03 | history | edited | Andy aka | CC BY-SA 4.0 |
added 313 characters in body
|
| Sep 10, 2020 at 10:59 | comment | added | Verbal Kint | I haven't seen varistors for a while on industrial designs. They tend to be a source of fire when they die. Most of the boards I see implement spark gaps included in the PCB. You may have one across the line, after the fuse, and sometime another one across the EMI filter to pass the lightning strike test. | |
| Sep 10, 2020 at 10:57 | comment | added | Ultra67 | Thank you, now I understand better your first answer. | |
| Sep 10, 2020 at 10:57 | vote | accept | Ultra67 | ||
| Sep 10, 2020 at 9:53 | comment | added | Andy aka | It's a numbers game. You don't know the surge impedance; however, your product claim is that it is protected against (for example) EN61000-4-5 to a certain impulse voltage level (usually 1 kV or 2 kV) that has a source impedance of (usually) 2 ohms for power lines. Grid impedance only adds to the surge impedance and hence makes life easier on the suppressor. Worst case scenario for 61000-4-5 is 2 ohms; cabling makes it more than 2 ohms and life gets easier. | |
| Sep 10, 2020 at 9:48 | comment | added | Ultra67 | It becomes clearer. From what I understand, how can I determine then the surge impedance? If the voltage transient comes from the grid, do I need to know the grid impedance to estimate the current peak ? | |
| Sep 10, 2020 at 9:32 | comment | added | Andy aka | TVS devices handle current; you can't talk about handling a transient voltage because that doesn't imply a surge impedance. There has to be a surge impedance so that the voltage is clamped by the suppressor taking a pulse of current for the duration of the event. The device you mention can take a single pulse of 100 amps for 1 ms (then it is at its lifetime limit) - that's the problem with varistors. It would handle 5 amp peaks indefinitely. | |
| Sep 10, 2020 at 9:00 | comment | added | Ultra67 | Thank you for your detailed answer. There is still something I don't understand. Let's for example take the S14K320 datasheet (tdk-electronics.tdk.com/inf/70/db/var/SIOV_Leaded_StandarD.pdf) at page 32. The diagram shows the maximum applicable transient current as a function of pulse duration. A customer asked me if the device could handle a 1kV transient for 1 ms. The nominal voltage at the input is 400VAC. What could be the transient current value ? (without any test setup where the output resistance is fixed, let's say a voltage surge coming from the grid). | |
| Sep 10, 2020 at 8:07 | history | answered | Andy aka | CC BY-SA 4.0 |