Dear colleagues, I hope someone can explain following statement in IEC 61439-1 10.10.3.1 General:
<Quote>
In absence of test at 60 Hz for currents above 800 A, the rated current at 60 Hz shall be reduced to 95% of that at 50 Hz.
<Unquote>
The Switchboards for Temperature Rise Test are rated for 450VAC/3ph/60 Hz.
Rated Current for Main busbars is 5000 A.
Test frequency is 50Hz.
Q1: By quickly thinking I would expect that the thermal effect would be higher in case of higher frequency (eddy currents, core losses etc.). That seems not be the case.
Q2: Formula for calculating heat effect on bus-bars.
Any comments on the issue above is well appreciated.
<Quote>
In absence of test at 60 Hz for currents above 800 A, the rated current at 60 Hz shall be reduced to 95% of that at 50 Hz.
<Unquote>
The Switchboards for Temperature Rise Test are rated for 450VAC/3ph/60 Hz.
Rated Current for Main busbars is 5000 A.
Test frequency is 50Hz.
Q1: By quickly thinking I would expect that the thermal effect would be higher in case of higher frequency (eddy currents, core losses etc.). That seems not be the case.
Q2: Formula for calculating heat effect on bus-bars.
Any comments on the issue above is well appreciated.