METAL ENCLOSED BUSDUCT

Metal enclosed busduct is an assembly of busbars with associated connections, joints and insulator supports within an earthed metal enclosure.

• Non-Segregated • Phase Segregated • Isolated Phase

Definition

Classification

• Connection between Generator and Generator Transformer;

• Connection between Transformer and Switchgear; • Connection between one Switchgear to another

Switchgear.

• Economical point of view: When the current rating required is high and length is short.

Application

• Air is the only insulating medium between three phases.

• Recommended up-to 660V systems with current

ratings up-to 4000A. • Specifically use for connection between secondary side

of distribution transformer and LV switchgear.

Non-Segregated Phase Busduct

6.6kV, 2000A , 40KA for 3 Sec

6.6/0.433kV 2500 KVA

6.6/0.433kV 2500 KVA

415V, 4000A, 50KA for 1 Sec

NSPB

• Insulated phase barriers are provided; • On high voltage systems up-to 6.6kV with current

ratings up-to 4000A. • Specifically use for connection between secondary side

of Power / distribution transformer and MV switchgear, tie between MV switchgear.

Phase-Segregated Busduct

• Separate enclosure for each; • On systems 11kV and higher with current ratings over

4000A. • Specially for generator leads (current>400A), IPBDs are

recommended.

Isolated Phase Busduct

IPBD

Continuous Non-Continuous

• Up-to 8000A rating may be left to the manufacturers of busduct & the selection based on availability, optimisation of capital cost & loss evaluation.

• Current rating over 8000A, only continuous type is

recommended to minimise the inductive heating of supporting structures etc. & associated losses.

Typical arrangement of continuous type of Isolated Phase Bus Duct

Typical discontinuous type of Isolated Phase Bus Duct

6.6kV SWGR

ST-3 40/25/25 MVA 220/6.9/6.9kV

220kV Switchyard

R

SB-3A SB-3B UB-3A

220kV Switchyard

UB-3B

R R R

UT-3 40/25/25 MVA 16.5/6.9/6.9kV

R

Generator 250 MW 16.5kV

GT-3 315 MVA 235/16.5kV

IPBD

SPBD

TO EXCT TRAFO

Voltage class of the Busduct may be selected from one of the following

standard ratings and shall be at least equal to the maximum voltage rating of the associated equipment:

0.66, 3.6, 7.2, 12, 24 and 36kV

Voltage Rating of the Busduct

Rated r.m.s. continuous current carrying capacity shall be at least equal

to the maximum current capability of the associated equipment (Which may be higher than nominal rated current) rounded off to the nearest higher standard current rating of the busduct.

Preferred standard current ratings are 100, 250, 400, 630, 800, 1250, 1600, 2000, 3150, 4000, 5000, 6300, 8000, 10000, 12500 and 15000A.

Continuous Current Rating

Rated r.m.s. short time current ratings of the busbar shall correspond to

the fault level of the system. The time shall take into consideration the operating time of backup protective devices on the incoming side but the duration shall not be less than 1 sec.

Momentary peak current rating shall be 2.55 times the short time r.m.s.

current rating of the busduct.

Short time Current Rating

Voltage The temperature rise of the conductor shall be as per IS-8084. Also the temperature of the busduct shall not exceed 2500C while carrying the specified short circuit current for 1 sec when fault occurs, at the operating temperature.

Temperature rise

Busbar support insulators are enclosed, the creepage distances & height

of insulators shall be the highest feasible and shall not be less than those for heavily polluted atmosphere as per IS:2544 & IS:5350 (Part-I) respectively to allow for dust accumulation and moisture condensation which can occur. Station/Post type insulator shall be used for supporting buses in metal enclosed busduct.

Bus support Insulator

Flexible connections such as braided or laminated flexible joints for

conductors and rubber bellows for enclosures shall be used for termination of busuct at the terminal of generator, transformer, switchgear etc. and similar flexible connections for conductors and metallic or rubber bellows with metallic shorting for enclosures shall be used in the run of the busuct such that they allow for vibrations & thermal expansion and do not impose any stress on terminal and bushings.

Terminations

Busduct shall be normally natural cooled (AN). Forced cooling may be

considered beyond 10000A rating as per IS:8084.

Cooling

.

Material for Bus and Enclosure

• Bus bar shall be either of copper or aluminium conductor.

• Copper conductor shall be of hard drawn (HD), high

conductivity conforming to IS:613.

• Aluminium conductors shall be of aluminium alloy grade 63401WP conforming to IS:5082.

• Material of enclosure for segregated & non-segregated type busduct shall be mild steel or aluminium.

• If the location where the busduct (Where mild steel are used for enclosure ) is to be installed is having corrosive atmosphere, it shall be galvanised after fabrication or it shall be painted preferably with epoxy based paint.

• For isolated phase type of busduct, the enclosure material shall be of aluminium alloy grade 63401WP conforming to IS:5082.

• Aluminium is cheaper to use than copper.

• Aluminium has les than one-third the density of copper. Weight of aluminium bus bar only half as much as copper bar of equal current capacity. The light weight of aluminium is of advantage in other ways too: for instance, it allows easier handling, transportation & erection.

• Outstanding resistance to corrosion, thus permitting its widespread use in electro-chemical & electroplating process where the atmosphere is highly corrosive.

Popularity of Aluminium Busduct over copper busduct:

• “Self-stifling” property.

• Nevertheless, Aluminium is the cheapest Non-magnetic metal. Hence suitable material for enclosure also.

Busduct- Electrical Parameter

TABLE-III

BUSDUCTSUPPORTING INSULATOR & SEAL OFF BUSHING

(BASED ON IS:2544 & IS: 5350 PART I)

* Note: Not available for Seal off bushing

24

Reference

• TCE Design Guide • INDAL Aluminium Bas bar • IS: 8084-1976 (Specification for interconnecting

busbars for AC voltage above 1kV up to and including 36kV)

• ANSI-C37-20