Selection of current-carrying busbar in high-voltage cabinet and current-carrying busbar in low-voltage cabinet
According to the plant power distribution design principles, the busbars at the following locations do not need to be checked for busbar thermal and dynamic effects.
(1) Adopt fuse protection and connect to the bus bar under the fuse (except current-limiting fuse).
(2) Busbar in the circuit of voltage transformer.
(3) The transformer capacity is 1250KVA and below, and the voltage is 12KV and below, so as not to damage the busbar due to failure. It is mainly used for busbars in non-important electricity consumption places.
(4) Parts that are not exposed to thermal and dynamic effects, such as the connection and sealing lines of the arrester.
Therefore, you should ensure that the width of the bus bar for your convenience is sufficient. Our PT uses 30*4.
2. When selecting the cross-section of the conductor, both the current-carrying capacity of the conductor and the ability to withstand short-circuit current must be considered; the designer usually selects the rated current-carrying capacity of the conductor and uses the thermal stability of the short-circuit current for calibration Verification; that is, the two aspects of the decision we call, one is the "maximum hope value decision" and the second is the "minimum regret value check";
2. In most cases, the cross-section of the conductor calculated by the thermal stability of the short-circuit current is larger than that calculated by the current carrying capacity of the conductor, especially where the short-circuit current is relatively large; in fact, this value is not large, because our common system In general, the short-circuit current generally does not exceed 31.5kA. If it exceeds, there is no way to select the bus, but the circuit breaker, transformer, transformer, cable, etc.; if the short-circuit current is too large, we The current can be reduced by raising the voltage, especially the short-circuit current, or by taking technical measures such as series reactors to reduce the short-circuit current;
3. In this example, if the bus bar is a rectangular copper bus bar, the thermal stability coefficient is 171, and the duration of the short circuit current is 3 seconds, according to the calculation formula: http://hi.baidu.com/tsgwg/ album/item/859a950155864246738da510.html#
The minimum conductor cross section capable of resisting 20kA is S=20*√3/171=202 (square millimeters), and the cross section of the rectangular busbar of 50X4 is 200 square millimeters, so this requirement is not difficult to meet; if you choose copper above 50X4 or 40X5 The bus bar can meet the requirements of 200 square millimeters above.
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