POWER January 2015 - 48

EMISSIONS
System Cost. Capital cost is also a significant
consideration in the selection process of
ESP power supplies, and the differences are
significant. For example, if the single-phase
power supply cost is 1.0, then the relative cost
for a like-sized high-frequency SMPS ranges
from 1.49 to 2.31. A like-size low-frequency
three-phase power supply's relative cost is
only 1.12 to 1.17.
Also, because the high-frequency power
supply designs are fully integrated, there is
less field wiring, so installation costs are less
than for the low-frequency option. Balancing
those installation cost benefits for the SMPS
are the increased capital costs for active cooling,
environmental protection of the equipment,
and higher overall maintenance cost.
System Reliability. The predicted reliability
of a power supply is difficult to
quantify. The reliability track record of the
single-phase ESP power supply is excellent,
and many installations have been in service
for over 40 years. This is a reliability benchmark
that low-ripple power supply designs
must match. Anecdotal evidence finds that
high-frequency power supplies have experienced
a poor reliability record; although
it has improved in recent years, it remains
lower than for single-phase designs.
Successful Field Testing
The result of laboratory testing was the finding
that the low-frequency three-phase power
supply option had the greatest potential for
improving ESP performance and reliability.
The final stage of the development program
was to field test the design in order to evaluate
its reliability against the familiar singlephase
option.
Field-testing of the low-frequency threephase
power supply was conducted on an
ESP at an active utility power plant. The unit
consists of a tangentially fired boiler burning
coal with sulfur content of 1.9 lb/MMBtu
with no selective catalytic reduction system
or flue gas desulfurization system. The test
was conducted during a consecutive sixmonth
period.
The ESP consists of two boxes with rigid
discharge electrodes and 16-inch-wide gas
passage. There are four fields (each 12 feet by
50 feet), and eight transformer-rectifier (TR)
sets per box (2 x 4 matrices). Fields 1 and 2
have 70 kV, 750 mA conventional TR sets;
fields 3 and 4 have 70 kV, 1,000 mA sets. All
TR sets are controlled by B&W PGG SQ300
automatic voltage controls. On the " A "
box, the inlet field 1A-1 TR set was replaced
with a 480 V, 109 A, 90 kV, 900 mA, threephase
TR set for the purpose of testing. The
field test results obtained when operating the
test low-frequency, three-phase power supply
in a compartment adjacent to a conventional
low-frequency single-phase power supply
are shown in Figure 3.
Field test results confirmed the laboratory
test results that the three-phase power
supply typically produced 50% more corona
power delivered to the ESP than from a conventional
power supply (average three-phase
power/average single-phase power) with low
total harmonic distortion. The installation
costs were on par with a standard singlephase
power supply. There were no failures
of the three-phase power supply during the
six-month test run. ■
-David F. Johnston (dfjohnston@
babcock.com) is operations manager,
precipitator electrical, and John A. Knapik
(jaknapik@babcock.com) is senior application
engineer for Babcock & Wilcox
Power Generation Group Inc. John
Walker (John.Walker@duke-energy.com)
is electrical engineer for Duke Energy,
Wabash River Station. This article is
based on a paper presented at the 2014
Power Plant Pollutant Control " MEGA "
Symposium.
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