Bus Duct

Bus Duct

INTRODUCTION

Bus duct is used for the effective and efficient supply of electricity in mostly industrial

locations. Copper or aluminum is used for the conductor of bus duct that be insulated and

enclosed completely for protection against mechanical damage and dust accumulation.

A bus duct system is an effective method of distributing power to your switchgear and

various loads. However, bus duct problems can lead to catastrophic damage and

extensive downtime.

Allow for the space requirements and weight of the bus duct. You may need to change

other components or select a different style of bus duct for your installation.

If you are installing bus duct outside, select a housing type that sheds rainwater - rather

than pooling it on top of the housing.

If you are going to install any part of the bus duct outdoors, use factory-installed pre-

wired space heaters with integral thermostats to prevent condensation problems.

Abus duct system is an effective method of distributing power to your switchgear and

various loads. Yet, bus duct problems lead to catastrophic damage and extensive

downtime. Let's look at how you properly order and install your system.

Ampacity. You may know the basic bus duct selection requirements already (see sidebar

below). One of those requirements is ampacity. Rather than establish ampacity based on a

standard chart's temperature assumptions, account for your actual operating environment.

Bus typically occupies the high-temperature area near the ceiling.

Once you've determined that area's maximum ambient temperature, factor in the specified

temperature rise from no load to full load. For example, it's common for industrial bus

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duct specifications to limit ampacity to 1000A per sq in. of copper conductor. However,

many brands of bus duct have current ratings based on 1800A per sq in. of copper; thus

the temperature rise (from no load to full load) increases. If your bus duct run is long and

operates at 1800A per sq in., you must accommodate voltage drop within the bus duct.

Location. Many bus ducts installed in industrial and commercial facilities are

immediately downstream of the transformers, but upstream of the main overcurrent

device. Thus, transformer protection devices often inadequately protect the bus duct zone

from fault. So, consider the value of extra protection with service conductor bus ducts.

The extra up-front cost is nothing compared to the savings in downtime.

Allow for the space requirements and weight of the bus duct. You may need to change

other components or select a different style of bus duct for your installation. One place to

pay particular attention is at the transformer. Since torque forces can easily induce

transformer-bushing seal leaks, you want to prevent vertical loading on transformer

bushings. To do so, ensure proper support for the vertical sections of the bus bars within

the bus duct enclosure. Also, the air terminal chamber at the transformer must be of

adequate structural design to assume the weight of the vertical bus duct as it terminates at

the transformer end. Otherwise, the weight of the bus duct may bend the air terminal

chamber - sometimes immediately, sometimes after several weeks. Contact the

transformer manufacturer for assistance with determining the suitability of this chamber

for the intended bus duct.

If you are installing bus duct outside, select a housing type that sheds rainwater - rather

than pooling it on top of the housing. Don't rely on sealants to make up for poor housing

selection. Even the best sealants age and crack - especially when exposed to sunlight.

Even microscopic cracks can admit sufficient water for a violent electrical explosion.

Don't forget those bus duct breather openings. Order them with factory-installed screens

to prevent insect penetration.

In humid climates, bus ducts installed outdoors need protection from internal and external

rust. You can provide this protection by choosing a housing made of a rust-resistant metal

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- such as stainless steel. Or you can coat the housing metal to prevent oxidation. You can

assure coatings will last a long time by starting with a two-part epoxy primer or chromate

vinyl wash primer and finishing with either a two-part polyurethane or catalyst-cured

polyester paint. Specify such finishes only if you can't get the rust-resistant metal to begin

with. The finishes are expensive and have environmental consequences.

If you are going to install any part of the bus duct outdoors, use factory-installed pre-

wired space heaters with integral thermostats to prevent condensation problems. These

are not expensive. Where the bus duct enters through an outside wall, use flame-

retardant, waterproof, and vapor-resistant wall entrance fittings. It's likely you'll need to

support the bus duct system at the wall. In such a case, the wall flange must be able to

carry the structural load of the bus duct weight.

Finally, don't forget the assembly hardware. Again, outside service is more demanding -

don't settle for anything less than stainless steel. Cost reduction from using cadmium-

plated hardware can be economically false due to problems resulting from rust.

Working with the manufacturer. The degree to which you must interact with the factory

depends on the size and lead time of your order - as well as your project deadlines. What

sets the stage for problems more than anything else is a specification problem.

Specifications are often incomplete, incorrect, or poorly communicated. Avoid changes

in specification midway through the manufacturing process by carefully planning

upfront. Pay special attention to dimensions. This is arguably the biggest problem area in

bus duct orders.

When you place your order, work with your sales representative to ensure the

manufacturer understands and approves of your specifications. In some cases, the

manufacturer will recommend specific changes that will improve performance,

reliability, or lead time. Consider such recommendations as advice from an expert, but be

sure to review them against the particulars of your installation.

To help assure longevity of your bus duct system, ask the manufacturer to wrap (or power

dip) the individual bus bars (within a given bus duct) with non-hygroscopic insulation (it

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doesn't absorb moisture). When you add insulating boots at joints (during installation),

you end up with a second insulation measure.

Always do an acceptance test before beginning the actual installation process. The first

step is to make sure the dimensions are correct. Then, check for completeness of your

order.

Do you have all the required transitions, wall flanges, transformer flanges, and

switchboard flanges? Do you have the copper braids that serve to connect the bus duct

bars to the transformer bushings? Are these the correct size and quantity for the ampacity

and physical characteristics? Check these braids for the right bar and pad size.

Ensure the bolt-hole sizes, bolt-hole relative locations, and bolt-hole diameters match at

each end of each factory-assembled braid. On a large order, it makes sense to visit the

factory and do the acceptance testing there. On smaller orders, do this testing as soon as

the order arrives - know ahead of time when that will be, and schedule someone to do the

testing.

Installation tips. Your bus duct joints and terminations should be silver-plated when

made of copper, and tin-plated when made of aluminum. Make every effort to use copper

bars when bolting to copper switchgear bars, and to use aluminum bus when bolting to

aluminum terminals. When mixing the two metals is unavoidable, liberally apply a

manufacturer-approved antioxidant compound to the dry aluminum bars immediately

prior to assembly. Ensure no moisture is present in the joint.

Bus manufacturers often provide assembly hardware kits that include bolts, nuts, flat

washers, locking devices, and Belleville washers. You'll save yourself considerable

design work and project administration headaches by using these kits instead of third-

party hardware. If you're not using such a kit, use the bolt material, type, and size the

manufacturer recommends for that particular bus duct. If using Belleville washers, use

the recommended size and type.

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With all assembly hardware, follow instructions precisely so you prevent high-resistance

connections or permanent damage to the bus system. While most Belleville washers do

not require a torque wrench for proper assembly, nuts and bolts do. Don't use generic

torque charts. These assume a bolt composition that probably won't match what you're

using. Use torque specifications from the manufacturer of the bolts you are using. Be sure

to note the composition (which may include more than the metal content of the bolt),

lubrication, hardness, thread pitch, and size when obtaining the torque specification.

Assign someone other than the assembler to test each joint after assembly - because it's

easy to miss something. Testing should include visual checks, torque checks (except for

Belleville washers), and resistance measurements. Belleville washers are usually at the

correct torque, if tightened just until they look flat.

After joints pass the testing, protect them with insulating boots. These should encapsulate

the entire array of bolt heads and nuts, since bolts often come very close to other bolts in

opposite phases or to the bus duct case.

As a final test, energize the bus with no load. Wait an hour or so, and then give it an

infrared scan. You shouldn't have any hot spots - if you do, repair them and scan again.

Once you complete this step, you are ready to put the bus into service. Then get ready for

a life of trouble-free operation.

Sidebar: Standard Requirements for Bus Duct Selection

• Has the correct voltage rating

• Has sufficient current rating

• Has right quantity of conductors (phase, neutral, and ground)

• Carries UL label or equivalent

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• Has adequate short circuit bracing

Fig. a typical bus duct system

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STANDARDS, APPLICATIONS AND TESTING

OF MEDIUM VOLTAGE BUS DUCT

There are basically three general categories of bus duct (all-metal enclosed). The non-

segregated phase bus implies a duct where all phase conductors are in a common metal

enclosure without barriers between phases. This definition applies to rigid and flexible

conductors such as the bar or cable duct.

Segregated phase bus is a duct where phase conductors are in a common metal enclosure

but are segregated by ground metal barriers between each phase conductor. Isolated

phase duct is when each phase conductor is enclosed in its own metal housing and

adjacent conductor housings are separated by an air space. This duct usually has higher

amp ratings than other types. The housing and conductors are tubular in shape and are

welded at site together. This duct is force-air cooled above a 25000A continuous rating.

APPLICABLE STANDARDS

ANSI C37.23 standard covers the design, manufacture, testing and ratings of the all-

metal enclosed bus duct, including cable duct systems. When part of the equipment, it

contains the associated equipment such as inter connections, enclosures, switches,

supporting structures and disconnecting links. This includes disconnects primarily used

with isolated phase duct but can be used with all other types of duct, including cable duct.

Outside the scope of this standard is duct rated to 600V or open type conductor

assemblies. The CSA C22.2 No. 201 standard is the Canadian measure for metal-

enclosed duct for voltages rated from 751V to 46kV, AC or DC. This standard covers the

design, manufacture, testing and ratings of all types of metal-enclosed bus duct including

cable duct systems. It includes all accessories associated with all types of duct, as does

ANSU. For isolated phase duct, it is limited to amp ratings up to 5000A continuous.

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APPLICATION

All three duct systems are actually identical as to application and have the same basic

ratings as previously listed. Price usually determines which application is most

appropriate for which type of duct. One should not consider the duct cost alone but

include the cost of installation, and therefore the total cost of the installed duct system. In

general, segregated bus duct can be considered slightly more reliable than non-segregated

duct based on the fact that a-bus-to-ground fault may be contained within the separate,

groundedmetal- barriered compartments. This is particularly true for initially low-level

ground faults that exist on an ungrounded, or high-resistance grounded, system.

Rigid conductor bus duct is basically factory manufactured and requires bolting sections

together in the field and installing insulated conductor joint boots. Accessories are

generally factory assembled, including equipment such as switchgear and transformers.

On the other hand, cable duct is normally supplied to the installing contractor on

nonreturnable reels for field installation and termination.

Standard switchgear or transformer connections are direct via the cable with suitable

stress kits or terminating kits, depending on the termination requirement. Special

terminating boxes with rigid copper conductor connections can be supplied to the cable

from which the duct is connected. With rigid duct, tee arrangements are quite practical. It

can also be accomplished with cable duct but with much more difficulty. The tee

arrangement is manufactured of rigid conductors in an enclosure in which the cable duct

system is connected to all sides. This requires stress cone kits or cable terminating kits at

each cable termination. Such an arrangement requires considerable space and is costly.

Hanger supports, wall supports and freestanding floor supports are basically similar for

all types of duct. Isolated phase duct, which becomes a requirement for generator feeds

due to the normal continuous current rating and minimum BIL level of 110kV, is

manufactured from aluminum tube type housings and conductors. The conductors are

supported on porcelain, post-type insulators, and the duct system is pre-manufactured in

specified lengths depending on the duct system’s physical arrangement. The installing

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contractor welds the conductors and housing in the field. Isolated phase ducts are used for

high ampacity requirements and can be supplied up to 25000A continuous rating without

forced-air cooling. Beyond this rating, forced-air cooling is required with all the

associated equipment. All accessories such as elbows, tees, the isolating switch and

termination to the equipment it feeds are specifically designed for the application and

generally come factory assembled, except for termination.

Isolated phase duct is quite special compared to the other duct systems described and

requires considerably more space. It is also significantly more expensive to purchase and

install, but deemed a unique system for specific applications and, in particular, as a

generator duct feed. In general, rigid conductor type bus duct length is measured from

centre line to centre line, and the equipment to which it is attached, to establish overall

duct-length footage. Bar extensions within a termination cubicle are considered part of

the termination equipment. For cable duct, the same criteria is used to establish length.

The only exception is that 60 inches of duct length must be added to establish overall

length dimensions, due to the cable extension leads required at each end. Such cable lead

extensions are considered part of the duct length, rather than part of the termination

equipment.

RATINGS

Non-segregated duct, which includes cable duct, basically has the same continuous

current ratings, from 600A to 6000A. Duct of higher ratings is supplied up to 12000A,

but this is for special applications requiring special design, manufacturing and installation

considerations. Ampacities are normally based on 40°C ambient where conductors have

silver-plated joints, and the allowable temperature rise of the conductor is 65°C. Non-

current carrying parts that can be readily touched are allowed a 40°C rise. Ambient

temperature range limits are -30°C to +40°C, and altitude is up to 1000 metres (3300

feet). Other ambient conditions need special consideration and may contribute to de-

rating. Voltage range for these types of duct are basically from above 600V to 34.5kV to

ANSI but to 46kV to CSA. In practical terms, the maximum rating is 38kV with a BIL

rating of 150kV. This includes cable duct, even though cable at nominally 38kV can have

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a higher BIL rating and can certainly have a higher insulating voltage class such as up to

33 per cent insulation on higher voltage ratings. To ANSI standards, corona extinction

levels are not specified, but they are to CSA standards and are considered a production

type test. Momentary ratings are not specified in the standards but the duct is expected to

be suitable and match the momentary rating of the equipment to which it is connected. In

general terms, the momentary ratings offered are 82 kA, 100kA or 150kA for 600V

ratings; 60kA, 80kA and 100kA for five and 15kV ratings; 6kA and 80kA for 25 and

38kV ratings. The DC bus duct nominal voltage rating is 300 to 3200 volt DC with

continuous ratings up to 6000A. Isolated phase duct continuous ratings go from 1200 to

24000A (self-cooled) although tests have been conducted to 25000A for self-cooled

current ratings.

Voltage ratings are 24.5, 29.5 and 34.5kV with corresponding BIL ratings of 110, 125

and 150kV for direct generator connections. Other than generator connection, voltage

levels are 15.5, 25.8 and 38kV with corresponding BIL ratings of 110, 125, and 150kV.

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GENERAL FEATURES AND APPLICATION

NON-SEGREGATED PHASE BUS DUCT

Non-segregated phase bus duct is available for voltages ranging from 600 volts through

38kV, with ratings up to 8000 amps. The duct has all phase conductors in a common

enclosure with air space between phases. There are no metallic barriers between phase

conductors of adjacent points. Conductors may be mounted on custom-molded,

fiberglass-reinforced polyester blocks or on post insulators. Enclosures that are totally

enclosed are preferred, but ventilated areas can be provided in indoor applications.

Typical applications include connections between transformers and switchgear, tie

connections between motor control centres and large motors, and as the main generator

lead for small generators.

SEGREGATED PHASE BUS

Segregated phase bus duct is available for voltages ranging from 600 volts through 38kV,

with ratings up to 8000 amps. Segregated phase bus has all phase conductors in a

common enclosure with metal barriers between adjacent phases. Conductors may be

mounted on molded, fiberglass-polyester blocks or on post insulators. This design is

primarily used as a generator lead in power plants, but it is also used in heavy industrial

applications and as a switchgear tie in metal-enclosed substations.

BUS WITH PORCELAIN SUPPORT INSULATORS

For voltages higher than 15kV and currents above 5000 amps, porcelain post insulators

are the preferred means of support for the phase conductors. However these post supports

may be used as the main conductor support at any lower voltage or current. Applications

are similar to those listed for nonsegregated phase and segregated phase bus duct.

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CABLE BUS

Cable bus consists of a metal enclosure containing conductors that are fully insulated

copper cables. Using support blocks, the cables are maintained at spacings slightly

greater than two cable diameters between centres to achieve maximum operating current

for each cable. Cable bus can be supplied at voltages up to 38kV and currents up to 5000

amps. Applications include connections between transformers and switchgear, ties

between switchgear and switchgear, and connections between motor control centres and

large motors.

DC BUS

The DC Bus voltage ranges from 300 to 3200V DC with amp ratings of 600 to 6000A. It

can be supplied to meet the needs of most direct current applications. DC bus is available

in two basic configurations: with both poles contained in the same enclosure, or with

each pole contained in a separate enclosure. If the termination areas for opposite poles are

located side by side, then the common enclosure configuration is used. When a

considerable distance exists between poles at the termination, or when the continuous

current or short-circuit rating is high, separate enclosures may be used. Applications

include generator exciter systems, power feeds for electric furnaces and various

connections in traction power installations.

APPROVALS

Rigid conductor bus duct systems are not U/L approved or certified, as there are no

standards in existence. CSA approval and labelling can be applied to rigid conductor bus

duct systems. Such approval is undertaken at the plant of manufacture and applied to an

individual project, as blanket approval is not obtainable. Special inspection authorization

is available in Canada in the field, in lieu of CSA approval in the plant. This is often more

economical and certainly less time consuming than in plant certification and labeling.

Cable duct approval has to be obtained in the field once the cable is installed and

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terminated, as it is only partially manufactured in the plant. Approval is not available as

with rigid conductor duct systems. Special in-field inspection is the only way to get

approval and this again can be CSA or special inspection, the latter being the preferred

way. The approach for the isolating phase duct is very much the same as cable duct since

it requires field certification and labelling.

PROS AND CONS FOR THE USE AND APPLICATION OF

EACH TYPE OF DUCT SYSTEM

For non-segregated, segregated and cable duct, the equipment price determines the

application and which type to use. In general, the cable duct is less expensive (equipment

wise). Based on actual cost examples evaluated over the years, a cable duct system costs

less overall than a rigid conductor type duct system for standard installations. A rigid

conductor duct type system requires strip heaters in the outdoor application to prevent

condensation forming on the insulated conductors. Cable duct does not, as standard

insulated cable is used, which is identical for indoor or outdoor application. Rigid duct is

normally totally enclosed, and cable duct is ventilated. Rigid duct requires periodic

checks to the bar joints to endure continued tightness of bolts along its entire length.

Cable duct only requires such checks at termination points, as the cable is a continuous

conductor along its length.

Rigid duct insulation levels are determined by the insulation level applied to the bar and

is fixed by standards. For example, cable duct can readily be increased by using cable

with a 133 per cent insulation level. Rigid duct requires accurate fixed dimensions in the

field and the duct has to be manufactured to the exact dimensions and these must be

maintained in the field to levels of plus or minus 1/4 inch. With cable duct, it is much

more site forgiving in dimensions as the cable is field installed. After the duct housing is

installed, the duct housing is more readily adjustable (length wise) than rigid duct, which

includes the conductor installed in the factory.

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DESIGN AND PRODUCTION TESTS

Design tests for rigid conductor type bus duct include dielectric tests; temperature rise

tests for the housing and the conductor to establish continuous current rating; momentary

current test to establish bar bracing; basic impulse test; and corona extinction tests to

meet Canadian standards. Production tests include dielectric tests and corona extinction

tests to comply with Canadian standards. Design tests can be performed as production

tests, but this is not recommended due to cost and the length of time it takes to do these

tests. Design tests for cable duct include dielectric test of the cable only; temperature rise

tests of the cable only (although design tests and calculations are originally conducted to

establish housing size and suitable ventilation); momentary current tests on cable only

(although calculations have been conducted to establish the cable support system within

the duct and their spacings); basic impulse tests on cable only; and corona extinction

levels on cable only. Production tests for cable duct generally only include a cable

dielectric test at the manufacturer’s plant. Design tests are not available as a production

test from the cable manufacturer, although duct system calculations can be provided at an

added cost.

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CALCULATION

Primary Substation % Impedance

If specific information is not available use the following as a guide

For transformers 501 to 10000kVA 3 phase and 501 to 5000kVA 1 phase

From Indian Standards Association Standard C57.12.10-1958

(Included in NEMA Transformer Standard TR-1-1962)

Transformer High Voltage, VTransformer Low Voltage

2400V and above  480V* 

2400 to 22900 5.50% 5.75%

26400 to 34400 6% 6.25%

43800 6.50% 6.75%

67000 7%  

- generally pertains to all voltages 600V and below

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Secondary Substation Impedance Data:

High Voltage 15kV Max, Low Voltage 600V Max

If specific information is not available use the

following as a guide

KVA, 3phaseNEMA Std., %

Imp.

General Range of

Mfgrs. % Imp.

Suggested X/R

Ratio for S.C.

Calcs

Suggested %

Imp.

112.5 2 Min. 2.3 - 5.2 5 3 Min

150 2 Min. 2.7 - 5.1 5 3.5 Min

225 2 Min. 4.4 - 5.0 5.5 4.5 Min

300 4.5 Min. 4.5 - 6.0 6 4.5 Min

400 Not Listed 4.5 - 6.0 6 4.5 Min

500 4.5 Min. 4.5 - 6.0 6 5 Min

750 5.75 5.75 7 5.75

1000 5.75 5.75 8 5.75

1500 5.75 5.75 9 5.75

2000 5.75 5.75 12 5.75

2500 5.75 5.75 12 5.75

Note: NEMA industry standards allow a maximum manufacturing tolerance of +/- 7.5%

of the specified transformer impedance value. However, any tolerance is usually ignored

in short circuit calculations on the assumption that plus tolerance offers an extra margin

of safety and minus tolerance is adequately compensated for by miscellaneous circuit

impedances not specifically included in the calculations. But if desired, multiplying the

specified impedance, reactance and resistance values by 0.925 will compensate for even

the most adverse tolerance conditions.

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Copper Conductor Cable Reactance and Resistance Data:

Typical Values - Use Exact data if Available.

Line-To-Neutral mOhm per 100 feet

Conductor Size

AWG or MCM

Three-Single Conductor Cables One Three Conductor Cable

In Magnetic DuctNot In

Magnetic Duct

In Magnetic

Duct

Not In

Magnetic Duct

Reactance

"X"

Resistance

"R"

React

"X"

Resist

"R"

React

"X"

Resist

"R"

React

"X"

Resist

"R"

14 Solid 7.51 258 5.94 258 5.15 258 4.48 258

12 Solid 6.96 161 5.51 161 5.02 161 4.36 161

10 Solid 6.74 101 5.34 101 4.93 101 4.29 101

8 5.93 67.9 4.74 67.9 4.54 67.9 3.95 67.9

8 Solid 6.06 65.9 4.85 65.9 4.64 65.9 4.04 65.9

6 5.67 42.7 4.54 42.7 4.34 42.7 3.78 42.7

6 Solid 5.88 41.5 4.7 41.5 4.5 41.5 3.92 41.5

4 5.3 26.9 4.24 26.9 4.06 26.9 3.53 26.9

4 Solid 5.55 26.1 4.44 26.1 4.25 26.1 3.7 26.1

2 4.98 17 3.98 16.9 3.81 17 3.32 16.9

1 5.04 13.5 4.03 13.4 3.86 13.5 3.36 13.4

1/0 4.95 10.8 3.96 10.7 3.79 10.8 3.3 10.7

2/0 4.83 8.6 3.86 8.5 3.7 8.6 3.22 8.5

3/0 4.67 6.9 3.73 6.7 3.57 6.9 3.11 6.7

4/0 4.53 5.43 3.62 5.33 3.47 5.43 3.02 5.33

250 4.65 4.72 3.72 4.59 3.56 4.72 3.1 4.59

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300 4.52 3.95 3.61 3.8 3.45 3.95 3.01 3.8

350 4.44 3.42 3.55 3.23 3.37 3.42 2.96 3.23

400 4.41 3.05 3.53 2.91 3.33 3.05 2.94 2.91

500 4.32 2.5 3.46 2.35 3.23 2.5 2.88 2.35

600 4.31 2.16 3.44 1.99 3.19 2.16 2.87 1.99

750 4.25 1.81 3.4 1.63 3.1 1.81 2.83 1.63

1000 4.19 1.53 3.35 1.35        

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Aluminum Conductor Cable Reactance and Resistance Data:

Typical Values - Use Exact data if Available.

Line-To-Neutral mOhm per 100 feet

Conductor Size

AWG or MCM

Three-Single Conductor Cables One Three Conductor Cable

In Magnetic DuctNot In

Magnetic Duct

In Magnetic

Duct

Not In

Magnetic Duct

Reactance

"X"

Resistance

"R"

React

"X"

Resist

"R"

React

"X"

Resist

"R"

React

"X"

Resist

"R"

8 3.94 129.11 3.43 129.11 5.14 129.11 4.11 129.11

6 3.99 81.24 3.47 81.24 5.21 81.24 4.17 81.24

4 3.77 51.07 3.28 51.07 4.92 51.07 3.93 51.07

2 3.67 40.51 3.19 40.51 4.79 40.51 3.83 40.51

3 3.57 32.12 3.11 32.12 4.66 32.12 3.73 32.12

1 3.71 25.47 3.20 25.47 4.85 25.47 3.88 25.47

1/0 3.50 20.19 3.05 20.19 4.57 20.19 3.66 20.19

2/0 3.41 16.02 2.97 16.02 4.46 16.02 3.56 16.02

3/0 3.33 12.70 2.90 12.70 4.35 12.70 3.48 12.70

4/0 3.26 10.07 2.83 10.07 4.25 10.07 3.40 10.07

250 3.28 8.68 2.85 8.54 4.28 8.68 3.42 8.54

300 3.20 7.27 2.80 7.13 4.20 7.27 3.36 7.13

350 3.15 6.27 2.76 6.12 4.14 6.27 3.31 6.12

400 3.11 5.53 2.73 5.36 4.09 5.53 3.27 5.36

500 3.01 4.51 2.68 4.29 4.02 4.51 3.21 4.29

600 2.99 3.84 2.69 3.58 4.04 3.84 3.23 3.58

750 2.88 3.18 2.64 2.88 3.96 3.18 3.17 2.88

1000 2.76 2.54 2.59 2.19 3.88 2.54 3.10 2.19

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1250 2.71 2.15 2.58 1.78 3.88 2.15 3.10 1.78

1500 2.65 1.89 2.55 1.51 3.83 1.89 3.06 1.51

1750 2.60 1.71 2.52 1.32 3.78 1.71 3.02 1.32

2000 2.57 1.57 2.50 1.18 3.75 1.57 3.00 1.18

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Square D Bus Duct Reactance and Resistance Data

Line-To-Neutral mOhm per 100 feet

Duct Current

Rating, A

Square D Feeder Duct Square D Plug-In Duct

Aluminum Copper Aluminum Copper

Reactance

"X"

Resistance

"R"

React

"X"

Resist

"R"

React

"X"

Resist

"R"

React

"X"

Resist

"R"

225         6.88 6.756 6.96 7.544

400         6.95 3.797 7.2 2.464

600 0.243 1.93     3.87 2.221 7.35 1.718

800 0.243 1.93 0.568 1.466 2.82 1.291 4.39 1.425

1000 0.468 1.52 0.243 1.215 2.8 1.081 4.58 0.914

1350 0.516 0.99 0.595 0.847        

1600 0.094 0.87 0.618 0.571        

2000 0.26 0.64 0.12 0.603        

2500 0.147 0.514 0.3 0.415        

3000 0.212 0.436 0.315 0.282        

4000 0.184 0.31 0.212 0.184        

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Rotating machine KVA and reactances for short circuit calculation

Motor Specifications

kV: Motor rated kV.

HP: Motor horsepower. Motors may be represented individually or as a lumped group.

FLA: The Full Load Amps.

PF: Motor operating power factor. This is used with the Efficiency to determine kVA.

Motor groups should use an average value of power factor.

EFF: Motor operating efficiency. This is used with the Power Factor field to determine

kVA. Motor groups should use an average value of efficiency.

kVA/HP: The motor or motor group kVA rating per horsepower. This is a simple way of

defining the kVA when full load amperes, or efficiency and power factor are not known.

Typical values for standard efficiency motors are listed below:

kVA/HP - Induction < 100 HP and 0.8 PF Syn Motors

0.95 kVA/HP - Induction 100 < 999 HP

0.90 kVA/HP - Induction > 1000 HP

0.8 kVA/HP - Synchronous 1.0 PF

Motor KVA Calculations

There are three ways to calculate motor kVA. Below the kVA calculation methods are

shown in priority order:

If the FLA is known, the motor kVA should be determined by the following equation:

KVA = (1.73)(FLA)(kV)

22

If the FLA is not available and the kVA/HP is known, the motor kVA should be

determined from the following equation:

KVA = (HP)(kVA/HP)

If both the FLA and the kVA/HP are not available, the motor kVA should be determined

from the following equation:

KVA = (HP)(0.746)/(EFF)(PF)

Motor Short Circuit MVA Contribution Calculation

Table below displays ANSI Standard impedances and interrupting duty multipliers. Code

numbers are chosen according to the motor types, sizes and modeling method. Using the

ANSI Code is the recommended method to determine motor impedances used for ANSI

Standard short circuit calculations:

Note: X" for induction motor groups >50 HP and <50 HP are typically assumed equal to

16.7%. Using the impedance multipliers, this corresponds to an equivalent motor

contribution of 3.6 to 4.8 times the full load current.

X/R: The reactance to resistance ratio from the motor nameplate or manufacturer spec

sheet [typical data].

23

X"dv: Subtransient reactance in percent on the motor HP base. Normally this is 16.7%

for induction motors. Average subtransient reactances for three phase synchronous

machines are:

0.09 for 2-pole turbine generators

0.2 for salient pole generators and motors

0.24 for air cooled condensers

Example: The short circuit MVA momentary contribution of the 15 MVA X"d=0.2

synchronous motor is equal to it's own MVA base (KVA time 1000) divided by it's own

per unit impedance time the ANSI code multiplier from the ANSI Code table above:

SC MVA = (KVA)(1000)/(X"dv)(ANSI CODE MULTIPLYER) = 15 MVA / ( 0.2 x 1.0)

    = 75 SC MVA

X/R = 15

24

TYPICAL DROWING OF DESIGN

Junction between two bas ducts

25

26

SPECIFICATIONS FOR COPPER BUSDUCT 4000A / 6000A

1. SCOPE:

This specification covers the requirements of 3 phase 415 V, 50 Hz, 4000 A / 6000 A

continuous rated, copper TPN bus with enclosure suitable for indoor / outdoor type.

The bus – duct shall be designed for the above current ratings and for a maximum

temperature rise of 400 C over an ambient temperature of 45°C.

2. The bus – bars shall be of hard drawn high conductivity electrolytic grade copper flats

of electrical grade 63401-WP as per IS: 5082. The bus- bars shall be of uniform cross

section along its entire length. No tapering of the bus bars’ cross-section is allowed.

3. The enclosure of bus – duct shall be of 14 SWG sheet steel of minimum thickness of 2

mm bolted on to an angle iron / structural steel framework. The bus duct shall be painted

after suitable pretreatment of all structural steel and plates with anti-corrosive epoxy base

primer paint & two coats of anti corrosive epoxy base paint externally with a colour of

pebble / flint gray shade RAL 7032and dried in a oven. The enclosure shall conform to

IP: 55 for out door and IP: 54 for indoor, as per Indian Standards. Inner surface of the bus

– duct shall be coated in the rubber paint.

4. The bare bus –bars shall be provided with a coat of Matt finish,

5. The joints in the bus –bars shall be of the bolted type and it shall be ensured that the

following precautions are observed.

i. The contact pressure must be ample and this shall be maintained during the time the

panel is in service.

ii. The surfaces of the conductors must be clean.

27

iii. With flat conductors, the overlap should be equal to or greater than the width of the

bars or ten times the thickness of the bar whichever is greater.

iv. The joints shall be treated by the application of joint compound to render the joint

moisture-proof.

v. For the joints use of bolts of cadmium plated high-tension MS bolts having expansion

characteristics due to temperature change similar to the conductor may be used with steel

nuts.

vi. Smearing the surfaces with oxide inhibiting grease just prior to making the joint in

order to preserve the efficiency of the joints. Minimum phase and earth clearance

required shall be maintained at joints. The joints shall be thoroughly shrouded.

6. The bus bar arrangement shall generally conform to IS: 5578 and IS: 11353. The bus –

duct shall be also supplied with suitable earth bus running all along the length of the bus

– duct made of copper strips. Current density at any part shall not exceed prescribed

limits. Two copper flats of same phase shall be stacked together or the spacing between

them shall be maximum of the thickness of one conductor.

7. The busbars shall be phase identified by colour, at intervals. Colour code shall be

RED, YELLOW and BLUE for phase and BLACK for the neutral bus – bar.

8. Bus – bars shall be supported on tough, non-hygroscopic, resin bonded self-

extinguishing fire retardant insulators preferably of SMC / DMC with ribbed construction

to prevent tracking due to dust paths. Bus – bars and supports shall withstand the

maximum stresses that are induced in the event of. The short-circuit currents being as

specified. The bus – bar support shall be at a minimum interval of 500mm.

9. The bus – bars shall be supplied with flexible expansion joints at both the ends and

also at bends. The supports and expansion arrangement shall be so chosen to avoid undue

stress to the bus – bars, supports and end connections.

28

10. Dust excluding gaskets of neoprene shall be used for enclosures to ensure water and

dust tightness. The duct shall be (mostly) suitable for outdoor installation. Minimum two

numbers of space heaters with thermostats shall be provided to prevent moisture

condensation and maintain cubicle temperature 5 Deg.C above the ambient.

11. The clearance between the individual bare phase power bus – bars and between the

phase and earth bus –bars in air shall be not less than 25 mm and 19 mm respectively.

12. Drain points shall be provided at die bottom of the bus – duct, at suitable locations.

The bus –duct shall be provided with silica gel breathers, in all sections.

29

BUS TRUNKING

System description

30

The busbar trunking system is used for both power transmission and distribution. The

system offers a high short-circuit rating and is particularly suited for the connection of

transformers to low-voltage main distribution boards and sub-distribution boards. In

applications where high powers are required, conventional systems frequently require the

use of parallel cables. The system offers optimal power distribution for both horizontal

and vertical busbar runs.

1 Accessories

2 Tap-off units

Degree of protection IP30 and IP54 (IP55 on request)

With fuse switch-disconnector from 125 A to 630 A

With circuit-breakers for 80 A to 1250 A

Early make PEN or PE contact

Load free switching via positive operating sequences

Coding brackets

3 Straight trunking units

With/without fire barrier

Degree of protection IP34 and IP54 (IP55 on request)

4- and 5-conductor systems

Standard lengths: 1.6 m, 2.4 m and 3.2 m

Optional lengths: 0.5 – 3.19 m

With/without tap-off points

Fire barriers: Fire resistance class S 120 conform to DIN 4102 – 9

4 Junction units

L unit

Z unit

31

U units

T unit

With/without fire barrier

5 Feeder units

Cable feeder units

Universal connection element for transformer/ distribution boards

6 Distribution board connection units

For connection from the distributor to the SIVACON system from above/ below

Connection units for non-Siemens distribution systems

System components

Preliminary comments

The busbar trunking systems should be as type-tested low-voltage switchgear and

controlgear assemblies TTA to IEC/EN 60439-1 and -2, DIN VDE 0660 Part 500 and

Part 502 (German standard), as a steel-encapsulated ready-to-connect system.

The distribution systems must be suitable for power transmission, e.g. between

transformer and low-voltage main distribution boards, as well as for power distribution

providing a supply of power to an entire area.

The brand offered must be a complete system consisting of system modules, including

transformers and elements for connection to the distribution boards, as well as such as

brackets, straight trunking units and junction units. All components should be available

both in straight and offset versions.

Trunking units with tap-off openings should be able to be equipped with coded tap-off

units. The tap-off units must be protected with coding brackets to prevent incorrect

32

mounting. Isolation of the tap-off units during dismounting should be assured via positive

operating sequences.

If required, the busbar trunking system should be capable of being equipped with

asbestos-free fire barriers which comply with fire resistance class S 120, and which have

been certified by the local or government authority responsible for building standards.

The trunking unit's steel enclosure is made of moulded steel profiles to permit large

clearances between suspension points. The enclosure is galvanized and painted with in a

light grey colour (RAL 7035).

The external dimensions may not exceed 180 _ 180 (240) mm.

The individual system modules are connected by hanging a hook from a bolt and

tightening a state-of-the-art maintenance-free single-bolt clamp. The conductor between

two system units should not be connected with screws.

The conductor material is made of Aluminium or of copper if the rated current requires.

The Aluminium conductor must be nickel-plated and tinned along its entire length, the

Copper conductor must be tinned and provided with an additional insulating layer of

epoxy-resin.

Fire load should not exceed the value stated in the technical specifications. Expansion

compensation units and fixed points should be engineered based on their requirements

and busbar run (horizontal mounting). In the case of vertically mounted trunking units, a

compensation unit and fixed point must be integrated in every system module. Junction

units with flexible connections or cable connections are not permitted.

The following certificates or declarations of conformity must accompany the offer:

DIN ISO 9001 QA certification

Proof of sprinkler testing

Proof of absence of halogen

Proof of prevention of propagation of an arcing fault

33

Proof that system is maintenance-free

Following the general information, a precise description of the system based on the

technical requirements should be provided as follows:

busbar trunking system technical data

1. Rated current

2. Degree of protection IP34/IP542)

3. Mounting position horizontal/vertical2)

4. Rated insulation voltage 1000 V AC/1200 V DC

5. Rated operational voltage 1000 V AC

6. Rated frequency 16 2/3 – 60 Hz

7. Rated peak withstand current Ipk

8. Rated short-time withstand current Icw (1s)

9. Conductor material Al/Cu2)

10. Number of conductors

a. L1 – L3 and PEN (4 busbars/4-pole)

b. L1 – L3 and m PEN (7 busbars/4-pole)

c. L1 – L3 and PEN (8 busbars/4-pole)

d. L1 – L3, N, PE (5 busbars/5-pole)

e. L1 – L3, m N, m PE (8 busbars/5-pole)

f. L1 – L3, N, m PE (9 busbars/5-pole)

11. Fire load without tap-off points

12. Enclosure dimensions

a. LDA1 to LDC3 180 _ 180 mm2)

b. LDA4 to LDC8 240 _ 180 mm2)

Important planning information:

The normal installation orientation of the busbar trunking system is a horizontal edgewise

mounting of the busbars. In exceptional cases, due to a particular busbar run or through

34

the option of attaching tap-off units on the side, it is not possible to avoid flat placement

of the busbars. Through the increased internal heating of the system in this case, a

derating of the rated current is necessary. The same applies for the vertical differences in

height > 1.3 m (see the “Key to type references” section in the following table). The LD

busbar trunking system is equipped with a ventilation system. When enhancing the

degree of protection from IP34 to IP54 (enclosed system), the rated current must be

derated as specified in the table in the following section.

Key to type references

The basic components of the LD-system are determined using the key to type references.

Type is defined and selected based on rated current, conductor material, system type and

degree of protection. The following type key permits precise definition of the system

required.

35

Selection example:

A rated current of 2500 A is required for a project. The conductor material to be used is

aluminium. A 4-pole system is prescribed. The cross-section of the protective conductor

should be same as the cross-section of the phase conductor.

The required degree of protection is IP34. The installation is implemented horizontally

edgewise, without differences in height. With the aid of the chart, the following type has

been determined:

System components

Size and configuration of the busbar package

The LD busbar trunking system comes in two sizes. Depending on the application in

question, the user can select the system type (4-pole/ 5-pole) and the size of the N/PEN

cross-section.

36

In the following drawings, a cut-out example of a 7 busbar system is shown. The position

of the individual phases and the PEN protective earth conductor is specified. The profile

of the enclosure can also be recognised.

LD busbar systems are available with aluminium (LDA....) and also copper (LDC....)

conductor materials. Due to the conductors’ special surface finishing, trunking units with

different conductor materials can be combined. Aluminium busbars are designed with

both a tin and nickel coating.

37

To ensure a high short-circuit rating and maintain proper distance between the busbars,

busbar supports are installed every 200 mm as shown in the diagram below.

Straight trunking units are used for transmitting electric power and supplying loads.

38

Without tap-off points

– Standard lengths

o 1.6 m: LD.....-1.6

o 2.4 m: LD.....-2.4

o 3.2 m: LD.....-3.2

– Optional lengths

o 0.50 m – 0.89 m: LD.....-1W*

o 0.90 m – 1.59 m: LD.....-2W*

o 1.61 m – 2.39 m: LD.....-3W*

o 2.41 m – 3.19 m: LD.....-4W*

– Straight trunking unit for expansion compensation:

o Standard length

1.2 m: LD.....-D

39

With tap-off points (top and/or bottom):

– Standard lengths with 1, 2 or 3 tap-off points

o 3.2 m: LD.....-K-3.2-3AD

o 3 tap-off points

o 3.2 m: LD.....-K-3.2-2AD

o 2 tap-off points

o 3.2 m: LD.....-K-3.2-AD

o 1 tap-off point

– Optional lengths with 2 tap-off points

o 2.20 m – 2.40 m: LD.....-K-2W*-2AD

o 2.41 m – 3.20 m: LD.....-K-3W*-2AD

o Optional lengths with 1 tap-off point

o 1.20 m – 1.60 m: LD.....-K-1W*-AD

o 1.61 m – 2.40 m: LD.....-K-2W*-AD

o 2.41 m – 3.20 m: LD.....-K-3W*-AD

– W = optional length = lengths in m

o AD= tap-off point

40

Important planning information:

Busbars in the trunking unit expand due to heat losses at the rated load. In order to

compensate for this linear expansion, linear expansion compensation must be installed at

defined intervals with horizontal installation. With vertical installation, each trunking unit

is equipped with an expansion compensation unit.

When planning trunking units with expansion compensation be sure to keep the following

in mind:

The max. permissible length of a straight run between two junction units may not

exceed 10 m in length.

The maximum permissible length of a straight run between a junction unit and

end flange is 25 m. If longer busbar runs are planned, the respective expansion

compensation units must be incorporated.

Tap-off points

Tap-off points are only possible on straight trunking units (both standard lengths and

optional lengths possible):

tap-off point on TOP: ...-AD

tap-off point BOTTOM: ...-ADU

tap-off points on TOP and BOTTOM:

41

-ADO+U

With a trunking unit with a tap-off point at the TOP and BOTTOM, only one tap-off unit

can be used at a time. The required distance between tap-off points is 1 m. The required

type should be determined during engineering, based on the mounting position of the

busbar. In the case of optional trunking units with tapoff point, a minimum clearance of

0.6 m is required between the end of the busbar and a tap-off point. A coding bracket is

located on both sides of a tap-off point. This guarantees non-interchangeability and

correct phasing sequence installation of the tap-off units.

42

Junction units

Elbow trunking units for horizontal installation:

Elbow LD.....-L...

X = 0.5 – 1.24 m

Y = 0.5 – 1.24 m

Z unit LD.....-Z.-Z*

X/Y = 0.5 m

Z = 0.36 – 0.99 m LD.1 – LD.3 180 x 180 mm

Z = 0.48 – 0.99 m LD.4 – LD.8 240 x 180 mm

43

U unit LD.....-U.-Z*

X/Y = 0.5 m

Z = 0.46 – 0.99 m LD.1 – LD.3 180 x 180 mm

Z = 0.58 – 0.99 m LD.4 – LD.8 240 x 180 mm

Elbow trunking units for horizontal and vertical installation:

Elbow LD.....-L.

X = 0.5 – 1.24 m

44

Y = 0.5 – 1.24 m

Offset elbow LD.....-L.

X = 0.5 – 1.24 m

Y = 0.5 – 1.24 m

Offset knee LD.....-L..-Z*

X/Y = 0.5

Z = 0.36 – 1.3 m LD.1 – LD.3 180 x 180 mm

Z = 0.42 – 1.3 m LD.4 – LD.8 240 x 180 mm

45

Connector unit for connection to non-Siemens power distribution systems

If the busbar system is to be connected to a non- Siemens distribution system, it is

possible to make this connection using the LD. .... - FA1 connection unit for connection

to non-Siemens systems. The connection unit is integrated into the distribution board and

provides the interface for the copper conductors to the distribution system. Rated currents

See the Technical Data for information on maximum rated currents.

The maximum temperature for the insulated busbars is 135 °C.

The terminal capacity for the copper connections can be found in the Technical

Data.

Installing the connection unit

The connections to the connection unit in the distributor must be made according to the

specifications or details provided by the manufacturer of the distribution board. The

manufacturer must ensure that the necessary shortcircuit rating is provided and that the

permissible limit temperature of the connection unit to non-Siemens distribution boards is

not exceeded.

46

Technical data

47

(4-pole, Aluminium)

48

(5-pole, Aluminium)

49

50

(4-pole, Copper)

51

(5-pole, Copper)

52

53

54

Dimension drawings

Trunking units

55

56

Tap-off units with LV HRC fuse switch-disconnector

57

58

Tap-off units with circuit-breakers

59

Accessories

60