According to IEC 60214 IIEC Publ.60214 1989] the following definitions apply:
rated through-current (Io or l-rr)
The current flowing through the OLTC towards the external circuit, which the
apparatus is capable oftransferring from one tapping to the other at the relevant
step voltage and which can be carried continuously while meeting the technical
data of the OLTC manufacturer.
maximum rated through-current ({n*)
The rated through-current for which both the temperature rise of the contacts and
the service duty test apply.
within the maximum rated through-current of the OLTC there may tre different
assigned combinations of values of rated through-current and corresponding rated
step voltage. When a value of rated step voltage is referred to a specific value of rated
through-current, it is called relevant rated step voltage.