Dead Point of an Alternator.
A two-phase alternator of the ordinary type connected as a motor to
another alternator cannot start itself, as it has dead points where the
relations and polarity of field and armature are such that there is no
torque or turning power.
Dead-Turns.
In the winding of an armature, a given percentage of the turns, it may
be 80 per cent., more or less, is assumed to be active; the other 20 per
cent. or thereabouts, is called dead-turns. This portion represents the
wire on such portions of the armature as comes virtually outside of the
magnetic field. They are termed dead, as not concurring to the
production of electro-motive force.
Dead Wire.
(a) The percentage or portion of wire on a dynamo or motor armature that
does not concur in the production of electromotive force. The
dead-turns, q. v., of a drum armature or the inside wire in a Gramme
ring armature are dead wire.
(b) A disused and abandoned electric conductor, such as a telegraph
wire.
(c) A wire in use, but through which, at the time of speaking, no
current is passing.
Death, Electrical.
Death resulting from electricity discharged through the animal system.
The exact conditions requisite for fatal results have not been
determined. High electro-motive force is absolutely essential; a
changing current, pulsatory or alternating, is most fatal, possibly
because of the high electro-motive force of a portion of each period.
Amperage probably has something to do with it, although the total
quantity in coulombs may be very small. As applied to the execution of
criminals, the victim is seated in a chair and strapped thereto. One
electrode with wet padded surface is placed against his head or some
adjacent part. Another electrode is placed against some of the lower
parts, and a current from an alternating dynamo passed for 15 seconds or
more. The potential difference of the electrodes is given at 1,500 to
2,000 volts, but of course the maximum may be two or three times the
measured amount, owing to the character of the current.
Decalescence.
The converse of recalescence, q. v. When a mass of steel is being heated
as it reaches the temperature of recalescence it suddenly absorbs a
large amount of heat, apparently growing cooler.
Deci.
Prefix originally used in the metric system to signify one-tenth of, now
extended to general scientific units. Thus decimeter means one-tenth of
a meter; decigram, one-tenth of a gram.
Declination, Angle of.
The angle intercepted between the true meridian and the axis of a
magnetic needle at any place. The angle is measured to east or west,
starting from the true meridian as zero.