METAL CLAD BUS-BARS AND CONNECTIONS

What Should Consider in Copper Bus-bar Jointing

We can list the major considering points for copper bus-bars jointing techniques are as below.

·        Bolted Joint;

·        Clamped Joint;

·        Riveted Joint;

·        Soldered Joint;

·        Welded Joint.

There are main two reasons for to bus-bar joint; to extend the bus-bars where linear joints are suitable to assemble and to tap off for connections where T-joints are perfect.

Two things must consider as important to bus-bar joints; joints be mechanically strong and electrically have low resistance.

Copper bus-bar uses not any special type of joint but the very familiar types of joints like bolting, clamping, riveting, soldering and welding, etc.  Bolted and clamped joints are a little easy and possible to use at the site, on the other hand, riveted and soldered/welded joints are used in factory pre-fabricated for special shape and to achieve low resistance joints.

Sponsored:

Bolted/clamped joints are easy to install and re-installed, but riveted/soldered/welded joints are difficult and need special arrangements to install and re-install or dismantle.  

 What Effect Should Consider a Bus-Bar Design

The Bus-Bar is usually a normal part of the electrical power generation, transmission, and distribution network system that carry the continuous rated current like other main equipment- generator, transformer, circuit breaker, etc.

Rated value is the basic requirement for any electrical design, but considering the short circuit condition what happens for a short period of time (1 to 4 sec) is very essential obligation.

The short circuit current is not the same every time, at every point of the circuit; but very often it becomes ten to twenty times of continuous current rating.

The short circuit effect may lead to dangerous overheating, including bus-bar the weak portion of the circuit mainly affected by hues amount of short circuit current.

During Bus-bar design, major considering points are as-

·        Short Circuit Heating Effect;

·        Electromagnetic Stress;

·        Corona Discharge.

When the conductor, herein bus-bar carries current in the same direction, an attractive magnetic force is produced. The magnetic force due to continuous rated current is negligible, but it becomes larger for short circuit current; so it should consider for a bus-bar design that may destructive factor for bus-bar insulators and other stuff.

When high voltage air insulated bus-bar is exposed with minor spacing between phase to phase, phases to earth, other metallic poles, or plane then there is a chance to happen flash-over or corona discharge. To avoid this unwanted situation must keep free from any sharp edges.  To better performance corona rings should be incorporated.

Select Sizes of Bas-bar for Maximum Working Current

The measurement of copper bar size for bus-bar is directly formulating is difficult. The change in temperature does not remain proportional to the size of the copper bar, but the continuous current rating is affected by temperature. The following figure will give a basic calculative idea of bus-bar cross-sectional area and maximum current rating.

Width (mm)	Thickness (mm)	Area (sqmm)	Max Current (A)
25 31.5 40 50 63 80 100 125 160	6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3	158 198 252 315 397 504 630 788 1008	530 639 776 932 1127 1390 1662 1987 2433

Case study:

If we consider there is a cable or conductor size is 500 sqm, then what will be the bus bar size?

So, for a 500sqmm conductor, the bus bar size must be 500sqmm or near about 500sqmm. From the above table, if we consider an 80 mm width copper bar and thickness is 6.3mm, then the total cross section will be 80x6.3= 504sqmm which is near to 5oosqmm.

or,

we can select a 40mm width with a 6.3mm thick copper bar, 2x40x6.3 sqmm= 504sqmm, which means doubling the 40mm instead of 80mm we can get the same result. Similarly, we can select different thicknesses.

What Should Consider in Bus-bar Connection

Metal clad Bus-bars and their connection should comply with British standard BS 159 and should be electrolytic copper unless otherwise agreed with the Engineer.

The bus bars, assembles and connections of equipment for services up to 33 kV should be of a type that does not rely solely on air for insulation purposes. The covering material should be non-deteriorating at the rated short-time maximum temperature of the bus bars and should have such thickness as is required to withstand rated line-to-line voltage between the bus bar and a conducting object on the exterior of the covering material for a period of not less than 60 seconds.

The bus bars and their connections, and insulation materials as appropriate should  be capable of withstanding, without damage, the thermal and mechanical effects of a through-fault current equivalent to the short-time rating of the switchgear.

Facilities to the approval of the Engineer should be provided to accommodate the thermal extension of the bus bars and associated components including the insulating medium if appropriate.

Bus bars should be contained in a separate compartment within the general casing of switchgear. Bus-bar barriers should be provided between switchgear equipment to prevent the spreading of ionized gases in the event of a fault.

Access to bus bars and the connections directly connected thereto should be gained only by the removal of covers secured by bolts or screws. Such covers should be clearly and indelibly marked “DANGER-BUSBARS”.

Bus bars should be extensible at both ends; such extension should entail the minimum disturbances to bus-bar compartments. Bus bars should be of uniform cross-sectional area throughout their length.