Medium Voltage—Autotransformer (2.3–6.6 kV). Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF

CTV-PRB004.book Page 38 Sunday, December 18, 2011 6:39 PM

Medium-Voltage Starter Types (2,300–6,600 Volts)

Figure 30. CenTraVac with a reduced-voltage autotransformer starter (CH530 unit controller)

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.

38 CTV-PRB004-EN

CTV-PRB004.book Page 39 Sunday, December 18, 2011 6:39 PM

CTV-PRB004-EN

Medium-Voltage Starter Types (2,300–6,600 Volts)

8. The S contacts open to open the autotransformer circuit.

9. The autotransformer is now connected as a series reactor with the motor.

10. Now, a secondT interlock and a second S interlock both close to energize the run contactor (2M).

11. The 2M contacts close to bypass the transformer and connect the compressor motor directly to the line.

Figure 31. Simplified autotransformer wiring diagram

LINE

VOLTAGE

F

1M

1M

1M

OL

OL

OL

AUTO-TRANSFORMER

2M

S

2M

S

50%

65%

80%

100%

MOTOR

CPT

F

START-

STOP

PR T 2M

1M

S

T

TRANSITION

S

PR

S

1M

T

2M

Standard features

• Control-power transformer

• Primary and secondary current transformers (CTs)

• Potential transformers (PTs)

• Grounding provisions

• Bolted line-power connections

• Bolted load-side connections for remote starters

• Standard motor protection

Environmental specification

• Designed, developed, and tested in accordance with UL 347

• NEMA 1 enclosure as standard

• Operation from sea level to 6,000 ft (1,829 m)

• Operating ambient temperature range 32°F to 104°F (0°C to 40°C)

• Relative humidity, non-condensing 5% to 95%

• Non-operating ambient temperature range -40°F to 158°F (-40°C to 70°C)

• Voltage utilization range ±10%

39