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Cable sizing Query for Harmonic Filter

seansasta
Hi, I'm looking for some advice on best practice & regulatory requirements in relation to the following project.

I have a main switchboard with a "future" PFC cubicle (ABB SACE EMAX E2.2H 3P+N 1250A EKIP TOUCH LSIG W/D); we are installing a Harmonic Filter (COMSYS ADF P300-360/480), which has a power rating of 249KVA (360A). The ADF is to be located within 25m cable run of the PFC feeder cubicle and I am proposing H07ZZ-F single core cables installed in trefoil (3+earth) as the supply cables. We have CT reference terminals available in a marshalling cubicle on the main switchboard monitoring the main incomer. The ADF has it’s own incoming fuses
My query is in relation to the proposed cable sizing versus the protection settings of the supply breaker. The most I can turn the ACB overload trip down is 0.4 x In (500A)…..Is it OK (reg compliant) to size the cables based on load rather than the minimum supply breaker setting…I’m proposing 1c 185mm (360A max with a derating factor of x1.3 to avoid overheating), Table 4F2A doesn’t have a specific example of 1c 185mm x3 for 3ph power and I am wondering do I need to change the 1250A ACB to an 800A (which I’d rather not do!)?
Any advice would be appreciated?

Regards, Seansasta
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  • 0
    In terms of cable ratings and protections, the exam question is always " is there a credible fault mechanism that would not be enough to operate the trip, at its low setting, and still be enough to overheat the cables.?"

    The general assumption is that  most equipment either fails to a clear open or a dead short, so you are left looking at the cable impedances and the PSSC at the origin and comparing that to the tripping times.


    As I understand the   data   the ADF is just connected in parallel with the supply to the rest of the building and it injects or withdraws current at the right parts of the mains cycle to make the load as seen by the incoming supply look entirely real - that is to say the current is in phase with the voltage, and a reasonably pure sine wave, so the supply thinks it is driving a resistor.


    Obviously the currents between the real loads and the ADF unit may be carrying any old wild waveform, within the range that the unit can add or subtract enough to compensate - about 360A if I have read the data sheet correctly.


    You do not mention where the actual loads are connected or how big they are - this is also important.


    regards Mike


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  • 0
    In terms of cable ratings and protections, the exam question is always " is there a credible fault mechanism that would not be enough to operate the trip, at its low setting, and still be enough to overheat the cables.?"

    The general assumption is that  most equipment either fails to a clear open or a dead short, so you are left looking at the cable impedances and the PSSC at the origin and comparing that to the tripping times.


    As I understand the   data   the ADF is just connected in parallel with the supply to the rest of the building and it injects or withdraws current at the right parts of the mains cycle to make the load as seen by the incoming supply look entirely real - that is to say the current is in phase with the voltage, and a reasonably pure sine wave, so the supply thinks it is driving a resistor.


    Obviously the currents between the real loads and the ADF unit may be carrying any old wild waveform, within the range that the unit can add or subtract enough to compensate - about 360A if I have read the data sheet correctly.


    You do not mention where the actual loads are connected or how big they are - this is also important.


    regards Mike


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