Improvements in Starting Apparatus for Shunt and Compound Motors.
Year: 1898

page_text: Date of Application (in United Kingdom), 19th Dec., 1898
Complete Specification Left, 19th Dec., 1898-Accepted, 17th June, 1899
Improvements in Starting Apparatus for Shunt and Compound
Motors.
I, JOHAN JETMUND THORESEN, Electrical Engineer, of Froguerkilens Fabrik,
Bygdo, near Christiania, Norway, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement : —
This invention relates to electrical starting apparatus for shunt and compound
motors. The object of the invention is to procure a starting apparatus of such a
construction, that the circuit is automatically opened in case the current should
cease or increase above a certain limit. This is obtained by putting the switch
lever under the constant action of a spring or the like, trying to swing the lever
into such a position that the current is broken, while the lever when the circuit is
closed and the intensity of the current does not exceed a certain previously fixed
maximum limit, is standing under the action of and is held in its working
position by a magnet, inserted in a circuit shunted to the main circuit, which
shunt may be short circuited by aid of another magnet inserted in the main circuit,
when the current intensity exceeds the maximum limits.
An arrangement of this kind is illustrated in the accompanying drawing shewing
a diagram of the apparatus and its connections.
The switch arc in the form illustrated consists of two parallel rails A and B,
the former of which is composed in the usual way of a series of contact pieces being
connected with each other through a starting resistance C. The rail B is undivided,
and from this rail issue the shunt windings mentioned below. D is an isolating
field. is the switch lever, whose contact piece is contacting with both rails
and which is standing under the constant action of a spring G trying to bring the
lever in a position over the isolating field. This lever E carries an anchor H
adapted to be influenced by a magnet K inserted in the shunt windings I I, and
which when the main circuit is closed, normally is magnetized by the current
passing through the shunt windings and thereby keeps the switch lever in its
working position. If, however, the main circuit current ceases from any reason
(line disorder etc.) the magnet K loses its magnetism, in which case the lever E is
carried on to the isolating field D by the action of the spring G, whereby the
circuit is opened. In order that the apparatus shall act also in case of too great
current intensity in the main circuit, there is inserted a magnet L provided with
Price 81

page_text: few windings, which magnet in case the circuit exceeds the maximum limit
attracts its anchor M. Hereby a swinging contact lever N, which is electrically
connected with the shunt I, is let loose, and by its weight or by aid of a spring is
carried against a contact 0, whereby the circuit through the line II and the
windings of the magnet K is cut short outside the magnet, whereby this one is
made unmagnetic and the switch lever is let loose and carried out of its working
position by the spring G.
The magnet K may suitably be constructed as a bell shaped magnet.
By the arrangement of the rail B constantly in contact with the switch lever E
and the first contact piece of the starting resistance the magnet of the shunt will
constantly be magnetized, so that the shunt current is not broken, when the
lever is turned off, which is advantageous, the sparking by shunts of high tension
being thereby prevented.
This apparatus is advantageous in that it inserts a resistance, when the current
is turned off, whereby the disagreeable sparking common to usual switches is
reduced to a minimum.
I am aware that there have been constructed apparatus, where a magnet is used
for keeping the switch lever in its normal position, and I therefore do not claim
this arrangement as my invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
Starting apparatus for shunt and compound motors etc. provided with a starting
lever, which is acted upon by some motive power (for inst. a spring), which latter
tends to bring the lever out of its working position, the said lever being by normal
strength of the current held in its working position by a magnet inserted in the
current and acting directly on the lever, said magnet becoming short circuited by
means of an auxiliary magnet, when the current raises above a certain maximuni,
and resistance being inserted by the starting lever when it is released, whereby the
sparking is reduced to a minimum.
1000
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.