CTV-PRB004-EN
31
Medium-Voltage Starter Types (2,300–6,600 Volts)
Table 7
shows the most common medium-voltage starter types available and compares inrush
current, torque, frequency of use, advantages and disadvantages, and typical acceleration time.
The inrush profiles are shown in
Figure 22
.
Which starter type is best?
One question often asked is: “Which is better, full voltage or reduced voltage?” Because medium-
voltage starters by nature use less current than low voltage, and therefore have significantly less
current inrush. Across-the-line medium-voltage starters are more commonly used; however, in
certain applications reduced voltage will be used to minimize starting strain on the electrical
system.
Unit- or remote-mounted?
Unit-mounted medium-voltage starters can save on installed cost and space.They are tested in the
factory and are shipped on the chiller. Remote-mounted starters are sometimes bussed together
in various configurations as shown in
“Multiple Starter Lineups (2,300–6,600 volts),” p. 61
. Remote-
mounted starters fromTrane can have special NEMA options, whereas unit-mounted starters are
NEMA 1. All starters conform to ANSI/NEMA ICS-6 enclosure standards unless otherwise noted.
Table 7.
Comparison of medium-voltage starters (2,300–6,600 volts)
Starter Type
(closed-transition)
Inrush
Current
% LRA
Percent
Rated
Torque
How
Often
Used
Advantages
Disadvantages
Typical
Acceleration
Time
(seconds)
Across-the-Line
(Full Voltage)
100
100
27%
• Low cost
• Least complex
• Least maintenance
• Draws highest inrush current
at startup
3–5
Primary Reactor
65% TAP
65
42
49%
• Good compromise between
first cost and inrush current
reduction
• More expensive than Across-
the-Line
• Larger than Across-the-Line
5–12
Autotransformer
65% TAP
45
42
22%
• Almost equal reduction of
torque and inrush current
• Lowest inrush current
• Most expensive
• Larger than Across-the-Line 5–12
AFD
<13
(<RLA)
Varies
2%
• Efficiency at part lift
• Power factor
• Very expensive
• Large and heavy
• Complex
5–12
Figure 22. Comparison of medium-voltage starting current
Across-the-Line
Autotransformer (65% tap)
0
1
2
3
4
5
6
7
8
9
10
Time (seconds)
0
20
40
60
80
100
120
% LRA
Primary Reactor (65% tap)
AFD
CTV-PRB004.book Page 31 Sunday, December 18, 2011 6:39 PM
