Improvements in Automatic Cut-outs for Rotary Electrical Converters and for Alternators.
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 10th Feb., 1900
COMPLETE SPECIFICATION.
Improvements in Automatic Cut-outs for Rotary Electrical
Converters and for Alternators.
We, THE BRITISHI THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of our
said invention (which has been communicated to us from abroad by Charles P.
Steinmetz, of Schenectady, County of Schenectady, State of New York, United
States of America, Electrical Engineer), and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
In the practical operation of rotary converters, we have found it desirable to
provide some automatically actuated means for cutting the machine out of circuit
or otherwise reducing its speed upon a predetermined rise in speed, as for
example, twenty per cent. above the normal. The causes which give rise to changes
in speed in a rotary converter are dependent upon the circumstances under which
the machine is operated. If the machine is used in the ordinary manner with
alternating current supplied thereto and direct currents taken from the direct
current end, the machine will run in synchronism with the frequency of the
alternating current supplied, and its speed will change only with changes in
frequency of the alternating current. It sometimes happens, however, that the
generators supplying the alternating current speed up abnormally, thus requiring
some safety device in connection with the rotary converters or other machines
driven therefrom in order to prevent too great rise in speed and consequent
destruction of the machines by the action of centrifugal force.
It also sometimes happens that the alternating supply mains of a rotary con-
verter are interrupted. If the direct current end of the rotary converter is
connected to an independent circuit no harm will result. If, however the direct
current end of the rotary converter be connected with the direct current end of
the rotary converters or indeed with any other source of direct current, the
immediate result is a reversal of current in the direct current side of the rotary
converter which thereupon runs as a direct current motor. If the machine is
provided with a series field winding, as usual, the field strength is reduced by
reversal of current through this winding and the machine therefore speeds up.
If, on the other hand. the function of the rotary converter is inverted by
normally supplying the same with direct current and deriving alternating
currents therefrom, the speed of the machine is varied not only by changes in
electro-motive force of the direct current supplied. but also by changes in the
character of the load on the alternating current end of the machine. Thus if an
inductive load is fed from the alternating mains, the lagging currents produced
thereby react upon the field magnets of the rotary converter. and cause a weaken-
ing of the same, the immediate result of which is a speeding up of the rotary
converter such as would take place in a direct-current motor if the field were
weakened. On the other hand, if leading currents flow in the alternating mains,

page_text: the effect of the same is to strengthen the field of the rotary converter and to
correspondingly decrease its speed. This has been a serious and in some cases a
prohibitive difficulty in the employment of inverted rotary converters.
In order to provide a speed-limiting mechanism suitable for employment in
the cases above mentioned, and in fact in connection with any dynamo-electric
machine generating alternating currents or to which alternating currents are
supplied, we make use of a circuit connected across the alternating mains and
responsive to the frequency of the electro-motive forces impressed thereon;
and this circuit is arranged to automatically actuate or control suitable devices
for cutting the machine or machines out of circuit or for otherwise reducing
their speed, when the frequency of the alternating electro-motive forces reaches
a pre-determined abnormal value.
Our invention will be more readily understood by reference to the following
description, taken in connection with the accompanying drawings, while its
scope will be clearly and particularly pointed out in the appended claims.
For purposes of illustration, we have shown our invention as applied to a rotary
converter, but it will be readily understood that the same may be utilized in
connection with any other alternating current dynamo-electric machine. At R
we have indicated diagrammatically a rotary converter, but for the sake of
convenience we have omitted showing the field windings, which however may
consist of the usual shunt and series coils. The particular construction of
the rotary converter is unimportant so far as our invention is concerned. The
direct current mains are indicated at a, b, and in series with the main & we have
shown a suitable circuit-breaker or other cut-out device, the same consisting of a
bridging piece e making contact with the terminals d, e, and held in place against
the same by a toggle connection f. The knuckle of the toggle is held in place
by the tripping lever g, the latter being actuated by current in the coil in a
manner to be hereinafter described.
The alternating current mains are indicated at i, j, k, and in series with two
of the mains j, k, are placed circuit-breaking devices, each similar in all respects
to that placed in the direct-current main 6. It is unnecessary to describe the
circuit-breakers in detail since they may be of any suitable and well known
construction. It will suffice simply to state that the circuit breakers are
actuated by means of current flowing in the respective coils and m.
The means which we have provided for energizing the coils h, l, m, for tripping
their respective circuit-breakers,, consists primarily of a tuned circuit placed
across one pair of the three-phase mains i, j, k, as for instance across the
mains j, k. This circuit includes a condenser C, and a device giving rise to
inductive reactance, which is here shown as a magnet M. We may, if desired,
provide an additional inductive device of any suitable form as indicated in dotted
lines at N. The core of the magnet M is vertically arranged, with two down-
wardly projecting legs, to one of which is pivoted one end of an armature 0, the
other end of which normally rests against a suitable stop S and is, by the latter,
maintained at a suitable distance from the other leg of the magnet core.
The free end of the armature 0 carries a wedge shaped contact P adapted
to be brought into engagement with and to connect the two terminals and o,
thus serving to complete the circuit of a local battery Q, or any other suitable
source of electro-motive force. through the circuit breaker coils h, l, m, which as
here shown are arranged in multiple with each other, but which might equally as
well, if desired, be arranged in series..
The capacity reactance and the inductive reactance in the tuned circuit are
so proportioned with respect to each other as to bring the circuit into resonance
at inat frequency of the electro-motive force in the alternating-current mains at
which it is desired to cut out.or otherwise act upon the rotary converter or other
dynamo electric machine, to reduce its speed. When this condition of resonance
i reached, the current in the tuned circuit increases very greatly, and the parts
are so proportioned that this increase of current is sufficient to cause the arma-

page_text: ture 0 of the magnet M, to be attracted thereby causing the contact P to close
the local circuit fed by the battery Q or other source of electro-motive force.
Current then passes through the circuit breaker coils h, l, m and operates the
circuit-breaking contacts used in connection therewith, thus opening the alter-
nating current and the direct current mains of the machine.
While we have shown a local circuit for operating the circuit-breakers in the
mains of a dynamo-electric machine, it will of course be obvious that any other
suitable means controlled from the tuned circuit may be employed for carrying
out the same functions.
Having now particularly described and ascertained the nature of our said
invention (which has been communicated to us from abroad) and in what manner
the same is to be performed, we declare that what we claim is :-
1 The combination of a dynamo-electric machine, conductors in connection
therewith on which alternating electromotive forces are impressed of a frequency
corresponding to the speed of the machine, a tuned circuit in connection with
said conductors, and means operative upon increase of current in said tuned
circuit to disconnect the mains of said machine.
2 The combination of a dynamo-electric machine, conductors in connection
therewith on which alternating electro-motive forces are impressed of a frequency
corresponding to the speed of the machine, a tuned circuit in connection with said
conductors, and a local circuit controlled by current in the tuned circuit for
operating circuit breakers in mains of said machine.
3-The combination of a rotary converter, alternating current and direct
current mains, circuit interrupting devices for said mains and a tuned circuit
connected across two of the alternating mains, and means operated by current in
said circuit for controlling the circuit interrupting devices.
4-The combination of a rotary converter, alternating current and direct
current mains, a circuit interrupting device for the direct current mains and a
tuned circuit connected across two of the alternating mains, and means controlled
by current in said circuit for controlling the circuit interrupting devices.
5 The combination of a rotary converter alternating current and direct
current mains, a tuned circuit supplied with energy from the alternating mains,
and means responsive to current in said tuned circuit for interrupting the direct
current circuit.
G-The combination of a rotary converter alternating current and direct
current mains, a tuned circuit supplied with energy from the alternating mains,
and means responsive to current in said tuned circuit for interrupting both the
alternating current and the direct current circuits.
THE BRITISH THOMSON-HOUSTON CO., LTD.,
J. J. MANHEIM,
A. R. MONKS,
Directors.
ALFRED CLEMENTS,
Assistant Secretary.