f is the frequency in hertz, and

produces the transformer core flux The flux produced

by 1. cuts the primary winding, N1, and induces a

N is the number of complete turns in the winding

counter voltage, Ec, 180° out of phase with E1 in this

For example, if the maximum flux density is 90,000

winding. The voltage, E2, induced in the secondary

lines per square inch, the cross-sectional area of the core

winding is in phase with the induced (counter) voltage,

is 4.18 square inches, the frequency is 60 Hz, and the

E., in the primary winding, and both lag the exciting

number of turns in the high-voltage winding is 1,200,

current and flux, whose variations produce them, by an

the voltage rating of this winding is

angle of 90°. These relations are shown in vector form

in figure 3-33, view C. The values are only approximate

and are not drawn exactly to scale.

When a load is connected to the secondary by

If the primary-to-secondary turns ratio of this

closing switch S (fig. 3-33, view A), the secondary

transformer is 10 to 1, the number of turns in the

current, I2, depends upon the magnitude of the

low-voltage winding will be

secondary voltage, E2, and the load impedance, Z. For

example, if E2 is equal to 120 volts and the load

impedance is 20 ohms, the secondary current will be

and the voltage induced in the secondary will be

If the secondary power factor is 86.6 percent, the

phase angle,

between secondary current and voltage

For a more in-depth explanation of voltage and

will be the angle whose cosine is 0.866, or 30°.

current relations, refer to NEETS, Module 2,

The secondary load current flowing through the

NAVEDTRA 172-02-00-88, Topic 5, Transformers.

secondary turns comprises a load component of

magnetomotive force, which, according to Lenz's law,

The waveforms of the ideal transformer with no

is in such a direction as to oppose the flux that is

load are shown in figure 3-33, view B. When E1 is

producing it. This opposition tends to reduce the

applied to the primary winding, N1, with the switch, S,

transformer flux a slight amount. The reduction in flux

open, the resulting current, Ia, is small and lags E1 by

is accompanied by a reduction in the counter voltage

almost 90° because the circuit is highly inductive. This

induced in the primary winding of the transformer.

no-load current is called the exciting, or magnetizing,

Because the internal impedance of the primary winding

current because it supplies the magnetomotive force that