Capacity Control Using Intraflow; Economizer Option; Motor Cable Type; Magnetic Bearings - Danfoss VTT Series Applications And Installation Manual

Capacity Control using
IntraFlow™

Economizer Option

Motor Cable Type

Magnetic Bearings

Page 14 of 73
M-AI-VT-001-EN Rev.C.1
Overview of the VTT Compressor
Introduction of DTC's patent-pending IntraFlow™
technology simplifies capacity control for
centrifugal compressors. The use of IntraFlow
eliminates the need for IGVs or mechanical
variable geometry diffusers.
Using this technology enables VTT series
compressors to use vanned diffusers, which
improves overall compressor efficiency.
The advantages of IntraFlow
TM
diffuser control include:
VTT series compressors use two-stage centrifugal
compression with inter-stage port availability.
This feature provides advantages of capacity and
efficiency improvement when an economizer
is installed. The improvements in efficiency and
capacity are a result of further sub-cooling of
the liquid refrigerant. Two types of economizer
arrangements can be used: sub-cooler (closed) or
flash tank (open). With either design, care must
be taken to ensure only refrigerant vapor enters
the compressor.
Management of the motor conductors has a large
influence on the electromagnetic interference
(EMI) characteristics of the system.
Installing screened (shielded) power cable is
the most effective means to alleviate potential
EMI problems. The screen (shield) forces the
noise current to flow directly back to the drive
module before it returns to the power network
or takes other undesirable and unpredictable
VTT compressors are designed following the
concept of the current TT series of compressors.
The shaft (including impellers) are suspended
by a magnetic field. The magnetic bearing
• Higher reliability
• Recirculated flow enhances second stage
TM efficiency/stability
• Using only an externally mounted flow valve
to direct refrigerant, there are no moving parts
needed to manipulate aerodynamic conditions
• Increased turn-down capabilities extend the
stable operating envelope far beyond what can
be achieved using IGVs or Variable Geometry/
Mechanical Diffusers
over mechanical • Improves full load efficiency and delivers high
part load efficiency
• Flow from volute energizes core flow at point
of injection
To determine compressor capacity and efficiency,
the economizer performance rating option is
available in the Compressor Performance Rating
(CPR) program.
The circuit must be properly designed to reflect
the specified heat exchanger approach with
minimized pressure drops across the liquid side
and expansion side. Piping design, including
expansion device selection and pipe sizing,
should be in accordance with the refrigeration
best practices.
high frequency paths. Unlike most signal wiring,
the screening on the motor cable is terminated
at both ends. If a screened motor cable is not
available, then 3-phase conductors connected
to ground in a conduit provide some degree
of protection. This technique is as effective as
screened cable due to the unavoidable contact
of the conduit with various points within the
equipment.
system keeps the shaft levitated during normal
operation. The backup bearing system holds the
shaft during shut down and in the unlikely event
of magnetic bearing failure.