Power Circuit Requirements. Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF

CTV-PRB004.book Page 54 Sunday, December 18, 2011 6:39 PM

Electrical System—Design Guidelines by a short circuit (fault current), it may be opened safely at any time. A low-voltage starter door may be opened only if the circuit breaker is in the “off” or open position.

Circuit breakers of various interrupt ratings are offered as options. The interrupting capacity of a circuit breaker must also be considered. An analysis of an installation is usually done by the electrical engineer to calculate the maximum available fault current (AFC) that could be delivered if a short circuit occurred.

When a low-voltage starter is ordered with a circuit breaker, the starter manufacturer furnishes a standard circuit breaker sized at approximately 125 percent of compressor RLA or larger.The trip current of a circuit breaker is adjustable so that it will not trip during starting and acceleration, but will trip instantaneously (typically within one cycle) if a short circuit occurs.

Short-Circuit Current Rating (SCCR)

The disconnect means and the short-circuit protection discussed above are either supplied and installed by the customer upstream of the starter or they can be supplied as options with theTrane ® starter. However, the starter’s SCCR must be communicated to the electrical engineer early in the project to ensure that the starter short-circuit current rating will meet the requirements. If the SCCR is not high enough, the electrical engineer will have to look for solutions upstream of the starter.

Each low-voltageTrane ® starter or frequency drive has a short-circuit current rating, based on the size of the starter as well as the type of disconnect or circuit breaker included. See the appropriate submittal drawings for the starter short-circuit current rating.

Note: Don’t confuse short-circuit current rating (SCCR) with silicone controlled rectifier (SCR)— utilized in solid-state starters and AFDs.

Medium-voltage short circuit interruption

All medium-voltage starters contain current-limiting fuses for short circuit protection.The currentlimiting fuses and isolation switch, which is furnished as standard, fulfill the request for a fused disconnect. If you need more detail on the fuses for a particular starter contact CenTraVac Field

Sales Support.

It turns out that the starter short-circuit current rating is not an issue with medium-voltage starters.

Because Trane ® medium-voltage starters meet UL 347, current-limiting power fuses are required and provided as standard, and the starter short-circuit current rating no longer applies. Mediumvoltage starters fromTrane have an interrupt rating based on the standard current-limiting fuses.

At 4,160 volts, the NEMA E2 fused-interrupt rating is 50,000 amperes or 400 MVA.

Medium voltage fuse coordination suggestions

Proper sizing of fuses and circuit breakers upstream of the starter is the responsibility of the customer or the electrical engineer.

Power Circuit Requirements

Starter Applications

When applying a starter to a chiller motor on a specified power circuit, the power circuit has to meet minimum criteria to allow for a successful chiller start without an immediate shutdown or safety trip.This applies to utility power, local or smaller-scale facility power, and backup or peak-shaving generator power.

The following are some considerations for motor starter power quality requirements:

• Size of the power circuit

• Source and/or total system impedance

• System regulation

• Inrush characteristics of the starter type

• Acceleration time

• Maximum voltage sag

• Maximum voltage swell

54 CTV-PRB004-EN


CTV-PRB004-EN

Electrical System—Design Guidelines

• Additional (non-chiller) loads on the power circuit

When evaluating a power system for a chiller-compressor motor with a specified starter type, calculations must be done in order to size or “correct” the power circuit properly in order to successfully start the motor and keep the motor-starter combination online during operation.

Table 9 and Table 10, p. 55 show specific starter characteristics and minimum power requirements.

Table 9.

Sizing requirements

Starter Type Voltage Range

Inrush

Current

% LRA

Chiller Controller

Maximum Acceleration

Time Setpoint (sec) (a)

Percent

Rated

Torque

Wye-Delta

Solid-State

X-Line

Primary Reactor

208–600 V

208–600 V

2.3–13.8 kV

2.3–13.8 kV

33

~45

100

65

27

27

6

16

33

33

100

42

Autotransformer

AFD

2.3–13.8 kV

460–600 V

45

<13

16

12

42

Varies

(a) The Chiller Controller Maximum Acceleration Time Setpoint is the maximum allowable acceleration time; if the chiller has not started within this time, a diagnostic will be set.

Table 10. Motor starter operational voltage range—during a start

Starter Size

155–606 amps

607–1,316 amps

607–1,856 amps

185–1,120 amps

180–960 amps

961–1,600 amps

155–1530 amps

Starter Description

Unit- and Remote-Mounted

Wye-Delta

Unit-Mounted

Wye-Delta

Remote-Mounted

Wye-Delta


Solid-State

Remote-Mounted,

High-Fault Solid-State

Remote-Mounted,

High-Fault Wye-Delta


Low Voltage AFD

Maximum

Line-to-Line

RMS Voltage Sag

25%

25%

20%

25%

25%

25%

25%

Maximum

Line-to-Line

RMS Voltage Swell

15%

15%

15%

15%

15%

15%

10%

94, 187, 205/288 amps

(205 reduced voltage, 288 full voltage)

Unit-Mounted

Medium Voltage

(2.3–6.6 kV)

94, 187, 360 amps

94 amps

61–250 amps @ 4,160 V

Remote-Mounted

Medium Voltage

(2.3–6.6 kV)

Remote-Mounted

Medium Voltage

(10–13.8 kV)

Remote Medium-Voltage AFD

25%

(20% w/additional protection)

25%


25%


25%

15%

15%

15%

10%

Note: The maximum allowable under/overvoltage during normal operation is ±10 percent.

55


Electrical System–Power Wire Sizing

This section provides guidance for sizing the power conductors forTrane CenTraVac water chillers including wiring from the distribution system to the starter, and wiring from the starter to the compressor motor. The information provided does not constitute a design manual and does not supersede local code requirements or National Electric Code (NEC) recommendations. Final wire size selection must be verified by the Engineer of Record for the installation.

Wire size and count should be coordinated with the starter selection so the starter can be ordered with the proper terminal lugs. The starter is shipped with standard lugs as shown on the as-built submittals. Alternate lugs are often available and can be purchased locally. Standard lugs accept a wide range of wire sizes, but not all possible combinations.

General wiring requirements

• When more than one lead per phase is used (paralleled conductors), the leads must be of the same size and length so that they share the load equally. Paralleled conductors are only permitted for wire sizes of 1/0 and larger.

• When two or more conduits are used, all three phases must be equally represented in each conduit to avoid overheating.

Specific requirements for distribution system to starter wiring

• Wiring to the starter must be copper. A discussion of why aluminum should not be used can be found in the Glossary ( “Aluminum conductors,” p. 73 ).

• Wiring to all starters must be in multiples of three.

Specific requirements for starter to motor wiring

• All wiring to the CenTraVac motor must be copper. The UL listing on the CenTraVac requires copper conductors, and the terminal blocks on the motor studs are only compatible with copper wire.

• Wiring to motors used with variable frequency drive, across-the-line, autotransformer, or primary reactor starters must be in multiples of three. Wire for these starters is sized following the procedure used for sizing supply wire from the distribution system to the starter.

• Wiring to motors used with wye-delta (also referred to as star-delta) or inside-the-delta solidstate starters must be in multiples of six.The solid-state starter wire sizing tables included here are only applicable to the inside-the-delta solid-state starter designs offered for CenTraVac chillers shipped since June 1999. All other solid-state starter designs should follow the acrossthe-line wire sizing tables.

• A minimum of three feet of flexible conduit is required at the connection to the motor junction box to provide vibration isolation.

Wire size guidelines

The following information is based on the 2011 National Electric Code (NEC). Most local codes are based on the NEC; however, local codes may vary from the NEC on specific details. Final wire size selection must be verified by the Engineer of Record for the installation.

Various factors are involved in selecting the proper wire including amperage draw of the load, type of load, voltage, temperature rating of the wire, number of conductors within a conduit, and ambient temperature. In addition, the wires connecting the starter to the motor may need to be sized differently than the wires that connect the distribution system to the starter.

Good circuit design also involves checking the voltage drop of the distribution circuit.The NEC does not require this step, but does suggest that 3 percent voltage drop on a branch circuit feeder and

5 percent overall will provide “reasonable efficiency of operation”.

The NEC requires HVAC manufacturers to calculate and include “minimum supply circuit conductor ampacity” (also referred to as Minimum Circuit Ampacity [MCA]) on the unit name plate

(section 440.4 [B]). MCA is equal to 1.25 times the RLA of the largest motor plus 100 percent of all

56 CTV-PRB004-EN


Electrical System–Power Wire Sizing other electrical loads. Branch circuit wires supplying the unit must have an ampacity greater than the MCA.

Table 11, p. 58 through Table 16, p. 60 are based on the 2011 NEC conductor ampacities tables for copper wire, run in conduit, in air, for several common wire types and configurations. Where required by the NEC the values in the tables have been adjusted for more than three wires in a conduit.

Table 11, p. 58 through Table 14, p. 59 are for 0–2000 V applications where the ambient temperature around the conduit is between 78°F–86°F (26°C–30°C); Table 15, p. 60 and Table 16, p. 60 are for 2,001 V–35 kV applications where the ambient temperature around the conduits is

104°F (40°C) or less. Installations with ambient temperatures outside these ranges require an additional ampacity adjustment for proper wire selection.

The tables provide an easy way to estimate wire size. Enter the appropriate table, knowing the nameplate MCA of the chiller; a table value greater than the MCA indicates a valid wire/conduit selection (for the conditions described earlier in this section).

Example

The example chiller has a remote-mounted wye-delta starter and the nameplate indicates an RLA of 300 and an MCA of 384 at 460 volts.

If 75°C conductors are used, the supply leads from the distribution system to the starter are sized using Table 11, p. 58 . Comparing the MCA to the table values indicates the conductors could be any of the following combinations:

• one conduit containing three 600 MCM conductors

• one conduit containing six 250 MCM conductors

• two conduits containing three 3/0 conductors each, and so on

Because this is a wye-delta starter the leads from the starter to the motor are sized differently than the supply leads to the starter. If 75°C conductors are used the leads from the starter to the motor are sized using Table 12, p. 58 . Comparing the MCA to the table indicates the following combinations are allowed:

• one conduit containing six 300 MCM conductors

• two conduits containing three 4/0 conductors each

• two conduits containing six 1/0 conductors each

Conductor ampacity tables

The wire selection tables ( Table 11, p. 58 through Table 16, p. 60 ) may be used for estimating conductor and conduit combinations that will support the amperage draw of CenTraVac chillers.

Wire sizes are given in units of AWG (American wire gauge) or kcmil (thousands of circular mils), also referred to as MCM or KCM.

Find the appropriate table based on voltage, wire temperature rating, and where the wire will be used. A table value greater than the nameplate MCA indicates a valid wire/conduit selection (for the conditions described earlier in this section). Then check that the selected combination will fit in the starter lugs by reviewing the starter submittal data. Final wire size selection must be confirmed by the Engineer of Record for the installation.

CTV-PRB004-EN 57



Table 11. MCA look-up table for 75°C copper conductors rated for 0–2,000 Volts (a)

Note: Use this table to select supply leads for all starters, and motor leads for remote-mounted across-theline, primary reactor, autotransformer, and Adaptive Frequency Drives. Value in table must be larger than the MCA to use the wire combination.

Wire Size

8

1 Conduit

3 Wires

50

1 Conduit

6 Wires

1

0

00

000

3

2

6

4

65

85

100

115

130

150

175

200

0000

250

300

350

230

255

285

310

400

500

335

380

536

608

600 420 672

(a) Based on 2011 NEC Table 310.15(B)(16)

240

280

320

368

408

456

496

2 Conduits

3 Wires ea.

300

350

400

460

510

570

620

670

760

840

3 Conduits

3 Wires ea.

450

525

600

690

765

855

930

1005

1140

1260

2 Conduits

6 Wires ea.

480

560

640

736

816

912

992

1072

1216

1344

4 Conduits

3 Wires ea.

600

700

800

920

1020

1140

1240

1340

1520

1680

5 Conduits

3 Wires ea.

750

875

1000

1150

1275

1425

1550

1675

1900

2100

6 Conduits

3 Wires ea.

900

1050

1200

1380

1530

1710

1860

2010

2280

2520


Note: Use this table to select motor leads for remote-mounted wye-delta and solidstate starters (inside-the-delta designs only).Value in table must be larger than the MCA to use the wire combination.

Wire Size

8

1 Conduit

6 Wires

69

2 Conduits

3 Wires ea.

86

1

0

00

000

3

2

6

4

179

206

241

275

89

117

137

158

0000

250

300

350

317

351

393

427

396

439

491

534

400

500

462

524

577

655

600 579 724


224

258

301

344

112

146

172

198

2 Conduits

6 Wires ea.

413

482

551

634

703

786

855

924

1048

1158

4 Conduits

3 Wires ea.

517

603

689

793

879

982

1069

1155

1310

1448

3 Conduits

6 Wires ea.

620

724

827

951

1055

1179

1282

1386

1572

1737

6 Conduits

3 Wires ea.

775

905

1034

1189

1319

1474

1603

1732

1965

2172

58 CTV-PRB004-EN




Wire Size

1 Conduit

3 Wires

1 Conduit

6 Wires

2 Conduits

3 Wires ea.

3 Conduits

3 Wires ea.

2 Conduits

6 Wires ea.

4 Conduits

3 Wires ea.

5 Conduits

3 Wires ea.

6 Conduits

3 Wires ea.

4

3

8

6

55

75

95

115

2

1

0

00

000

0000

250

300

350

400

500

600

130

145

170

195

225

260

290

320

350

380

430

475

272

312

360

416

464

512

560

608

688

760

340

390

450

520

580

640

700

760

860

950

510

585

675

780

870

960

1050

1140

1290

1425

544

624

720

832

928

1024

1120

1216

1376

1520

680

780

900

1040

1160

1280

1400

1520

1720

1900

850

975

1125

1300

1450

1600

1750

1900

2150

2375

1020

1170

1350

1560

1740

1920

2100

2280

2580

2850

Note:

Use this table to select supply leads for all starters and motor leads for remote-mounted across-the-line, primary reactor, autotransformer, and

Adaptive Frequency Drives. Value in table must be larger than the MCA to use the wire combination.

(a) , Based on 2011 NEC Table 310.15(B)(16)


Wire Size

8

1 Conduit

6 Wires

75

2 Conduits

3 Wires ea.

94

2 Conduits

6 Wires ea.

4 Conduits

3 Wires ea.

3 Conduits

6 Wires ea.

6 Conduits

3 Wires ea.

1

0

00

000

3

2

6

4

0000

250

300

350

103

131

158

179

200

234

269

310

358

400

441

482

129

163

198

224

250

293

336

387

448

500

551

603

469

537

620

717

800

882

965

586

672

775

896

1000

1103

1206

703

806

931

1075

1200

1324

1448

879

1008

1163

1344

1500

1655

1810

400

500

524

593

655

741

600 655 819 1310 1637 1965 2456

Note:

Use this table to size motor leads from remote-mounted wye-delta and solid-state starters (inside-the-delta designs only). Value in table must be larger than the MCA to use the wire combination.


1048

1186

1310

1482

1572

1779

1965

2224

CTV-PRB004-EN 59



Table 15. MCA look-up table for 90°C copper conductors rated for 2,001–5,000 Volts (a)

Wire Size

1 Conduit

3 Wires

2 Conduits

3 Wires ea.

3 Conduits

3 Wires ea.

1

0

00

000

4

2

8

6

155

180

205

240

55

75

97

130

360

410

480

540

615

720

0000

250

350

500

750

280

315

385

475

600

560

630

770

950

1200

840

945

1155

1425

1800

Note: Use this table to select line-side wiring to the starter and load-side wiring between the starter and the motor. Value in table must be larger than the MCA to use the wire combination.

(a) Based on 2011 NEC Table 310.60(C)(73)

Table 16. MCA look-up table for 90°C copper conductors rated for 5,001–35,000 Volts (a)

Wire size

1 Conduit

3 Wires

2 Conduits

3 Wires ea.

3 Conduits

3 Wires ea.

0

00

000

0000

2

1

6

4

195

225

260

295

83

110

150

170

390

450

520

590

585

675

780

885

250

350

500

750

330

395

480

585

660

790

960

1170

990

1185

1440

1755

Note:

Use this table to select line-side wiring to the starter and load-side wiring between the starter and the motor. Value in table must be larger than the MCA to use the wire combination.

(a) Based on 2011 NEC Table 310.60(C)(73)

60 CTV-PRB004-EN

Power Circuit Requirements. Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF 82 Pages

Power Circuit Requirements. Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF

Power Circuit Requirements

Electrical System–Power Wire Sizing

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Power Circuit Requirements. Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF 82 Pages

Power Circuit Requirements. Trane Drives, CVHG, Starters, CVHF, Electrical Components, CVHE, CDHG, CDHF