Basler Electric DECS-400 - Manual (Page 70)

58 9369700990 Rev R
The limiter reduces the stabilizer’s upper limit, V
PSS_ULMT
, at a fixed rate until zero is reached or overvoltage
is no longer present. The limiter does not reduce the AVR reference below its normal level; it will not
interfere with system voltage control during disturbance conditions. The terminal voltage limiter has a per-
unit setting range of 0 to 10 with 0.01 increments. The error signal (terminal voltage minus limit the limit
start point) is processed through a conventional low-pass filter to reduce the effect of measurement noise.
The low-pass filter is controlled by a time constant which is adjustable from 0.02 to 5 seconds in 0.01
second increments. All terminal voltage limiter settings are accessed on the Output Limiter tab of the
BESTCOMS PSS screen.
Rate of Frequency Change Blocking
The PSS rate-of-change function adjusts the PSS output to compensate for a generator rate-of-frequency
change that exceeds the user-defined threshold. This threshold has an adjustment range of 0 to 10 hertz
per second. When the generator frequency rate of change threshold setting is exceeded for the duration
of a user-defined time delay, the PSS output is driven to zero and then ramped up to its previous, nominal
value during the duration of a user-specified block timer. The delay time and block time are each
adjustable from 0 to 20 seconds. The rate of PSS output ramping is adjusted by low-pass filter time
constant and washout filter time constant settings. These two settings have an adjustment range of 0 to
20 seconds.
Field Isolation Module
A Field Isolation Module (Basler P/N 9372900100) is required for each DECS-400 unit. The Field Isolation
Module receives isolated operating power from the DECS-400 and supplies the DECS-400 with isolated,
field current and field voltage signals. A cable, supplied with the Field Isolation Module, connects the Field
Isolation Module (connector J1) to the DECS-400 (connector P1).
Field current sensing is supplied to the Field Isolation Module by a user-supplied current shunt with an
output rating of 50 mVdc or 100 mVdc. The field current sensing input is designed to accept up to 300%
of the nominal current range. The field current signal is converted to a voltage signal in the range of 2 to
9.5 Vdc and sent to the DECS-400 through connector J1.
Field voltage sensing is supplied to the Field Isolation Module directly from the field. The Field Isolation
Module accepts five ranges of field voltage: 63, 125, 250, 375, and 625 Vdc. The field voltage sensing
input is designed to accept up to 300% of the nominal voltage range. The field voltage signal is low-pass
filtered, converted to a voltage signal in the range of 0.9 to 9.1 Vdc, and sent to the DECS-400 through
connector J1.
Field Isolation Modules are identified by two part numbers: 9372900100 and 9372900101. Part number
9372900100 identifies the Field Isolation Module assembly. Part number 9372900101 identifies the Field
Isolation Module packaged for shipping and should be specified when requesting a replacement module.
Functional Description DECS-400