Hanbell RC2-AVI Series, Руководство пользователя

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5
(C) Discharge:
Gas is discharged from the interlobe space when the leading lobe crosses the discharge port with designed volume
ratio.
Figure 2.2: Compression process
2.6 VFD application
The following are the instructions that explain the variable frequency drive (VFD) applied in RC2-AVI series screw
compressor. Please read all of the instructions before commissioning.
1. Maximum rotation frequency must be within nominal rotation frequency of the motor; minimum rotation frequency is
variable under specified working condition (please refer 2.9 Application Limits).
2. If the compressor has to operate outside the frequency spectrum mentioned above, please consult Hanbell before
commissioning. Higher or lower rotation frequency may result in lower efficiency or damage to the compressor and
motor.
3. Wiring of chiller controller and compressor protection modules such as PTC thermistors or oil level switch should
be insulated from wiring of the VFD’s power input/output for prevention of interference.
4. The VFD and the compressor must be well-grounded respectively.
5. Nullify functions of phase loss and phase sequence in motor protector INT69HBY for their duplication in the VFD’s
protection and prevention of interference.
6. To prevent reverse running of compressors due to incorrect wiring, verification of high/low pressures should be
monitored by pressure switches or programming in commissioning.
7. Compressor high/low pressure difference should be kept above 4kg/cm
2
, especially under very low rotation speed.
If an external oil circuit is used, the oil flow switch should be installed and oil pressure in the main oil return line
should be monitored for adequate lubrication of compressors.
8. If high/low pressure difference or oil pressure in the main oil return line can’t be maintained, an oil pump or
pressure regulation valve must be installed.
2.7 Capacity control system
The mechanism of capacity modulation of RC2-AVI is achieved by the variation of motor’s rotation speed.
Compared to modulation by slide valve, adjustable rotation speed through VFD significantly enhances efficiency of
compression, especially volumetric efficiency at part load. On the other hand, VFD can supply motor adequate voltage
and power input based on the requirement; in this way, variation of power input during capacity modulation becomes
more linear and that reduces unnecessary power losses. Overall, capacity modulation by VFD is superior to that by
slide valve in volumetric efficiency and power consumption.
Capacity modulation by VFD is similar to stepless capacity modulation by slide valve. As long as VFD receives analog
signals e.g. DC 0~10V or 4~20mA from PLC or microcontroller, it can make compressors run at corresponding rotation
speed proportionally to achieve capacity modulation.
To let PLC or microcontroller control VFD stably, pay attention to the following notes:
1.
Wiring for analog signals should be well-insulated to prevent interference and noise.
2. Wiring for signals connected to VFD should be isolated from VFD power supply at a distance.
3. PLC or microcontroller as well as VFD should be well-grounded respectively to prevent cross interference.
Procedures for initial setting are as follows:
1.
When completing VFD setting, remove wiring of VFD power output, and check if VFD’s output frequency and
corresponding voltage comply with PLC or microcontroller’s output signal, e.g. for DC 0~10V with 380V/3P/80Hz
motor, when analog signal is 10V, VFD’s output should be 80Hz and 380V; when analog signal is 7.14V, VFD’s
output should be 57Hz and 272V and so on.
2. VFD’s output current can’t be verified under no load but its frequency and output voltage still can be registered by
VFD’s display. Because VFD’s output voltage is not normal A/C voltage, it can’t be measured by general clamp
meter.
3. In addition to analog signals, other communication between microcontroller and VFD should be checked as well,
such as VFD’s failure feedback or reset command…etc.
(A) Suction and sealing
(
B) Compression
(C) Discharge