Low Voltage or Sags : Sags might be due to undersized distribution lines, connection of large loads to the network, ground faulty, units located towards end of a long supply line, etc.
High Voltage or Surges: Surges might be generated by disconnection of large loads, increase coltage at generating plant, atmospheric events, units located close to start of a supply line, etc.
Unbalanced Voltage : Phase to phase unbalancing in voltage is generally observed where multiple consumers draw power from a common distribution line or in remote locations far from power grid.
The duration of the above phenomena depends on the cause and is not easily predictable. Generally, voltage is low during the daytime and high during the night hours. Moreover, on holidays, peak hours, rainy days and when the commercial/agricultural load is switched off, the voltage rises quite sharply.
If your unit is suffering from low/high/unbalanced voltage, you need to install a stabilizer soon. Industrial units having acute/higher failure rate of electrical equipment such as bulbs, tubes, chokes, starter, contactor coils, motors etc. should verify that it may be due to voltage variation (esp. high voltage). You may note down hourly readings of incoming voltage for a few days continuously. If you find that input voltage is lower or higher than 230V (single ph)/400V (3-ph) even for few hours a day, then you definitely require a stabilizer.
