2011 EMC Directory & Design Guide - Interference Technology

adiated emissions
G o ing from A n a l o g t o Digi ta l
data record of emissions traces that the system creates when
a survey or set of emissions measurements is carried out.
This type of emissions record keeping will be beneficial
when EPRI develops an on-line emissions database. Such
a database can provide researchers and customers with
access to historical and recent emissions data. Data from
past surveys may even be converted to digital data which
can be uploaded to the database.
Figure 2. Radiated electric field spectra, 10 kHz to 1 GHz, antenna
position 1 in control room (Unit 1).
munications facilities, and to date collected emissions data
for more than ten digital upgrade projects in NPPs. Data
gathered during this survey process furthered the understanding
of the EMC for the DCS project at this major US
nuclear power plant.
This automated system continues to be used to conduct
POI surveys in NPPs and other types of facilities where
surveys are needed or where EMI problems persist. One of
the primary benefits of using this system is the permanent
MEASUREMENT DATA
Antenna Positions
Figure 1 illustrates the location of the three antenna positions
near the system cabinets that now contain the new
digital control system. These same cabinets previously contained
the analog control system. All three antennae were
used at these positions during the emissions measurements.
High-Frequency Radiated Emissions Data –
Electric Fields: 10 kHz – 1 GHz
1) Antenna Position 1
Figure 2 illustrates the final radiated emissions trace (i.e.,
the maxima of each measurement point in this frequency
band occurring among several thousand traces during the
collection of data at this antenna position) for electric fields
taken at Antenna Position 1 from 10 kHz to 1 GHz adjacent
to one of the system cabinets for the plant control system.
Figure 1 contains the data for both the analog control system
(green trace) and the digital control system (blue trace).
From the trace, one can see that a few characteristics of the
analog control are that it peaks at 1.34 MHz at 99.2 dBμV/m
and at the high-frequency end at 928 MHz at 76.6 dBμV/m.
The blue trace from digital control system has a similar
signature starting from 10 kHz but lower amplitude and
does not contain the 1.34 MHz peak. From 2.31 to 3.51
MHz, the radiated energy from the DCS is higher than that
of the analog control system (ACS). From 6.71 MHz out to 1
GHz, the radiated energy from the DCS is just about always
higher than that of the ACS. There are two distinctive peaks
that are present on the DCS trace, which are not present on
the ACS trace. These are at 468 MHz (71.6 dBμV/m) and
826 MHz (94.5 dBμV/m). One of the peaks at the higher
frequency area at 928 MHz peaked at 113.5 dBμV/m, which
is 36.9 dBμV/m higher when the DCS system was installed.
Two limit lines are placed on the plot as well. One is
the 140 dBμV/m limit line (red line)—a susceptibility limit
line defined in NUREG 1.180 (Rev 1) and also in EPRI TR-
102323. The second limit line (yellow line) is the highest
composite plant emissions envelope limit, originally defined
in EPRI TR-102323 (Rev 1) in 1997. While there is more than
an 8 dB safety margin between the peak of either trace and
the 140 dBμV/m limit line, one will notice that the emissions
from the DCS equipment at 928 MHz are near the allowable
plant emissions limit line.
Two other limits are also placed on the graph of Figure 2.
These are equipment emissions limit lines. One is the limit
line defined in NURED 1.180. The other is also an equipment
emissions limit line defined in EPRI TR-102323 (Rev.
96 interference technology emc Directory & design guide 2011