[AMPS] High Voltage fuses

Tue, 21 Jul 1998 10:28:37 -0700

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Hi to all,
I am presently building a 500ma 2kv power supply and the subject on HV
(High Voltage) fuses discussed some time ago by John Lyles has me
curious on this subject. Most HV power supplies described in the ARRL
handbook include a HV fuse in the HV output.  The power supply I am
building contains commercial 38kv 10amp diode stacks, a 60uf oil cap,
and a 40-ohm 250w surge resistor at the HV output lead. The HV
transformer resistance is 65 ohms on each 1.5kv AC leg.

The ground return of this supply has a current sensor which controls a
standard 24-volt primary AC contactor which shuts off AC supply in the
event of an overcurrent in the HV load.  I wonder if a HV fuse would
actually be of any use here.  In the event of a PA flashover,  the
contactors will shut off AC power anyway.

I remember several years ago when I took over the maintenance of an FM
transmitter . This system was poorly maintained and flashovers always
occurred.  Every time a flashover occurred, the primary AC contactors
merely tripped and we could always restart without need of replacing any
fuses. A flashover once happened while I was right beside the PA
(4CX10000) and it was a very interesting experience. We had to keep the
rig running like this until the scheduled down time was reached and the
power supply never sustained any damage.

I think it is very difficult to make HV fuses work properly due to the
flashover that occurs inside of them during a trip, thereby greatly
prolonging its actual cutoff time.  Considering that HV fuses are
expensive and rare, does anyone have any experience with installing
several (maybe 5ea?) standard 250v fast acting fuses in series?

73's, Alex Samson ke6vkj

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Hi to all,
 I am presently building a 500ma 2kv =
power supply and the subject on HV (High Voltage) fuses discussed some =
time ago by John Lyles has me curious on this subject. Most HV power =
supplies described in the ARRL handbook include a HV fuse in the HV =
output.&nbsp; The power supply I am building contains commercial 38kv =
10amp diode stacks, a 60uf oil cap, and a 40-ohm 250w surge resistor at =
the HV output lead. The HV transformer resistance is 65 ohms on each =
1.5kv AC leg.

<P><FONT SIZE=3D2 FACE=3D"Arial">The ground return of this supply has a =
current sensor which controls a standard 24-volt primary AC contactor =
which shuts off AC supply in the event of an overcurrent in the HV =
load.&nbsp; I wonder if a HV fuse would actually be of any use =
here.&nbsp; In the event of a PA flashover,&nbsp; the contactors will =
shut off AC power anyway.</FONT></P>

I remember several years ago when I =
took over the maintenance of an FM transmitter . This system was poorly =
maintained and flashovers always occurred.&nbsp; Every time a flashover =
occurred, the primary AC contactors merely tripped and we could always =
restart without need of replacing any fuses. A flashover once happened =
while I was right beside the PA (4CX10000) and it was a very =
interesting experience. We had to keep the rig running like this until =
the scheduled down time was reached and the power supply never =
sustained any damage.

<P><FONT SIZE=3D2 FACE=3D"Arial">I think it is very difficult to make =
HV fuses work properly due to the flashover that occurs inside of them =
during a trip, thereby greatly prolonging its actual cutoff time.&nbsp; =
Considering that HV fuses are expensive and rare, does anyone have any =
experience with installing several (maybe 5ea?) standard 250v fast =
acting fuses in series?</FONT></P>
<BR>
<BR>

<P><FONT SIZE=3D2 FACE=3D"Arial">73's, Alex Samson ke6vkj</FONT>
</P>

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