Enclosed bus duct

Posted by bruce zhu on October 15th, 2022

Enclosed bus duct

Enclosed bus duct is called bus duct for short. Enclosed bus duct and bus duct refer to the same thing. Enclosed bus duct is a busar machine system consisting of metal plate (steel plate or aluminum plate) as protective shell, conductive bar, insulating material and relevant accessories. It can be made into a plug-in enclosed bus with a plug-in junction box at an interval, or a feeder enclosed bus without a junction box in the middle.

Chinese name Closed busar bending machine Foreign name Closed bus way is widely used in 50MW electric power components to reduce interphase short circuit Closed bus way.The enclosed bus duct (bus duct) can be divided into air type plug-in bus duct, dense insulation plug-in bus duct and high-strength plug-in bus duct according to the insulation mode. According to its structure and use, it can be divided into dense insulation, air insulation, air additional insulation, fire resistance, resin insulation and sliding contact bus duct; According to the shell material, it can be divided into steel shell, aluminum alloy shell and steel aluminum hybrid shell bus duct

Isolated phase enclosed bus

1、 Purpose

The isolated phase bus is a large current transmission device widely used in the busbar bender outgoing line circuit of 50MW and above generators and the auxiliary branch circuit

2、 Features

The conductor and shell of the isolated phase bus are rolled and welded with aluminum plates, which have the following characteristics:

1. Reduce the grounding fault to avoid interphase short circuit isolated phase enclosed bus. Because of the enclosure protection, it can eliminate the external moisture and dust as well as the grounding fault bus caused by foreign objects. The isolated phase enclosed bus is also used to prevent interphase short circuit.

2. Eliminating the heating of steel structure Isolated phase enclosed bus using shell shielding can fundamentally solve the problem of induced heating of steel structure.

3. Reduce the electric power of interphase short circuit. The short-circuit electric power of interphase conductor is greatly reduced due to the double shielding effect of eddy current and circulating current on the shell.

4. Improve the safety and reliability of operation. The pot insulators of the plant are pressed by SMC to form bus bars to prevent insulator condensation. At the same time, hydrogen measurement and temperature measurement devices are used. The measurement signals can be displayed locally or transmitted to the DCS system to improve the safety and reliability of operation. After bus bars are closed, conditions are created for ventilation and cooling.

5. The enclosed busbar is manufactured in complete sets by the factory with guaranteed quality, small operation and maintenance workload, simple construction and installation, and simplified the requirements for civil engineering without setting grid.

6. The enclosure, including the branch circuit in the same phase, adopts the electrical full connection type and multi-point grounding to make the enclosure basically in the equipotential grounding mode, which greatly simplifies and eliminates the risk of personal electric shock.

7. The insulation level of isolated phase enclosed bus is higher than the Chinese national standard GB/T8349, American national standard ANSIC37.23 and British national standard BS159

Editing and broadcasting of common box enclosed bus

1、 Purpose

The common box enclosed bus includes non isolated phase common box enclosed bus, isolated phase common box enclosed bus and AC/DC excitation common box bus. It is widely used for current transmission between the outgoing line of generator below 100MW and the low-voltage side of main transformer or between the low-voltage side of auxiliary transformer of 75MW and above units and the high-voltage power distribution device. The common box enclosed bus can also be used for the AC/DC excitation circuit of generator, The power used in the substation is led into the busbar or the power lead of other industrial and civil facilities.

2、 Features

Copper aluminum bus bar or aluminum slot copper slot is used as the conductor of the closed bus with a compact structure, which is convenient for installation, operation and maintenance. The protection level is IP54, which can basically eliminate the grounding fault caused by external moisture, dust and foreign objects

The shell is made of aluminum plate, which has good anti-corrosion performance, and avoids the additional eddy current loss caused by the steel shell. The shell is electrically connected and grounded at multiple points, which eliminates the danger of electric shock and simplifies the requirements for civil engineering. According to the user's needs, heat shrinkable sleeves can be sleeved on the bus bar to install heaters and respirators in the box to strengthen insulation

The application scope of split phase enclosed bus in large power plants is: from the generator outlet terminal to the main circuit bus leading out of the terminal at the low voltage side of the main transformer, and the independent circuit bus leading out to the branch lines of the plant high-voltage transformer, voltage transformer, lightning arrester and other equipment cabinets.

Split phase enclosed bus is mainly used for large generator sets. The purpose of using split phase enclosed bus in the outgoing line circuit of 200MW and above generators is:

(1) Reduce ground fault and avoid phase to phase short circuit. The short circuit current at the outlet of the large capacity generator is very large, which brings great difficulties to the manufacture of the circuit breaker. The generator can not withstand the impact of the short circuit at the outlet. Enclosed bus can basically eliminate external moisture due to enclosure protection. The ground fault caused by dust and foreign objects can improve the continuity of generator operation. The bus needs to be closed by phases, and the occurrence of interphase short circuit is basically eliminated.

(2) Eliminate heating of steel structure. The exposed large current bus makes the surrounding steel structures and reinforcement generate eddy currents and circulations under electromagnetic induction, resulting in high heating temperature and high loss, reducing the strength of the structure. The enclosure shielding of enclosed busbar can fundamentally solve the problem of induced heating of steel structure.

(3) Reduce the electric force of interphase short circuit. When the short-circuit current with large short-circuit current flows through the bus, the short-circuit electrodynamic force of the interphase conductor will be greatly reduced due to the shielding effect of the shell.

(4) After the bus is closed, it is possible to adopt micro positive pressure operation mode to prevent insulator condensation, improve operation safety and reliability, and create conditions for bus ventilation cooling mode.

(5) The enclosed bus is produced in a complete set by the factory, with guaranteed quality, small operation and maintenance workload, simple construction and installation, and no need to set grid bars, simplifying the structure and simplifying the requirements for civil structure.

In the outgoing line circuit of 200MW and above generators, the advantages of using split phase enclosed bus are as follows: because the bus is enclosed in the enclosure, it is not affected by the environment and pollution, to prevent interphase short circuit and eliminate the grounding fault caused by external moisture and dust, and because the enclosure is grounded at multiple points, to ensure the safety of timely human contact; Due to the shielding effect of eddy current and circulating current in the shell, the magnetic field in the shell is greatly weakened, and the electric force between buses is greatly reduced in case of external short circuit; When the current passes through the bus, the circulating current induced by the shell also shields the magnetic field outside the shell, solving the heating problem of nearby steel structures; The enclosure can be used as a channel for forced cooling, which improves the current carrying capacity of the bus; The workload of installation and maintenance is small. However, there are also some disadvantages, mainly: due to the existence of circulation and eddy current, the shell will have losses; Large consumption of non-ferrous metals; The heat dissipation condition of bus is poor.

Components

Enclosed bus duct (bus duct for short) is a bus system consisting of metal plates (steel plates or aluminum plates) as protective shells, conductive bars, insulating materials and relevant accessories. The utility model can be made into a plug-in enclosed bus duct with a plug-in junction box at an interval, or a feeder enclosed bus duct without a junction box in the middle. In the power supply system of high-rise buildings, the power and lighting lines are often set separately, and the bus duct, as the main power supply line, is installed vertically along the wall for one or more times in the electrical shaft. One bus duct is generally composed of starting bus duct, straight bus duct (with and without jack), L-type vertical (horizontal) bent bus, Z-type vertical (horizontal) offset bus, T-type vertical (horizontal) three-way bus, X-type vertical (horizontal) four-way bus, variable capacity bus duct, expansion bus duct, terminal head, terminal junction box, plug box, bus duct related accessories and fastening devices. The bus duct can be divided into air type plug-in bus duct, densely insulated plug-in bus duct and high-strength plug-in bus duct according to the insulation mode.

Operating environment

The surface treatment of conductive enclosed bus shell is a very important work, which includes pickling, phosphating, drying, powder spraying, curing and other processes. The shell sprayed with polyester epoxy powder has strong surface adhesion and can be used for insulation for a long time.

(1) Conductive copper bar - consists of pure copper bar, and the surface of the conductive copper bar joint shall be uniformly tinned or silvered.

(2) Insulating material - composed of polytetrafluoroethylene and polycarbonate high-strength insulating plastic blocks.

(3) Fixing bolt, insulating sleeve and cover plate.

The enclosed bus installation site should not exceed the altitude of 2000m. The ambient air temperature should not be higher than+40 ℃ and not lower than − 5 ℃. The average temperature of the product within 24 hours should not exceed+35 ℃. The relative humidity of the air should not exceed 50% at 40 ℃ and 90% at 20 ℃. The surrounding air is clean and dust-free. It is a corrosive and insulating gas in Egypt [1].

Enclosed bus is applied to low-voltage and high current power supply and distribution system, which is generally installed in the electrical shaft. A single central bus system is used to supply power to each floor. The enclosed busbar system can be composed of various busbar units;

(1) Linear busbar unit

The linear bus unit is used to extend the power supply and distribution lines. The enclosed bus with tap off device is used together with the plug box to distribute power load.

(2) Starting busbar unit

The starting busbar unit and the starting incoming box form the connecting part of the busbar and cable, and the starting busbar unit can also be connected with the transformer or distribution cabinet.

(3) Expansion bus unit

The expansion bus unit is used to absorb the axial change of bus due to thermal expansion. When the bus length exceeds 80m, a section of expansion bus unit shall be installed.

(4) Variable diameter bus unit

The variable diameter bus unit is used for the connection of different rated current units in the same system, so as to make the power supply of the whole bus system more economical and reasonable.

(5) Various busbar bending units

There are four types of busbar bending connection units, namely L-type, T-type, Z-type and+type, which are used for the connection of horizontal and vertical power supply and distribution and the change of direction, and can flexibly connect the busbar system.

(6) Bus terminal box

The bus terminal box is used for the termination end of the enclosed bus to ensure the power supply safety of the bus system.

(7) Plug box

The plug box is used to lead out the power outlet on the enclosed bus. The plug box is equipped with an automatic air switch for cutting off and connecting the power.

Finished product protection, editing and broadcasting

1. After the installation of the enclosed plug-in bus, the power transmission operation cannot be carried out temporarily. Obvious signboards shall be set on the site to prevent damage.  

2. After the installation of enclosed plug-in bus, if there are other types of work, the enclosed plug-in bus shall be protected to avoid damage.  

3. When using high stools and ladders, do not collide with walls, corners, doors and windows, and do not erect high stools and ladders against walls; When erecting high stools and ladders on the decorated ground, the stool feet and ladder feet shall be wrapped with protective articles to avoid scratching the ground and preventing slipping