Improvements in and relating to the Distribution of Electricity.
Year: 1897

page_text: Date of Application, 9th Apr., 1897-Accepted, 22nd May, 1897
COMI LEID
DIECIFICATION,
Improvements in and relating to the Distribution of Electricity.
I, HORACE FIELD PARSHALL, of 83, Cannon Street, in the City of London,
Electrical Engineer, 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 :-
My invention relates to the distribution of electricity more particularly in
traction systems wherein an overhead trolley with earth return is used.
The object of my invention is to create and maintain in the earth return circuit
the same potential as that of the earth at the generating station. Hitherto this
object has been effected in some degree by means of an independently driven
generator the armature of which has been in series with its field and both on the
same feeder, and in such case a back feeder may or may not be used. The
objection to this is that the potential in the earth return is neglected, but since
the Board of Trade rules require in all electric tramway systems a constant or
fixed difference of potential in earth returns of not exceeding 7 volts, it is now
necessary to provide means for so limiting the voltage and that is the aim of my
invention.
According to my method I place on one side of a circuit (which may be either
the positive or negative side) an exciting coil in series with the feeder, and on the
other side of the circuit an armature in series with the feeder, the said armature
being driven at fixed or approximately constant speed. In further description of
my invention I will refer to the accompanying diagram which illustrates the
adaptation of my invention to a tram-line going out for a long distance from the
generating station A and passing in its return near to same. T T¹ represents
the insulated overhead trolley line, E E¹ the earth return or rails and E³ the
normal earth at the station. C is the series coil of a dynamo D connected to one
side of the circuit T T¹ by and in series with the feeders F F¹. The armature d of
the dynamo D is driven at a fixed speed and excited by the said coil C, and it is
connected by and in series with the feeders G G to the other side of the circuit,
viz., the returns EE. Thus the current passing through the coil C is proportional
to the current in the system T T and the electro-motive-force generated by the
armature d is proportional to the current in the earth returus E E¹ so that it acts
to take from the normal earth return E2 or rails a certain amount of current
which is proportional to and capable of regulation by the adjustment of the series
coil C.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
In a system of electrical distribution such as is above referred to, the method of
creating and maintaining in the earth return circuit the same potential as that of
earth at the generating station, which consists in placing on one side of a circuit an
exciting coil in series with the feeder and on the other side of the circuit an

page_text: armature in series with the feeder and driven at approximately constant speed
substantially as set forth.
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