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Primary voltage(s) stated in standard transformer
specifications (or customer-specified in an inquiry) are
the nominal voltages. These voltages may vary during
times when line supplies are at heavy loads (nearly
always around dinnertime), or light loads (when most
people are asleep). Drops or rises in this voltage can
be as much as 10% of the nominal and vary considerably
from country to country. This change in voltage will be
reflected on the secondary voltage (on and off-load) by
the standard transformation relationship:
Example:
A toroidal transformer is rated at
12v and the primary is rated at 117v 60 Hz. The line
supply regulation is stated as ± 6% by the utility
company.
The secondary voltage when
the line is at its lowest voltage will be:
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