38
CTV-PRB004-EN
Medium-Voltage Starter Types (2,300–6,600 Volts)
Medium Voltage—Autotransformer (2.3–6.6 kV)
Autotransformer Starter (2,300–6,600 volts)
Another medium-voltage starter type is the autotransformer. To illustrate a typical starting
sequence using a generic (non-Trane) schematic, refer to
Figure 31, p. 39
and the starting sequence
below.
Starting sequence
1. A “start” signal from the chiller controller energizes the pilot relay (PR).
2. The pilot relay contacts close to energize the shorting contactor (S).
3. The S contacts close to complete the autotransformer circuit.
4. An S interlock closes to energize the start contactor (1M).
5. The 1M contacts close to connect the compressor motor to the line with the motor in series with
the autotransformer.
6. A time-delay relay or current-monitoring device initiates transition by energizing the transition
relay (T).
7. The T contacts open to de-energize the S contactor.
Figure 30. CenTraVac with a reduced-voltage autotransformer starter (CH530 unit controller)
CTV-PRB004.book Page 38 Sunday, December 18, 2011 6:39 PM
