DECS-100 Functional Description
3-6
Overexcitation Limiting (Field Current)
The DECS-100 field current limit is adjustable from 0 to 15 amperes in 0.1 ampere increments with an
adjustable time delay that has a range of 0 to 10 seconds in 1 second increments. Both settings are made
through BESTCOMS software. When the overexcitation limit is exceeded, the OVEREXCITATION LIMITING
indicator on the front panel and in BESTCOMS lights. When the adjustable time delay expires, the relay
output closes and the DECS-100 shuts down. When the DECS-100 is powered up following overexcitation
limiting, the OVEREXCITATION LIMITING indicator will light for 5 seconds.
Soft Start
The DECS-100 also incorporates an adjustable soft start feature that controls the time for generator voltage
or field current to ramp to the regulation setpoint. The ramp rate is adjustable from 1 to 7,200 seconds in 1
second increments through BESTCOMS. The underfrequency feature is also active during soft start and
takes priority in control of the generator voltage.
Voltage Matching (Optional)
The DECS-100 voltage matching option automatically matches the RMS generator output voltage with the
RMS bus voltage prior to synchronizing. The DECS-100 compares and matches the generator voltage with
the bus voltage by adjusting the dc excitation current. Voltage matching is automatically disabled if bus
voltage is not 10 percent of the nominal sensing range selected. The voltage matching option is
enabled and disabled through BESTCOMS software. When enabled in BESTCOMS, voltage matching is
enabled or disabled through external contacts connected to the voltage matching contact input circuit. The
voltage matching speed setting is adjustable from 0 to 300 seconds in 0.01 second increments.