DIGITAL VOLTAGE REGULATOR (DVR A3) MODULE OPERATION - Continued
Voltage Droop When Connected In Parallel
When generators are operated in parallel, the engine speed regulator (i.e. GSC via LSM A4) controls the sharing
of the real power requirements (kW) of the total system load. The DVR controls the sharing of the reactive power
requirements (kVAR) of the total system load. If the output voltage of one generator is set slightly higher than the
other(s), it will supply lagging reactive current to the other generators in the group. This current will circulate
between the generators, possibly causing ampere overloading. One method of minimizing this effect is to cause
an individual generator output to sag, or "droop", in proportion to the lagging reactive current flow from it. As
reactive lagging generator output current increases, the DVR will cause the output voltage to droop (voltage will
decrease) proportionally. If the measured reactive output current is leading, the output voltage will rise (voltage
will increase) proportionally. In either case, this action will reduce the reactive current for better KVAR sharing
with other units. The droop percentage (parameter :30) determines how much the generator output voltage will
vary for a given amount of reactive current.
LOAD SHARING MODULE (LSM A4) INTERNAL OPERATION
The LSM consists of load power monitoring, load comparator, sync dynamics summer, speed trim summer, pulse
width modulation (PWM) output, A4K1 relay, circuits and a power supply for internal circuitry.
Load Power Monitoring
The output of current transformers CT-7, CT-8, and CT-9 is input to the load power monitoring circuit. Each current
is multiplied by the voltage monitored at pins 1, 2, and 3 of the LSM to generate voltages proportional to the
power in each phase of the output. These voltages are summed and input to a variable gain amplifier. The
amplifier can be calibrated, using the load gain potentiometer, to compensate for variations in components. The
output of the amplifier is input to the load comparator circuit.
Load Comparator Circuit
The load signal connection to the load comparator circuit on pins 22 and 23 is used for setup only. The load
sharing lines input (pins 10 and 11) to the load contactor circuit are connected to the paralleling connectors J32
and J33 in this generator set. Therefore, this point is connected to all other LSM in other generators. This
connection is made through J32, J33, the paralleling relay PAR in the generator set, and A4K1 in this module.
Refer to DC circuits (FO-1 Sheet 2 and Sheet 3 ) for interconnections external to LSM. By connecting the load
sharing lines of this module to those in other generator sets (via the paralleling cables), the load signal voltage is
balanced with the other generator sets connected here. The load comparator circuit has a load gain
potentiometer to adjust each generator set load signal so that the load signal voltage of each is the same at full
load. This compensates for different CT ratios or different generator set sizes. In droop mode (A4K1 not
energized), some of the power signal from the variable gain amplifier is subtracted from the main power signal by
the differential amplifier in the load comparator circuit. The setting of the Droop potentiometer (only active in
Droop) controls the amount in the load comparator circuit. This reduces engine power according to the droop
percentage set by this potentiometer.
Sync Dynamics Summer
The sync input (pins 24 and 25) comes from the GSC and is a 5 Vdc signal developed to control the speed
of the engine (and hence the generator). This signal is processed by the sync dynamics circuit and summed with
the output of the load comparator circuit.