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CTV-PRC007-EN14
Figure O-2 – Typical Equipment Room Layout – Unit-Mounted Star-Delta Starter
Figure O-1 – Typical Equipment Room Layout – Conventional Remote Star-Delta Starter
•
System Design Time Cost Savings
System design time is reduced, since
all starter components and
interconnecting wiring are pre-
engineered and selected.
•
Complete package available with
Agency Approval
•
Application
The Trane unit mounted starter can be
applied on low voltage (600 volts) and
below applications up to
approximately 1300 tons capacity. To
determine the unit mounted starter to
be used with a particular selection, it is
necessary to know the current draw of
the compressor motor. The starter
current draw must be greater than, or
equal to, the compressor motor
current draw.
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Reliability
The unit mounted starter is a star-delta
closed transition electromechanical
starter. Motor starters of this
configuration have proven reliability in
thousands of centrifugal chiller
applications around the world. The
proven electromechanical concept plus
the use of industrial quality
components makes the CenTraVac unit
mounted starter dependable in all kinds
of service applications.
Unit
Options
Unit Mounted
Starter (Cont.)
Operation
The unit mounted starter is a star (wye)
delta, closed transition, reduced voltage
starter. When starting and during
acceleration, the motor is connected in
its wye configuration. Because of this
arrangement the voltage applied to the
motor windings is reduced to one
divided by the square root of three or
0.58 times line voltage. This reduction in
winding voltage results in a reduction in
inrush current. The inrush current is 0.33
times the full voltage locked rotor current
rating of the motor. The accelerating
torque of the motor is also reduced to
0.33 times the full voltage torque rating.
This is sufficient to fully accelerate the
compressor motor. The unit control
panel monitors motor current during
operation via current transformers
located in the starter enclosure. When
during acceleration the line current
drops to approximately 0.85 times rated
load current, transition is initiated. The
closed transition feature provides for a
continuous motor current flow during
transition by placing resistors in the
circuit momentarily. This prevents
buildup of damaging torques to the
system during this period. With the
completion of transition, the motor
windings are connected in the delta
configuration with full line voltage.
Three precision current transformers
monitor phase current. Contactor
position and various voltage signals
provide extensive interlocking between
the starter and the microcomputer in the
CenTraVac
™
control panel. All logic and
subsequent instruction originate in the
unit control panel. Protection against the
following starter defects is provided:
•
High motor current (starting and
running)
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Improper starter circuitry
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Excessive accelerating time
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Incomplete starting sequence
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Loss of phase
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Phase amperage unbalance
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Phase reversal
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Distribution fault
Features
The Trane CenTraVac Unit Mounted
Starter includes the following standard
features:
•
NEMA 1 enclosure, designed to
accommodate padlock
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3 KVA control power transformer with
120V secondary
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Fused 120V control circuit
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3-phase incoming line terminals
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6 output load terminals factory-
connected to the motor