118 6LE008146B
Alarm management
7.7 Voltage monitoring alarms
The voltage monitoring alarms signal an alert is there is a brief variation in the voltage of the
electrical network.
In accordance with the IEC 61000-4-30 standard, when the network voltage falls or increases
by 5% or more of the nominal voltage during at least one period of the electrical network. A
voltage monitoring alarm is generated.
Falls or dips may be caused by a rapid change in load, such as the start of a motor, the
switching of heavy loads or a short-circuit.
They can result in an increase in current consumption, which represents an additional load for
all electrical equipment and, if prolonged, an increase in operating temperature and, ultimately,
a build-up of heat. In the worst-case scenario, this could cause fluctuations in the electrical
grid or even a general outage in the electrical grid.
The graphic below shows the typical wave shape of a phase-neutral voltage dip.
Voltage peaks are less common than voltage dips. They can be caused by a ground fault on a
single line, which briefly increases the voltage level of the other phases. They can also occur
when a heavy load ceases.
This can cause overheating and result in the stoppage of some equipment. It may also
damage electronic devices and other sensitive equipment.
This illustrates the wave shape typical of several phase-neutral voltage peaks also called
"voltage swells".
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