They
are two popular and important power quality problems present in electrical
distribution network that strongly affect the proper functioning of the loads
in modern society.
What do under voltage and voltage sag (dip) mean?
Under
Voltage: is the decrease in AC
RMS voltage at power frequency to less than 90% of the network nominal voltage
and for duration longer than one minute. According to IEEE 1159/1995, decreased
voltage will range from 80% to 90% of the nominal voltage and for duration
longer than one minute.
Voltage
Sag: is the decrease in AC
RMS voltage at power frequency to the rang between 10% to 90% of the network
nominal voltage and for duration rang from 0.5 cycle (10 ms) to one minute. According
to IEEE 1159/1995, decreased voltage will range from 10% to 90% of the nominal
voltage and for duration rang from 3 sec to one minute.
What are the causes of under voltage and voltage sag?
Under
Voltage Causes:
(1) Load
switched on and power factor correction capacitors switched off.
(2) Poor
system voltage regulation.
Voltage
Sag Causes:
(1) Local
and remote faults that happen in transmission and distribution especially
faults in parallel feeders and customers installation.
(2) Connection
of heavy loads and starts up of large motors.
What are the impacts of under voltage and voltage sag?
These
two problems have dangerous effects on electrical equipments and electrical
distribution network components as following:
Under
Voltage Impacts:
Under
voltage causes many problems with the equipments that required steady state
voltage especially modern load so it causes malfunction, miss operation and in
some times full operation stoppage.
Voltage
Sag Impacts:
Voltage
sag causes many problems like:
(1) Malfunction
of information technology equipments which called microprocessor based control
systems (PLC, ASD, PCs……etc) that may lead to process stoppage.
(2) Tripping
of contactors and electromagnetic relays.
(3) Disconnection
and less efficiency in rotating machines.
Thanks. Very much helpful
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