TRANSFORMER
A transformer is an electrical device used to convert AC power at a certain voltage level to
AC power at a different voltage level, but at the same frequency.
The construction of a transformer includes a ferromagnetic core around which multiple
coils, or windings, of wire are wrapped. The input line connects to the 'primary' coil, while
the output lines connect to 'secondary' coils. The alternating current in the primary coil
induces an alternating magnetic flux that 'flows' around the ferromagnetic core, changing
direction during each electrical cycle. The alternating flux in the core in turn induces an
alternating current in each of the secondary coils. The voltage at each of the secondary
coils is directly related to the primary voltage by the turns ratio, or the number of turns in
the primary coil divided by the number turns in the secondary coil. For instance, if the
primary coil consists of 85 turns (Np) and carries 240 volts (Vp) and a secondary coil
consists of 300 turns (Ns), the secondary voltage (Vs) is then:
Vs = Vp x (Ns / Np): Vs = 240V x (300/85), Vs = 240V x 3.5, Vs = 850V
Vp = Vs X (Np / Ns): Vp = 850V X (85/300), Vp = 850V X .28, Vp = 240V
A transformer may have multiple secondary coils to feed a number of electrical loads;
however, power must be conserved, so the sum of the output power must equal the sum
of the input power minus losses. Energy losses in transformers are due to a number of
factors: these are copper losses in the coils themselves due to material resistance, core
losses due to hysteresis (the reluctance of the material's magnetic domains to reverse
during each electrical cycle), and eddy currents.