Protection Relay Settings

Yes, RTFM (Read The Fine Manual) that came with your relay to learn exactly how the settings affect the operation. In your case the electricity board has decreed that you are not allowed to exceed 25 MVA (peak) nor are you allowed to operate in the band between 21.1 to 25 MVA for any appreciable time.

The VIT curve allows you to operate for limited periods just above 21.1 but as you get closer to 25 MVA the time shortens quite rapidly. This is a form of variable demand limiting, and you will have to be very careful not start any loads with a high transient starting current (like a big motor) when you are on the steep portion of the curve or you may be dumped before the transient is over.

The logic for the SEPAM relay's trip curves has a pickup setting "Is" that you specify (in this case 350A). The various time trip curves might pick up at that value, but if you look at the curve (most of which are some form of a time-inverse function), at minimum pickup it will take an extremely long time until tripping occurs.

For the Very Inverse Trip (VIT) curve, as well as some of the others, Schneider does not specify an actual time to trip value for less than 1.2 x Is. Since this is done in digital logic, it gives some "buffer" around the pickup setting. Only when current reaches 1.2x pickup will the relay actually start the timing of its trip circuit. Schneider calls it the "minimum operate threshhold."

You didn't say which model of SEPAM relay you have (although I think they all use the same curves), and which particular VIT curve specified (IEEE, IEC, IAC), but the snapshot of one of the types shows the curves not starting at 1.0x pickup, but rather at a somewhat higher point.

I think the electricity board is correct. Look into the VIT Type 1.2 curve for the relay (http://www.powerlogic.com/literature/63230-216-208C1.pdf). With this type of the curve, the relay will not trip with I/Is less than 1.2.

However, I would suggest you to confirm it with the relay vendor.

Hope it helps.

- MS