Bus ducts are used for connection of high power machines in power plants, distribution plants and industry.

There are three construction types:
  • insulated phase bus duct (IPB),
  • not segregated bus duct, all phases in same enclosure,
  • segregated bus duct, all phases in same enclosure, but with metalic barrier between phases.

CARACTERISTICS OF ISOLATED PHASE BUS DUCTS (IPBs)

Isolated phase bus ducts are mainly used to connect generators with step up transformers in large power plants. Interonnections are realized with medium voltage and with high current capacity. Principally, bus duct phase enclosure sections are connected by welding and on all ends there are shunt plates welded between phases. System impendancy is very low and works as non saturated transformer with ratio 1/1 where secondary current flows through enclosures (enclosure current is about 95-98 % of conductor current, but in opposite direction). System is very well compensated with low magnetic field impact to the enviroment. Enclosures are isolated from the supports and earthed in only one point to avoid parasite currents.

Aluminium 99,5% conductors are supported by porculain or epoxide insulators. Sections are welded together so are maintenance free. Expansion joints compensate lenght termal extention. Insulators have to be calculated for short circuit electrodinamic stres.

Generator circuit breaker (GCB) is very often part of the system as well as current and voltage transformers, overvoltage protection (HV cappacitors, and surge arresters) .

Conductor and enclosure flexible joints to machines are very important for the system reliability. Conductors are connected with copper braids and enclosures with rubber sleeves.

Overtemperature depend of construction, enviroment conditions and location and has to be calculated for every case. If necessary sun protection for outdoor installation is provided. In extreme cases forced cooling system is added.

System advantages are:
  • electro magnetic field around is very low, about 5% only, so not power losses and overheating in surrounding steel structures, cables or pipes. reduced number of supporting points because of high mechanical resistance. total personal security, enclosures are grounded and conductivity is very high. no possibility for short circuit between phases because of three air and two methalic bariers. Unlikely possible short circuit is always limited to phase to ground. electrically, bus duct can be constructed for up to 36 kV and for currents up to 36 kA (with natural cooling up to 25 kA). mechanical protection degree is IP65, can be pressurized with dehumidified air with few milibars to avoid dust infiltration and water condensating.
  • reduced number of supporting points because of high mechanical resistance. total personal security, enclosures are grounded and conductivity is very high. no possibility for short circuit between phases because of three air and two methalic bariers. Unlikely possible short circuit is always limited to phase to ground. electrically, bus duct can be constructed for up to 36 kV and for currents up to 36 kA (with natural cooling up to 25 kA). mechanical protection degree is IP65, can be pressurized with dehumidified air with few milibars to avoid dust infiltration and water condensating.
  • total personal security, enclosures are grounded and conductivity is very high. no possibility for short circuit between phases because of three air and two methalic bariers. Unlikely possible short circuit is always limited to phase to ground. electrically, bus duct can be constructed for up to 36 kV and for currents up to 36 kA (with natural cooling up to 25 kA). mechanical protection degree is IP65, can be pressurized with dehumidified air with few milibars to avoid dust infiltration and water condensating.
  • no possibility for short circuit between phases because of three air and two methalic bariers. Unlikely possible short circuit is always limited to phase to ground. electrically, bus duct can be constructed for up to 36 kV and for currents up to 36 kA (with natural cooling up to 25 kA). mechanical protection degree is IP65, can be pressurized with dehumidified air with few milibars to avoid dust infiltration and water condensating.
  • electrically, bus duct can be constructed for up to 36 kV and for currents up to 36 kA (with natural cooling up to 25 kA). mechanical protection degree is IP65, can be pressurized with dehumidified air with few milibars to avoid dust infiltration and water condensating.
  • mechanical protection degree is IP65, can be pressurized with dehumidified air with few milibars to avoid dust infiltration and water condensating.

CARACTERISTIC OF SEGREGETED AND NON SEGREGETED BUS DUCT

Condactors are done from copper or aluminium flat or ‘U' profiles black painted to improve temperature exchange. Connecting surfaces are not treated or silvered.

Enclosures are usualy done by aluminium sheet but can be done by other material sheet. Mechanical protection degree is usualy IP55. External paint colour for outdoor installation is light to avoid overheating by solar radiation. In extreme conditions sun bariers are provided too.

Porcelain or epoxid insulators have to be calculated for short circuit electrodinamic stres.

Segregated and non segregated bus duct are used for voltage levels up to 36 kV and currents up to 6 kA.


QUALITY CONTROL

Used materials have to be according to specified standards for ex. IEC, BS, ASTM, UNI.

Type test has to be issued by certified laboratory.

Manufacturing control and site control plan are according to client specification.

Site welds are visualy checked and could be also random cheked with liquid penetrants for superficial porosities.

Usual site final control consist completion control ac. to documets and dwgs, paint control, tightness check, current carying contacts check, earthing control, air leakage test and electrical tests (insulation check, conductivity measurement and high voltage test with industrial frequency).


ALUMINIUM WELDING

Base material and welding wire is aluminium purity 99,5 % or more. Welding proces has to insure constant quality, mechanical resistance and particularly high electric conductivity of conductors and enclosures. Welder qualification has to be according to relevant standards.

Welding proces usualy used is MIG, DC inverse polarity Inert gas is Argon with high purity

Aluminium site welding is very sensitive. Good preparation and following procedure is esential. Our qualified and experienced welders with top class equipment are capable to perform high quality welding in extreme climate and microclimate conditions.


BUS DUCT MAINTENANCE

Bus ducts are static installations so no intensive maintenance is required. Anyway after five years of service or short circuit in proximity, it is necessery to check flexible connections, supporting insulators, neoprene rubber joints, etc. Important indicator of pressurized bus ducts general state is eventual air leakage. Periodical electrical insulation check is higly recomanded.

In colaboration with our clients we are able to advise and propose maintenence program, testing metods and acceptance levels for specific bus duct unit. We can suggest list of spare parts and supply them as well as suggest and execute modernization of older units to make them more reliable.