The word busbar, derived from the Latin word omnibus ('for all'), gives the idea of a universal system of conveyance. In the electrical sense, the term bus is used to describe a junction of circuit...
Bus bar calculationsFull description
Size calculation of Bus Bar as per Schneider Electric Medium Voltage Guide
MCC Bus bar Sizing CalculationFull description
Full description
ghhhhhhhhhhhhhh
Bar screen design
ac machines
Different types of bus bar arrangementFull description
Descripción: Campo ubicado en el Lago de Maracaibo
Descripción completa
Bus AmphibiFull description
ASI BUS
Full description
i likeFull description
managementFull description
BUS-BAR DESIGN INTRODUCTION :
Bus-bars are current carrying conductors. They are designed to carry certain normal current continuously. In this note OBJECTIVE is (i)
to design the bus-bars on the basis of treated normal current and permissible temperature-rise,
(ii)
to be able to check the suitability of a given bus-bar of the power panel.
BUS-BAR DESIGN :
The bus-bars are designed to carry certain rated normal current continuously within the permissible rise in temperature. The value of cross-section so obtained is verified for temperature rise under short time short-circuit current. This figure is further used from the protection point of view while considering the relay setting. In fact, the relay should be set such that under fault condition no damage is caused to these bus-bars. Bus-bar conductors are separated on post insulators or strain insulators. These insulators experience electrodynamics forces depending upon the current being handled. these forces produce bending moments on the insulators. These bending moments, therefore, become the ruling factor to decide the spacing between insulators (span). The following factors are taken into consideration while designing a bus-bar :(i) (iii)
Bus-bar material, Cross-section of conductors,
R. Sharma (BSNL Electrical Zone Patna)
2
Derations for these two factors are obtained from the table 1 & 2 given below and multiplied to get the overall derating factors. TABLE - 1 Temperature rise
Rating factors
1.
Bar temperature rise 40 C over ambient of 35 C
0.88
2.
Bar temperature rise 30 C over ambient of 35 C
0.75
TABLE-2
Enclosure
1.
Outdoors
2.
Indoors where the enclosure itself is in a well - ventilated room
3.
Indoors where the enclosure itself is poorly ventilated ant the room temperature is high.
(Cross sectional area of bus-bar)/ (Total cross sectional area of Enclosure) <1% <5% < 10 % <1% <5% < 10 % <1% <5% < 10 %
Derating factor
0.95 0.90 0.85 0.85 0.75 0.65 0.65 0.60 0.50
After calculating the overall derating factor, the required current rating is obtained by
R. Sharma (BSNL Electrical Zone Patna)
Where, A T θF θI ISC
= = = = =
3
Cross-sectional area of conductor (Sq. mm.) Duration of fault (Sec) Final conductor temperature after the fault (C) Initial conductor temperature before the fault (C) Short circuit current in kilo - Amp.
The above formula can further be simplified as follows : A
=
13.88 ISC √T Sq. mm; upto 6.6 KV 13.7 ISC √T Sq. mm. ; for 11 KV
The insulators are selected by considering mechanical bending load occurring at that instant of peak short circuit current. During short circuit the insulators supporting the bus-bars experience a bending force and unless these insulators have enough cantilever strength to withstand the dynamic force occurring during short circuits they will fail. Let ISC be the short circuit current in KA & Ipeak be the peak short circuit current in KA, Ipeak = 2.55 ISC If L be the length of the bus-bars in metres and r be the phase to phase spacing (in metres) then total force F developed in Kgf is 2 peak x
F = 2.04 I
Force per metre length on bus-bars,
-5
L/r X 10 Kgf.
R. Sharma (BSNL Electrical Zone Patna)
4
The washers (Plain and spring) should also be used. They should be aluminized or electrogalvanised. The following sizes are recommended :Bolt size (mm)
