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Friday, January 30, 2015

Voltage and Current

Voltage and current values for each T-R set should be recorded; they indicate ESP performance
more than any other parameter. Most modern ESPs are equipped with primary voltage
and current meters on the low-voltage (a.c.) side of the transformer and secondary
voltage and current meters on the high-voltage rectified (d.c.) side of the transformer.
When both voltage and current meters are available on the T-R control cabinet, these values
can be multiplied to estimate the power input to the ESP. (Note that the primary current reading is multiplied by the primary voltage reading and the secondary current
reading is multiplied by the secondary voltage reading). These values (current times voltage)
represent the number of watts being drawn by the ESP and is referred to as the corona
power input. In addition, whenever a short term spark occurs in a field it can be detected
and counted by a spark rate meter. ESPs generally have spark rate meters to aid in the performance
evaluation.
The power input on the primary versus the secondary side of the T-R set will differ
because of the circuitry and metering of these values. The secondary power outlet (in
watts) is always less than the primary power input to the T-R. The ratio of the secondary
power to the primary power will range from 0.5 to 0.9 and average from 0.70 to 0.75 (U.S.
EPA 1985).
Voltage and current values for each individual T-R set are useful because they inform the
operators how effectively each field is operating. However, the trends noted within the
entire ESP are more important. T-R set readings for current, voltage, and sparking rates
should follow certain patterns from the inlet to the outlet fields. For example, corona
power density should increase from inlet to outlet fields as the particulate matter is
removed from the gas stream.
The electrical meters on the T-R cabinets are always fluctuating. Normal sparking within
the ESP causes these fluctuations in the meter readings. These short term movements of
the gauges indicate that the automatic voltage controller is restoring the maximum voltage
after shutting down for several milliseconds to quench the spark. When recording values
of the electrical data from the T-R meters it is important to note the maximum value that is
sustained for at least a fraction of a second.

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