Specifications

17
Sag and Swell
Any short term voltage decrease
(sags) or increase (swell) for a time
from half cycle to 3 seconds. It is
normally caused by the equipment
shutdown, circuit breaker operations,
high peak current absorbed by the
equipments, or short-circuit.
Consequences:
The major effects may be the loss of
data or the lights flicker, very
unpleasant for the people exposed to
these effects.
Transients
Transients are rapid, very high
overvoltages of up to 20 kV. They
are caused mainly by lightning (which
is random in its location, duration
and amplitude) but also by faults on
the high-voltage network, the
switching of inductive loads or the
powering of highly capacitive loads.
Consequences:
Transients destroy inadequately
protected equipment (melting of
wires, perforation of isolation in
motors, badly-timed release of
protection devices, etc.).
Power quality and mains disturbance
Electronic equipment functions
properly as long as the utility is
available and with high quality.
Unfortunately not always this is
possible because most of the power
quality events are caused by factors
beyond the control of the Distribution
Company. These factors may occur
either externally (in the network
distribution system) or internally (in
the facility when the system is
located). External causes may be for
example storm, lightning, high wind,
tree limb contact, construction
activities etc, while the internal
causes may be switching of the
machine, capacitor banks, fault or
maintenance activities.
Depending on the events the power
quality disturbances may vary in
type, duration and intensity.
Typical power supply disturbances
that cause major bad effects on your
load are listen below.
Power outage
Power interruption for a time of more
than 3s is called an outage or
commonly “blackout”. This is
normally caused by atmospheric
accidents to the high voltage
distribution network or a failure in the
power supply equipment.
Consequences:
- Computer applications
Complete system shutdown with
loss of data, possible hardware
damage and long periods of
employee inactivity.
- Industrial applications
Huge impact in the production
activity with consequent
production loss and/or unexpected
safety consequence.
Blackout
Undervoltage
It is a voltage reduction in amplitude
for a time between 10 ms to 1 s.
expressed as a percentage from 10
and 100% of the rated voltage. This
is caused for example by short
circuits in the resident distribution
systems or the large inrush current of
the transformers.
Consequences:
- Computer applications
Overheating of the electronic
components with consequent
operational breakdown.
- Industrial applications
Instability of asynchronous motors
and loss of synchronization of
synchronous motors, opening of
contactors (voltage drop > 30%),
power-off discharge lamps (voltage
drop > 50% for 20-40 ms) with
subsequent return of power after
several minutes and consequent
operational breakdown.
Overvoltages
Overvoltage is an increase in voltage
for a time of more than 10 ms.
Overvoltages may be caused by the
disconnection of major loads
(interruption in manufacturing
processes of industrial companies,
reduction in the speed of electric
motors, arc furnaces, rolling mills,
etc.) or natural events such as
lightning.
Consequences:
Faults in all electric/electronic
equipment (100%<overvoltage<150%);
e.g. damage to boards, power
supplies, computers/servers, faults in
lighting systems, etc.
Undervoltage