In
electrical engineering
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, isolated-phase bus (IPB), also known as phase-isolated bus (PIB) in some countries, is a method of construction for circuits carrying very large currents, typically between a
generator
Generator may refer to:
* Signal generator, electronic devices that generate repeating or non-repeating electronic signals
* Electric generator, a device that converts mechanical energy to electrical energy.
* Generator (circuit theory), an eleme ...
and its step-up
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
in a steam or large
hydroelectric
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...
power plant.
![Isolated phase bus Bui dam Ghana](https://upload.wikimedia.org/wikipedia/commons/b/b7/Isolated_phase_bus_Bui_dam_Ghana.jpg)
Each
phase
Phase or phases may refer to:
Science
*State of matter, or phase, one of the distinct forms in which matter can exist
*Phase (matter), a region of space throughout which all physical properties are essentially uniform
* Phase space, a mathematic ...
current is carried on a separate conductor, enclosed in a separate grounded metal housing. Conductors are usually hollow aluminum tubes or aluminum bars, supported within the housing on porcelain or polymer insulators. The metal housings are electrically connected so that induced current, nearly of the magnitude of the phase current, can flow through the housing, in the opposite direction from the phase current. The
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
produced by this current nearly exactly cancels the magnetic field produced by the phase current, so there is almost no external magnetic field produced. This also limits the amount of force produced between conductors during a
short circuit
A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit ...
. The external housings of the conductors remain at a low potential with respect to earth ground and are usually bonded to ground.
By enclosing the conductors in separate housings a high degree of protection from two-phase and three-phase faults is obtained. Almost any fault would instead be a single-phase earth fault which does not produce a large fault current. The conductors between the generator and the first
circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
are even more important to protect against two- and three-phase faults because there is no breaker that can stop the fault current from the generator. While most modern circuit breakers will interrupt the fault current in less than 50 ms, the fault current from the generator will take several seconds to interrupt because the field current in the rotor takes this amount of time to discharge. The consequences of a two- or three-phase fault between the generator and the first circuit breaker are therefore much more serious and often result in severe damage to the busbars and nearby equipment.
Isolated-phase bus is made in ratings from 3000 amperes to 45,000 amperes, and rated for voltages from 5000 volts up to about 35,000 volts. In the larger current ratings, dry air is forced through the enclosures and within the tubular conductors for
forced-air
A forced-air central heating system is one which uses air as its heat transfer medium. These systems rely on ductwork, vents, and plenums as means of air distribution, separate from the actual heating and air conditioning systems. The return ...
cooling of the conductors. The cooling air is recirculated through a heat exchanger. Some items of switchgear, such as
circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
s and isolating switches, are made in housings compatible with the isolated-phase bus. Accessories such as instrument transformers, surge arresters, and capacitors are also made in compatible housings. Due to the expense of its construction and the energy loss, isolated-phase bus is usually used in short segments; a large underground powerhouse may have isolated-phase bus up to about 250 metres or so to connect generators to transformers in a cavern.
Forced-air cooling can approximately double the rating over the same size conductors used in a self-cooled system. The extra cost of losses and cooling fan power consumption must be balanced against the lower capital cost of the bus.
[{{cite web , url=http://www.specfabipb.com/ps-isolated-phase-bus.php , title=SpecFab IPB | Products & Services , website=www.specfabipb.com , access-date=6 June 2022 , archive-url=https://archive.today/20130203044649/http://www.specfabipb.com/ps-isolated-phase-bus.php , archive-date=3 February 2013 , url-status=dead]
Various forms of flexible terminals, expansion joints, and weatherproof or fire-proof bushings and terminals are used with isolated-phase bus. Some types of apparatus such as disconnecting switches, circuit breakers, and instrument transformers are made in enclosures that can be welded to become an integral part of the isolated-phase bus system. Isolated-phase bus is usually custom manufactured for a particular project and requires accurate dimensions of the connected equipment for manufacturing.
A smaller type of isolated-phase bus is manufactured for direct-current circuits; this may be used in the field circuit of a generator.
Currently, the isolated-phase bus world record current is 52,000 A, for bus manufactured by
Alstom Power
Alstom SA is a French multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the AGV, TGV, Eurostar, Avelia ...
(since 2015
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
Power) and installed at the
Civaux Nuclear Power Plant
The Civaux Nuclear Power Plant is located in the commune of Civaux ( Vienne) at the edge of Vienne River between Confolens (60 km upstream) and Chauvigny (14 km downstream), and 44 km south-east of Poitiers.
It has two operating un ...
, in 1997.
Other types of bus are:
* Metal-enclosed segregated phase bus
* Low and high impedance bus duct
* Bare flat or tubular bus bars
* Non-segregated Phase Bus (NSPB)
These are used at lower ratings or where adequate protection of the circuit by overcurrent devices is possible.
See also
*
Busbar
In electric power distribution, a busbar (also bus bar) is a metallic strip or bar, typically housed inside switchgear, panel boards, and busway enclosures for local high current power distribution. They are also used to connect high volt ...
*
Bus duct
A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
References
Electric power systems components