Application Note

20 Fluke Corporation Power Quality Troubleshooting
500
400
300
200
140
120
110
100
90
80
70
40
0
Applicable to 120, 120/208, and
120/240 nominal voltages
110 V
90V
1µs
1ms 3ms 20ms 0.5s 10s Steady
state
0.001c 0.01c 0.1c 0.5c 1c 10c 100c 1000c
Duration of disturbance in cycles (c) and seconds (s)
Percent of nominal voltage (RMS or peak equivalent)
Voltage-Tolerance
envelope
Voltage susceptibility profile
The new ITIC profile (Informa-
tion Technology Industry Coun-
cil) is based on extensive
research and updates the
CBEMA curve. The CBEMA
curve (Computer Business
Equipment Manufacturers Asso-
ciation, now ITIC) was the origi-
nal voltage susceptibility profile
for manufacturers of computers
and other sensitive equipment.
Similar curves are being devel-
oped for 230V/50Hz equipment
and for adjustable speed drives.
Sensitive equipment should be
able to survive events inside the
curve. Events outside of the
curve could require additional
power conditioning equipment
or other remedial action. A ma-
jor change in ITIC is that the
ride-through times for outages
as well as the tolerance for sags
have both been increased.
The field troubleshooter must
keep in mind that the profiles
are recommendations and that
a particular piece of equipment
may or may not match the pro-
file. Having said that, the pro-
files are still useful because,
when recorded events are plot-
ted against them, they give a
general idea of the voltage
quality at a particular site.
Transient voltage surge
suppressors (TVSS)
Fortunately, transient protection
is not expensive. Virtually all
electronic equipment has (or
should have) some level of pro-
tection built in. One commonly-
used protective component is
the MOV (metal oxide varistor)
which clips the excess voltage.
TVSS are applied to provide
additional transient protection.
TVSS are low voltage (600V)
devices and are tested and cer-
tified to UL 1449. UL 1449 rates
TVSS devices by Grade, Class
and Mode. As an example, the
highest rating for a TVSS would
be Grade A (6000V, 3000A),
Class 1 (let-through voltage of
330V max) and Mode 1 (L-N
suppression). The proper rating
should be chosen based on the
load’s protection needs:
•
A lower Grade might result in
a TVSS that lasts one year in-
stead of ten years. The solid
state components in a TVSS
will themselves deteriorate as
they keep on taking hits from
transients.
•
A lower Class might permit too
much let-through voltage that
could damage the load. Class
1 is recommended for switch
mode power supplies.
•
A Mode 2 device would pass
transients to ground, where
they could disrupt electronic
circuit operation.
Figure 4.4 ITIC Curve.