When undervoltage protection is selected from the list and added to Breaker unit, the user can configure its parameters. Like in overcurrent protection, there are three different stages of undervoltage protection – U<, U<< and U<<<. The configuration of undervoltage protection is shown in ( Figure 9.15 ).
“Phase selection type” defines the protection selection type. There are three types to choose from – Phase to Ground, Phase to Phase, Positive sequence.
“Time setting” defines protection tripping time.
“Voltage setting” defines minimum element voltage at which protection will trip.
“Minimal current” defines minimum current at which protection can operate.
The table shown in Figure 9.15 , depicts protection sensitivity values of each short-circuit type based on voltage setting. If sensitivity value is between 1 and 2, cell color is yellow, if sensitivity value is less that one or infinity, cell color is red.
