Over Voltage and Voltage Swell

They are considered as a sever power quality problems present in electrical distribution network that have damage effects on the electrical equipments.

What do over voltage and voltage swell mean?

Over Voltage: is the increase in AC RMS voltage at power frequency to greater than 110% of the network nominal voltage and for duration longer than one minute. According to IEEE 1159/1995, increased voltage will range from 110% to 120% of the nominal voltage and for duration longer than one minute.

Voltage Swell: is the increase in AC RMS voltage at power frequency to the rang between 110% to 180% of the network nominal voltage and for duration rang from 0.5 cycle (10 ms) to one minute. According to IEEE 1159/1995, increased voltage will range from 110% to 120% of the nominal voltage and for duration rang from 3 sec to one minute.

What are the causes of over voltage and voltage swell?

Over Voltage Causes:

(1) Load switched off and power factor correction capacitors switched on.

(2) Poor system voltage regulation.

Voltage swell causes:

(1) Single line to ground fault .  

(2) "Start – Stop" of heavy loads.

(3) Bad dimensioned power supply and bad regulated transformer mainly at off-peak hours.

What are the impacts of over voltage and voltage swell?

These two problems have more dangerous effects on electrical equipment's and electrical distribution network components than under voltage and voltage sag as following:

Over Voltage Impacts:

Over  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 Swell Impacts:

Voltage swell causes many problems like:

(1) Data loss and flickering of lighting and screens.

(2) Stoppage or damage of sensitive electrical equipments especially if the voltage values are too high.