Low Voltage-Remote-Mounted Adaptive Frequency Drive - Trane Starters Engineering Bulletin

Low-Voltage Starter Types
Harmonics
Harmonics has become a frequently used term in the power quality arena. Of all the power quality
issues encountered today, harmonics is the least understood and most feared; unfortunately, this
has resulted in overstating the impact of harmonics.
Harmonics is not a "thing" but a way to define current or voltage distortion on a power line.
Harmonics can be directly linked to nonlinear loading of a power system. Nonlinear loads are
created by devices connected to a given power system that draw current from the power source
with a waveform that is not a pure sine wave.
All nonlinear loads, including variable-frequency drives, will create current and voltage distortion.
Typically harmonics is not an insurmountable issue when applying an AFD on a centrifugal chiller.
Harmonic attenuation
Harmonic attenuation is standard on the unit-mounted refrigerant-cooled AFDs and includes:
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Note: TDD is a direct affect of variable-frequency drives and is a larger and more critical value than
IEEE 519
It is important to recognize that IEEE 519 relates to the entire system, not specifically to any one load
or product. IEEE 519 establishes requirements at the point of common coupling (PCC) where the
building connects to the utility system.The standard contains no specific requirements for the
internal electrical loads.
Even thoughTrane AFD-equipped chillers will attenuate their own harmonics, other nonlinear
loads on the same system could still create harmonic problems. In buildings where harmonics
might be a concern,Trane recommends conducting a power-distribution system analysis to
determine if there is a need to further attenuate harmonics at the system level.
Low Voltage—Remote-Mounted Adaptive Frequency Drive
Depending on the application,Trane also offers a remote free standing Adaptive Frequency Drive
(AFD).The remote AFD comes as a complete, free-standing package that includes the necessary
controls, control power and programming needed for operation. EachTrane Adaptive Frequency
Drive arrives completely programmed with all chiller control communication logic installed. Input
voltage options include 460, 480, 575, and 600 volts. Most of the low-voltage AFDs in the industry
are designed to work at 460/480 volts only. In HVAC applications were the voltage is 575/600, a
transformer would be need to apply an AFD. With theTrane remote AFD, a transformer would not
be needed, thereby eliminating the associated extra design time, space requirements, installation
costs and energy losses.
The design
The remote AFD design is a voltage-source, pulse-width modulated (PWM) type. It consists of three
primary power sections.
Rectifier.
sine wave into DC voltage that will be stored in the DC Bus section
DC Bus Section.
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Integrated active rectification control of the building AC power assures low line-generated
harmonics back to the user's power grid.This results in less than 5 percent current harmonic
distortion (TDD) as measured at the AFD.
Active input rectifier will regulate to a displacement power factor of 0.98 or better at full load
and a value of 0.96 at part load.
Full motor voltage is applied regardless of the input voltage.
the amount of total harmonic distortion (THD). As measured at the AFD, the amount ofTHD
will be less than theTDD.
Constructed of silicon controlled rectifiers (SCR), which convert the incoming utility AC
A capacitor bank that is used to store energy for use within the inverter section
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