Bus electrodynamic effect
For the 31.5kA/4S system, the minimum cross-sectional area of the grounded copper busbar is:
S=330×86.7% =287mm2
Calculated according to the above formula, corresponding to various rated short-time withstand currents, corresponding to several commonly used rated short-time withstand currents in switchgear and control equipment, the minimum cross-section of the busbar and the minimum specifications of the copper busbar and aluminum busbar used are shown in Table 1 :
Aluminum bus bar in the equipment
Minimum cross-section (mm2) 425 540 685 1075 1365
4.2 Electrodynamic effects of busbars
The bus bar is a conductor that carries current. When a current flows, it will inevitably produce a force on the bus bar. The force exerted by the bus on the current is related to the current, the shape of the bus, and the distance between the buses. Busbars placed in parallel are the most common in switchgear.
Determine the maximum span of the busbar (the maximum distance between the two supports) according to the rated peak withstand current
Principle: The acting stress acting on the busbar kg/cm≤ the allowable stress of the busbar.
Formula: js=1.76L2ich2×10-3/aW≤y
In the formula: js—acting stress acting on the bus, kg/cm2;
Y—The maximum stress of the bus bar is allowed, 1400 when the bus bar is copper, and 700 when the bus bar is aluminum;
L-support distance between busbars (cm);
A—the distance between each other (cm);
W——Rectangle bus section coefficient, cm3;
Ich—rated peak withstand current, (kA)
According to the above formula:
The maximum span of the copper busbar is L copper MAX≤(1400aw 103/1.76 ich2) 1/2= 892(aw)1/2/ ich
The maximum span of the aluminum bus bar is L aluminum MAX≤(700aw 103/1.76 ich2)1/2= 631(aw)1/2/ich
Coefficient of rectangular bus section:
For the horizontally arranged three-phase bus, when the bus is laid flat; or for the vertically arranged three-phase bus, when the bus is placed upright: (that is, the thickness direction of the bus is opposite, the force effect is good at this time)
W1 = 0.167bh2; where h is the bus width (cm) and b is the bus thickness (cm). Substitute W into the above formula to get
L copper MAX≤365h（ab) 1/2/ ich
L aluminum MAX≤258h（ab) 1/2/ ich
For example: for a 31.5kA system, ich takes 80kA, such as for KYN28-12 switchgear a=28, for the maximum span of TMY100×10 and LMY100×10 type busbars. The busbar width is 100/10=10cm, and the thickness is 10/10=1cm.
L copper MAX≤240 (cm).
L aluminum MAX≤170（cm）
For the horizontally arranged three-phase bus, when the bus is placed upright; or for the vertically arranged three-phase bus, when the bus is laid flat: (that is, the width direction of the bus is opposite, the electrodynamic effect is not good at this time)
W2 = 0.167b2h;
Then: L copper MAX≤365b（ah) 1/2/ ich
L aluminum MAX≤258b（ah) 1/2/ ich
