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M-AI-VT-001-EN Rev.C.1
M-AI-VT-001-EN Rev.C.1
Overview of the VTT Compressor
The inverter section is made up of six IGBTs,
commonly referred to as switches. One switch
is necessary for each half phase of the three-
phase power, for a total of six. The six IGBTs
are contained in three modules with two in
each, onepositive (+) and one negative (-) for
each phase.
A Hall effect type current sensor is on each phase
of the output to measure motor current. This
type of device is used instead of more common
current transformer (CT) devices to reduce the
amount of frequency and phase distortion that
CTs introduce into the signal. With Hall sensors,
the average peak and earth leakage currents can
be monitored.
Drive Module Control
Input and Output Signals
A serial communication protocol signal
(RS-485) from the CCM supplies commands
and references to the drive module.
Drive Module
Electromagnetic
Compatibility (EMC)
Considerations
Electrical and Fire Hazard
Protection
Drive Module Cooling
Cooling Fans
To obtain electromagnetic compatibility (EMC),
the following basic issues need to be considered
when installing a drive module:
• Safety grounding: For safety reasons the drive
module must be earthed appropriately due
to high leakage current. Comply with all local
safety regulations.
• High-frequency grounding: Keep the grounding
wire connections as short as possible.
Connect the different earth systems at the lowest
possible conductor impedance by keeping
the conductor as short as possible and using
the greatest possible surface area. The metal
cabinets of the different devices are mounted
on the cabinet rear plate using the lowest
possible high frequency impedance. This avoids
having different high frequency voltages for the
individual devices and risk of radio interference
currents running in connection cables that
may be used between the devices. To obtain
a low high frequency impedance, use the
fastening bolts of the devices as high frequency
connections to the rear plate. Remove
insulating paint or similar obstructions from
the fastening points.
The standard VTT drive module provides a high
degree of EMC. However, if maximum EMC is
desired the drive can be ordered with the high
EMC option. In either case, following these
installation instructions will ensure the best
possible EMC.
Branch circuit protection
In order to protect the installation against
electrical and fire hazard, all branch circuits in an
installation, switch gear, machines etc., must be
protected against short-circuit and over-current
according to national/international regulations.
Over-current protection
DTC recommends that the chiller manufacturer
provide overload protection to avoid fire
hazard due to overheating of the cables in the
installation. Fuses or circuit breakers can be used
to provide the over-current protection in the
installation. Over-current protection must always
adhere to national regulations.
Short-circuit protection
The Drive Module provides full short-circuit
protection in case of short-circuit on the motor
output. DTC recommends use of the fuses
specified in the Service Manual as a replacement/
spare part for built-in fast acting fuses.
The Drive is cooled through combination of air
flow and refrigerant cooling of the back plate.
Under most operating conditions all heat is
removed by air flow through the drive heat sinks.
Monitoring the IGBT temperatures indicate peak
power requirements which activates additional
refrigerant cooling.
The drive module is equipped with cooling fans
to provide airflow along the heat sink. Units have
a fan mounted in the enclosure door to provide
more airflow to the unit. Each fan has tachometer
feedback to the control card to confirm that
the fan is operating correctly. On/off and speed
control of the fans is provided to reduce overall
acoustical noise and extend the life of the fans.
The fans are activated as needed by drive module
control logic.