About Methode

Capacitance

The capacitance for a bus bar can be designed to achieve specific results. The construction of the bus bar can be manipulated so as to perform as required by the system. The dielectric constant of the insulator you choose will have the greatest effect on capacitance, without having to physically change the bus structure. The capacitance can be altered without affecting the inductance within the system, assuming you will still meet your dielectric breakdown voltage requirement as shown in this formula:
C = .225bEr/a
C = pF
= Conductor Length
b = Conductor Width
Er = Dielectric Constant
a = Dielectric Thickness

Inductance

Inductance is always present whenever there is voltage passing through a conductor. How you manage that inductance makes the difference. A laminated bus structure can effectively control the inductance generated in power distribution systems by maintaining a consistent distance between conductors. This enables the designer to accurately calculate what inductance will be generated in the system. Generally, the physical length of the bus bar will be determined by the system. Where the components to be powered are located will have a direct result on the bus bar configuration. The greatest effect on reducing the inductance, with little affect on the overall assembly, is by reducing the distance that the conductors are separated by. The conductors should also be designed to be as wide as is allowed by the system or practical as shown in this formula:
L = 31.9a/b
L = nH
= Conductor Length
a = Dielectric Thickness
b = Conductor Width

Current

The current (amperage) rating is based upon the cross-sectional area of the conductor. This directly reflects the temperature rise at given amperage. A general rule of thumb for determining the current carrying capacity is:
I = [(W)(T)]/.00036
I = Amperage
W = Width of conductor
T = Thickness of conductor
.00036 = 360 sq. mils per amp

In most cases this should result in less than a 30°C rise at operating currents.

Impedance

Impedance is a function of inductance and capacitance in the bus bar. When the bus bar is supplied with alternating current, the current builds up voltages that act in opposition to the flow of that current. This opposition is called reactance and it must be combined with the resistance to find the impedance. In order for a power source that has an internal impedance to transfer maximum power to a device that also has impedance, the two impedances must be matched. Impedance matching is important in any electrical or electronic system in which power transfer must be maximized. The calculation for impedance is:
Zo = √L/C (Ω)
Zo = Impedance
L = Inductance
C = Capacitance

Voltage Drop

If power is being distributed over long distances or components require precise voltage requirements, voltage drop across the distance between the input and output connections of the bus bar can be very important. You can calculate how much voltage will be lost with the formula:
Vd = [(2p)(L)(I)]/[(W)(T)]
Vd = Voltage Drop
p = Conductor Resistivity (Ω in.)
p = 10.43" 10-7 (Ω in.) (De-Rated)
L = Conductor Length
W = Conductor Width
T = Conductor Thickness
I = Amperage