Low Voltage—Remote-Mounted Adaptive Frequency Drive. Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF

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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:

• 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.

Note: TDD is a direct affect of variable-frequency drives and is a larger and more critical value than the amount of total harmonic distortion (THD). As measured at the AFD, the amount ofTHD will be less than the TDD.

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 though Trane 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.

Constructed of silicon controlled rectifiers (SCR), which convert the incoming utility AC sine wave into DC voltage that will be stored in the DC Bus section

DC Bus Section.

A capacitor bank that is used to store energy for use within the inverter section

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Low-Voltage Starter Types

Inverter IGBTs.

Use the pulse width modulation (pwM) method to convert the DC voltage from the capacitor bank into a synthesized output AC voltage that controls both the voltage and frequency applied to the motor

Figure 21. Front view, remote-mounted AFD

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Features

The standard design features for the AFD include:

• Free standing NEMA 1, ventilated enclosure with a hinged door, tested to a short-circuit current rating of 65,000 amps. Enclosure locking provisions are standard.

• Lockable, door-mounted circuit breaker/shunt trip with an AIC rating of 65,000.

• Amps, and enclosure short circuit rating of 65,000 amps standard.

• UL/CUL listed as a package.

• Simple, front access only design.

• 460/480/60/3 input power ±10 percent.

• 575/600/60/3 input power ±10 percent.

• Minimum efficiency of 97 percent at rated load and 60 hertz.

• Displacement power factor at 0.96 at all loads.

• Soft-start, linear acceleration, coast-to-stop.

• Adjustable frequency from 38 to 60 hertz.

• 150 percent instantaneous torque available for improved surge control.

• Output line-to-line and line-to-ground short-circuit protection.

• Ground fault protection (UL listed).

Optional Items

• NEMA 12 enclosure.

• 100,000 amp enclosure short-circuit current rating (SCCR) with 100,000-amp AIC circuit breaker available as a design special.

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Low-Voltage Starter Types

Environmental specification

• Operating temperature: 32°F to 104°F (0°C to 40°C).

• Storage temperature: -4°F to 149°F (-20°C to 65°C).

• Humidity: 95 percent non-condensing.

• Maximum elevation: 3280 ft (1000 m) rated output current.

• Derate 4 percent/3280 ft over rated altitudes up to 9840 ft (3000 m).

Dimensions

Table 6 provides some basic reference dimensions and weights for the remote AFD. Always refer and use the Trane submittals for actual dimensions.

Table 6.

Remote AFD dimensions

F3

F4

Frame

D3/D4

E2

Power (hp) Max. Amps Power (hp) Max. Amps

150–350 394 150–400 356

450–600

N/A

650–750

950–1050

1150–1350

649

N/A

791

1031

1360

450

500–650

750–1050

N/A

1150–1550

400

560

840

N/A

1258

Width (in.) Depth (in.) Height (in.) Weight (lb)

48 24 86 1220

56

64

127

127

150

24

24

24

24

24

90

90

90

90

90

1635

1680

2885

3185

3720

Digital data display

The following points are digitally displayed at the chiller controller:

• Frequency command

• Input line voltage

• Load-side amps

Harmonics

The remote AFD is a standard six pulse design. Therefore the harmonic level is ~35 percent total demand distortionTDD as measured at the AFD input. If lower levels of attenuation are required, upstream filtering would be required.

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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 mediumvoltage 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.

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

Across-the-Line

(Full Voltage)

Primary Reactor

65% TAP

Autotransformer

65% TAP

AFD

100

65

45

<13

(<RLA)

100

42

42

Varies

27%

49%

22%

2%

Advantages

• Low cost

• Least complex

• Least maintenance

• Good compromise between first cost and inrush current reduction

• Almost equal reduction of torque and inrush current

• Lowest inrush current

• Efficiency at part lift

• Power factor

Disadvantages

Typical

Acceleration

Time

(seconds)

• Draws highest inrush current at startup 3–5

• More expensive than Acrossthe-Line

• Larger than Across-the-Line

5–12

• Most expensive

• Larger than Across-the-Line 5–12

• Very expensive

• Large and heavy

• Complex

5–12

Figure 22. Comparison of medium-voltage starting current

120

100

80

60

Across-the-Line

Primary Reactor (65% tap)

Autotransformer (65% tap)

AFD

40

20

0

0 1 2 3 4 5 6

Time (seconds)

7 8 9 10

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 . Remotemounted 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.

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