Selection of 6kV system cables
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Can 3.6kV/6kV cables be used in 6kV feed circuits or on the power side of 6kV generators (both at 6kV or above)? Is it necessary to use 6/6kV or 6/10kV cables?
First, let’s explain the cable model: The 3.6kV/6kV rating for cables refers to the rated voltage between phases of the power cable core in an AC system, which must not be lower than 6kV； In AC systems, the rated voltage between the core of the power cable and its insulation shield or metal sheath is not less than 3.6 kV. The specific selection can be based on the following principles: 1. The rated voltage between phases of the power cable core in an AC system must not be lower than the operating line voltage of the circuit in question. 2. The selection of the rated voltage between the core of the power cable and the insulation shield or metal sheath in AC systems shall comply with the following provisions: (1) In systems where the neutral point is directly grounded or grounded through a low impedance, when the grounding protection operates to disconnect the fault within 1 minute, the voltage of 100% of the operating phase voltage of the circuit in use shall be applied. (2) For power supply systems other than those mentioned in item (1), the operating phase voltage of the circuit in use should not be lower than 133% ； In cases where a single-phase ground fault may persist for more than 8 hours, or in situations where high safety requirements apply to circuits such as generator circuits, it is advisable to use a circuit operating phase voltage of 173%.
The first floor meets the regulatory requirements. In practical applications, a 6/10 rating is used at least for 6KV feeding circuits. . 8.7/15 is generally used. Even 10/15. The insulation class of the cable has little impact on the cost.
The insulation class of the cable does matter; choose it according to your needs – there’s no need to opt for a higher voltage class.
For 6/10 kV cables, although the voltage at 6 kV is relatively low with respect to ground, in the event of single-phase grounding the phase voltage rises to the line voltage of 6 kV; the maximum value can reach 7.2 kV, so it’s not feasible
The opinion on the 2nd floor is the exact wording from GB50217. I partially agree with the opinion on the 3rd floor!