Speaking of surge and EFT I have been looking into the real life performance of
equipment installed in the field. My equipment is three phase ITE and is
typically in operation in a "Heavy Industrial" environment previously defined
in EN 50082-2. In particular this equipment appears to be affected by EFT
within the facility, but has previously passed EN 61000-4-4 tests at a
recognized test site.
While I believe the problem to be EFT, I also want to understand the issue of
Surge. Reading an on-line article on surge performance it states that there are
two government definitions for surge, one being MODE 1 the other Mode 2. These
are defined as follows:
Mode 1: Normal Mode (Line to Neutral suppression)
Mode 2: All Modes (L-n, L-G, N-G) (Also defined as common mode)
The article states that "ONLY mode one is a concern because modern equipment is
inherently immune to common mode surges". Further it states that "placing MOVs
in a Mode 2 application may actually cause harm to the equipment by forcing the
spike on to ground. Modern power supplies simply ignore common mode surges".
That said, it was my understanding that MOVs (Mode 2) are the primary design
element for Surge and EFT within a power supply.
I took the opportunity to bench test a large 3000W 48V supply to EN 61000-4-5
on the bench. Placing small load on the output I captured the pulse on the DC
output. With a 1000V pulse on the input I see a 300V PP spike on the DC output.
So my questions are as follows:
1. Should the. design of the power supply (under a surge test scenario)
attenuate the output voltage to essentially zero on the DC output? Is a 300V
spike surprising to anyone?
2. Should MOVs be used in Mode 2 environments for EFT and Surge?
3. If EFT is the identified problem, and the power supplies are compliant with
EN 61000-4-5 is the problem most likely grounding?
4. Lastly my power supply has documentation establishing compliance with ANSI
C62.41. The parameters of this standard appear similar to those of EN 61000-4-4
(EFT) Is there something I am missing here?
Thanks in advance
Rick Busche
Evans & Sutherland
rbus...@es.com
(801) 588-7185
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