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direction even for a very short time.
Basically, voltages generated in each phase of a polyphase alternator or circuit are called phase voltages. In
a three-phase circuit, three sine wave voltages are generated, differing in phase by 120 electrical degrees.
The order in which the three voltages of a three-phase system succeed one another is called phase
sequence or phase rotation. This is determined by the direction of rotation of the alternator. When rotation is
clockwise, phase sequence is usually called "ABC", when counterclockwise, "CBA".
This direction may be reversed outside the alternator by interchanging any two of the line wires. It is this
possible interchange of wiring that makes a phase sequence indicator necessary if the operator is to quickly
determine the phase rotation of the motor.
Proper compressor motor electrical phasing can be quickly determined and corrected before starting the
unit. Use a quality instrument, such as the Associated Research Model 45 Phase Sequence Indicator.
1.
Check the unit in "Stop" mode from TD7 display.
2.
Open the electrical disconnect or circuit protection switch that provides line power to the line power terminal
block(s) in the starter panel (or to the unit mounted disconnect)
3.
Connect the phase sequence indicator leads to the line power terminal, as follows:
4.
Turn power on by closing the unit supply power fused-disconnect switch.
5.
Read the phase sequence on the indicator. The "ABC" LED on the face of the phase indicator will glow if
phase is "ABC".
6.
If the "CBA" indicator glows instead, open the unit main power disconnect and switch two line leads on the
line power terminal block(s) (or the unit mounted disconnect). Reclose the main power disconnects and
recheck the phasing.
CAUTION - Equipment Damage!
Do not interchange any load leads that are from the unit contactors or the motor terminals.
The terminal connection of the compressor after maintenance must be consistent with Trane wiring
diagrams. Do not interchange any load leads that are from the unit contactors or the motor terminals to
prevent compressor from damage in a reverse rotation. Do not operate compressor without terminal box
cover in place.
7.
Reopen the unit disconnect and disconnect the phase indicator.
Water System Flow Rates
Establish a balanced chilled water flow through the evaporator within the allowable range in
flow rates should fall between the minimum and maximum values. Chilled water flow rates below the
minimum values will result in laminar flow, which reduces heat transfer and causes either loss of EXV control
or repeated nuisance, low temperature cutouts. Flow rates that are too high can cause tube erosion.
Water System Pressure Drop
Measure water pressure drop through the evaporator at the field-installed pressure taps on the system water
piping. Use the same gauge for each measurement. Do not include valves, strainers fittings in the pressure
drop readings.
Pressure drop readings should be approximately those shown in
Curves
and
Table
Phase Sea. Lead
Black (Phase A)
Red(Phase B)
Yellow (Phase C)
4.
Terminal
L1
L2
L3
Figure 10 Evaporator Water Pressure Drop
43
Table
4. The
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