Basler DECS-250, Instruction Manual

Page: 65 / 352

9440300990 Rev J 49
DECS-250 Protection
Field protection provided by the DECS-250 includes field overvoltage, field overcurrent, an exciter diode
monitor, and power input failure.
Field Overvoltage
A field overvoltage condition occurs when the field voltage exceeds the field overvoltage threshold
A
for the
duration of the field overvoltage time delay
B
. Field overvoltage protection can be enabled and disabled
C
without altering the pickup and time delay settings. Field overvoltage pickup and trip elements in
BESTlogic
Plus can be used in a logic scheme to initiate corrective action in response to the condition.
BESTlogic Plus field overvoltage settings are illustrated in Figure 36.
Figure 36. Field Overvoltage Protection Settings
A
Field Overvoltage Pickup (V) : Adjustable from 0 to 325 Vdc in 1 Vdc increments.
B
Field Overvoltage Time Delay (s) : Adjustable from 0.2 to 30 seconds in 0.1 second increments.
C
Field Overvoltage Mode : Select Disabled or Enabled.
Field Overcurrent
A field overcurrent condition is annunciated when the field current exceeds the field overcurrent pickup
level
A
for the duration of the field overcurrent time delay. Depending on the selected timing mode
B
, the
time delay can be fixed or related to an inverse function. Definite timing mode uses a fixed time delay
C
. In
inverse timing mode, the time delay is shortened in relation to the level of field current above the pickup
level. The time dial
D
setting acts as a linear multiplier for the time to an annunciation. This enables the
DECS-250 to approximate the heating characteristic of the generator and generator step-up transformer
during overexcitation. The field current must fall below the dropout ratio (95%) for the function to begin
timing to reset. The following equations are used to calculate the field overcurrent pickup and reset time
delays.
𝑡𝑡
𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
=
𝐴𝐴 × 𝑇𝑇𝑇𝑇
𝐵𝐵 +
√𝐶𝐶
+ 𝑇𝑇 × 𝑀𝑀𝑀𝑀𝑀𝑀
Equation 9. Inverse Field Overcurrent Pickup
Where:
t
pickup
= time to pick up in seconds
A = -95.908
B = -17.165
C = 490.864
D = -191.816
TD = time dial setting <0.1, 20>
MOP = multiple of pickup <1.03, 205>
𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇
𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
=
0.36 × 𝑇𝑇𝑇𝑇
(
𝑀𝑀𝑀𝑀𝑀𝑀
𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
)
2 − 1
Equation 10. Inverse Field Overcurrent Reset