CTV-PRB004-EN
17
Low-Voltage Starter Types
Table 5
shows the most common low-voltage starter types available and lists their advantages and
disadvantages.Typical inrush acceleration profiles for these starters are shown in
Figure 6, p. 18
.
It is very uncommon to see a full-voltage starter in a low-voltage application due to the high inrush
current; however, it is represented on the chart to provide a frame of reference.
Which starter type is best?
The wye-delta starter has been around a long time and, except for an AFD, it draws the lowest
inrush current.Wye-delta starters are electromechanical and service technicians are typically more
comfortable with them. The solid-state starter is a relatively newer design compared to the wye-
delta, and has a slightly higher inrush current in chiller applications.The solid-state starter inrush
can be set lower (the starter takes longer to get the motor up to speed), but it must be above the
minimum inrush required to develop the proper starting torque. The solid-state starter is
comparable in price to the wye-delta starter and has a smoother inrush curve without any current
spikes.The wye-delta’s transition spike is not long enough to set utility demand ratchets or reduce
the life of the motor. The starter type chosen ultimately depends on the application.
Trane Adaptive Frequency Drives provide motor control, but they are much more than just starters.
They also control the operating speed of the compressor-motor by regulating output voltage in
proportion to output frequency. Varying the speed of the compressor-motor can translate into
significant energy savings.
Applications that favor the use of an AFD exhibit increased operating hours at reduced condenser
water temperatures and high energy costs. However, it is important to recognize that all variable-
speed drives, including theTrane AFD, require more energy near full-load design conditions, often
coinciding with the peak electrical demand of the building. This may result in higher demand
charges and diminish the overall energy savings. An analysis of the full-year operation of the chiller
plant using an hour-by-hour simulation program that does not use blended kW and kWh energy
rates will help determine whether an AFD is appropriate for a specific application and location.
Unit or remote mounted?
Unit-mounted starters can save on installed cost and space, and they can be tested in the factory
and shipped on the chiller in a NEMA 1 enclosure. Remote-mounted starters provide more options
for multiple starter lineups, and may be chosen in order to implement some of the industrial starter
options such as high-fault and NEMA 12/3R.
Table 5.
Comparison of low-voltage starter types
Starter Type
(closed-transition
Inrush
Current
% LRA
Percent
Rated
Torque
How
Often
Used
Advantages
Disadvantages
Typical
Acceleration
Time
(seconds)
Wye-Delta
(Star-Delta)
33
33
60%
• Equal reduction of torque and
inrush current
• Low cost
• Can be unit mounted
• Only applicable up to
600 volts
• “Spike” at transition
5–12
Solid-State
~45
33
15%
• Gradual inrush/ramp up
• No “spike” at transition
• Price comparable to the wye-
delta
• Higher level of service
expertise than wye-delta
• Higher inrush current than
wye-delta
• Starting harmonics may be an
issue
5–12
Adaptive Frequency
Drive (AFD)
<13
(<RLA)
varies
25%
• Lowest inrush current
• Better chiller efficiency at
reduced lift
• Most expensive
• Efficiency loss at full load
• Harmonics may be an issue
8–30
CTV-PRB004.book Page 17 Sunday, December 18, 2011 6:39 PM
