DECS-200 Functional Description 3-7
operating software. RAM is volatile and serves as temporary storage for data. EEPROM is nonvolatile
and stores the settings and configuration.
Protection Functions
Eight protection functions are available in the DECS-200:
• Field overvoltage
• Field overcurrent
• Generator undervoltage
• Generator overvoltage
• Loss of sensing
• Generator frequency below 10 hertz
• Loss of field
• Exciter diode monitor
Each protection function can be indicated locally on the front panel display, remotely through
communication port Com 0 or Com 2, and any of the three programmable output relays.
Field Overvoltage
When the field voltage increases above the Exciter Field Overvoltage Level setting for the duration of the
Field Overvoltage Delay setting, a field overvoltage condition is annunciated. A field overvoltage condition
is annunciated on the front panel metering screen and may be assigned to a programmable output relay
for external annunciation. The Exciter Field Overvoltage Level setting is adjustable from 1 to 325 Vdc in 1
Vdc increments. The Exciter Field Overvoltage Delay setting is adjustable from 0.2 to 30.0 seconds in 0.1
second increments. If the field overvoltage timer is timing down and the field voltage drops below the
Exciter Field Overvoltage Level setting, the field overvoltage timer is reset. The field overvoltage function
may be disabled without changing the level or time delay settings.
Field Overcurrent
When the field current increases above the Exciter Field Overcurrent Level setting for the duration of the
Exciter Field Overcurrent Delay setting, a field overcurrent condition is annunciated. Field overcurrent is
annunciated on the front panel metering screen and may be assigned to a programmable output relay for
external annunciation. The Exciter Field Overcurrent Level and Exciter Field Overcurrent Delay settings
are related by an inverse function. This means that the higher the field current goes above the threshold,
the shorter the time to an annunciation. The Exciter Field Overcurrent Delay setting is a linear multiplier
for the time to an annunciation. The Exciter Field Overcurrent Level setting is adjustable from 0.1 to 20
Adc in 0.1 Adc increments. The Exciter Field Overcurrent Delay setting is adjustable from 0.1 to 20.0 in
increments of 0.1. The field overcurrent protection function may be disabled without changing the level or
time delay settings. Figure 3-2 shows a set of typical field overcurrent timing curves. Notice that field
current levels below 103% of the field overcurrent setpoint value are unpredictable and may not cause an
annunciation. Also, field current levels greater than 250% (field current multiple of 2.5 in Figure 3-2) of the
setpoint value cause an annunciation in the same amount of time as the 250% level.
Figure 3-2. Field Overcurrent Timing Curves
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