This M-3401 offers three-phase line to line or line to ground configuration,

optimal pickup/ seal-in time delays from 2 to 8160 cycles, and negative

sequence voltage (47S) as well as undervoltage (27S) supervisory functions

that ensure security and reliable operation.

To ensure that all data is collected during a load-shedding event the M-3401

has oscillographic recording, storing 180 cycles of all measured parameters.

Additionally, the M-3401 has a Sequence of Events (SOE) recorder built-in to

capture and store a total of 32 events with 1mSec resolution time stamp.

• Asymmetrical voltage depressions occurring from single to phase-to-ground, phase

-to-phase, and phase-phase to ground faults are detected by using a negative

sequence overvoltage element (47S) as a supervision. Typically set to 0.05 to 0.1 pu

of nominal voltage, if the adjustable threshold is exceeded, the undervoltage load

shedding is blocked.

• Three-phase faults that decrease the voltage symmetrically across all three phases,

as well as complete de-energizations of the parts of the power system due to fault

clearing or other sectionalizing, are detected by using undervoltage supervision

(27S) on all phases. The undervoltage supervision is typically set lower than the lowest

survivable undervoltage that could occur from lack of reactive support before the entire

system voltage collapses, typically from 0.9 to 0.7 pu. If any phase voltage is lower

than the adjustable setting, it is assumed that the condition is from a fault (any type,

including three-phase) or complete de-energization of that part of the system.