Appendix
217
Detecting Anomalies and Phenomena Due to Drops in
Power Quality
• The light flickers.
• Light bulbs burn out more quickly.
• The OA device malfunctions.
Detecting phenomena
• Sometimes the device does not work correctly.
• The reactor's condenser overheats.
• Sometimes the electrical overload, reverse phase, or missing
phase relays malfunction.
Troubles due to drops in power quality:
Interruptions in the reception transformer and malfunctions in the terminal control device
Power quality Waveform display Phenomenon Malfunction
Transient
overvoltage
(impulse)
Occurs due to phenomena such
as lightning, breaker point dam-
age, or closure on the circuit
breaker or relay.
Often occurs when there is a
radical change in voltage or
when the peak voltage is high.
Close to the source of the break,
the device’s power is damaged
because of exceptionally high volt-
ages and this may cause the device
to reset.
Voltage dip
(SAG)
A momentary voltage drop
occurs caused by large rush
currents in the load, such as
starting-up a motor.
A drop in voltage may cause the
device to stop operating or reset.
Voltage swell
(SURGE)
Occurs when power lines sub-
ject to lightning strikes or heavy
loads are opened and closed,
causing the voltage to surge
momentarily.
A surge in voltage may cause the
device’s power to be damaged or
the device to reset.
Flicker
Blast furnaces, arc welders, and
thyristor control loads cause
flicker, and voltage impulses
occur regularly during single
and multiple cycles.
Because this phenomenon reoc-
curs regularly, it may cause the light
to flicker or the device to malfunc-
tion.
Interruption
Circuit breaker trips occur,
mainly caused by accidents at
power companies (such as
stops in power transmission
because of lightning strikes) or
short circuits, and the power
supply stops momentarily or for
an indefinite time.
Recently, due to the spread of UPS
(uninterruptible power sources),
most of these problems can be
fixed using a computer, but this
may cause the device to stop oper-
ating due to an interruption or to
reset.
Harmonics
Many device power sources
now use semiconductor control
devices and harmonics occur
because of distorted voltage or
current waveforms.
When harmonic components
become too large, they can cause
serious accidents, such as over-
heating the motor transformer or
burning out the reactor connected
to the phase advance capacitor.
Unbalance
factor
When the load of the specified
phase becomes too heavy due
to fluctuations in loads con-
nected to each power line
phases, or when operating an
uneven device, the voltage and
current waveforms become dis-
torted, causing voltage drops
Voltage imbalance, reverse phase-
to-neutral voltage, and harmonics
may cause accidents such as
uneven motor rotation, 3E breaker
trips, and overload heating in the
transformer.
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