Transformer, Hedgehog.
An induction coil transformer whose iron core is composed of a bundle of
iron wires, which after the wire windings are in place have their ends
spread out to reduce to some extent the reluctance of the circuit, which
at the best is high, as the air acts as the return circuit.
This transformer has a low degree of hysteresis; and its efficiency for
very small loads or for no load is superior to that of the closed
magnetic circuit transformer.
Fig. 340. SWINBURNE'S HEDGEHOG TRANSFORMER.
Transformer, Multiple.
A transformer connected in parallel with others between the two leads of
the primary circuit. The term refers to the connection only and not to
any peculiarity of the transformer itself.
Transformer, Oil.
A transformer with oil insulation. The advantage of this insulation is
that if pierced it at once closes, so that no permanent injury ensues.
It is a self-healing form of insulation.
Transformer, Series.
Transformers connected in series upon the primary circuits. The term,
like "multiple transformers," only applies to the connection, not to the
transformer. Series transformers are but little used.
Transformer, Shell.
A transformer with its iron core entirely outside of and enclosing the
primary and secondary winding. It may be made by the use of outer iron
wire windings as core.
Transformer, Welding.
The transformer used for electric welding. (See Welding, Electric.) It
is a transformer with very long primary and exceedingly short and thick
secondary. It is used with the alternating current in the primary, and
produces in the secondary circuit which includes the bars to be welded a
very low potential difference.
Owing to the very low resistance of the secondary circuit this low
electro-motive force produces a very strong current, which develops the
requisite heat. The same type of transformer is used for brazing and
similar purposes.