Air-load tests are generally conducted on cool, inoperative ESPs through which no gas is
flowing. This test should be conducted when the ESP is new, after the first shutdown, and
every time off-line maintenance is performed on the ESP. These air-load V-I curves serve
as the basis for comparison in the evaluation of ESP maintenance and performance. A typical
air-load curve is shown in Figure
meters. The following procedures can be used by the ESP operator to develop an air-load
curve.
1. Energize a de-energized T-R set on manual control (but with zero voltage and current),
and increase the power to the T-R set manually.
2. At corona initiation the meters should suddenly jump and the voltage and near zero
current levels should be recorded. It is sometimes difficult to identify this point precisely,
so the lowest practical value should be recorded.
3. After corona initiation is achieved, increase the power at predetermined increments
[for example, every 50 or 100 milliamps of secondary current or every 10 volts of AC
primary voltage (the increment is discretionary)], and record the values for voltage
and current.
4. Continue this procedure until one of the following occurs:
• Sparking
• Current limit is achieved
• Voltage limit is achieved
5. Repeat this procedure for each T-R set.
When the air-load tests have been completed for each field, plot each field's voltage/current
curves. When ESPs are equipped with identical fields throughout, the curves for each
field should be nearly identical. In most cases, the curves also should be similar to those
generated when the unit was new, but shifted slightly to the right due to residual dust on
the wires (or rigid frames) and plates of older units. These curves should become part of
the permanent record of the ESP.
The use of air-load curves enables plant personnel to identify which field(s) may not be
performing as designed. Also, comparison of air-load curves from test runs taken just
before and after a unit is serviced will confirm whether the maintenance work corrected
the problem(s).
One major advantage of air-load tests is that they are performed under nearly identical
conditions each time, which means the curves can be compared. One disadvantage is that
the internal ESP conditions are not always the same as during normal operation. For
example, misalignment of electrodes may appear or disappear when the ESP is cooled
(expansion/contraction), and dust buildup may be removed by rapping during ESP shutdown.
flowing. This test should be conducted when the ESP is new, after the first shutdown, and
every time off-line maintenance is performed on the ESP. These air-load V-I curves serve
as the basis for comparison in the evaluation of ESP maintenance and performance. A typical
air-load curve is shown in Figure
Typical air-load voltage and current readings
An air-load V-I curve can be generated with readings from either primary or secondarymeters. The following procedures can be used by the ESP operator to develop an air-load
curve.
1. Energize a de-energized T-R set on manual control (but with zero voltage and current),
and increase the power to the T-R set manually.
2. At corona initiation the meters should suddenly jump and the voltage and near zero
current levels should be recorded. It is sometimes difficult to identify this point precisely,
so the lowest practical value should be recorded.
3. After corona initiation is achieved, increase the power at predetermined increments
[for example, every 50 or 100 milliamps of secondary current or every 10 volts of AC
primary voltage (the increment is discretionary)], and record the values for voltage
and current.
4. Continue this procedure until one of the following occurs:
• Sparking
• Current limit is achieved
• Voltage limit is achieved
5. Repeat this procedure for each T-R set.
When the air-load tests have been completed for each field, plot each field's voltage/current
curves. When ESPs are equipped with identical fields throughout, the curves for each
field should be nearly identical. In most cases, the curves also should be similar to those
generated when the unit was new, but shifted slightly to the right due to residual dust on
the wires (or rigid frames) and plates of older units. These curves should become part of
the permanent record of the ESP.
The use of air-load curves enables plant personnel to identify which field(s) may not be
performing as designed. Also, comparison of air-load curves from test runs taken just
before and after a unit is serviced will confirm whether the maintenance work corrected
the problem(s).
One major advantage of air-load tests is that they are performed under nearly identical
conditions each time, which means the curves can be compared. One disadvantage is that
the internal ESP conditions are not always the same as during normal operation. For
example, misalignment of electrodes may appear or disappear when the ESP is cooled
(expansion/contraction), and dust buildup may be removed by rapping during ESP shutdown.
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