Derating is not an error condition. It only means that the
requested speed cannot be accomodated at the moment,
to keep the compressor and drive within specified
operating limits.
Drive Power Derating
The compressor speed is limited to keep the drive power
below its maximum power limit. This limit is a function of
the line voltage input to drive.
In AC mode, the fan speed will be increased to keep the
drive power below its maximum limit. This is done to
lower condensing pressure and thereby power
consumption.
Drive Temperature Derating
The compressor speed is limited to keep the drive
temperature below its maximum limit.
Max Condensing Pressure Derating
The compressor speed is limited to keep the condensing
pressure below its maximum limit. The maximum
condensing pressure is a function of suction pressure, and
part of the envelope protection.
In AC mode, the fan speed is increased to keep the
condensing pressure below its maximum limit.
Min Condensing Pressure Derating
In AC mode, the fan has control over the condensing
pressure. When the condensing pressure is lower than
minimum, the fan speed decreases.
Min Suction Pressure Derating
If the suction pressure is lower than the minimum suction
pressure, then the compressor speed decreases.
In HP mode, the fan speed also increases if the suction
pressure is lower than the minimum.
6.3.5.6 Discharge temperature cut out
The discharge temperature is for 90 s allowed to be above
the max. discharge temperature, after that the drive will
stop and go into a safe mode condition. When the
temperature has dropped below the allowed max.
temperature, the drive automatically restarts when the
restart timer has elapsed.
6.3.5.7 Max Suction Pressure (MOP)
When the suction pressure exceeds the maximum
operating pressure, the EEV controller decreases its
opening degree. If the suction pressure exceeds the
maximum operating pressure for more than 90 s, the
controller stops the compressor and restarts after the
restart time has elapsed.
6.3.5.8 Frequency Cancelation
Variable speed systems sometimes are characterized by
showing mechanical resonances at critical compressor
speeds. Therefore Danfoss has established parameters to
set 5 bypass speeds with individual bandwidths. If a
mechanical resonance occurs, i.e. at 1600 RPM compressor
speed, this speed can be set to one of the bypass
frequencies. To define the bandwidth, a bypass range can
be set, i.e. 200 RPM. In this example the compressor would
not be operated between 1500 and 1700 RPM. If the
system demand requires a speed of more than 1500 RPM,
the drive remains at 1500 RPM, until the system demand
exceeds 1600 RPM; then the speed is increased to 1700
RPM and vice versa.
Critical bypass speed can be set individually in the field
using a Modbus service tool; however, it is recommended
to search for resonances in the design phase of variable
speed air-conditioning or heat pump systems.
The bypass speed can be set within the entire operation
range of the drive from 900-4200 RPM. The controller can
skip five speed ranges. Each range is specified as a centre
frequency and a bandwidth.
6.3.5.9 System Status
The system status is expressed in the content of several
Modbus registers. Also refer to
Embedded Application Contro...
VLT
®
Inverter Scroll CDS 801 Operating Instructions
MG10V402 - VLT
®
is a registered Danfoss trademark
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