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Current Technology’s Selenium Story vs.
Emerson Network Power’s Surge Protection Array
Our Analysis
Introduction
Recently, Current Technology posted a two part video on
YouTube that was intended to demonstrate the ability of a
selenium plate to withstand temporary overvoltage’s (TOVs).
Part one of the video shows a 150 volt metal oxide varistor
(MOV) subjected to a series of 30 cycles (1/2 second) TOVs,
starting at 150 volts, and then moving to 170v, 200v, 220v
and finally 240 volts. The MOV is shown to do nothing until
220 volts (starts to clamp) and then completely fails at 240 volts.
Figure 1, (left), shows the
MOV under test in the
video.
Figure 1
The conclusion reached
by the presenter in the
video essentially says that
surge protectors which
rely solely on MOVs are
vulnerable to TOVs or
swells. This video in essence “sets-up” video two
which is the introduction
of the MOV/Selenium
configuration, see Figure
2, (left).
The proposal here is that
when paralleled, the selenium can withstand TOVs
and enables the MOV to
survive the incident. As
Figure 2
in the first video, the selenium/MOV combination
is subjected to a 30 cycle TOV starting at 150 volts and then
ramps up to as high as 270 volts.
In this experiment, the selenium is shown to start to conduct
at 200 volts (16.4 amps measured) and shows that it remains
functional (along with the MOV) through 270 volts (at which
point they measure 39.2 A through the Selenium).
Their conclusion? For the best results under these TOV conditions, you should incorporate a selenium based hybrid device.
MOVs are used to attenuate transients, which are microsecond events. Lightning and other “typical” power line
disturbances fall into this microsecond duration category.
However, swells do occur, so determining how your device
will handle these conditions is a valid point.
After viewing the Current Technology videos, it became clear
their MOV representation did not reflect Emerson Network
Power’s approach to MOV based protection. When designed
and installed within Emerson Network Power’s 500 Series, of
surge protective devices (SPDs), the protection is actually
provided as a custom MOV array that parallels multiple
components, symmetrically places the MOVs within the
module, voltage matches and then individually fuses each
MOV. The “MOV array” is then placed in parallel with other
arrays (as surge requirements increase).
Figure 3
So as we set out to duplicate the test, we decided to accurately represent the Emerson Network Power design by
choosing a single surge protection “MOV array” instead of a
single MOV component. The set-up was similar to the one in
the Current Technology video; a variac was used to increase
the voltage, a timer/
relay that enables 30 cycles and an oscilloscope to record the
results. Figure 3, (above), shows the set-up (including the
module and current probe).
“After viewing the Current Technology videos, it
became clear their MOV representation
did not reflect Emerson Network Power’s
approach to MOV based protection.”
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The Results
We tested the module’s capability to survive at various voltage levels for 30 cycles, simulating a swell condition.
Test 1 = (150 volts) — Oscilloscope shows no data, did not
register any current flow at 150V. The Emerson “MOV
Array” survived the event.
Test 1
Test 2 = (170 volts) — Oscilloscope shows no data, did not
register any current flow at 150V. The Emerson “MOV
Array” survived the event.
Test 2
Test 3 = (200 volts) — Oscilloscope shows module clamps, 10
amps measured into the module. The Emerson “MOV Array”
survived the event.
Test 3
Test 4 = 220 volts — shows module clamps, 23.2 amps
measured into the module. The Emerson “MOV Array”
survived the event.
Test 4
“The Emerson “MOV Array” survived the event.”
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The Results
Testing continued....
Test 5 = (240 volts) — shows module clamps, 37.2 amps
measured into the module. The Emerson “MOV Array”
survived the event.
Test 7 = (320 volts) — shows module clamps, 114 amps
measured into the module. The Emerson “MOV Array”
survived the event.
Test 6 = (270 volts) — shows module clamps, 65.6 amps
measured into the module. The Emerson “MOV Array”
survived the event. This is the final point tested in the
Current Technology video.
Conclusion
As mentioned before, the purpose of an SPD is to attenuate
transients or microsecond events. However, this test pushes
the limits of the typical application and attempts to determine how a SPD will respond during a swell condition, moreover, it will determine whether a Emerson Network Power
surge protection array can perform in the same manner as
Current Technology’s selenium hybrid design.
The test subjected the SPD to a line swell of various voltage
levels. The swell duration is 30 cycles, which represents an
IEEE defined instantaneous swell duration. As you can see
from our test results, the paralleled “MOV array” performed
in the same manner as the selenium hybrid design. In fact,
we extended the level to 320 volts and noted that the array
survived.
This clearly demonstrates that in the case of an instantaneous
swell condition, a properly designed paralleled MOV array,
such as those incorporated in the Emerson Network Power
500 Series of SPDs will survive and attenuate in the same
manner as the selenium hybrid approach.
“As you can see from our test results, the paralleled “MOV array”
performed in the same manner as the selenium hybrid design.”
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100 Emerson Parkway
Binghamton, NY 13905
P (607) 721 8840
P (800) 288 6169
F (607) 722 8713
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