Factors Affecting Turns Ratio Measurements
With a theoretical, "ideal" transformer, the ratio of the
physical turns on any winding could be established simply by measuring the
rms output voltage on one winding, while applying a known rms input
voltage of an appropriate frequency to another winding.
Under these conditions, the ratio of the input to output
voltages would be equal to the physical turns ratio of these windings.
Unfortunately, however, "real" transformers include a
number of electrical properties that result in a voltage or current ratio
that may be not equal to the physical turns ratio.
The following schematic diagram illustrates the
electrical properties of a real transformer, with the ideal transformer
component shown in the center, plus the electrical components that
represent various additional properties of the transformer.
- L1, L2 and L3 represent the primary and secondary leakage inductance
caused by incomplete magnetic coupling between the windings.
- R1, R2 and R3 represent the resistance (or copper loss) of the primary
and secondary windings.
- C1, C2, and C3 represent the interwinding capacitance.
- Lp represents the magnetizing inductance core loss.
- Rp represents the core loss of which three areas contribute, eddy
current loss (increases with frequency), hysteresis loss (increases with
flux density) and residual loss (partially due to resonance).