Basler Electric DECS-400 - Manual (Page 61)

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hertz limiter and can be adjusted from 0 to 3 in increments of 0.01. The V/Hz Time Limiter setting
establishes the time delay for the volts per hertz limiter and can be adjusted from 0 to 10 seconds in 0.1
second increments.
Var Limiter
The var limiter monitors and limits the level of reactive power exported from the generator. Var limiting is
useful in an application where the turbine rating has been increased but the generator rating was not
increased. In this case, the generator is considered to be var-limited since the generator power factor
rating has increased. The var limiter functions as a summing-point limiter only.
Var limiting is configured with a setpoint and a time delay. The setpoint is expressed in kilovars and has a
range determined by the rated kVA of the generator (entered on the Rated Data tab of the BESTCOMS
System Configuration screen). When the level of exported vars exceeds the setpoint, the DECS-400 acts
to limit the var flow after the time delay expires. The time delay has a setting range of 0 to 10 seconds
with 0.1 second increments.
Limiter Scaling
When the accessory input signal is configured for limiter scaling, the stator current limiter (SCL) and
overexcitation limiter (OEL) low-level values can be automatically adjusted. Automatic adjustment of the
SCL and OEL is based on six parameters: signal and scale for three points. The signal value for each
point represents the accessory input voltage and is adjusted from –10 to +10 Vdc in 0.01 steps. The scale
value defines the limiter low level as a percentage of rated field current for the OEL and rated stator
current for the SCL. The range of scale values is 0 to 200% with 0.1% increments. For accessory input
voltages between two of the three defined points, the low-level limiter setting is linearly adjusted between
the two scale values.
Operation with Paralleled Generators
DECS-400 units can be used to control the excitation level of two or more generators operating in parallel
so that the generators share the reactive load. The DECS-400 accommodates either reactive droop
compensation or reactive differential schemes for reactive load sharing. Line drop compensation can be
used in either scheme.
Droop Compensation
When droop compensation is employed for a generator paralleled with the utility power grid, the bus
voltage droops (decreases) as the reactive, lagging power factor load is increased. The DECS-400 droop
compensation setting can be accessed through BESTCOMS or the front panel HMI. Droop compensation
is expressed as a percentage of the generator rated terminal voltage and has an adjustment range of –30
to +30%.
Reactive Differential
Reactive differential (cross-current compensation) is facilitated in the DECS-400 by a dedicated current
sensing input at terminals A7 and A8. The DECS-400 cross-current compensation setting can be
accessed through BESTCOMS or the front panel HMI. Cross-current compensation is expressed as a
percentage of the system CT rating and has an adjustment range of –30 to +30%.
Line Drop Compensation
Line drop compensation offsets line or transformer impedance drops and moves the regulation point
beyond the terminals of the generator. The DECS-400 line drop compensation setting can be accessed
through BESTCOMS or the front panel HMI. Line drop compensation is applied to both the real and
reactive portion of the generator line current. Line drop compensation is expressed as a percentage of the
generator terminal voltage and has an adjustment range of 0 to 30%.
DECS-400 Functional Description