Bitzer VARIPACK FD+6 Instructions De Service page 34

The "start to start interval" limits the maximum number
of compressor starts. If the defined time since the last
compressor start has not yet elapsed, the compressor
start is delayed. If the compressor is operated for a
longer period than the "start to start interval", it can be
restarted immediately after the stop. As standard, the
minimum "start to start interval" recommended for the
compressor is set. It can be extended to any desired
period in order to improve the operating performance of
the system and to increase the system efficiency by
avoiding very short cycles. If required, shorter time val-
ues than the preset and recommended ones can be
configured.
Relay "Compressor running" (DO2)
The relay "Compressor running" indicates the operating
condition of the compressor. It can be used, for ex-
ample, for switching off the oil heater or switching on
the additional fan or as a signal for the electronic ex-
pansion valve. The relay is switched on after a suc-
cessful compressor start and after having reached the
minimum frequency and is switched off as soon as the
frequency falls below the minimum value.
"Hold time after start at minimum frequency"
In temperature-controlled systems with only one com-
pressor, there may be significant pressure drops in the
low-pressure circuit after the compressor start. The
reason for this is that, due to the high setpoint devi-
ation, the compressor is powered up too fast so that the
pressure cannot be regulated quickly enough by the ex-
pansion valve. This can be avoided by setting a time in-
terval after the start during which the minimum fre-
quency of the compressor is maintained before the
compressor switches to normal operation. As standard,
the value of 0 s is set.
34
Operation at 50 Hz (Force)
In case of long pipelines and rising lines or a not optim-
ally selected suction gas line, there is a risk of oil mi-
gration during the long partial load phases. If the fre-
quency and therefore the mass flow is increased, the
oil can be circulated back and a compressor shut off
can be avoided. This can be realized by the "Force"
function of the VARIPACK frequency inverter. If a lack
of oil in the oil tank or compressor is signaled, the di-
gital input DI2 of the VARIPACK frequency inverter can
be activated to operate the compressor at at least
50 Hz.
"Resonance avoidance"
If vibrations that are not easy to eliminate occur in a
specific range of operating frequencies, these frequen-
cies can be avoided. For this, two frequency ranges
can be defined in which the compressor should not re-
main during operation. When the setpoint exceeds the
defined initial value, the frequency remains at this value
until the setpoint has exceeded the end value and the
frequency range is skipped. When shutting down, the
frequency is maintained until the setpoint has fallen be-
low the initial value.
Automatic limitation of the maximum frequency
During operation in the field weakening mode, the
VARIPACK frequency inverter limits automatically the
operating frequency as soon as the maximum operat-
ing current of the compressor or the VARIPACK fre-
quency inverter is reached. This allows an economic di-
mensioning of the combination of compressor and
VARIPACK without running the risk that the VARIPACK
frequency inverter under exceptional operating condi-
tions (high condensing temperature, start-up or start
after a long standstill) switches to fault due to overcur-
rent.
CB-100-2