Hello Boštjan:
I would use a 1:1 transformer with a grounded
shield between primary and secondary.
The transformer core will saturate with differential
mode transients thus reducing the differential mode
transients in the secondary.
The shield will eliminate the capacitance between
primary and secondary, thus reducing the common mode
transients in the secondary.
Remember that conventional transient attenuators, i.e.,
varistors and gdt's, have to absorb the transient energy.
So, they have to be suitably rated for use on OVC IV
circuits. (Remember that varistors degrade with every
operation, and thus have a limited performance lifetime.)
Most transient attenuators don't have an input or output
as they are connected across the mains, in parallel with
all mains-connected loads. They attenuate the whole line,
but the amount of attenuation at any point between the
source of the transient to the point of connection of the
transient attenuator depends on the inductance of the line.
Best regards,
Richard Nute
Product Safety Consultant
Bend, Oregon, U.S.A.
On 8/21/2014 11:19 PM, Boštjan Glavič wrote:
Dear experts,
We have an IT product intended for connection to OVC IV (6kV
transients). Input filter also comprises two IEC 61051-2 certified
varistors (L to middle point, N to middle point) and one GDT (middle
point to PE).
Annex G of IEC 60950-1 is saying that we need to measure transient
voltages (level of transient after the input filter) with any surge
supressors in primary circuit disconnected.
Is this also applicable for certified varistors and GDT? How can
manufacturer reduce transient level? Use of IEC 61643 certified SPD is
not possible.
Thank you for your support.
Best regards,
Bostjan
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