The plant engineer’s worst fear…
Just as high
blood pressure can create stress and serious problems in the human body, high
levels of harmonic distortion can create stress and resultant problems for the
utility’s distribution system and the plant’s distribution system, as well as
all of the equipment that is serviced by that distribution system.
The result may be the plant engineer’s
worst fear - the shutting down of important plant equipment ranging from a
single machine to an entire line or process.
Equipment shutdown can be caused by a
number of events. As an example, the higher voltage peaks that are created by
harmonic distortion put extra stress on motor and wire insulation, which
ultimately can result in insulation breakdown and failure. In addition,
harmonics increase rms current, resulting in increased operating temperatures
for many pieces of equipment, greatly reducing equipment life.
Table below summarizes some of the
negative consequences that harmonics can have on typical equipment found in the
plant environment.
Negative
Consequences of Harmonics on Plant Equipment
|
Equipment
|
Consequences
|
|
Current Harmonic Distortion Problems
|
|
|
Capacitors
|
Blown fuses, reduced capacitor life
|
|
Motors
|
Reduced motor life, inability to
fully load motor
|
|
Fuses/breakers
|
False/spurious operation, damaged
components
|
|
Transformers
|
Increased copper losses, reduced
capacity
|
|
Voltage Harmonic Distortion Problems
|
|
|
Transformers
|
Increased noise, possible insulation
failure
|
|
Motors
|
Mechanical fatigue
|
|
Electronic loads
|
Disoperation
|
While these effects are categorized by
problems created by current and voltage harmonics, current and voltage harmonic
distortion usually exists together (current harmonic distortion causes voltage
harmonic distortion).
Harmonic
distortion disrupts plants. Of greatest importance is the loss of productivity,
throughput, and, possibly, sales.
These occur because of process
shutdowns due to the unexpected failure of motors, drives, power supplies, or
just the spurious tripping of breakers. Plant engineers realize how costly
downtime can be and pride themselves in maintaining low levels of plant
downtime. In addition, maintenance and repair budgets can be severely
stretched.
For example, every 10°C rise in the
operating temperatures of motors or capacitors can cut equipment life by 50%.
